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ENGINEERING DESIGN GUIDE PETROCHEMICAL PLANT DESIGN PIP~G
STRESS ANALYSIS
Prepared by Michael D Vasse
This document and the d=ign it avers are the property of BECHTEL. They are merely loaned and on the borrower’s express agreement that they will not be reproduced, copied, loaned, exhibited, or used except in the limited way and private use permitted by any written mnsent givm by the lender to the borrower.
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BY DES. 6UIOE NO.
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TABLE OF CONT-
1.0
PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4
2.0
SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4
3.0
ASSOCIATED DESIGN GUIDES AND FORMS . . . . . . . . . . . . . . . . . . 3.1 Design Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .,.4 3.2 Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...4
4.0
DEFINITION
5.0
GENERAL PHILOSOPHY
6.0
RESPONSIBILITIES
7.0
GENERAL WORKING METHODS
m **
4 F :.
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5
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6
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7 r
8.0
9.0
10.0
SPECIFIC WORKING ~~ODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Thermal Loads and StressComidemtiom . . . . . . . . . . . . . . . . . . 8.2 Sustained hadsand StressComidemtiom Stress Considerations . . . . . . . . . . . . 8.3 Dynamic andOtherhadsand 8.4 had Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Rotating Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...16 8.6 Air Cooled Heat Exchangers(Air Fans) . . . . . . . . . . . . . . . . . . . . 8.7 Shelland Tube Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . ...18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...18 8.8 FlredHeaters 8.9 Nozzle Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...18 8.10 Buried Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...19 8.11 Cryogenic Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...21
10 10 12 13 15 17
RECOmmG AND TRANS~TTAL OF S=S ENGINEERING DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...22 9.1 Piping CriticalUlne Lii . . . . . . . . . . . . . . . . . . . . . . . . . . . ...22 9.2 Stress Sketches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..22 9.3 Calculation Index . . . . . . . . . . . . . . . . . . . . . . . ..$. .$.. . ...23 9.4 Expansion Joint Data Sheets . . . . . . . . . . . . . . . . . . . . . . . . . ...23 9.5 Spring Data Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...23 CHECKING STRESS CALCULATIONS. . . . . . . . 10.l Preliinary Review... . . . . . . . . . . . . . . . 10.2 Criticallines in Dossiers . . . . . . . . . . . . . . . 10.3 Calculations relatingto the Groups in10.2 . . .
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I . APPENDIX A
APPENDIX B
BASIC DATA REQUIRED AT START OF PROJECT AND DEFAULT VALUES FOR INITIAL CALCULATIONS.
3 Pages L
A SIMPLIFIED METHOD FOR PIPING D~IGNERS TO ASS= PIPING FLEXIBILITY.
2 Pages
APPENDIX C
PIPING Sm!j
1 Page
APPENDIX D
S-S
APPENDIX E
STRESS CALCULATION INDEX
SKETCH (CAD DRAFTED)
AND SUPPORTS CRITICAL LINE LIST
1 Page 1 Page
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I . 1.0
PURPOSE The purpose of this Design Guide is to provide uniform guidelines and information for use by Piping Stress Engineers to ensure a cohesive approach to the piping stress analysis of petrochemical plants.
2.0
SCOPE This Design Guide does not cover all the technical aspects of the piping stress analysis. It is a general one covering most circumstances, but may be deviated from, to suit specific job or local requirement with the expressti agreement of Engineering Management.
3.0
ASSOCIATED DESIGN GUIDES AND FORMS
3.1
Design Guides EDG-P5401-L (Rev. O)
Pipe Suppofis.
EDG-P5302-L
Piping Stress Critid
EDG-(tba)-L
3.2
Ii
(Rev. O) (Rev. O)
Line List
Design Guide for Equipment and Nozzle hadings.
Forms P & CE L-5421 FEB 78
Bellows Expansion Joints Data Sheet
GR(A4) 2356 7/90
Bechtel Standard Calculation Sheet.
Appendix C
Piping Stress Sketch. (CAD Drafted)
Appendix D
Stress and Supports Critical Line List
Appendix E
Stress Calculation Index
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I . 4.0
DEFINITION Critical Line Lti
(EDGP5302-L)
In this Design Guide, the Cntid
5.0
Line List refers to the Piping Stress Critical Line List.
GENERAL PHILOSOPHY The basic responsibility of the Stress Engineer is to ensure that piping is routed and supported so that no damage occurs to either the pipe or associated equipment due to the effects of thermal expansion or contraction, or loads resulting from weight, pressure, wind earthquake, pulsation, shock, foundation settlement, etc. The purpose of this Design Guide is to ensure the sound and uniform approach to the review of the mechanical safety of the piping and related systems and to be able to produce evidence that this has been done satisfactorily. It is also to ensure that evidence of compliance with applicable codes is produ~. To aid in this endeavour, the following poinfi should be followed:a.
Only enter essential results / data on stress sketches.
b.
Identify worst operation cases before running wmputer checks, then run these cases only.
c.
If a “Worst case” is not immediately obvious, run all the nwssary cases but after a visual review of the outpufi, choose only the extreme cases for detailed review and results transposition with a note saying that these are the worst load/stress conditions and the other conditions that were reviewed to come to this wnclusion.
d.
,-
Review all configurations using visual/approximate methods prior to computer calculations so the wnfigurations with obvious problems may be discussed with the piping designers prior to setting up the mmputer run. EL
e.
Inform piping design of any wnfigurations that have been passed but have loads or stresses that are close to the allowable values, and “freeze” the arrangement.
f.
Keep the designs realistic: Minimise the use of “super” special supports requiring high tolerances or complex designs. If these are required it tends to indicate that a re-route is necessary.
g“
Wherever possible, avoid the use of flexible connectors (bellows, etc). The use of springs and snubbers should also be kept to a minimum.
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. h.
The use of “cold spring” should be kept to a minimum and should not be used around any rotating equipment.
i.
Where max. operating or design temperatures appear high by mmparison with other available data, discuss it with the systems/mechaniM engineer prior to calculation of the system, highlighting the impact on the piping/equipment if the temperature proves inaccurate.
6.0
RESPONSIBILIT~
6.1
The Stress Engineer shall:
6.1.1
Establish the Critical Line List. Continuously update the List to record the progress of work on all critical lines.
6.1.2
Establish the allowable imposed nozzle loads onto the equipment by consultation with the mechanical/equipment group at the outset of a contract
6.1.3
Carry out a flexibility and support review of any Piping Studies produ~ if required.
6.1.4
Ensure that all Code, Client and Inspection Authority requirements pertaining to Piping Stress Analysis are taken into account.
6.1.5
Establish all operating functions for lines to be analyzed by reference to the line designation tables and/or discussions with the systems/mechanid engineer. These include start-up, shutdown, steam-out, various wmbinations of equipment working and idle, bypasses in and out of use, de-inking, etc.
6.1.6
In the early design stage, review Piping Studies for flexibility and support of major critid lines, and comment accordingly.
6.1.7
Review all lines on the Critical Line List and formally wmment via the Stress Sketch or Stress Comment Forms as appropriate.
6.1.8
Evaluate nozzle loads as required and transmit to relevant section, if limiting values are not known.
6.1.9
Check flanges for leakage where bending moments are large, including flanged connections at equipment.
6.1.10
Establish with the civil/structural engineer any criteria for settlement, loads on pavements, platforms, piperacks and any other structure.
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I 6.1.11
Calculate and transmit all significant support, guide and anchor loads on structures and/or foundations to Civil/Structural group. Significant loads are loads greater than 5 KN or 1000 lb, loads greater than those established in section 6.1.10, and loads not established in section 6.1.10.
6.1.12
Locate and design all spring supports and indicate required loads and movements on the Stress sketch.
6.1.13
Check all pipe supports produced for the critical lines, and revise where necessary.
6.1.14
Specify any reinforcement required at branch connections, (other than for intemal/extemal pressure considerations which are revered by the Piping Material Specification), or at wncentrated loading points.
6.1.15
Specify expansion joints as rquired.
6.1.16
Specify any cold spring found to be necessary.
6.1.17
Check position of fixed and sliding supports of heat exchangers, horizontal drums, etc. L
6.1.18
Review Vendor’s Drawings for equipment nozzle loadings. Comment as necessary and discuss with Equipment Engineer any special requirements (eg leaving heater nozzles unrestrained so as to utilize the inherent flexibility of the tubes, etc).
6.1.19
Ensure all information affecting other groups and/or Vendors is properly recorded and promptly transmitted.
6.1.20
Prepare and file all calculations in accordance with the requirements of this instruction and project requirements.
6.1.21
Investigate queries r~ived
6.1.22
When requested, check critid pipe supports and expansion joint installations at site prior to mechanical completion to confirm that design requirements have been met.
7.0
GENERAL WORKING METHODS
7.1
The method of assessing pipes will mme under one of three categories : a.
Computer.
from site giving advim and solutions as necessary.
In this case the piping system will be modelled and calculated using a piping stress computer program. (Bechtel’s ME101 LEAP, Caesar II, or any other program approved/specified by the client on a project.)
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I b.
Approximate. In this case hand dculation techniques using nomography, charts, simplified formulae, or simplified computer programs are UW to prove the acceptability of the system. They may also be approval by comparison with similar systems. Simplified computer programs are hand calculator type programs that analyses simple shapes using standard calculation methods (e.g. elastic mntre method) and should be checked and approved before use.
c.
7.2
Visual.
In this case simple techniques of approximate “guided cantilever” type or by background knowledge/experien~ are used to approve the system with minimal calculations.
The approval method is ultimately the responsibility of the individual Stress Engineer. The basic split of calculation types is as follows: a.
Visual or Approximate :
(The temperatures refer to Design temperatures)
Lines attached to rotating equipment: Lines of 50mm (2’’)NB and under. Lines of 100mm (8’’)NB and under@ less than 150°C (300°F) Lines of 150mm (6’’)NB and greater @ between -20°C (4°F) and 70°C (150°F) —-
All other lines: Lines of 80mm (3’’)NB and under.
I
The following sizes must be also@ above -45°C (-43°F): Lines of 150mm (6”)NB through 300mm (12’’)NB @ under 155°C (400°F) Lines of 350mm (14”)NB and greater@ under 150°C (300”F) The above list is to be used as a guide only, and for any special piping (e.g. lined pipe) computer dculations should always be considered. b.
Computer Calculations : All lines not in a. and lines over 80mm (3’’)NB attached to sensitive equipment.
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I
‘i 7.3
For all dculations, the wmbination of conditions that muld tharetidly occur so as to produ~ the maximum stress and equipment loading should be considered. This wnsideration should include but not be restricted to the following areas (See also Paragraph 8.4): a.
Thermal expansion due to : Design Temperature Steam out. Steam or electrical tracing. Any Purging. Atmospheric and Solar Temperatures.
b.
Movement of pipe’s attachments due to: Vessel or equipment thermal growth. Column or other vessel or equipment Sway. Structural sway. Settlement.
(from seismic, wind or any other source). (from seismic, wind or any other source). r
c.
Wind, snow or other environmental loadings.
d.
Dead weight and pressure loadings.
e.
Vibration caused by:
\
Earthquake. “water hammer”. sudden valve opening or closing. Pulsating flow. Mechanically indud vibration from compressors or other equipment. Vortex Shedding. ?
7.4
After a review, the Stress Engineer indicates any rerouting, additional supporting or guiding and locates any anchors or line stops required. If there-routing is not acceptable alternatives are discussed with appropriate back-up calculations until an acceptable arrangement is found.
7.5
Where appropriate, wpies of the Stress sketch together with the Stress Sketch Continuation Sheet showing imposed loadings is passed to the Equipment group and/or the Civil/Structural group.
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8.0
SPECIFIC WORKING METHODS
This section addresses various specific topics within the scope of piping stress engineering without any reference to any specific project. Hence they are recommendations that should be tempered by the n-ssities of the specific project concerned and good engineering judgement.
8.1
Thermal bads
8.1.1
Elastic Modulus
and Stress Considerations F
Thermal loads should be calculated using the elastic modulus at the maximum temperature for hot lines, and the minimum temperature for cold lines. Thermal stresses should be calculated using the elastic modulus at 70°F (21. 1‘C) for all hot lines and the elastic modulus at the minimum temperature for mld lines. Hot lines are those primarily subject to thermal expansion, and cold lines are those primarily subject to thermal contraction. 8.1.2
r
Flexibility Temperatures The temperatures to be considered in thermal analysis are: a)
r-
Design/Upset Temperature.
t..
This temperature is quoted in the line designation tables and is the maximum temperature that the line is wnsidered to see. If the line considered is un-insulated, the design temperature used, if above 38°C (1OO”F)maybe up to 5 % less (dculated from installation temperature - see also appendix A.2). This value should be wnfirmed with the systems engineer. b)
Normal Operating Temperature. This temperature is quoted in the line designation tables and is the temperature that the line is considered to see during normal operation. Generally this temperature is not considered unless adjacent connecting pipe or equipment have a higher differential between their operating temperatures, than between their design temperatures.
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I c)
Solar and Ambient Temperatures. These temperatures should be considered when dculating line stress mges and must be wnsidered for applied loads if higher than the Design temperature.
d)
Steam out. Steam out temperatures and the lines which will be steamed out should be established with the process group at the beginning of the project. Steam out temperatures will be considered for flexibility analysis if in excess of design conditions. As this event is of short term duration, the allowable stress may be increased by 1.33 times as per ASME B3 1.3 section 302.2.4. It should also be considered that loads on equipment for this condition may be increased by up to 2 times for short term duration. However, this should be confirmed with the equipment manufacturer as soon as possible during design. Consideration should also be given to whether equipment and piping are st~med out together or separately.
e)
Steam tracing. Steam tracing temperature should be used for flexibility calculations if it is greater than the design temperature. (Electrically trad lines should be calculated using their design temperature.)
f)
Regeneration ,
Catalyst regeneration should be considered carefully and accurate values for temperature, frequency and duration of the pruss obtained. The allowable stress range may have to be redud as per table 302.3.5 of ASME B3 1.3 to avoid fatigue failure. g)
DeCoke m.
This extreme condition that is of short duration. It will be considered for flexibility analysis, but the allowable stress may be increased by 1.33 times as per ASME B31.3 section 302.2.4. h)
Fire Temperatures produced by fire are a special consideration. For this case the design considered should be that the system maybe over-strained, but it must not fail under fire conditions. The principal is that after a fire all affected piping would be replaced. Fire temperaturesare obtained from the systems engineer.
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Internally Lined Pipe. For wncrete lined pipe for water lines, the expansion temperature to be used is the Solar temperature, or if the line is buried or externally insulated the line will be at ambient condition.
B. .-
L
For Refractory lined pipe, the metal temperature will be significantly less than the commodity temperature. An accurate skin temperature should be obtained. j)
Pipe Bowing .
Where there is seen to be a differential temperature around the circumference of a pipe, as in a flare line subject to radiant heat on the top of it, or a LNG line at start-up when the lower half of the pipe is cooled before the line fills and CQOIS the top half of the pipe, then the effect of pipe bowing should be wnsidered. Temperature differentials should be obtained from the process group. 8.2
Sustained Loads and Stress Considerations
8.2.1
Design Pressure This Pressure is quoted in the line designation tables and is the maximum pressure that the line is considered to see.
8.2.2
Bourdon Tube Effect This is the stiffening effect at the elbows caused by the internal pressure tending to straighten the pipe out. It is most notimble, and should be particularly considered in thin walled large diameter pipe. This effect should not be considered in cold lines where the pipe is contracting as it aids the contraction of the pipe and is hen= a less conservative assumption.
8.2.3
Operating Pressure This pressure is quoted in the line designation tables, and is used in injunction with the operating temperature when dculating total operating loads on equipment
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I 8.2.4
Hydrotest / Pneumatic Test The support system should be strong enough to support the pipe when it is being hydrotested with temporary supports if necessary. Itcanbe assumed that theline is not insulated during hydrotesting. If the pipe cannot be supported or if it will cause load problems on the structural steel, then a pneumatic test may be considered. The piping wall should be sufficiently thick to resist hydrotest or air test without yielding.
8.2.6
Vacuum Design Lines subject to vacuum or sub-sea lines with a resultant external pressure should be checked to ASME section VIII Div. 1 section UG-28 (“Thickness of Shells and Tubes under extemd pressure”)
8.2.7
Operating Weight k
Operating weight is the weight of the pipe with all insulation, commodity included, and all items permanently attached to it. 8.2.8
mmponents
and
Occasional Weight This is an added weight that occurs occasionally such as snow, im, wind etc. In addition the affects of traffic on buried pipelines should be considered.
8.3
Dynamic and Other Loads and Stress Considerations
8.3.1
Seismic In the absence seq.) method imposed static if required by
of project specific information use the UBC (UBC Part III sec. 2330& to model seismically generated dynamic loads as equivalent laterally loads. A Dynamic response spectrum analysis should only be mnsidered the project.
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I 8.3.2
Dynamic loads from equipment. Some equipment, noticeably reciprocating compressors and pumps generate pulsations causing vibration. To minimise this problem fluid damping bottle should be designed into the system, and the stress engineer should ensure that the fundamental frequencies of the system (dculated from a computer dynamic analysis) is not a multiple of the operating speed of the equipment. Similarly, the stress engineer should dculate the span for the hold-downs such that the piping mechanical frequency does not match the machine’s natural frequency. (See also API 618)
F, .*.
C
In some cases, notably that of reciprocating compressors, an analog study is undertaken, usually by a s~ialist or outside consultant.
8.3.3
Wind :
8.3.4
PSV and Rupture Disc Reaction
See Appendix A
The load generated when a PSV opens or a Rupture Disc ruptures should always be wnsidered. Simplified formulae to give these loads are (including an impact factor of 2): PSV Reaction:
Force F = o.6&+l)AP
.
Rupture Disc Reaction:
Form
F = 0.378~+
l)AP r-
Where
h= A= P =
Cplcv Orifim Area Absolute Pressure
L..
(All in mnsistent units) If the loads calculated from the above formulae are unduly large, then the calculation quoted in code ANSI/ASME B31. 1 should be used to calculate the load more accurately. 8.3.5
Slug Flow and Valve opening/closure Slug fIow is the condition of a bolus of liquid flowing along a pipe. A similar effect can occur when a valve is suddenly shut off or opened and a shock wave passes down the pipe (“Waterhammer”). The impact of a slug or the wave front of liquid from an opening valve onto an elbow can be excessive, so that this condition should be kept to a minimum by using dtemative designs if possible.
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I The static force on a 90° Elbow due to slug flow impinges at 45° to the direction of flow into the elbow radially outwards from the elbow. The load with a 2 times impact factor is:
F =2.0x Where
pxAx
V2/g
F
=
P
=
A=
v= g= 8.3.6
(in consistent units) Force, Density of fluid Pipe internal area Fluid Velocity gravitational constant
Settlement Loads and stresses caused by differential settlement between different supports and quipment should always be considered. This often is achieved by the use of flexible piping and the use of springs.
8.3.7
Friction bads on supports, anchors, guides, line stops and equipment nozzles should always consider friction effects. Friction effects can never be used to reduce applied loads. .—
8.4
had
Combinations
8.4.1
Load Summary:
,.
a)
bads and stresses should be considered to be caused by expansion due to the worst OR Design Temperature. Normal Operating Temperature. Solar / Ambient Temperatures (Depending on Insulation). Steam out. Steam tracing. Regeneration Decoke Pipe Bowing Equipment Expansion
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e.
I b)
Sustained bads
and Stresses should be considerd
due to:
Design Pressure Hydrotest / Pneumatic Test Vacuum Design Operating Weight Occasional Weight Hydrotest Load c)
Dynamic and Other Mads and Stress: \ :-
Seismic Dynamic loads from equipment. Wind PSV and Rupture Disc Reaction Slug Flow and Valve opening/closure Settlement 8.4.2
8.4.3
Equipment and Pipe Support Loads a)
Maximum allowable loads applied to equipment Nozzles should be agreed with the equipment vendor as early as possible, but in the absence of any other information the values quoted in the Design Guide for Equipment and Nozzle hadings (EDG-(tba)-L) should be used.
b)
hads on equipment and pipe supports that should be mnsidered are the maximum wmbination of cases shown in (8.4.1). Dynamic and other loads (8.4.1 (c)) need not be considered to be acting simultaneously, except for settlement.
Pipe Stress Maximum Allowable Stress wmbinations that should be considered are the maximum Stress Range (8.4. 1 (a)), Sustained Stress and mional Stress combination of cases shown in (8.4.1). Dynamic and other loads (8.4.1 (c)) need not be considered to be acting simultaneously, except for settlement.
8.5
Rotating Equipment
8.5.1
Pumps a)
The kd Stress Engineer must review tie client and job s~ifications on each project to ascertain the philosophy regarding types of pumps and their allowable nozzle loads.
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8.5.2
b)
Generally it is recommended to use API 610 type pumps wherever possible. When ANSI pumps are used, allowable nozzle loads should be requested from the vendors.
c)
A full investigation of all possible operating ~nfigurations of a set of two or more pumps should be conducted before the worst case or cases are analyzed.
Compressors and Turbines. a)
Generally, the allowable loads on these pieces of equipment are governed by a multiple of the loads quoted in NEMA SM 23.
b)
Wherever possible, the deadweight loads on the nozzles should be as close to zero as practical by the use of spring supports (As per mmments in NEMA SM 23)
c)
Spring support variability around the equipment should be kept as low as practical to keep cold nozzle loads to a minimum.
c)
Piping systems with Mission-Duo type Check Valves should be well supported because of rotational creeping of the flange faces due to the long stud bolts.
d)
\
r
Turbine piping analysis should include bypass line hot with trip and throttle valve closed (i.e. equipment cold) as well as all operating and upset conditions.
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8.6
Air Cooled Heat ~changers
8.6.1
Number of passes
(Air Fans)
,– i.
a)
An Air Fan with an odd number of passes has the inlet and outlet header boxes at opposite ends of the exchanger and is preferred as there is no problem with differential expansion between headers.
b)
With even pass Air Fans, the inlet and outlet are on the same header box at one end of the exchanger. If the header box is separated into two parts instead of a design with a centre baffle, the differential expansion between the headers is no longer a problem. Otherwise, the differential expansion between the inlet and outlet manifolds should be carefully considered, and adequate flexibility put into the discharge lines from the exchanger to the manifold.
c)
The expansion of the tubes can be controlled by placing directional anchors at the header box. The location of these anchors should be carefully mnsidered to optimise the piping routing. It may be an advantage to allow some header boxes to float free and be moved by the manifold expanding through short feed lines.
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I d)
In some cases it is advisable to install thrust blocks between header boxes to remove the loads transmitted to the nozzles via friction resistanm of the header boxes. If the gap between the header boxes is large (over 200mm) the use of PTFE slide pads should be considered instead of thrust blocks.
e)
The clearances between the header box and the steel supports as it may be necessary to cold-spring the headers to accommodate the thermal expansion.
8.7
Shell and Tube Exchangers
8.7.1
Anchor Location
?’ <
The stress Engineer should ensure the fixed and sliding ends are located on the ends that give the best advantage. 8.7.2
t“
Stacked Exchangers Where exchangers are stacked, all interconnecting pipes should be reviewed for stress. Where vendors supply exchanger arrangements that appear questionable, the stress engineer should ask for back-up calculations from the vendor to prove that there will be no flange leakage.
8.7.3
Exchangers equipped with bellows should be checked for loading, deflection or angulation. Usually, expansion joints on exchangers are not designed for appreciable lateral deflection.
8.8
Fired Heaters
8.8.1
Full appreciation of the effect of the external piping on the internals of the heater should be considered and full consultation with the heater vendor should be conducted to =rtain all the expansions and movementi within his heater before a rigorous stress analysis is conducted.
8.9
Nozzle Flexibility
8.9.1
Loads on Columns, drums, tanks and horizontal vessels by wnsidering the flexibility of the nozzle connections to the vessel, instead of considering it as a fixed anchor.
8.9.2
If the nozzle flexibility is not available from the equipment vendor, it can be calculated using one of the following documents:
r
L
a)
British Standard BS5500 Appendix G : “Stresses from local loads. ”
b)
Bechtel S.F. Standard Drawing : C-722 : “spring Nozzles in Cylindrical Shells. ”
constants
for ro~tion of
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EDGP5301-L
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Page 18 OF 25
c)
Welding Research Bulletin No. 34 (1957) “Computation of the Stresses from Local Loads on Spherid Pressure Vessels and Pressure Vessel Heads” by P.P. Bijlaard.
d)
Welding Journal Research Supplement (1955) ‘Stresses from Radial bads External Moments in Cylindrical Pressure VesselsWby P.P. Bijlaard.
and
Note: The methods and charts in (a) and (b) above were derived from (c) and (d) above. 8.10
Buried Pipe
8.10.1
Buried pipe, for the most part, is fully restrained with wtions above ground only partially restrained.
8.10.2
The loads built up within the fully restrained line tend to be very large, and the stress built up in the pipe means that the temperature range of pipes that can be buried is limited.
of it where it emerges
For Carbon Steel, with an allowable hot and cold Stress of 20 ksi (137.9 MPa) giving an allowable stress range (Sa) of 30 K1 (206.9 MPa) and a value of the Elastic modulus (E) of 29.5 x lU psi (203395 MPa) the maximum allowable strain is : Strain
=
Sa/E=
=
(30/29.5) x 10-3in/in (mm/mm) 1.22 in/100 ft (1.017 mm/m)
This is equivalent to a temperature range of 11‘C to 100”C
I
I
Similarly for Austenitic Stainless Steel with an Sa value of 30 ksi (206.9 MPa) and an E value of 28.3 x I@ psi (195121 MPa), the allowable Strain is : 1.27 in/100 ft (1.06 mm/m) This is equivalent to a temperature range of 11‘C to 75°C 8.10.3
The Buried Pipe will have valves and other pi-s of quipment set in pits. These items will have to be protected by anchor blocks adjacent to the pit to prevent pipe expansion into the pit. These anchors are designed by the civil group from loads given by the stress engineer. The load applied to the anchor is the totally restrained load and is hence : (Lb) Fa = E.e.r(D-t)t
11
(N) ~
Where
e D= t
ENGINEERING DESIGN GUIDE
= =
Strain Pipe Outside Diameter Nominal Wall Thickness
EDGP5301-L
Rev. O
(in/in) (in) (in)
_ (mm) (mm)
Page 19 OF 25
.
I As a rough guide, if the height of the anchor block is ‘ht’ (ft) (m), its width is ‘1’ (fi) (m) and the depth of the bottom of the block from the surfam of a sandy soil is ‘H’ (ft) (m) then the maximum allowable anchor load (with a factor of safety. of 1.5) is ‘AL’ (Lb) (KN):
Where
8.10.4
AL
=
k.H2.1
with
k
=
Coefficient =
45 in imperial units 7 in Si units.
w +2
ht > H/2
It is also necessary to know the expansion out of a buried section of pipe into the open. The position where a buried line becomes fully restrained is known as the virtual anchor. The distance of the virtual anchor from where the line ceases being buried is ‘L’ (Ft) (m) Then :
L
=
((E.e - p.S) + P.a)/f
Where
A= a e E P s P f
= = = = = = =
Cross Sectional Area of Pipe Metal Flow Area of Pipe Thermal Strain Elastic Modulus Poissons Ratio Hoop Stress in the Pipe Internal Pressure in the Pipe Soil Friction
—
(in2) (in’) (in/in) (psi)
(mm*) (mm?
(psi) (psi) (Lb/ft)
(MPa) (MPa) (N/m)
\
_ ‘
(MPa)
. ,.
Soil friction can be simplified to: f Where
=
Wg = = Ws = = Wp D= h d
=
K1 fr
= =
= =
Wg.fr (wS + Wp) Total Weight acting on the pipe (2. D.h.d/~) Weight of soil on the pipe Weight of Pipe and Contents Pipe Diameter Height of soil above top of pipe Density of Soil (Typically 100 lb/f?) Unit mrrection coefficient Coefficient of Soil Friction (Typically = 0.5)
(Lb/ft)
(N/m) m.
(Lb/ft) (Lb/ft) (in) (in) (lblft’)
(N/m) (N/m) (mm) (mm) (N/m’)
(12)
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This formula for Ws applies to fairly rigid pipe and must be re-considered for thin walled lines over 24” NB. The growth out of the buried section of the pipe into the open is ‘Def’ (in) (mm) and can be calculated from: Def =
8.10.5
K1.L. [e + (P.ti(A.E))
T *-,
- (mu.S/E) - (f. L/(2. A.E))]
The buried pipe must also be checked for stability to ensure that the compressive force in the restrained section does not make the pipe bow out of the ground. To check this bowing wndition the following steps should be taken (Using nomenclature as per section 8.10.4 and 8.10.3) a)
Calculate the Critical BucNing Length Lc :
Where:
b)
Lc
=
u (4. E, I/Fa)ln
(in)
(mm)
I
=
Pipe Section Moment of Inertia
(in’)
(mm’)
Calculate the theoretical height of pipe bowing @b) due to compression. Db
.
c)
=
8.11
[(4.e.ti/#)
- (D2/2)]1n
(in)
(mm)
Calculate the pipe sag (Dw) due to weight over the same length. Dw =
d)
~
If
(Wg.Lc4/(384.E. I.Kl))
Dw > Db
(in)
(mm)
then the system is stable, otherwise extra weight should be put on tie pipe to prevent it bowing out of the ground.
Cryogenic Pipe
Cryogenic piping includes all piping that operates below -lOO°C (-148”F), and is more critical than other low temperature piping as: a)
Special attention is required to prevent water incursion into the insulation as this will freeze and breakdown the insulation. This is achieved by ensuring a vapour barrier around the whole system without any breaks.
ENGINEERING DESIGN GUIDE
EDGP5301-L
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Page 21 OF 25
. .
I
I b)
Special cryogenic supports and anchors have to be used to prevent low temperatures affecting the support steel and stopping iw build-upon the suppotis creating unwanted anchor points. Cryogenic anchors and line-stops should be given special attention as they tend to be bulky and require more room than normal line-stops to install. (See Standard Supports Al 1, S31, S32 and S33)
c)
1. ;.
The material Elastic modulus increases by around 5% at these temperatures making the whole system stiffer and incraing loads and stresses. I I
d)
Special care must be made with any bellows as they must be protected from icing up and being crushed. One method of doing this is to use a double bellows system separated by insulation where the external bellows is used as a vapour banier, preventing the formation of ice in the active internal bellows. The material of the bellows should be specially considered to prevent any brittle fracture of the thin flexing membrane. Cryogenic systems antaining bellows should not normally be hydrotested as water will tend to be caught in the convolutions forming ice that damages the convolutions during service.
9.0
RECORDING AND TRANSMI’ITAL OF STRESS ENGINEERING DATA
9.1
Piping Critical Line Liit
—
The Piping Critical Line List is produced and operated in amrdance Design Guide EDG-P5302-L: Piping Stress Critical Line List.
9.2
with Engineering
Stress Sketches The Stress Sketch is used to transmit the following information:a.
Pipe Support/ Anchor /Guide details.
b.
Routing revisions: For piping design.
c.
High line movements over 75mm (3”): for piping layout.
information to piping design, including spring
I 1--
d.
Equipment loads: for the vessel and mechanical equipment groups.
ENGINEERING D~IGN
GUIDE
EDGP5301-L
Rev. O
Page 22 OF 25
9.3
Calculation Index This will be produced in conjunction with the critical line list. See Engineering Design Guide EDG : Critical Line List.
9.4
Expansion Joint Data Sheets
9.4.1
Bellows Expansion Joints Form No. : P & CE L-5421 FEB 78 “Bellows Expansion Joints Data Sheet” or similar document is used for the requisition of bellows expansion joints.
9.4.2
Victaulic and Viking-Johnson Type Expansion Joints These types of expansion joints fall within the category of “Piping Specials” and are therefore specified using a standard drawing sheet (Form No P & CE A-5204 or alternative) showing a sketch of the joint together with the appropriate dimensions and movements etc.
9.5
-
_ .
Spring Data Sheets Appropriate data sheets for the type of spring designed, together with an index sheet and spring summary sh~t (see EDG-P5401-L “Pipe Supports”) are used to requisition Pipe Support Springs. The data sheets must be supplemented by a Spring Design Specification and the appropriate Paint Spification.
10.0
CHECKING STRESS CALCULATIONS
10.1
Preliminary Review
10.1.1
At the preliminary issue stage, all Stress Sketehes shall be reviewed by the Stress Engineer to approve the general approach to the dculation and to ensure the overall dculation looks reasonable.
10.1.2
Subsequent to this issue, the stress dossiers shall be maintained with details of any signifies.nt changes marked on the redueed mpies of the stress sketches, dated with appropriate mmments relating to the aeeeptanee or otherwise, of the changes.
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n.
.,
‘e
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Page 23 OF 25 m
10.2
Critical lines The checking of calculations fall into 3 categories:
10.2.1
Complete check. This check will require the following : a)
If it does not exist, a plot of the input geometry may be created to assist checking. If multiple computer runs have been run, the secondary runs may also be plotted.
b)
Complete check of the computer input gmmetry and inputted parameters (weight, expansion rates, applied loads and movements etc .). Ensure the date of the runs match the latest version in the network.
c)
Check of the basic Data: Temperatures, Pressures, Insulation, Commodity, Pipe Material and wall thickness against the latest line list and Piping material specification.
d)
Check additional dculations of line weight, expansion rates, modulus of elasticity, allowable stresses, wind loads, sway, seismic coefficients, nozzle deflections etc.
e)
Check results tally with values and comments shown on the stress sketch.
o
Check that all relevant load cases have been run.
g)
Check that the piping system is adequately supported / restrained.
h)
Check that de
7—
I.
10.2.2
compliance is documented. \.
General check a)
If it does not exist, a plot of the input geometry may be creati to assist checking. If multiple computer runs have been run, the ~ndary runs may also be plotted.
b)
Spot check of the computer input geometry (10% of dimensions + reviewing (a) above). Check inputted parameters (weight, expansion rates, applied loads and movements etc.).
c)
Ch~k of the basic Data: Temperatures, Pressures, Insulation, Commodity, Pipe Material and wall thickness against the latest line list and Piping material specification.
ENGINEERING
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Page 24 OF 25
\
I
.. A
10.2.3
d)
Review additional dculations of line weight, expansion rates, modulus of elasticity, allowable stresses, wind loads, sway nozzle deflations etc. (i.e. ensure the values are reasonable)
e)
Check results tally with values and comments shown on the stress sketch.
f)
Check that all relevant load cases have been run.
g)
Chuk that the piping system is adequately supported / restrained.
h)
Check that code compliance is documented.
General Review In this case the stress sketch should be reviewed to ensure the basic temperature data relates to the latest Line List and any associated calculations are correct.
10.3
Calculations relating to the Groups in 10.2
10.3.1
The calculations falling within “complete check” category (See paragraph 10.2. 1) are as follows: All calculations relating to the following equipment : a)
Air fans
b)
Compressors
c)
Turbines
d)
Arrangements temperatures.
e)
All other equipment where Nozzle loads are above 75% of the allowable values
f)
All calculations where the stress range is above 75% of the basic SA value in ASME B31.3.
of three pumps connected together by piping at elevated
10.3.2
The calculations falling within “General check” category (See paragraph 10.2.2) are all computer dculations not included in 10.3.1.
10.3.3
The calculations falling within “General Review” category (See paragraph 10.2.3) are all non-computer calculations (approximate calculations and visual review).
ENGINEERING D~IGN
GUIDE
EDGP5301-L
Rev. O
Page 25 OF 25
I
k APPEND~
A TO ENG. DESIGN GUIDE EDGP5301
APPENDIX A
REV. O
PAGE Al OF A3
Basic Data Required at the Start of a Projeet and Default values for Initial Calculations.
r,
The following information should be confirmed with the appropriate project standards and specifications at the outset of a project. If the information is not readily available the values given below may be used as interim values until confirmation can be obtained from the client or appropriate authority. A. 1
w ‘.. .:
Piping Code: Chemical Plant and Petroleum Refinery Piping ASME B3 1.3 (Latest Edition)
A.2
Temperatures: England
Ambient Installation solar
“. -10”C (14”F) to 300c (860F) : 5°C (41”F) : 35°C (95”F)
Northern Europe & Canada
Ambient Installation solar
.o -20”C (-4°F) to 30°C (86”F) : O°C (32”F) : 35°C (95”F)
Central Europe
Ambient Installation solar
“. -20°c (-4”F) to 40”C (104”F)
USA
Ambient Installation
Middle East Africa, Far East & Tropical Climates All Locations
:
: O“C (32”F) : 50”C (122”F)
solar
.o -20”C (-4”F) to 40”C (104”F) : O°C (32”F) or 21°C (70”F) : 50”C (122”F)
Ambient Installation solar
: O“C (32”F) to 50”C (155°F) : 20”C (68”F) : 85°C (185”F)
Steam out
: 150”C (302”F)
L
I
‘k APPENDIX A TO ENG. DESIGN GUIDE EDGP5301
A.3
REV. O
PAGE A2 OF A3
Wind Loads: Wind loads may be Ca.lculatti using one of the following codes: a)
Based on BS CP3 Chapter 5:
Code of Basic Data for the Design of Buildings - Chapter 5: bading - Part 2: Wind Loads .
In the absence of further information, use a design wind speed of 40 m/s with a Topography factor S 1 of 1.0, ground roughness of 2 witi building class B (to calculate factor S2 as per table 3), and factor S3 of 1.0. b)
Based on Uniform Building Code Part II : Wind Design In the absence of further information, use a basic wind speed of 90 mph with a Exposure type C, Cq factor of 0.8, qs factor of 20.8 lb/f~ and an Importance factor of 1.0.
A.4
~
Wind Deflection of Columns and Structures Initial calculations can use a value of L/200 where L is the elevation of the column or structure. This should be confirmed by the vessel/structural group for the specific column of structure as soon as possible.
A.5
Coefficient of Friction steel to steel Steel to Concrete S-1 to PTFE/ Polished Stainless Steel
A.6
. : Coefficient of Friction = 0.3 : Coefficient of Friction = 0.8 : Coefficient of Friction = 0.1
Settlement 5. Values for absolute and differential settlement on a plant should be established at the outset of the project.
A.7
Earthquake Values for earthquake accelerations on a plant should be established at the outset of the project.
.. .,
Use : Uniform Building Code Part III : Earthquake Design
R.
I ,
lb
APPENDIX A TO ENG. DESIGN GUTDE EDGP5301
A.8
REV. O
PAGE A3 OF A3
Column Skirt Expansion The temperatures used for calculating skirt expansions are taken from the equation:
T *2
Average Skirt Temp (“C)= (T-Ta)F + Ta Ta= T = F = K=
Ambient Temp. (“C) Temp @ top of Skirt (“C) 83.6/((Kh/t’”) + 15.5) [(Kh/P5) > 120] Insulation Constant = 1.0 Firebnck Insulated = 1.6 Non-insulated h = Skirt Height t = Skirt wall thickness. A.9
Insulation Weight Until definitive values are available use 150 Kg/m3 (9.4 lb/F~) or 175 Kg/m3(11 lb/ft) insulation density.
A. 10
Pipe Wall Thickns
T
Retirement Thickness
When calculating the pipe wall thicknesses for piping classes etc., if the pressure is low, the thinnest wall thickness required for pressure design may be too thin for reasonable mechanical strength. Hence a minimum thickness is required for basic mechanical strength purposes. This value is known as the retirement thickness. Thus, if the pressure design thickness calculated is less than the retirement thickness the retirement thickness should be used in its place. The Retirement thickness values to be used are: Line size Range (NB) : (in) (mm)
Retirement Thickness: (in) (mm)
1/2 to 2t04 6 to 14 to 26 to 48 and
0.02 0.06 0.09 0.12 0.15 0.20
1 1/2 12 24 46 above
15 to 40 50 to 100 150 to 300 350 to 600 650 to 1150 1200 and above
0.51 1.52 2.29 3.05 3.81 5.08
E.
APPENDIX B TO ENG. DESIGN GUIDE EDGP5301
APPENDIX B
REV. O
PAGE B1 OF B2
A Simplified Method for Piping Designers to Asses Piping Flexibility.
w .&
B. 1
PURPOSE
B1.1
The purpose of this guide is to assist the piping designers to allow for sufficient flexibility whilst routing piping.
B1.2
The method to be employed is simple, quick, and conservative, but does not consider equipment loads. This is not seen as a problem as the Stress Engineers will cover this check during their review of the piping.
B1.4
This guide is NOT intended to circumvent the assessment of piping systems by the stress Engineer.
B.2
THE STRESS FLEXIBILITY EQUATION
B2.1
The quation is based on the guided cantilever method.
B2.2
To dculate
F
the required leg, use the following Equation:
(s= also fig Bl) Lr
=
Where
B2.3
K. (D. T. Le)ln Lr D= T Le= K=
= =
Required leg to absorb expansion of Le. Pipe Actual OD in inches (of Lr) Pipe Design Temperature - 10”C (50”F) Length of pipe that is expanding. Constant see B2.3
(mm) (in) (“C) (mm)
(in) (in) (“F) (in)
Values of the constant K: Material
Carbon St~l & bw to 5Cr Steel
Value of K in: Imperial Units
S1 Units except NB
Alloy Steel
12 Cr Steel and Austenitic Stainless Steels (Not L grade)
0.185
1.25
0.21
1.4
k
I APPENDIX B TO ENG. DESIGN GUIDE EDGP5301
REV. O
PAGE B2 OF B2
Fig. B1 Diagram Showing Expansion of Typical ‘L’ Shape
B3
METHOD LIMITATIONS
B3. 1
This equation becomes less accurate for pipes in the following categories: ..*-
a)
Lines with a Le/D ratio less than 5
b)
Non-Metallic Piping
c)
Using the K values given for Pipes at Temperatures over 300°C (572”F).
d)
Pipe runs with changes in diameter in length Lr.
-4
r,
B3.2
This method is based on allowable piping stress. It does not consider imposed moments on anchor points or equipment nozzles. Hence for sensitive equipment, this method is only a first pass method for the designer to get a feeling of the sort of leg sizes that are required.
.
.
I .
APPENDIX C TO ENG. DESIGN GUIDE EDGP5301-L
REV. O
PAGE Cl OF Cl
CAD Drafted Piping Stress Sketch : stored in file STRESS2.DGN
r
.
..
—
I
APPENDIX D TO ENG. DESIGN GUID E EDGP5301-L
REV. O
Stress and Supports Critical Line List: stord in file S-S1
.DGN
PAGE 1)1 OF D1
1 -Cl
ENGINEERING STANOMD ST~S
~ -TS
CJ?ITCM lIM
am L~T
mm
. 1
1
I
1
i
1
I
i
i
I
I I I I
I
1 1
i
1
1
\
I
1
, 1
I
J
I I t
1 I
I
I
I
I
I
\ I
I t I I
1
I
I
I
I
1
1
1 KH2
a
I
I
I
I i
1
FOR ~V&
I
I
STATUS :
MCHTEL
CMPORATW
., ,-
t
-.
APPENDIX E TO ENG. D~IGN
GUID E EDGP5301-L
REV. O
PAGE El OF El
Stress Calculation Index: stored in file S-S1.DGN .—
ENGINEERING
STANDARD
STRESS C4CULATION
NDEX
—
w.
I
,.
,.
—
STRESsREVIEW COOE (METHOD): ..
m
.
C : COUPuTER tiYSiS A.: ~OXUATE C&CUiTION v : Vlsuk INSPECTION
PIPING STRESS Calculation”
INDEX
Pw
l“-
k
1
m.
1’ i-:
