Instrumentation Selection -When it has been decided that instrument is required to be installed for specific service, the next job is to select to most suitable instrument type. The following are several factors that should be considered when choosing the right instrument: Process condition and properties -The fluid phase is the first thing to concern: gas, liquid or two-phase. Some type instruments are only suitable for particular phase while some others work properly on all kind of fluid phase.
-Selected instrument shall also withstand to pressure and temperature operating of process fluid. -The process condition of fluid whether clean, dirty or containing slurries will also limit the instrument type selection. In addition, corrosiveness of fluid will determine the selection of its material. -Range of process variable to be measured shall be specified. The wide range will require instrument type which has high turn down ratio; it means some type of instrument which has low turn down ratio will not be applicable. -Some instrument type is not designed for high viscosity services. Turbine meter will not work properly in high viscosity liquid, the float of magnetic level gauge might stuck and not floating to follow the level interface change -Other properties such as Reynolds number shall be satisfied to particular number for some type of flow instrumentation. Performance requirements Each Instrument has static and dynamic characteristics. Accuracy, repeatability and linearity are some of characteristic that mostly being concern. The selection of instrument based on performance requirement is depend on the purpose of the instrument whether is it for process monitor, process control, safety, inventory measurement or custody transfer metering. Environmental condition -The location of instrument shall be identified whether it is classified as hazardous area or not. If so, the design of instrument shall be properly chosen to certified device which comply with the indented area. -Ingress protection of instrument enclosure shall be specified to suit the environment whether it is located in dry, dusted, offshore installation, etc. -The ambient temperature shall also be considered because it will affect some parts such as electronic parts, elastic material such as seal, packing.
-For harsh environment such as extreme temperature, the use of additional instrument enclosure which is equipped with heater shall be taken into account.
Installation -Space usually becomes an issue especially in offshore platform. For example, the issue in flow measurement is that some type of instrument requires straight run. -In other example, installation of level instrument which measuring low elevation sometime became an issue when its bottom might contact with the structure surface.
Maintenance There are several factors which will impact during maintenance process:
Requirement of process shutdown
The capability of instrument to be calibrated in bench or vendor workshop
Ease of dismantling
Special tools/equipment requirement
Requirement of specialist personnel
Availability of spare part
Cost Besides initial cost of the goods price and its installation, maintenance cost should be thoroughly evaluated in all aspects which comprise of spare part price, third party service and downtime/production loss if the instrument required by plant operation. For flow measurement, DP type flow meter creates process cost (pressure loss). If the pressure outlet of the system is lower than the requirement, it needs more compression or pumping system which will significantly increase the budget.
Instrument Data Sheet Description:
Instrument Data Sheet is a document containing specification and information of an instrument device.
Including the following: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Tag number identification Service description Location (line number/equipment no.) P&ID number Process data Calibrated range (if applicable) Material Performance details (such as accuracy, linearity – if applicable) hazardous certification (for electrical device) accessories required
References documents:
1. 2. 3. 4. 5.
Process Data Project Specifications Calculations Vendor catalogue Code and standard
References drawings:
1. P&ID
Notes: When the data sheet completed, it is attached to requisition which to be sent to several vendors. Vendors will offer their quotation with various model and manufacturer among the offers. It is an instrument engineer responsibility to evaluate all quotation and determine which offer is technically acceptable. Having been considered its technical and commercial aspects, the instrument is purchased. Following the purchase order, vendor will submit supporting document and drawing. Based on vendor data, instrument data sheet may be updated to accommodate details to make the data sheet “as-built”. Finally, data sheet along with its supporting vendor data are stored in library or document control and will be referred during construction, operation and maintenance.
Instrument Interconnection Block Diagram
Description:
Interconnection block diagram is a drawing showing interconnection between each device including instrument, junction box, marshaling cabinet, panel, etc Interconnection block diagram should also indicate cable number. This drawing can provide a glance view of overall connection of system.
References Documents:
1. 2. 3. 4.
Instrument index Junction boxes list Marshaling cabinet list Control panels
References Drawings:
1. Instrumentation cable layout 2. Instrumentation and control architecture
Notes: As a reference for preparing junction box wiring diagram/ connection list and marshaling cabinet wiring diagram which both subsequently are required for preparing instrument loop diagram. Together with instrument cable layout, this drawing is also used as a reference for preparing instrument cable schedule.
Instrument Cable Schedule
Description:
Cable Schedule is a document containing list of instrument cable. This document shows cable as well as gland required by each instrument or connection. Including the following: 11. 12. 13. 14. 15. 16. 17.
Cable number Cable type Cable specification Cable size Cable length Source and destination termination description Cable gland and size for each incoming cable
References documents:
6. Instrument index 7. I/O list References drawings:
2. Instrument cable layout 3. Interconnection block diagram
Note: Instrument cable layout and interconnection block diagram will make the preparation of cable schedule more convenience in specifying cable source and destination. Cable schedule is a reference in preparing Material Take-Off of cable for procurement. However, cable lengths shown on this document are approximate only. Therefore, there should be contingency for material procurement to allow spare for cable cutting, unexpected barrier in the field, riser, etc. Cable schedule will be referred also during construction phase, however it is not recommended to cut the cable based on the length information stated on the cable schedule. For actual cutting during installation, the common practice is to pull the cable from its drum and cut in the field.
Instrument Index Description:
Instrument index is a document containing list of instrument devices within a plant. Instrument index shall include tag number of all physical instruments (e.g. field instrument, physical alarm and indicator) and pseudo instrument which commonly named “soft tag” (e.g DCS indication, alarm, and controller). Instrument index shall be created at the beginning of project and considered as a live document which should be kept updated even though the plant has been operated. Instrument index shall be revised if there is any plant or system modification which impact to additional, removal, or resetting of instrument. Including the following: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Tag number Loop Number Type of Instrument Location Service description P&ID Number Line number or equipment number I/O Type Control System Range or set point along with engineering unit used Applicable reference Document (Instrument Data Sheet Number, Hook-up Drawing Number, Instrument Layout Number, Loop Drawing Number) 12. Package Number 13. Manufacturer 14. Model Number References documents:
1. Cause & Effect References drawings:
4. P&ID 5. HMB (Heat and Material Balance)
Note: From its self explanatory name, instrument index will be referred as an index for many purposes as follow:
As a basis to prepare the I/O list by extracting only the tag number which has I/O point Searching, Listing, Filtering a tag number
Instrument Layout Drawing Description:
Instrument Layout is also known as instrument location plan. This drawing shows the exact position of each instrument with reference to plant layout.
The point indication of instrument position and its mounting stand where instrument to be mounted and process tap location. Often the tap location and the instrument are separated quite distant. In some project, it is not mandatory to show the process tap location. Elevation information of instrument (and its mounting stand) and process tap. Junction box location including its elevation. Instrument Air Manifold location including its elevation.
To prepare instrument layout, designer should obtain piping plan which will used as a background. Refer to Piping isometric and P&ID to verify the location of tapping point location. Instrument shall be mounted on instrument stand at location as close as possible to the tapping point or at location where required by operator for ease maintenance/reading.
References documents:
1. Cause & Effect References drawings:
1. P&ID 2. Isometric 3. Piping Plan
Note:
Instrument Hook-up Drawing Description:
Hook-up drawing is a detailed drawing showing typical installation of instrument in a correct manner so that instrument operates properly (gives accurate indication and prevent any issued which could potentially affect the measurement such as liquid trap in gas impulse line). Including the following:
Instrument Tag No. Instrument Type. Instrument Location & Description Tubing between instrument and taping point Tubing slopes Position of instrument in reference to process tapping point, Scope break between instruments vs. piping. Bulk material required for each installation. Bulk material details and specification (size, type and material) and the quantity.
Types of Hook up Drawing: Process Hook-Up This hook-up drawing contains typical installations for instrument which connects to the process Pneumatic Hook-Up. This hook-up drawing contains typical installations for instrument which requires instrument air such as control valve, actuated valve .
References documents:
1. Instrument Data Sheet 2. Instrument Catalogs and operation Manuals 3. Instrument Index References drawings:
4. 5. 6. 7.
P&ID, Installation Detail Specification Piping Specification Piping GA
Notes:
During project construction phase, this drawing is also referred as a guidance of how to install the instrument properly. The Symbols must be as per ISA Standard ISA 5.1
