32371011 Nov 09

PETRONAS TECHNICAL STANDARDS DESIGN AND ENGINEERING PRACTICE

MANUALS

INSTALLATION OF ON-LINE INSTRUMENTS

PTS 32.37.10.11 NOVEMBER 2009

© 2010 PETROLIAM NASIONAL BERHAD (PETRONAS) All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner.

PTS Circular 2009 - SKG14-006 PTS No:

32.37.10.11

Publication Title:

Installation of On-Line Instruments

Base PTS Version:

This revision of PTS 32.37.10.11 – Installation of On-Line Instruments has been updated incorporating PETRONAS Lessons Learnt, Best Practice and new information issued by relevant industry code and standards. All updates in the document are highlighted in italic font. The previous version of this PTS (December 2007) will be removed from PTS binder/ e-repository from herein onwards.

Document Approval

Revision History Date

Version

Description of Updates

Author

SUMMARY OF CHANGES Section

Description of Changes

1.3.2 Abbreviations

1.1.1 MTBF

2.2.1 Remote Mounting Concepts

2.2.3.7 Design aspects

Following abbreviations were added: Mean Time Between Failure

MVC

Measurement Validation and Comparison

TCoO

Total Cost of Ownership

MESC reference were removed as follows (bold and strikethrough) The remote mounting concept has proven to be very valuable and covers all frequently applied hook-up arrangements. Typical hook-up arrangements with MESC-coded component listings are available for liquid, gas and steam applications as given in standard drawings S 37.001 (metric version) and S 37.002 (imperial version). Rephrase as follows (bold): For the direct mounting concept, the following aspects need specific attention: • To prevent too high stresses on the process nozzle, the length and weight of the instrument with its accessories need to be reviewed, especially in vibrating service and on small bore process piping and very high temperature service. Co-ordination with Mechanical Engineering is required. • Direct mounting is less suitable for applications that require rodding out of process connections. However, if auto-rodder is used, direct mounting is preferred.

3.1 General

Rephrase as follows (bold): If a liquid contains vapours, dissolved gas or low temperature (below ambient temperatures) liquids e.g. LNG, LPG, etc, the process connection should be installed in a vertical line. If a process connection can only be made available from a horizontal line, the tapping should be either at the side or pointing downwards at an angle of up to 45 degrees from the horizontal axis except for low temperature liquids where the process connection shall remain horizontal or pointing upwards. The impulse lines shall slope downwards to the instrument so that gas is automatically vented back into the process, as shown in Figure 7. Downward-pointing tappings in horizontal lines are vulnerable to fouling and may only be used if approved by the Principal. If downward-pointing tapping is used, provide proper flushing facility as shown in Figure 7a; further consideration on this configuration in 4.3. Following figure were added

Instrument

Figure 7a (new) 4.1 Specification

Para 3 (adding in bold)

Flush line

Downward-pointing tapping with flushing facility

Section

Description of Changes

of Components

For applications where AISI 316 stainless steel is not suitable, other materials such as Duplex, Super Duplex, Incoloy, Monel, Hastelloy, Tantalum or Titanium should be applied. Para 4 (adding new list and rephrase notes - bold) UNS S32750 Alloy 2507 e.g. Super Duplex 2507

NOTES:

1. However for super duplex tubing, only super duplex fitting shall be used, the three groups of tubing materials, listed above, may be used in conjunction with AISI 316 type stainless steel compression fittings. 2. The hardness of the high nickel alloy tubing shall be within the range of 77 HRB to 83 HRB, hardness of super duplex tubing shall be within 30 HRC.

Para 5 (rephrase - bold) Stainless steel impulse line components may be selected on the basis of the MESC numbers given on standard drawings S 37.001 (Instrument impulse lines, metric version) or S 37.002 (Instrument impulse lines, imperial version). Gauge blocks shall be provided with a 1/2 inch female threaded gauge adapter (not applicable when gauges integral with tube adapter are used). The type of thread for the pressure gauge (tapered 1/2 inch NPT or parallel G 1/2 inch) shall be specified by the Principal. To reference PTS 32.31.09.31 for calculation on TCoO. 4.2.1 General

Additional notes added: Note: The protective shade should be installed for exposed instrumentation in tropical and desert environment

4.2.2.3 Instrument location and routing of impulse line tubing

1.1.1.1 Para 2 rephrase as follows (bold): For straight lengths up to a maximum of 1 m the tubing is self-supporting, for longer lengths the tubing shall be supported up to maximum of 1 m intervals with proper tube supports/clamps.

PREFACE

PETRONAS Technical Standards (PTS) publications reflect the views, at the time of publication, of PETRONAS OPUs/Divisions. They are based on the experience acquired during the involvement with the design, construction, operation and maintenance of processing units and facilities. Where appropriate they are based on, or reference is made to, national and international standards and codes of practice. The objective is to set the recommended standard for good technical practice to be applied by PETRONAS' OPUs in oil and gas production facilities, refineries, gas processing plants, chemical plants, marketing facilities or any other such facility, and thereby to achieve maximum technical and economic benefit from standardisation. The information set forth in these publications is provided to users for their consideration and decision to implement. This is of particular importance where PTS may not cover every requirement or diversity of condition at each locality. The system of PTS is expected to be sufficiently flexible to allow individual operating units to adapt the information set forth in PTS to their own environment and requirements. When Contractors or Manufacturers/Suppliers use PTS they shall be solely responsible for the quality of work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will expect them to follow those design and engineering practices which will achieve the same level of integrity as reflected in the PTS. If in doubt, the Contractor or Manufacturer/Supplier shall, without detracting from his own responsibility, consult the Principal or its technical advisor. The right to use PTS rests with three categories of users: 1) 2) 3)

PETRONAS and its affiliates. Other parties who are authorised to use PTS subject to appropriate contractual arrangements. Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to under 1) and 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards.

Subject to any particular terms and conditions as may be set forth in specific agreements with users, PETRONAS disclaims any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any PTS, combination of PTS or any part thereof. The benefit of this disclaimer shall inure in all respects to PETRONAS and/or any company affiliated to PETRONAS that may issue PTS or require the use of PTS. Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, PTS shall not, without the prior written consent of PETRONAS, be disclosed by users to any company or person whomsoever and the PTS shall be used exclusively for the purpose they have been provided to the user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of PETRONAS. The copyright of PTS vests in PETRONAS. Users shall arrange for PTS to be held in safe custody and PETRONAS may at any time require information satisfactory to PETRONAS in order to ascertain how users implement this requirement.

TABLE OF CONTENTS 1. 1.1 1.2 1.3 1.4

INTRODUCTION ........................................................................................................1 SCOPE........................................................................................................................1 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS .........1 DEFINITIONS .............................................................................................................1 CROSS-REFERENCES .............................................................................................3

2. 2.1 2.2

GENERAL...................................................................................................................4 INTRODUCTION ........................................................................................................4 DESIGN CONCEPTS .................................................................................................4

3. 3.1 3.2

INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE INSTRUMENTS ..........8 GENERAL ...................................................................................................................9 INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING CONCEPT.................................................................................................................11 INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING CONCEPT.................................................................................................................11

3.3 4. 4.1 4.2 4.3 4.4 4.5

GENERAL SPECIFICATION FOR IMPULSE LINES ..............................................12 SPECIFICATION OF COMPONENTS .....................................................................12 MOUNTING ARRANGEMENTS...............................................................................13 FILLING, FLUSHING, VENTING AND DRAINING...................................................14 PAINTING AND COATING .......................................................................................15 TESTING...................................................................................................................15

5. 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10

SPECIAL APPLICATIONS AND CONSIDERATIONS FOR IMPULSE LINES ......16 STEAM SERVICE.....................................................................................................16 OXYGEN SERVICE..................................................................................................16 HYDROGEN FLUORIDE (HF) SERVICE.................................................................16 FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK ..............17 FLUIDS CONTAINING SUSPENDED SOLIDS........................................................17 FOULING AND WAXY SERVICE.............................................................................17 SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUID SLUGS ......................................................................................................................17 LOW TEMPERATURE SERVICE.............................................................................18 VERY TOXIC SERVICE ...........................................................................................18 ‘SOUR’ OR ‘WET H2S’ SERVICE ............................................................................19

6. 6.1 6.2 6.3 6.4 6.5

SEALING AND PURGING .......................................................................................20 LIQUID SEAL ............................................................................................................20 LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS ..................21 DIAPHRAGM SEALS................................................................................................25 EXTERNAL PURGING .............................................................................................27 SELF-PURGING .......................................................................................................28

7. 7.1 7.2 7.3 7.4

HEATING AND INSULATION ..................................................................................29 GENERAL .................................................................................................................29 STEAM HEATING.....................................................................................................29 ELECTRICAL TRACING...........................................................................................30 INSULATION ............................................................................................................30

8.

REFERENCES .........................................................................................................31

APPENDICES APPENDIX 1

PRESSURE AND TEMPERATURE LIMITATIONS OF SS TUBING AND PACKINGS ......................................................................................................0

APPENDIX 2

EXAMPLE OF CALCULATIONS OF THE EFFECT OF PROCESS VARIABLE CHANGES ON dP LEVEL MEASUREMENTS...............................1

PTS 32.37.10.11 November 2009 Page 1 1.

INTRODUCTION

1.1

SCOPE This PTS specifies requirements and gives recommendations for installation of on-line instruments. This PTS is a revision of the PTS of the same number, dated December 2007.

1.2

DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS Unless otherwise authorised by PETRONAS, the distribution of this document is confined to companies forming part of or managed by PETRONAS, and to Contractors nominated by them. This PTS is intended for use in oil refineries, chemical plants, gas plants, supply/marketing installations and in exploration and production facilities. If national and/or local regulations exist in which some of the requirements may be more stringent than in this PTS, the Contractor shall determine by careful scrutiny which of the requirements are the more stringent and which combination of requirements will be acceptable as regards safety, environmental, economic and legal aspects. In all cases the Contractor shall inform the Principal of any deviation from the requirements of this PTS which is considered to be necessary in order to comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned with the object of obtaining agreement to follow this PTS as closely as possible.

1.3

DEFINITIONS The Contractor is the party which carries out all or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor. The Manufacturer/Supplier is the party which manufactures or supplies equipment and services to perform the duties specified by the Contractor. The Principal is the party which initiates the project and ultimately pays for its design and construction. The Principal will generally specify the technical requirements. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal. The word shall indicate a requirement. The word should indicate a recommendation.

PTS 32.37.10.11 November 2009 Page 2 1.3.1

Specific definitions Direct mounting

A mounting concept, whereby an on-line instrument (with or without manifold) is mounted directly on and supported by the process connection(s). NOTE:

This mounting concept is sometimes referred to as ‘close coupled’. This term is however also used in the literal sense for instruments mounted on a separate stand in the direct vicinity of the process connection(s). To avoid confusion, the term ‘close coupled’ is no longer used in this PTS.

Electrical Engineering

Term used in this PTS to identify activities or devices/components which are considered outside the responsibility of the typical Instrument Engineering discipline serving a project. It is not intended to preclude a particular project from reassigning responsibilities, but primarily to identify areas which may otherwise be overlooked.

Impulse line(s)

Components used to connect an on-line instrument to its process connection. It includes but is not limited to tubing, fittings and manifold blocks plus components for filling, flushing, sealing, purging, heating, insulation, venting, draining, mounting and supporting.

Mechanical Engineering

Term used in various parts of this PTS to identify activities or devices/components which are considered outside the responsibility of the typical Instrument Engineering discipline serving a project. It is not intended to preclude a particular project from reassigning responsibilities, but primarily to identify areas which may otherwise be overlooked.

On-line instrument

Instruments connected to process and utility lines or equipment via small (maximum DN 50) block valves. They are subjected to the pressures of the piping systems or equipment on which they are installed. The block valves are referred to as primary isolation valves in the context of this PTS. Instruments with diaphragm seals are also considered to be on-line instruments, if they are connected to process and utility lines or equipment via primary isolation valves of any size. For more detailed definition, refer to: PTS 32.31.00.32: Instruments for Measurement and Control.

Remote mounting

A modular mounting concept, whereby an on-line instrument (with or without manifold) is installed on a dedicated instrument mounting support and connected with the process connection via tubing, capillary or pipe.

Very toxic

See definition in PTS 00.00.01.30


1.4

Abbreviations LRV

Lower Range Value; the lowest quantity that a device is adjusted to measure

MTBF

Mean Time Between Failure

MVC

Measurement Validation and Comparison

TCoO

Total Cost of Ownership

URV

Upper Range Value; the highest quantity that a device is adjusted to measure

CROSS-REFERENCES Where cross-references are made, the number of the section or sub-section referred to is shown in brackets. All publications referred to in this document are listed in (8).


GENERAL

2.1

INTRODUCTION The best hook-up arrangement for each on-line instrument shall be determined on the basis of the specifications given in Sections (4) and (5) and the additional requirements of sections (6) and (7) on sealing, purging, heating and insulation. The selected hook-up shall guarantee proper measurement at all normal and abnormal process operating and climatic conditions. Instrument sealing and purging shall only be used if alternative hook-ups arrangements are less attractive from a TCoO, measurement accuracy or maintenance point of view. To obtain acceptable response times, the kinematic viscosity of liquids in impulse lines shall be kept below 200 mm2/s under all normal and abnormal conditions. In locations where freezing may occur, the water-filled parts of sensing lines and the instrument shall be winterised (i.e. heated and insulated), see (7). For access requirements and guidance on selecting the location of instruments and instrument process connections, refer to PTS 32.31.00.32. Impulse lines for sample take-off and transport for on-line process stream analysis are covered by PTS 32.31.50.10. Installation drawings for instrument impulse lines shall be prepared in accordance with the requirements of PTS 32.31.00.10.

2.2

DESIGN CONCEPTS This PTS covers the requirements for two distinct design concepts: -

Remote mounting concept, as example given in Figure 1; Direct mounting concept, as example given in Figure 2.

Figure 1

Example of remote mounting concept.

PTS 32.37.10.11 November 2009 Page 5

Figure 2

2.2.1

Example of direct mounting concept

Remote mounting concept In the early 1980s, a modular mounting concept was developed for transmitters mounted remotely from the process connection(s): a mounting plate, attached to a dedicated instrument mounting support, accommodates the transmitter, manifold, heating element with terminal box, insulation covers, nameplate and protective shade, as required. Tubing with compression fittings interconnects manifold and process connection(s). Maintenance requirements have dominated the design of the remote mounting concept. The concept is based on a need for permanent access and includes facilities for in situ testing and calibration. The remote mounting concept has proven to be very valuable and covers all frequently applied hook-up arrangements. Typical hook-up arrangements with component listings are available for liquid, gas and steam applications as given in standard drawings S 37.001 (metric version) and S 37.002 (imperial version). Metric tubing (12 mm OD) and compression fittings should be used for new projects. The application of imperial sized tubing (1/2 inch OD) and related compression fittings should be restricted to locations which have standardized on imperial sizes and requires approval by the Principal. The reliable and proven use of compression fittings requires that: -

all compression fittings in a plant, including those supplied with equipment packages, shall be of the same size, make, type and suitable material composition as the tubing. Mixing of fittings of different size (e.g. metric with imperial) or different make/type will result in unreliable joints and might consequently result in loss of containment; the make is subject to Principal’s approval.

-

the fittings and tubing shall be installed by skilled personnel, strictly in accordance with Manufacturer's instructions; e.g. avoidance of over-tightening, use of correctly sized tubing, etc.

-

the impulse lines shall be pressure-tested after installation, see (4.5).


Direct mounting concept Reduced access needs for modern instrumentation, the increased TCoO awareness and product developments have paved the way for alternative mounting concepts, such as direct mounting. In the direct mounting concept, the on-line instrument and its manifold are mounted directly on and supported by the process connection(s). Some designs combine the primary isolation valve and instrument manifold in one component, for instance in a monoflange-type device. This concept is characterised by a small number of components, forming a compact design. This concept is not standardized (no standard forms), but leaves the market forces to find economically attractive and technically sound solutions within the constraints specified in this PTS. Consequently, the solutions offered by the various Manufacturers will be different and the role of the Manufacturer will be that of a solution-provider rather than just a material Supplier.

2.2.3

Comparison of design concepts

2.2.3.1

General It is essential to make the selection between the remote mounting and the direct mounting concept in an early project stage. This Section lists aspects to be considered.

2.2.3.2

Accessibility The remote mounting concept provides some freedom regarding instrument location and the resulting accessibility. For maintenance purposes, permanent and easy access used to be the dominant factor in selecting the physical location of remote mounted instruments. Long impulse lines and additional ladders/platforms were the result. The location of a direct mounted instrument is fully determined by the physical location of the process connection, which typically provides limited freedom for positioning. Major improvements in MTBF, MVC techniques and remote diagnostics via ‘intelligent’ communication have drastically reduced the need for on-the-spot maintenance of modern field instruments. Minimum accessibility requirements are specified in PTS 32.31.00.32

2.2.3.3

TCoO The cost involved with the remote mounting concept is high due to the large number of components, the need for an instrument mounting support and the labour intensive installation and testing. Furthermore, tubing and fittings are vulnerable to damage, particularly in the construction phase of a project. These disadvantages do not apply to the direct mounting concept. Furthermore, the use of fewer components and connections can be a major cost saver. When the direct mounting concept is chosen, extra cost may be involved to meet the minimum access requirements for specific field instruments (e.g. instruments that require regular in situ testing and/or calibration).

2.2.3.4

Performance and maintenance aspects The compactness of the direct mounting concept brings the sensor closer to the process which improves the measurement accuracy and makes the measurement less susceptible to the proper functioning of heating and insulation. Shorter runs and fewer fittings reduce vulnerability to damage and leaks.

PTS 32.37.10.11 November 2009 Page 7 2.2.3.5

Responsibilities, risks and construction timing The remote mounting concept entails a clear demarcation of scope between the Mechanical and Instrument Engineering disciplines. The design is proven and the components are available as commodity items. The installation of a remote mounted transmitter (material delivery/erection/wiring/loop testing) is hardly affected by the progress of piping installation activities and therefore not time critical. Most direct mounting concepts include the primary isolation valve (e.g. by using monoflanges), which requires additional co-ordination between the Mechanical and Instrument Engineering disciplines, as the concept should satisfy the requirements of both disciplines. The Manufacturer should be selected in an early project phase, as proprietary design details affect plant design. Furthermore, the primary isolation valve should be installed before pressure testing of equipment and process piping, which might not be the appropriate time for transmitter installation and associated instrumentation activities.

2.2.3.6

Variety control If the direct mounting concept is selected, it will not be suitable for all applications, so both concepts will be mixed on a specific project. This will increase the variety of components and Engineering effort.

2.2.3.7

Design aspects For the direct mounting concept, the following aspects need specific attention: •

To prevent too high stresses on the process nozzle, the length and weight of the instrument with its accessories need to be reviewed, especially in vibrating service and on small bore process piping and very high temperature service. Co-ordination with Mechanical Engineering is required.

•

Direct mounting is less suitable for applications that require rodding out of process connections. However, if auto-rodder is used, direct mounting is preferred.

•

The compactness of most direct mounting designs causes the instrument housing to operate close to the process operating temperature. The upper and lower temperature limits of sensor fill fluids/electronics of instruments restrict the use of the direct mounting concept in low and high temperature applications.

•

When the direct mounting of a differential pressure type flow meter is considered, the transmitter/manifold shall be supported by only one of the tappings and connected by tubing to the second tapping. If the transmitter is supported by two tappings pointing in the same direction, as shown in Figure 3, a slight misalignment of the tapping points causes leakage and undue stress at the mounting bolts. Furthermore, the thickness of an orifice plate depends on the plate type and its nominal pipe size.


Figure 3

Incorrect direct mounting of a DP flow transmitter/manifold by supporting it from both tapping


3.

INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE INSTRUMENTS

3.1

GENERAL Process connections for on-line instruments shall have dedicated primary isolation valves to allow disconnection from the process. Only if a loop requires multiple instruments to cover the full operating range may the primary isolation valve(s) be shared, providing that secondary isolation is available for each instrument. NOTE:

In certain applications, a straight-through type primary isolation valve, e.g. gate, ball or plug valve, may be required to allow rodding out of plugged connections.

The flange facing finish of direct mounting components (e.g. gauge blocks) and lap joint tube adapters shall be in accordance with ASME B16.5. The number of connections shall be minimised. Where required, compression fittings and/or flanged connections are preferred. For certain applications, the Principal may specify threaded connections. Parallel threaded connections with soft annealed metal sealing rings, as shown in Standard Drawings S 37.808 and S 37.809, have preference over tapered sealing connections for their leak tightness. NOTE:

Tapered threaded connections such as NPT require a thread sealant such as PTFE. See Appendix 1 for temperature limitations.

Figure 4

Top tappings

Instrument process connections on horizontal process lines shall be located at the top (vertically up or pointing upwards at an angle of up to 45 degrees from the vertical axis) to limit the blocking risk by solids, dirt or pipe scale, as shown in Figure 4. For liquid measurements on horizontal process lines, however, this arrangement can cause gas to collect in the impulse lines. In such cases, side tappings are preferred but if this is not feasible, the effect on the measurement accuracy should be limited by installing seal pots to allow regular venting and/or by minimising the difference in elevation between the top of the impulse line and the instrument process connection, as shown in Figure 5 and Figure 6. If a liquid contains vapours, dissolved gas or low temperature (below ambient temperatures) liquids e.g. LNG, LPG, etc, the process connection should be installed in a vertical line. If a process connection can only be made available from a horizontal line, the tapping should be either at the side or pointing downwards at an angle of up to 45 degrees from the horizontal axis except for low temperature liquids where the process connection shall remain horizontal or pointing upwards. The impulse lines shall slope downwards to the instrument so that gas is automatically vented back into the process, as shown in Figure 7. Downward-pointing tapping in horizontal lines are vulnerable to fouling and may only be used if approved by the Principal. If downward-pointing tapping is used, provide proper flushing facility as shown in Figure 7a; further consideration on this configuration in 4.3.


Figure 7

Figure 5

Instrument below top tapping

Figure 6

Instrument above top tapping

Vapour or dissolved gas in liquid, instrument below side tapping

Instrument

Figure 7a

Flush line

Downward-pointing tapping with flushing facility

PTS 32.37.10.11 November 2009 Page 11 3.2

INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING CONCEPT Process connections for on-line instruments shall, wherever possible, terminate in a DN 15 lap joint flange with lap joint tube adaptor. Primary isolation valves, lap joint flanges, gaskets and bolts, including their heating/insulation, are the responsibility of Mechanical Engineering. The responsibility of Instrument Engineering starts at the lap joint tube adaptor.

3.3

INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING CONCEPT Flanged gauge blocks shall be used for direct mounted pressure gauges. Similar blocks may be used for process connections of other instrument types. Some Manufacturers offer components that combine the primary isolation valve and instrument manifold in one housing, for instance in a monoflange style. Such designs may be considered in consultation with Mechanical Engineering in the light of the issues identified in (2.2.3).


GENERAL SPECIFICATION FOR IMPULSE LINES

4.1

SPECIFICATION OF COMPONENTS The general rules for material selection of impulse line components are similar to those for wetted parts of instruments, as detailed in PTS 32.31.00.32 Material selection is subject to Principal's approval. Where process conditions allow, the wetted instrument impulse line components (i.e. tubing, compression fittings, manifolds etc.) shall be made of AISI 316 type stainless steel. Stainless steel tubing and compression fittings shall be suitable for a maximum allowable working pressure of at least 413 bar (ga) at temperatures between -200 °C and +38 °C. For maximum allowable working pressures at higher temperatures, see Appendix 1. NOTES:

1. The maximum allowable working pressure of at least 413 bar (ga) applies to SS fittings only Lower maximum allowable working pressures apply to CS or brass fittings. 2. The maximum allowable working pressure of the impulse line components shall equal or exceed the upper design pressure of the process it serves.

For applications where AISI 316 stainless steel is not suitable, other materials such as Duplex, Super Duplex, Incoloy, Monel, Hastelloy, Tantalum or Titanium should be applied. Components of such materials may however be very costly and may at a later stage be inadvertently interchanged with unsuitable stainless steel components. Alternative ‘hook-up’ arrangements (e.g. diaphragm seals) or alternative measurement principles (e.g. in-line flow instruments or internal level measurements) should be considered as a first choice. Austenitic stainless steel tubing (including insulated tubing) is vulnerable to chloride stress corrosion if exposed to temperatures above 60 °C. Impulse and steam tracer tubing installed under such conditions shall be constructed from any of the following materials: -

ASTM B 423 alloy (UNS N08825) tubing, e.g. Incoloy 825 or Nicrofer 4221; ASTM B 668 alloy (UNS N08028) tubing, e.g. Sanicro 28; UNS S 312 254 SMO. UNS S32750 Alloy 2507 e.g. Super Duplex 2507

NOTES:

1. However for super duplex tubing, only super duplex fitting shall be used, the three groups of tubing materials, listed above, may be used in conjunction with AISI 316 type stainless steel compression fittings. 2. The hardness of the high nickel alloy tubing shall be within the range of 77 HRB to 83 HRB, hardness of super duplex tubing shall be within 30 HRC. 3. Chloride stress corrosion on the outside of the tubing may be caused by chlorides present in rain water (especially in marine and coastal locations) and by water-soluble chlorides in insulation material. 4. Some Manufacturers offer pre-insulated tubing or tubing bundles (impulse and tracer tubing plus insulation), including a wide range of dedicated sealing and installation accessories. If the Manufacturer’s instructions regarding installation and sealing are followed, such products may be considered in view of their commercial attractiveness and better ingress protection than field fabricated insulated bundles. If such products are chlorides free (e.g. not containing any PVC) and if water tightness can be guaranteed during construction and plant operation, chloride stress corrosion will not occur and austenitic stainless steel may be used.

Stainless steel impulse line components may be selected on the basis of the given on standard drawings S 37.001 (Instrument impulse lines, metric version) or S 37.002 (Instrument impulse lines, imperial version). Gauge blocks shall be provided with a 1/2 inch female threaded gauge adapter (not applicable when gauges integral with tube adapter are used). The type of thread for the pressure gauge (tapered 1/2 inch NPT or parallel G 1/2 inch) shall be specified by the Principal. NOTE:

Gauge blocks are provided with adapters to allow dial positioning.


MOUNTING ARRANGEMENTS

4.2.1

General Subject to environmental conditions, instruments may require protective shades; see PTS 32.31.00.32. The shade shall be fixed in a way allowing quick installation and removal. Note:

The protective shade should be installed for exposed instrumentation in tropical and desert environment

4.2.2

Mounting aspects of the remote mounting system

4.2.2.1

Instrument mounting supports In the remote mounting concept, instruments are installed on dedicated mounting supports. The use of instrument mounting supports mounted on the process line requires the approval of the Principal. They shall not be applied on: -

process line sizes smaller than DN 100; insulated process piping; vibrating service.

If instrument mounting supports are clamped around process piping of a different material, insulating barriers (e.g. tape or gasket material) shall be applied to prevent galvanic corrosion. Instrument mounting supports shall not be fixed to grating, as this does not provide sufficient stiffness and does not allow the grating to be removed for painting. If instrument mounting supports have to be fixed to fireproofed plant structures, these supports should be welded to the steel structure before the fireproofing is applied. Typical examples of instrument mounting supports are shown on standard drawing S 37.004. 4.2.2.2

Standardized mounting plates In the remote mounting concept, the instrument with its manifold is mounted on a standardized mounting plate. If required, the heating element with terminal box, insulating covers and protective shade are also installed on this plate. See standard drawings S 37.815 and S 37.816 for standardized mounting plates with and without protective shades respectively. These plates have facilities for installing nameplates in accordance with PTS 32.31.00.32

4.2.2.3

Instrument location and routing of impulse line tubing Impulse line tubing shall be as short as possible and the number of joints shall be kept to a minimum. ‘Horizontal’ lines shall slope at a ratio of approximately 1:5. For straight lengths up to a maximum of 1 m the tubing is self-supporting, for longer lengths the tubing shall be supported up to maximum of 1 m intervals with proper tube supports/clamps. Insulating spacer material shall be applied to separate the tubing from its supports to prevent galvanic corrosion. Impulse lines shall be grouped closely together. Heavy components such as seal pots shall be properly supported to prevent stress on or damage of compression fittings and tubing.

PTS 32.37.10.11 November 2009 Page 14 For remote mounted instruments the impulse lines shall be so arranged that any movement will not exert excessive force on any connection. Such movement may be caused by thermal expansion (e.g. in steam or LNG service) or vibration of process pipes. Thermal expansion can be absorbed by expansion loops. Instruments connected to vibrating process pipes shall be installed on dedicated instrument mounting supports, with the tubing arranged sufficiently flexibly to take up the vibration and to prevent the tubing from vibrating excessively. Typical examples of hook-ups for thermal expansion or vibrating service are shown on standard drawings S 37.001 (Instrument impulse lines, metric version) and S 37.002 (Instrument impulse lines, imperial version). NOTES:

4.2.2.4

1. Special attention shall be given to long impulse lines running horizontally. This type of installation shall be avoided to prevent mechanical damage or the formation of "pockets" which may result in false readings. 2. Where fittings are used in parallel tubing runs, their locations may require staggering to provide proper access. 3. Flexible components shall not be used to absorb movement by thermal expansion or vibration.

Connections between differential pressure measuring instruments and manifolds For connections between differential pressure type measuring instruments and manifolds, one of the following connection types should be selected: − Connections with standardized mating dimensions as specified in IEC 61518, type A (with an extended spigot) for a maximum allowable working pressure of 413 bar (ga) at 38 °C, with O-ring dimensions according to ISO 3601-1. − Connections not standardized by an international body, such as coplanar type connections. The design is vendor dependent.

4.3

FILLING, FLUSHING, VENTING AND DRAINING The Principal should be contacted about his policy on venting, draining and removal of (contaminated) seal and process fluids from impulse lines. Draining/venting is one option; disposal into the process by means of a mobile seal liquid refill pump unit is another frequently used option. The impulse line hook-up should include the necessary connections to connect such a pump unit. NOTES:

1. The design of the mobile seal liquid refill pump unit requires the approval of the Principal. 2. The practice of ‘venting and draining’ fluids is no longer recommended, as it leads to a large number of small and vulnerable connections to flare and drain systems. Furthermore, the cost involved with such fixed connections is high.

Vent and drain valves shall be provided with a device to prevent tampering. Approximately 500 mm tubing shall be fitted to vent or drain connections and directed downwards. Filling/flushing connection(s) are at least required for the following cases: − Handling of the process fluid and/or seal liquid poses a danger to human beings or to the environment. Flushing and neutralising of the instrument and manifold is necessary before disconnecting the instrument. − Process liquids or seal liquids in impulse lines need regular replacement. Filling/flushing connectors consist of a non-return valve with a capped off compression fitting. When the connectors are not in use, a compression-type plug shall be fitted and secured by a bead-type chain to the non-return valve. The connector shall be selected for: -

d/p cells applied for measurements with a seal liquid for ease of filling; d/p cells in use for toxic & corrosive applications which require flushing before removing the instrument.


Figure 7b

4.4

Typical Connector

PAINTING AND COATING All supports, brackets etc., shall be protected by a corrosion resistant paint or coating (e.g. galvanising) in accordance with the requirements of PTS 30.48.00.31. Surfaces which will be inaccessible after installation shall be treated before installation. Instruments and stainless steel components shall not be painted or coated. Painting shall not foul threaded connections or jeopardise the proper operation of moving parts such as valve handles.

4.5

TESTING All on-line instruments and impulse line components shall be pressure-tested to the design pressure limit of the instrument or to a pressure of 1.5 times the upper design pressure of the process, whichever is lower. NOTES:

1. Local regulations may specify a higher test pressure, e.g. twice the intended operating pressure. 2. Primary isolation valves shall be closed during flushing of process equipment and piping.

Instrument air, nitrogen or demineralised water shall be used for pressure testing. After pressure testing with water, the instrument and the impulse lines shall be carefully drained and blown out. Impulse line pressure testing may be integrated with pressure testing of process equipment and piping, depending on the flushing medium, scope demarcations and timing aspects. If the process equipment or piping is tested with another medium than specified above, the primary isolation valves shall be closed to prevent it from entering the impulse lines.


SPECIAL APPLICATIONS AND CONSIDERATIONS FOR IMPULSE LINES

5.1

STEAM SERVICE Steam entering the impulse line(s) shall condense before reaching the instrument to prevent damage by overheating. In freezing climates, steam/condensate impulse lines shall be winterised by tracing and insulation. For remote mounted instruments, seal pot(s) shall be provided to establish a firm condensate reference point(s). The impulse line(s) shall slope downwards from the seal pot(s) to instrument process connection and to the instrument. For differential pressure type instruments, these condensate reference points shall be at the same elevation, as shown in Figure 8. For direct mounted pressure instruments, a gauge block with integral siphon should be applied. Manufacturer’s solutions for direct mounted, differential pressure type instruments may be acceptable, if a firm condensate reference point can be established. Figure 8

5.2

Steam flow measurement

OXYGEN SERVICE All components in oxygen service shall meet the requirements of PTS 31.10.11.31 NOTE:

5.3

Any medium containing more than 21% oxygen by volume or a system with air at a pressure above 50 bar (ga) is to be considered as oxygen service.

HYDROGEN FLUORIDE (HF) SERVICE The material selection for wetted parts of instruments and components shall meet the requirements of PTS 31.38.01.11 Stainless steel type AISI 316 may, under certain conditions, be subject to pitting and/or stress cracking if exposed to process fluids containing HF.

PTS 32.37.10.11 November 2009 Page 17 Impulse line tubing in HF service shall be constructed from ASTM B 165 UNS NO4400 (Monel) with Monel compression fittings. Alternatively, Monel or carbon steel welded pipes may be applied (see PTS 31.38.01.11). All valves shall be of Monel. NOTES:

5.4

1. Cold deformation shall be minimised by the application of the largest possible bending radius, limiting the extreme fibre deformation to 5% maximum. In practice, this amounts to a minimum bending radius of 10 to 15 times the diameter for small bore piping (less than DN 25). 2. Before HF is put into the system, a careful check of the tightness of compression joints and screwed connections is required. Fluorides formed upon leakage will produce a very hard metal surface which will make re-tightening of the joint practically impossible. 3. The Principal shall be consulted for the selection of impulse line material for HF service. 4. PTFE seals may be used in valves in HF service.

FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK Liquids which solidify at ambient temperatures shall be prevented from entering process tappings, primary isolation valves and impulse lines to prevent malfunctioning, blockage and/or damage. Special attention shall also be given to those gas services where hydrates may form at low temperatures. A liquid seal (6.1), diaphragm seal (6.3), external purging (6.4) or heating (7) may be applied to prevent solidification and hydrate formation.

5.5

FLUIDS CONTAINING SUSPENDED SOLIDS If process fluids contain suspended solids, these solids may settle in process tappings, primary isolation valves and impulse lines, and may ultimately cause complete blockage. If the concentration of the suspended solids is relatively low, blockage may be prevented by sloping the process connections and (short) impulse lines downwards to the process at an angle of approximately 45°. If the concentration of suspended solids is high, a liquid seal (6.1) or external purging (6.4) should be applied.

5.6

FOULING AND WAXY SERVICE Impulse lines in fouling/waxy service are likely to become plugged, even if heating is applied. In such cases, instruments with extended diaphragms or with remote diaphragm seals should be considered. In the latter case, additional purging may still be required to prevent plugging between the equipment/pipe wall and the remote seal. NOTE:

5.7

Vacuum Flashed Cracked Residue (VFCR) is known to be a non-stable liquid: delayed cracking will form coke, which plugs impulse lines. In such situations, remote seals with external purging have been successfully applied.

SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUID SLUGS Experience shows that standard 10 mm OD impulse line tubing with an internal diameter of 7 mm has a limited self-draining capability. If used in gas or vapour service, condensate formed may not flow back into the process, not even in vertical lines. Droplets tend to cluster and slugs of liquids ‘hang’ in the impulse line. ‘Hanging slugs’ have a considerable impact on pressure or differential pressure sensing instruments with a relatively low adjusted range.


For pressure and differential pressure sensing instruments with an adjusted range of 2 bar or below, one or more of the following remedial measures should be considered: − apply heat tracing to keep the process fluid in the impulse lines in the vapour phase; − apply wet legs; − mount pressure sensing instruments in the direct vicinity of the process connection, if feasible, to limit the tubing length and elevation difference between instrument and process connection; − apply wide bore tubing/piping (DN 15 or DN 20) instead of standard 10 mm OD tubing to restore the self-draining capabilities. NOTE:

5.8

If very long impulse lines are required for differential pressure sensing (e.g. differential pressure measurement across a high column or between columns), two independent pressure sensing instruments may be installed, whereby the differential is determined by subtraction. For details and limitations of this alternative, see PTS 32.31.00.32

LOW TEMPERATURE SERVICE Process liquids operating at temperatures below ambient that vaporise at ambient temperatures will evaporate upon entering the impulse lines before reaching the remote mounted instruments. The vapours so formed will push the liquid back towards the process until an equilibrium is established. This self-purging phenomenon occurs for instance in cryogenic processes operating typically between -100 °C to -170 °C. Where required, heating shall be considered to assist self-purging (e.g. LPG applications). For details, see (6.4) and (6.5). Low temperature services require expansion loops in their impulse line tubing, see (4.2.2.3).

5.9

VERY TOXIC SERVICE For personnel protection and for environmental reasons, facilities should be provided to dispel very toxic liquids from instrument impulse lines into the process equipment so that maintenance can be performed safely. A mobile seal liquid refill pump unit should be used to displace very toxic liquids by safe liquids during operation. See also (4.3). For sites where the ‘vent and drain’ concept is still applied, the following shall apply to very toxic fluids: • • • • • •

Manifold valves shall be provided with an interlocking system. All vents from instruments/manifolds and seal pots shall be connected to flare. All drains shall be connected to a drain vessel or covered pit which is allocated for very toxic products and for which adequate disposal should be arranged. The required length of tubing for the vent and drain lines shall be added on the relevant hook-up drawing. The instrument or the manifold shall be provided with filling/ flushing connector(s), if flushing and neutralising of the instrument and manifold is necessary before the instrument is disconnected. For details see (4.3). The maximum allowable concentration of very toxic components in fluids which may be vented to atmosphere shall be approved by the Principal.


‘SOUR’ OR ‘WET H2S’ SERVICE ‘Sour’ or ‘Wet H2S’ service is defined in PTS 31.38.01.11 Materials which, under any process condition, are in contact with process water or aqueous condensate shall comply with ISO 15156 or NACE MR0103, as applicable, and the relevant piping class. If impulse line components cannot be obtained in accordance with these standards (e.g. the rolled thread of some male compression fittings), the Principal shall be consulted. Valve head spindles and/or parts of them in contact with sour fluids shall be constructed from 17-4 PH stainless steel, stellite-coated stainless steel, stellite or Hastelloy-C, complying with ISO 15156 or NACE MR0103, as applicable. NOTES:

1. ISO 15156 shall apply to oil and gas production facilities and natural gas sweetening plants. NACE MR0175 is equivalent to ISO 15156. 2. NACE MR0103 shall apply to other applications (e.g. oil refineries, LNG plants and chemical plants). 3. The front ferrules of compression fittings are the second or third sealing in the fitting and, since they need to have higher hardness in order to function properly, they may be exempted from the hardness limitations.


SEALING AND PURGING

6.1

LIQUID SEAL Seal liquids for use in impulse lines shall be selected in consultation with the party responsible for the process design, considering the following aspects: -

effect of process fluid on seal liquid, i.e. the resistance/stability of the seal liquid in contact with the process fluids (polymerisation, disintegration, solubility of process Some sealing liquids decay in sour service. H2S reacts for instance with fluid);Example: silicon oil and causes polymerisation.

-

effect of seal liquid on process fluid (process fluid contamination, poisoning of catalyst);

-

maintenance: the seal liquid and the selected hook-up shall guarantee a low maintenance effort. A seal liquid that needs frequent replacement or replenishment for instance is not acceptable;

-

seal liquid properties (temperature expansion coefficient, evaporation and freezing point, kinematic viscosity, handling safety, cost of purchase, tracing, disposal etc.). This includes the following aspects: • the seal liquid density in the (traced) impulse line shall be higher than the density of any of the process fluid components to prevent gradual replacement of sealing liquid by components from the process fluid; • the kinematic viscosity in the impulse line shall not exceed 200 mm2/s to obtain an acceptable response time; • the seal liquid shall not evaporate under any operating condition at local ambient conditions; • the seal liquid shall not freeze or shall be protected against freezing at local ambient conditions; • the seal liquid shall not be very toxic or flammable.

Three groups of seal liquids are listed below in order of preference: − ‘Familiar’ seal liquid: One of the heavy components, present in the process fluid, is selected as sealing liquid. If the process fluid contains water, water should be considered as a first choice, as it is attractive for its chemical and physical properties (non-toxic, non-flammable, non-viscous, immune to H2S, density higher than hydrocarbons, low temperature expansion coefficient), low cost, high availability, ease and safety of handling and disposal. − ‘Foreign’ seal liquid: A fluid not present in the process fluid. It shall not harm nor be harmed by the process fluid. − Process liquid: The process liquid is used as seal liquid.

PTS 32.37.10.11 November 2009 Page 21 Frequently used low-cost seal liquids are water, glycol, glycerine and silicon oil (e.g. used silicon oil, drained from transformers). NOTES:

1. The process liquid is only suitable as sealing liquid, if it is self-condensing under any normal and abnormal operating pressure at the highest ambient temperature. 2. If the process liquid is a mixture of for instance hydrocarbons, the density of process fluids in wet legs may gradually drift away from the density in the associated equipment as a result of ‘stripping’. 3. If the composition of a process liquid mixture in the equipment changes gradually from light to heavy, self-condensing will replace the light components of the process fluid in the reference leg by heavier components, such as water. This will for instance happen in hydro-conversion plants, that are started up with a light feedstock and subsequently converted to heavier feedstock with a composition that change gradually as a result of decaying catalyst activity. 4. Applications using ‘familiar’ and ‘foreign’ seal liquids have the advantage that the wet leg(s) can be filled prior to start-up and eventually zero checked. This will give a reasonable instrument reading at initial plant start. 5. Level applications using process liquid in the wet reference leg require a liquid level in the equipment above the lower nozzle elevation and sufficient pressure to fill the legs with process fluid at initial plant start.

Where the above considerations do not result in a satisfactory solution, the use of remote seals or another measurement principle should be considered. Where seal liquids are used in impulse lines, a nameplate shall be installed near the instrument with information about the seal liquid, such as the seal liquid name. Additionally, the seal liquid density and the height of the wet leg(s) in mm shall be mentioned for pressure and dP type level/pressure measurements.

6.2

LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS

6.2.1

Introduction The selection of seal liquids and the hook-up arrangement for differential pressure type level instruments with wet legs is defined in global terms in PTS 32.31.00.32 This PTS section provides further guidance. NOTES:

1. Seal liquid selection for the reference leg applications requires special attention, since the LRV calculation includes a term for elevation difference (upper nozzle < > transmitter) times density of the reference leg. The LRV shifts if the actual density in the reference leg differs from the one used for LRV calculation. 2. For transmitters mounted just below the lower equipment nozzle (i.e. transmitters located less than 150 mm below the lower equipment nozzle), only density changes in the reference leg affect the LRV. For transmitters mounted well below the lower equipment nozzle (i.e. transmitters located more than 150 mm below the lower equipment nozzle), changes in density in the measurement leg will also affect the LRV and may justify the use of seal liquids in the measurement leg. 3. For transmitters mounted well below the lower equipment nozzle, changes in densities in the legs will partially counteract each other in their effect on LRV. The density drift in the measurement leg may however differ from the density change in the reference leg and even if they are equal, a density drift in the reference leg is only partially compensated by the same density drift in the measurement leg. 4. Apart from LRV errors resulting from liquid density changes, the operating pressure affects the measurement accuracy in two ways: − −

The transmitter accuracy is affected by variations in operating pressure. This effect is however minor compared to other measurement errors; The LRV calculation includes a term for elevation difference (upper nozzle < > 0% level) times vapour density, which varies with operating pressure. This effect of vapour density on the LRV may be considerable for high pressure applications, as shown in Appendix 2.

5. Appendix 2 provides examples for the effect of changes in process variables on the measurements.


Apart from general seal liquid selection aspects discussed in (6.1), the following additional aspects are specifically relevant for wet leg level measurements, as they may cause measurement errors: − If the selected seal liquid dissolves gases such as hydrogen, a (sudden) pressure drop will cause the liquid in the reference level to rise (a phenomenon comparable with the opening of a ‘coca-cola’ bottle) and overflow into the equipment. The loss of reference leg liquid will cause a zero error. − The density of some seal liquids (e.g. silicon oil) varies considerably with temperature. To limit the effect of changing densities, it should be considered to keep seal liquids in wet legs at a constant temperature by the use of tracing and insulation. − If dry inert gas is continuously fed into the vapour space of equipment (e.g. blanketing gas), the process liquid and the wet leg seal liquid will gradually evaporate. Wet reference legs (i.e. without remote seals) are unsuitable for such applications. 6.2.2

In situ calibration The accuracy tolerance class for each measurement shall be defined in accordance with the requirements of PTS 32.31.00.32 In situ calibration may be required to mitigate measurement errors caused by liquid density variations and operating pressure. Two types of hook-ups can be distinguished: −

A hook-up that allows in situ zero and span check at the actual operating pressure. If the liquid density in the wet leg(s) varies considerably over time, the resulting measurement error might become unacceptable. Similarly, if the instrument is zero checked at atmospheric pressure, the measurement error caused by a (high) gas density might become unacceptable. This type of hook-up should be selected if calculations show that the measurement error caused by variations in wet leg liquid density and/or actual gas density is unacceptable.

− A hook-up that does not allow in situ zero and span check. This hook-up may be selected in all other cases. In situ zero and span checks require an equalising line between the lower and upper equipment connections. NOTES:

1. Some examples of measurement errors caused by liquid or gas density variations are given in Appendix 2. 2. One of the cases in Appendix 2 reflects the measurement error caused by transmitter calibration at atmospheric pressure. The resulting measurement error for this high pressure application is extremely high and would thus require a hook-up that allows in situ calibration. 3. If the lower nozzle elevation corresponds with the LRV (0% level), in situ zero calibration is performed with an empty but pressurised equalising line. Similarly, if the upper nozzle elevation corresponds with the URV (100% level), in situ span calibration is performed with a full and pressurised equalising line. 4. If nozzle elevations do not correspond with the LRV and URV, in situ calibration with a standard hook-up arrangement is still possible for ‘intelligent’ measuring devices. As a first step, the LRV and URV are determined with an empty and full equalising line respectively. This provides the actual density figures required to calculate the final LRV and URV settings. As a second step, the final LRV and URV are entered into the transmitter by remote communication. 5. If nozzle elevations do not correspond with the LRV and URV, in situ calibration of ‘non-intelligent’ measuring devices is only possible if the hook-up is modified so that the equalising line can be filled to the levels corresponding with the 0% and 100% readings.


6.2.3

Hook-up selection The table below should be used for hook-up selection of wet leg level measurements.

Table 1

Hook-up selection table for wet leg level measurements (see notes 1 and 2)

Transmitter elevation (note 1)

Less than 150 mm below the lower equipment nozzle (see Figure 9) ↓

Liquid in measurement leg (see note 2) Liquid in reference leg (see note 2) Zero & span calibration at operating pressure

More than 150 mm below the lower equipment nozzle (see Figure 10)

Process liquid ↓ Process liquid ↓

↓

Yes

No

↓

↓

Process liquid

The same ‘familiar’ or ‘foreign’ seal liquid in both legs

↓ ‘Familiar’ or ‘foreign’ seal liquid ↓ ↓

↓ Process liquid ↓

↓

Yes

Yes

No

No

↓ ‘Familiar’ or ‘foreign’ seal liquid ↓ ↓

Yes

↓

↓

No

Yes

No

↓

↓

Resulting installation requirements (see note 6) ↓ Seal pot in reference leg Seal pot in measuring leg Equalising line Manifold valves (see note 5)

Figure 9

↓

↓

↓

↓

↓

↓

↓

No

Yes

No

Yes No

Yes

Yes

Yes

No

Yes

No

Yes

No

Yes

No

Yes

No

I-I-V-V

I-I-E-V

I-I-V-V

I-I-V-V

I-I-V-V

I-I-E-V

I-I-V-V

I-I-V-V

I-I-V-V

I-I-V-V

Typical hook-up for transmitter, mounted less than 150 mm below the lower equipment nozzle


Figure 10

NOTES:

Typical hook-up for transmitter, mounted more than 150 mm below the lower equipment nozzle

1. If ‘familiar’ or ‘foreign’ seal liquid is used for the measurement leg, the transmitter shall be mounted more than 150 mm below the equipment nozzle to permit seal pot installation. 2. For the definition of ‘familiar’ and ‘foreign’ seal liquids, see (6.1). 3. For process equipment operating under partial or full vacuum conditions, filling of wet legs is cumbersome. For such applications, diaphragm seals or another level measurement principle should be considered as a first choice. 4. For standardization reasons, the Principal may decide to use only a limited number of the hook-up types presented in Table 1 for all applications. 5. Manifold valves ‘I-I-V-V’ means Isolate/Isolate/Vent/Vent and ‘I-I-E-V’ means Isolate/Isolate/Equalise/Vent, see Figure 11 and Figure 12. 6. Hook-up requirements are based on the following rationale: a) Seal pots with vent valves are provided as buffer volume for all wet reference legs. b) Seal pots with vent valves are provided as buffer volume in measurement legs if: • the transmitter is mounted more than 150 mm below the lower equipment nozzle and zero and span calibration is required or • the transmitter is mounted more than 150 mm below the lower equipment nozzle and the measurement leg contains ‘familiar or ‘foreign’ liquid. c) The vent valves on the seal pots are required for zero & span calibration at operating pressure and/or for filling of the wet leg with process fluid. d) An equalising line between the upper and lower equipment nozzle is needed for all applications, where zero and span calibration at operating pressure is required, see Figure 9 and Figure 10. e) Manifolds for wet leg level measurements shall only be provided with an equalising valve (see Figure 12) if required to fill the reference leg with process liquid, i.e. both legs contain process liquid and no equalising line is installed between the upper and lower equipment nozzle (Figures 9 and Figure 10). In all other cases, the manifold shall be provided without equalising valve (Figure 11) to prevent mixture of measurement and reference leg liquids and/or partial loss of the wet reference leg.


Figure 11

Double isolate/vent type manifold

Figure 12

Double isolate/ equalise/vent type manifold

Valves provided I-I-V-V Valves provided I-I-E-V

6.3

DIAPHRAGM SEALS

6.3.1

Introduction Remote diaphragm seal applications and their installation (tracing/insulation) is covered by PTS 32.31.00.32 This PTS Section provides additional requirements for installation and calibration of diaphragm seal type level transmitters.

6.3.2

Remote seals for level applications

6.3.2.1

Reducers For new installations, the equipment nozzle shall match the flange size of the diaphragm seal. If reducers are required to match the nozzle size of existing equipment (e.g. DN 50) with the diaphragm seal size (e.g. DN 80), eccentric reducers shall be used and the bottom of the reducer shall be flush with the bottom of the primary isolation valve to prevent dirt from collecting/settling.

6.3.2.2

In situ calibration If the remote seal was selected to prevent impulse line plugging in fouling or waxy service, an equalising line would also become plugged and shall therefore not be installed. Hence in situ zero and span calibration at the actual operating pressure is not possible. Apart from flushing/purge connections, vent connections are required for in situ zero calibration at atmospheric pressure (see Figure 13). For remote seals, used in applications where no plugging risk exists and where the liquid kinematic viscosity can be kept below 200 mm2/s, an equalising line may be installed between the lower and upper nozzle to allow in situ zero/span calibration at the actual operating pressure (see Figure 14). Drain/vent or flushing/purge connections shall be installed as required.


Figure 13

Figure 14

Hook-up without equalising line

Hook-up with equalising line

Flushing rings may be ordered with the diaphragm seals. Alternatively, butt-welded primary isolation valves may be used provided with orifice flanges on the diaphragm seal side. The installation details and scope split shall be agreed with Mechanical Engineering.


EXTERNAL PURGING External purging may be considered only if other methods to eliminate problems caused by condensation, vaporisation or plugging are not practicable. Its use however, should be avoided whenever possible since it could cause false differentials, the installation costs are higher and more frequent maintenance is required. Since the process fluid may enter part of the impulse line on purge failure, the selected impulse line materials shall be suitable for the process fluid. The purge fluid shall be free from solids, non-corrosive and in single phase at all operating temperatures and pressures. The purge fluid shall not interfere with the process nor react with the process fluid. Purge systems shall have a guaranteed source of supply at a pressure which is permanently higher than the maximum process pressure, but lower than the design pressure of the process equipment or piping. A low but constant flow rate shall be maintained. The fluid velocity at the process connection shall be approximately 0.06 m/s for liquid purge and 0.6 m/s for gas or steam purge. The purge injection point should be close to the process connection(s) to limit the effect of pressure drop caused by the purge flow in the impulse line(s). NOTES:

1. Purge gas injection near the instrument may cause considerable measurement errors in low pressure and vacuum applications due to relatively high pressure drop in the impulse lines. 2. The purge injection point may be located close to the instrument, if calculations show that the pressure loss in the impulse line(s) has a negligible effect on the measurement accuracy.

A purge assembly should be used, consisting of a filter, soft seated non-return valve(s) and vent valve with anti-tamper facilities. A constant purge flow can be reached by one of the following methods: − A restriction orifice in the form of a purge orifice nipple. A restriction orifice may be used, if the purge supply pressure is constant and high enough to guarantee a stable purge flow under all operating conditions. For gas and steam service, this is reached at critical flow across the restriction orifice, i.e. the purge flow rate is independent of variations in process operating pressure. For details on purge orifice nipples, see standard drawing S 37.805. − A constant flow device. For side mounted purge pipes in equipment, see Standard Drawings S 38.047 and S 38.048. Top or side mounted purge pipes and primary isolation valves are the responsibility of Mechanical Engineering. Instruments with gas purging shall be mounted above the maximum liquid level and the impulse lines shall slope downwards from the instrument/manifold to the process connection(s).


SELF-PURGING

6.5.1

Remote mounted instruments Where self-purging is applied, process connections should be located on the top or side of the equipment/process piping. For process connections at the side of the equipment/process piping, the impulse line(s) shall drop vertically downwards from the instrument and then continue horizontally with a slope of approximately 1:5 down to the primary isolating valve(s) at the process connection(s). To prevent measurement errors due to liquid static head if the self-purging is not operating properly, the vertical drop from the instrument shall be as short as possible, see also (5.7). The first part of the impulse line(s) at the primary isolation valve side shall be insulated over a length of at least 300 mm to reduce heat influx into the process. The remaining part shall have either: − an exposed, bare length of at least 300 mm to enable evaporation of the process fluid by heat influx from the surrounding atmosphere. This arrangement shall be used if all process liquid components evaporate under all normal and abnormal operating pressures at the lowest ambient temperature; or − a heated and insulated length of at least 300 mm to assist evaporation. This arrangement shall be used, if the liquid contains heavy components which will not evaporate under any of the normal or abnormal operating pressures at the lowest ambient temperature.

6.5.2

Direct mounted instruments The currently available direct mounting products are less suitable for instruments in low temperature service, due to the requirement to reduce heat influx into the process and low temperature limits of instruments, see also (2.2.3). NOTE:

The lower temperature limit of instruments depends on the applied sensor fluid and on limits for the electronics. The temperature drop between the process and a direct mounted instrument depends on the properties of the direct mount components, such as dimensions/exposed area/number and type of joints and materials of construction.


HEATING AND INSULATION

7.1

GENERAL The type of heating (steam heating, electrical tracing or other means) of instruments and impulse lines shall be established in consultation with the Principal. Tracing temperatures shall be carefully selected to prevent overheating, resulting in boiling impulse line liquid.

7.1.1

Remote mounted instruments If transmitters require heating, pre-assembled instrument housings with heating facilities and insulation shall be provided around the manifold and transmitter housing.

7.1.2

Direct mounted instruments If direct mounting of heated instruments is considered, the following aspects need specific attention:

7.2

−

interface with heating and insulation of the process piping or equipment;

−

availability of prefabricated and readily removable enclosures with heating facilities and insulation for instruments within the selected direct mounting concept;

−

length and additional weight resulting from heating and insulation to prevent too high stress on process nozzles.

STEAM HEATING Steam heating systems shall comply with PTS 31.38.30.11. The steam supply and condensate return piping shall be short. The steam supply and condensate return piping (including steam trap) are the responsibility of Mechanical Engineering. The manifold and instrument body shall be heated by means of a tracer block. Special tubing (see 4.1) should be used to heat instrument impulse lines. Special tubing should also be used if impulse lines are winterised by steam heating. To prevent overheating, non-conducting spacers shall be fitted between the impulse and heater tubing at 400 mm intervals. The arrangement shall be such that the instrument can be removed without disconnecting the tracer tubing and/or tracer block. If steam heating is applied for reasons of high fluid pour point, the heater tubing and the impulse line shall be clamped together. Clamping material shall be stainless steel. The total number of joints in the tracer tubing shall be kept to a minimum. NOTES:

1. Steam heating of in-line instruments (e.g. control valves, vortex meters, turbine meters, positive displacement meters, etc.) is the responsibility of Mechanical Engineering. 2. Hollow bolts shall not be applied for heating of instruments.

Each instrument shall have a dedicated steam supply and condensate return line with isolating valves, labelled with the instrument tag number. The steam supply to one instrument shall not be divided into parallel sections, i.e. for each instrument a single continuous path is required from the steam supply point up to the steam trap. The steam flow in the tracer tubing shall be downwards and pockets in the tubing shall be avoided because build-up of condensate will prevent a continuous steam flow. Each tracer line shall terminate in a condensate return line via a steam trap.


ELECTRICAL TRACING The heating equipment shall satisfy the requirements for electrical safety in accordance with the area classification. NOTE:

Certain elements are certified only when installed in the manifold block. In such cases, power to the heating elements shall be switched on only when the elements are inserted in the manifold block.

The arrangement of the electric tracing shall be such that transmitters can be removed without disconnecting the electrical heating block. All electrical trace heating components (except the electrical heating block and/or electrical heater attached to the manifold) are the responsibility of Electrical Engineering and are covered in PTS 33.68.30.32 Electrical tracing shall not be applied in processes where the upper design temperature exceeds the temperature limit of the selected heating tape. If self-regulating tracing tape is used (e.g. for winterising), its ‘power off’ point shall be below the temperature at which the impulse line liquid starts to strip/evaporate.

7.4

INSULATION Traced impulse lines, traced instrument parts and all steam supply and condensate return lines shall be insulated. All couplings in the tracer tubing and the impulse lines shall be accessible without removing the complete insulation. Insulation of impulse lines, seal pots, steam supply lines and condensate return lines is part of the scope of Mechanical Engineering. For insulating the instrument bodies, manifold blocks and tracer blocks, prefabricated enclosures shall be applied fitting closely around the parts which are to be heated. These are part of the scope of Instrument Engineering. The body enclosure shall be constructed so that it can easily be removed in the event that the instrument needs maintenance. NOTES:

1. The electronic parts of instruments should not be installed within an enclosure in order to prevent overheating and downgrading of the area classification around that part. 2. Winterising shall not be provided for impulse lines in freezing climates when they are installed in temperature-controlled buildings, such as demineralised water plants.


REFERENCES In this PTS reference is made to the following publications: NOTE:

Unless specifically designated by date, the latest edition of each publication shall be used, together with any amendments/supplements/revisions thereto.

PETRONAS STANDARDS Index to PTS publications and standard specifications

PTS 00.00.05.05

Definition of temperature, pressure and toxicity levels

PTS 01.00.01.30

Painting and coating of new equipment

PTS 30.48.00.31

Gaseous oxygen systems

PTS 31.10.11.31

Piping - general requirements

PTS 31.38.01.11

Protective steam heating of piping systems

PTS 31.38.30.11

Instrument engineering procedures

PTS 32.31.00.10

Instruments for measurement and control

PTS 32.31.00.32

On-line process stream analysis - sample take-off and transportation

PTS 32.31.50.10

Electrical trace heating

PTS 33.68.30.32

STANDARD DRAWINGS Instrument impulse lines - metric version

S 37.001

Instrument impulse lines - imperial version

S 37.002

Instrument mounting supports

S 37.004

Purge orifice nipple

S 37.805

Parallel threaded connections

S 37.808

Details of parallel threaded pressure transducers

S 37.809

Mounting plate type A2

S 37.815

Mounting plate type B2

S 37.816

Purge pipe for carbon steel and low-alloy steel equipment

S 38.047

Purge pipe for stainless steel and non-ferrous equipment

S 38.048

AMERICAN STANDARDS Pipe flanges and flanged fittings, NPS 1/2 through NPS 24

ASME B16.5

Issued by: American Society of Mechanical Engineers 345 East 47th Street New York NY 10017, USA

Standard specification for seamless and welded austenitic stainless steel tubing for general service

ASTM A 269

Standard specification of nickel-copper alloy

ASTM B 165

Standard specification for seamless and electric welded low-alloy steel tubes

ASTM B 423


Standard specification for UNS N08028 seamless pipe and tube

ASTM B 668

Issued by: American Society for Testing and Materials 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959 USA

Materials resistant to sulfide stress cracking in corrosive petroleum refining environments

NACE MR0103

Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas production

NACE MR0175

Issued by: NACE International 1440 South Creek Dr. Houston, TX 77084-4906, USA

INTERNATIONAL STANDARDS Mating dimensions between differential pressure (type) measuring instruments and flanged-on shut-off devices up to 413 bar

IEC 61518

Issued by: Central Office of IEC (Sales Dept) 3, Rue de Varembé P.O. Box 131 Geneva CH-1211 Switzerland Copies can also be obtained from national standards organisations.

Fluid systems - Sealing devices – O-rings ISO 3601-1 Part 1: Inside diameters, tolerances and size identification code Plain end steel tubes, welded and seamless General tables of dimensions and masses per unit length

ISO 4200

Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas production

ISO 15156

Issued by: International Organisation for Standardization 1, rue de Varembé CH-1211 Geneve 20 Switzerland Copies can also be obtained from national standards organizations

SHELL DOCUMENTS Measurement Validation and Comparison – Issue 2.0

OP 98-30219

PTS 32.37.10.11 November 2009 Appendix 1 APPENDIX 1

PRESSURE AND TEMPERATURE LIMITATIONS OF SS TUBING AND PACKINGS

Table 2 Design temperature, °C

- 200 - 150 - 100 -50 +38 +50 +100 +150 +200 +250 +300 +350 +400 +450 +500 +538 NOTES :

Pressure and temperature limitations of SS tubing and packing Maximum allowable working pressure, bar (ga) SS tubing 12 mm OD wall thickness 2.0 mm 470 470 470 470 470 470 470 450 400 370 357

SS tubing 1/2” OD wall thickness 0.083” 462 462 462 462 462 462 462 443 392 365 350

SS components with grafoil packing 413 413 413 413 413 399 351 320 297 276 260 245 235 200 -

SS components with PTFE packing and PTFE tape 400 400 400 400 350 300 200 -

1. The maximum allowable working pressures P for 10 mm OD x 1.5 mm wall thickness stainless steel tubing as per MESC specification 74/051 have been calculated using the formula:

P=

2 × S m × t min Domax − 0.8 × t min

in which: P Sm

= =

maximum allowable working pressure; the maximum allowable stress in the material caused by internal pressure

tmin

=

at the design temperature; the minimum standard wall thickness;

Domax = the standard maximum outside diameter. 2. The tolerances for metric sized tubing are in accordance with ISO 4200 and those for imperial sized tubing are in accordance with ASTM A 269.

PTS 32.37.10.11 November 2009 Appendix 2 APPENDIX 2

EXAMPLE OF CALCULATIONS OF THE EFFECT OF PROCESS VARIABLE CHANGES ON dP LEVEL MEASUREMENTS

Figure 15

Effect of process variable changes on dP level measurement

Applicable formulae:

dU =

(12.03 × MW × P ) [(t + 273.16)Z ]

PTS 32.37.10.11 November 2009 Appendix 2 Table 3

Effect of process variable changes on dP level measurements Scenarios for process variable changes Ref. Higher Calibration Lower Higher Higher Lower P at atm. MW t dL dTH case Pressure

Process data Pressure Molecular Weight Gas temperature Compressibility Process liquid density Measured leg density

P MW t Z dL dTX-H

bar (abs) g/mol °C kg/m3

181 28 20 1 820

190

1

181

28 20 1 820

28 20 1 820

22

Reference leg density

dTX-L

kg/m3 kg/m3

dU LRV URV

kg/m3 mbar mbar

181 28

181 28 20 1

20 1 820

1 820

861

1000

1000

1000

1000

1000

1000

1000

1000

1000

1000

1000

1000

35

Combined

181 28 20 1 820

190 22 35 1

861 990 990

990 990

Calculated results Gas density Lower Range value Upper Range Value

208.0

218.3

1.1

163.4

197.8

208.0

208.0

163.2

-179.2 -59.2

-177.0 -58.9

-224.9 -64.2

-189.1 -60.2

-185.5 -59.4

-178.2 -50.1

-176.8 -56.7

-185.7 -48.8

-

1.3 0.4

-25.5 -8.6

-5.5 -1.8

-1.2 -0.4

0.6 15.3

1.4 4.1

-3.6 17.6

Measurement errors Shift in LRV Shift in URV

% %

Last page of this PTS

32371011 Nov 09

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