Piping Stress Analysis PartPart -II -II -G.Palani
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Table of Content How are piping system classified by stress? Advantage in using accurate restraint stiffness Piping Nozzle Evaluation
Methods for analyzing equipment nozzle loads Centrifugal Pumps and Pressure Vessel nozzle load details Expansion Loops
Expansion Loop Examples Thermal Expansion Equipment – Anchors Equipment Using Coordinates to find free expansion Expansion influencing vessel anchor end Different Expansion Coefficients Coefficients – Pi – Pipin Piping pingg System S
Table of Content How are piping system classified by stress? Advantage in using accurate restraint stiffness Piping Nozzle Evaluation
Methods for analyzing equipment nozzle loads Centrifugal Pumps and Pressure Vessel nozzle load details Expansion Loops
Expansion Loop Examples Thermal Expansion Equipment – Anchors Equipment Using Coordinates to find free expansion Expansion influencing vessel anchor end Different Expansion Coefficients Coefficients – – Pi Pipin Piping pingg System System Sys tem Line Spacing Requirement Locating Friction Balance Attachments
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Force Nomograph Stress Nomograph Stress Pipeway Layout (Attached Separately)
How are piping system classified by stress?
Critical Service Piping Systems – By computer analysis b) Intermediat Intermediate e Service Piping Systems – By manual manu ma nual al calculation calc ca lcul ulat atio ionn c) Mild Service Piping Systems – By Visual Inspection a)
Table of Content How are piping system classified by stress? Advantage in using accurate restraint stiffness Piping Nozzle Evaluation
Methods for analyzing equipment nozzle loads Centrifugal Pumps and Pressure Vessel nozzle load details Expansion Loops
Expansion Loop Examples Thermal Expansion Equipment – Anchors Equipment Using Coordinates to find free expansion Expansion influencing vessel anchor end Different Expansion Coefficients Coefficients – – Pi Pipin Piping pingg System System Sys tem Line Spacing Requirement Locating Friction Balance Attachments
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Force Nomograph Stress Nomograph Stress Pipeway Layout (Attached Separately)
How are piping system classified by stress?
Critical Service Piping Systems – By computer analysis b) Intermediat Intermediate e Service Piping Systems – By manual manu ma nual al calculation calc ca lcul ulat atio ionn c) Mild Service Piping Systems – By Visual Inspection a)
How are piping system classified by stress?
Critical Service Piping Systems – By computer analysis b) Intermediat Intermediate e Service Piping Systems – By manual manu ma nual al calculation calc ca lcul ulat atio ionn c) Mild Service Piping Systems – By Visual Inspection a)
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Expansion Loops a) b) c) d) e)
Need for Expansion Loop Disadvantage Points to Remember Expansion Loop Requirements Locating Pipeway Loops
Expansion Loops a) b) c) d) e) f)
Need for Expansion Loop Disadvantage Points to Remember Expansion Loop Requirements Locating Pipeway Loops Multiple Loops
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Points to Remember (Example & Drawings)
Points to Remember (Example & Drawings)
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Points to Remember (Example & Drawings) Cont…
Points to Remember (Example & Drawings) Cont…
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Points to Remember (Example & Drawings) Cont…
Points to Remember (Example & Drawings) Cont…
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Expansion Loop Examples
Expansion Loop Examples
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Kellogg Charts CC -11 & C12 for Symmetrical Expansion Loop sizing and Calculating Forces & Moments
Kellogg Charts CC -11 & C12 for Symmetrical Expansion Loop sizing and Calculating Forces & Moments
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Kellogg Charts CC -11 & C12 for Symmetrical Expansion Loop sizing and Calculating Forces & Moments (Cont.)
Kellogg Charts CC -11 & C12 for Symmetrical Expansion Loop sizing and Calculating Forces & Moments (Cont.)
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Expansion Loop Example 3
Expansion Loop Example 3
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Thermal Expansion a) b) c) d) e)
Equipment – Anchors Using coordinates to find free expansion Expansion influencing Vessel Anchor End Different expansion coefficients have an effect in the piping expansion calculation Line Spacing Requirement
Thermal Expansion a) b) c) d) e) f)
Equipment – Anchors Using coordinates to find free expansion Expansion influencing Vessel Anchor End Different expansion coefficients have an effect in the piping expansion calculation Line Spacing Requirement Locating Friction Balance
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Thermal Expansion (Example(Example -4)
Thermal Expansion (Example(Example -4)
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Thermal Expansion (Example(Example -5) CaseCase -1
Thermal Expansion (Example(Example -5) CaseCase -1
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Thermal Expansion (Example(Example -5) CaseCase -2
Thermal Expansion (Example(Example -5) CaseCase -2
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Thermal Expansion (Example(Example -6)
Thermal Expansion (Example(Example -6)
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Thermal Expansion (Example(Example -7)
Thermal Expansion (Example(Example -7)
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Thermal Expansion (Example(Example -8)
Thermal Expansion (Example(Example -8)
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Thermal Expansion (Example(Example -9)
Thermal Expansion (Example(Example -9)
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Line Spacing Requirement
Line Spacing Requirement
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Thermal Expansion (Example (Example-10)
Thermal Expansion (Example (Example-10)
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Thermal Expansion (Example(Example -10) Cont…
Thermal Expansion (Example(Example -10) Cont…
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Advantage in using accurate restraint stiffness
CaseCase -1: -1: 1:
C Casease-2: -2:
Advantage in using accurate restraint stiffness
CaseCase -1: -1: 1:
C Casease-2: -2:
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Piping Nozzle Evaluation
Steam Turbine Centrifugal Pumps Centrifugal Compressors Air Cooled Heat Exchangers Pressure Vessels
-
NEMA SMSM-23 API 610 API 617 API 661 WRC 107 / 297
Methods for Analyzing Equipment Nozzle loads
Performing a test Finite Element Analysis
Piping Nozzle Evaluation
Steam Turbine Centrifugal Pumps Centrifugal Compressors Air Cooled Heat Exchangers Pressure Vessels
-
NEMA SMSM-23 API 610 API 617 API 661 WRC 107 / 297
Methods for Analyzing Equipment Nozzle loads
Performing a test Finite Element Analysis International Codes and Standards
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API -610 APICentrifugal Pumps Allowable Pump Nozzle loading details
API -610 APICentrifugal Pumps Allowable Pump Nozzle loading details
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AnnexureAnnexure -F (Criteria for Piping Design)
Horizontal Pumps Pumps - Conditions of AnnexureAnnexure -F
AnnexureAnnexure -F (Criteria for Piping Design)
Horizontal Pumps Pumps - Conditions of AnnexureAnnexure -F
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AnnexureAnnexure -F (Criteria for Piping Design) Cont… Vertical Pumps Pumps - Conditions of AnnexureAnnexure -F
AnnexureAnnexure -F (Criteria for Piping Design) Cont… Vertical Pumps Pumps - Conditions of AnnexureAnnexure -F
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WRC Bulletin 107 Analysis WRC Local Coordinates and Stress Points •
WRC 107 should not be used if either of the following inequalities is not satisfied: d/D < 0.33 D/T > 50 Where: D =mean diameter of vessel, in D d =outside diameter of nozzle, in d T =thickness of vessel wall, in T
WRC Bulletin 107 Analysis WRC Local Coordinates and Stress Points •
WRC 107 should not be used if either of the following inequalities is not satisfied: d/D < 0.33 D/T > 50 Where: D =mean diameter of vessel, in D d =outside diameter of nozzle, in d T =thickness of vessel wall, in T
Caesar Program Table format
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ASME Section VIII VIII – – Div. 2 Requirements on WRCWRC -107 107
AD -160 Fatigue Evaluation ADOperating Experience Rules to determine need for Fatigue Analysis of Integral parts
AD -160.1 ADADAD -160.2 160.2 of Vessels: ADAD -160.3 160.3 Rules to determine need for Fatigue Analysis of Nozzles with separate reinforcement and nonnon -integral attachments such as pad type reinforcement, fillet welded attachment etc. The three calculated stress intensities using WRC WRC-107 must now be compared to: Pm Pm < Sm Pm + Pl Pl < 1.5 Sm Sm Pm + Pl + Q Q < 3.0 Sm (Sm is the average Sm at cold and hot hot temperatures)
ASME Section VIII VIII – – Div. 2 Requirements on WRCWRC -107 107
AD -160 Fatigue Evaluation ADOperating Experience Rules to determine need for Fatigue Analysis of Integral parts
AD -160.1 ADADAD -160.2 160.2 of Vessels: ADAD -160.3 160.3 Rules to determine need for Fatigue Analysis of Nozzles with separate reinforcement and nonnon -integral attachments such as pad type reinforcement, fillet welded attachment etc. The three calculated stress intensities using WRC WRC-107 must now be compared to: Pm Pm < Sm Pm + Pl Pl < 1.5 Sm Sm Pm + Pl + Q Q < 3.0 Sm (Sm is the average Sm at cold and hot hot temperatures)
Where, Pm Stresses due to internal pressure in the vessel Pl WRC 107 calculated stresses due to sustained loads Q - 7/15/2011 WRC 107 calculated stresses due to expansion loads Sm - Allowable stress intensity for the material at operating temperature
WRC Bulletin 297 Analysis Conditions of WRC 297 are:
d/D < d/D< d/t > d/t 20 20 d/T> d/T >
Where:
0.5 0.5 20 < D/T < 5
2500 2500
WRC Bulletin 297 Analysis Conditions of WRC 297 are:
d/D < d/D< d/t > d/t 20 20 d/T> d/T >
0.5 0.5 20 < D/T < 5
2500 2500
Where: d = d = D D = = t = t = T= T = 7/15/2011
outside diameter of nozzle, in in mean diameter of vessel, in thickness of nozzle, in thickness of vessel, in
8.
References:
Design of Piping Systems – The M.W. Kellogg Company Introduction to Pipe Stress Analysis – Sam Kannappan. P.E. Fluor Corporation – Stress Analysis Practice Piping Handbook - Mohinder L. Nayyar Coade Pipe Stress Analysis Seminar Notes
8.
References:
Design of Piping Systems – The M.W. Kellogg Company Introduction to Pipe Stress Analysis – Sam Kannappan. P.E. Fluor Corporation – Stress Analysis Practice Piping Handbook - Mohinder L. Nayyar Coade Pipe Stress Analysis Seminar Notes APIAPI -610, Centrifugal Pump Tenth Edition Oct Oct2004 CaesarCaesar -II – Technical Reference Manual
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ANY QUERIES ????????
ANY QUERIES ????????
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SEMINAR ON
Piping Stress Analysis Part-II – G.Palani
“KNOWLEDGE IS NOTHING, UNLESS IT
SEMINAR ON
Piping Stress Analysis Part-II – G.Palani
“KNOWLEDGE IS NOTHING, UNLESS IT IS SHARED”
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Piping Stress Analysis Part-II – G.Palani Table of Content: 1. 2. 3.
How are piping system classified by stress? 3 Advantage in using accurate restraint stiffness 3 Piping Nozzle Evaluation 5 3.1 Methods for analyzing equipment nozzle loads 6 3.2 Centrifugal Pumps and Pressure Vessel nozzle load details 6 4. Expansion Loops 14 4.1 Expansion Loop Examples 19 5. Thermal Expansion 26 5.1 Equipment – Anchors 26 5.2 Using Coordinates to find free expansion 26 5.3 Expansion influencing vessel anchor end 27 5.4 Different Expansion Coefficients – Piping System 32 5.5 Line Spacing Requirement 33 5.6 Locating Friction Balance 37 6. Attachments 39 6.1 Force Nomograph 39 6.2 Stress Nomograph 40 6.3 Stress Pipeway Layout (Attached Separately)
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Piping Stress Analysis Part-II – G.Palani 1
How are piping system classified by stress? A. Critical Service Piping Systems – By computer analysis
Pump, turbine, blower and compressor piping Piping designed for 500°F or greater Piping designed for 1000 psig or greater Piping greater than 24 inch diameter Piping connected to sensitive equipment such as fired heaters, finfan coolers, reactors and boilers Piping supported or guided from stress-relieved vessel Jacketed piping
B. Intermediate Service Piping Systems – By manual calculation
Piping designed for 250 to 499 °F Piping designed for 500 to 999 psig Piping from 6” to 24” diameter Nonmetallic piping Vacuum lines Pipeway and yard piping
C. Mild Service Piping Systems – By Visual Inspection
2
Other piping not included in Critical and Intermediate Piping Systems
Advantage in using accurate restraint stiffness
Caesar II default restraint stiffness is in the range of 1E12 lb/in. Case-1:
For a rigid piping configuration, considering both ends anchor, the following are the data for the piping configuration: 12” Sch STD, Low carbon steel pipe @ 350 °F as shown below,
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According to beam theory (Guided Cantilever Method): =
Pl3 / 12EI = el M = Pl/2 Solving for P: P = 12EI / l3 Solving for M: M = 6EI / l2 Solving for Se: Se = 6EI / l2Z = 6ER
/
l2
The above Se equation shows that the stress range decreases with the square of the length of the absorbing leg, so longer the leg absorbing the displacement, the lower the stress range. For the above configuration (Fig. 2-20) =
1.88 E -3 x (10 x 12) = 0.23” Se = 6 x 29 E6 x 6.375 x 0.23 / (10 x 12)2 = 17,720 psi Note: This calculation does not consider the SIF at the elbow at the top of the leg. If SIF is considered (for long radius elbow SIF is 2.8) the stress range would result in 49,600 psi, which is excessive. Case-2:
If the restraint has a lateral stiffness of 10,000 lb/in (instead of 1E12) the thermal growth is partially absorbed by the pipe and partially absorbed by the restraint: Page 4 of 40
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For 12” std wall pipe, I = 279.3 in^4 & Z = 43.8 in^3 Se = 2675 psi This significantly reduces the stress range from the previous value of 17,720 psi. Vessel nozzle stiffnesses can be calculated manually using WRC 107/297 or some equivalent. 3
Piping Nozzle Evaluation:
Piping loads on nozzles of equipment such as pumps, compressors, turbine, and heat exchangers have the tendency to deform or overstress equipment casing, overload bearings or cause shaft binding. The following are the standards to calculate the allowable nozzle loads due to piping for the below equipments, Steam Turbine Centrifugal Pumps Centrifugal Compressors Air Cooled Heat Exchangers Pressure Vessels
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-
NEMA SM-23 API 610 API 617 API 661 WRC 107 / 297
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Piping Stress Analysis Part-II – G.Palani WRC Bulletin 107 (Local Stresses in Spherical and Cylindrical Shells due to External Loadings) / 297 (Local Stresses in Cylindrical Shells due to External Loadings on Nozzles – Supplement to WRC Bulletin 107) 3.1
Methods for Analyzing Equipment Nozzle loads:
Performing a test Finite Element Analysis International Codes and Standards 3.2
3.2.1
The following are the International Codes and Standards for evaluating the nozzle loads due to piping for Centrifugal Pumps and Pressure Vessels,
API 610 – Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries (Tenth Edition, Oct-2004) ISO 13709:2003, (Identical) – Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries
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3.2.2
WRC Bulletin 107 Analysis:
Based on the work done by Bijlaard, WRC 107 was prepared. This Bulletin uses the finite element analysis program to examine the stresses in vessel nozzles due to external load attachments. WRC Bulletin 107 (Local Stresses in Spherical and Cylindrical Shells due to External Loadings) Note that WRC 107 computes stresses in the vessel shell at the nozzle/vessel interface. Stresses in the nozzle wall are not computed. WRC 107 is used to analyze attachments to cylindrical or spherical vessel attachments. WRC 107 method should not be used when the nozzle is very light or when dimensionless parameters fall outside the limits of their respective figures. WRC 107 should not be used if either of the following inequalities is not satisfied: d/D < 0.33 D/T > 50 Where: D d T
= = =
mean diameter of vessel, in outside diameter of nozzle, in thickness of vessel wall, in
WRC 107 nomenclature and orientation of loads is shown below,
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3.2.2.1
Based upon various dimensional ratios of the vessel/nozzle configuration, the engineer selects 12 parameters from 12 different curves. These parameters are used in 15 equations to calculate 48 different stresses – Circumferential membrane and bending, longitudinal membrane and bending and shear stresses (in two directions) at each of eight locations in the vessel (6*8 = 48 stresses). These eight locations are the inner and outer edges (subscript l and u respectively) of the vessels at 0, 90, 180 and 270 degrees around the nozzle. ASME Section VIII – Div. 2 Requirements on WRC-107: AD-160 Fatigue Evaluation AD-160.1 Operating Experience:
When the user is considering experience with comparable equipment operating under similar condition as related to the design and service contemplated (Synonyms: Consider as a possibility), fatigue evaluation shall not be performed.
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Piping Stress Analysis Part-II – G.Palani AD-160.2 Rules to determine need for Fatigue Analysis of Integral parts of Vessels:
A fatigue analysis need not be made provided all of Condition A or all of Condition B is met. If neither Condition A nor B is met, a detailed fatigue analysis shall be made in accordance with the rules of Appendices 4 and 5 for those parts which do not satisfy the conditions. AD-160.3 Rules to determine need for Fatigue Analysis of Nozzles with separate reinforcement and non-integral attachments such as pad type reinforcement, fillet welded attachment etc.:
A fatigue analysis of pad type nozzles and non-integral attachments need not be made provided all of Condition AP or all of Condition BP is met. The rules of Condition AP are applicable only to vessels constructed of materials covered by Figs. 5-110.1 to 5-110.4. If neither Condition AP nor BP is met, a detailed fatigue analysis shall be made in accordance with the rules of Appendices 4 and 5 for those parts which do not satisfy the conditions. 3.2.2.2
Caesar WRC107 Program Table Format:
The table shown below contains 72 values – eight entries on each of nine lines. The eight entries represent the stresses at the eight locations Au, Al, Bu etc. The nine lines are three groups of three lines – the groups representing radial (circumferential), tangential (longitudinal), and shear stresses, while the three lines in each represent the loadings from the pressure, sustained and expansion load cases.
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The stress terminology shown above is: Pm - Stresses due to internal pressure in the vessel. The Hoop and Longitudinal values of these stresses can be readily calculated by hand. Due to the discontinuity of the nozzle cutout; there can be no hoop stresses at location C or D and no longitudinal stresses at locations A or B. Also shear stresses in the vessel wall due to pressure are negligible. Pl -
WRC 107 calculated stresses due to sustained loads
Q-
WRC 107 calculated stresses due to expansion loads
Sm - Allowable stress intensity for the material at operating temperature The three calculated stress intensities must now be compared to: Pm < Sm Pm + Pl < 1.5 Sm Pm + Pl + Q < 3.0 Sm (Sm is the average Sm at cold and hot temperatures) 3.2.3
WRC Bulletin 297 Analysis:
297 (Local Stresses in Cylindrical Shells due to External Loadings on Nozzles – Supplement to WRC Bulletin 107)
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Piping Stress Analysis Part-II – G.Palani Conditions of WRC 297 are: d/D d/t 20 d/T
< > < >
0.5 20 D/T < 5
2500
Where: d D t T 4
= = = =
outside diameter of nozzle, in mean diameter of vessel, in thickness of nozzle, in thickness of vessel, in
Expansion Loops Need for Expansion Loop:
One of the device used to improve the flexibility of piping are expansion loops. Piping systems with high temperature expands. The objective in piping design is not to restrain this expansion but to redirect, absorb and control its direction without overstressing the system. Loop absorbs piping expansion. Loops provide the necessary leg of piping in a perpendicular direction to absorb the thermal expansion. Expansion loops may be symmetrical or non-symmetrical. Disadvantage:
They are safer but take more space and piping. In some cases, it may require additional supports.
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Piping Stress Analysis Part-II – G.Palani Points to Remember:
Hotter and larger lines are placed outside as outer loops because the longer absorbing length (H) is needed. Smaller lines with lower temperature are placed as inside loops. Guide is used on both sides of the loops for proper functioning, because guide directs the expansion into the bend along the axis of the pipe, which avoids shifting the lines sideways as shown in Fig. 5.6 below.
Three dimensional loops are widely used because this arrangement does not block the routing of low temperature lines under the loop. The usual raiser height is about 3 feet.
Vertical loops are placed at road crossing and sometimes are nonsymmetrical due to the location of the road.
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To control the expansion of the piping, anchor must be located at the middle of the piping so that the expansion will be equal at the bend ends (if the expansion is less than 10”) – Refer Fig. 1-29 below.
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Guides must be placed on two sides of the anchor to prevent the line from “snaking” and wandering into adjacent lines – Refer Fig. 1-29 above. To reduce the structural forces: a) Place the heavy lines near column, not near the center of a long span as shown in fig. 1-30. b) The anchor forces due to piping expansion must be balanced or must be within an allowable limit as shown in fig. 1-30.
Expansion Loop Requirements:
Generally, if the total expansion in any direction on the pipeway is less than 10”, the loop could be avoided by locating the anchor in the middle of the run. The total expansion between the loop anchors should not exceed 12” Locating Pipeway Loops:
Ideally loops shall be located centered between anchors with equal legs on either side of anchor as shown in fig. 1-37 below.
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When this is not practical make legs on either side of anchor as equal as possible. By making these legs equal, the forces at the anchor should remain nearly balanced.
Multiple Loops:
More than one loop may be required when:
Spacing between braches and neighboring lines or steel is limited. It is impossible to make branch connections flexible enough. When loop becomes too large to support or fit into space available. Anchor forces between too unbalanced and steel cannot be economically braced.
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Fig. 1-41 shows a poor arrangement, since the unbalanced forces are more and the total expansion between loops to absorb (14”) exceeds allowable limit of 12”. The alternate way of approach is to make use of multiple loops as shown in fig. 1-42 below,
4.1
Expansion Loop Examples: Example 1:
Find the size of the loop to absorb expansion in 200 ft of 12” carbon steel pipe at 400°F. Assume the height to width ratio.
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Piping Stress Analysis Part-II – G.Palani Answer:
Total Expansion = 200 (0.027) = 5.4” Using the nomograph, to determine loop size as shown below, Read L2 (Bend length required to absorb expansion) in ft as 50 ft.
Assume H = W, then L2 = 2H + W = 50 ft. Thus H = W = 17 ft, making L2 = 51 ft. By Calculation (Guided Cantilever Method), L2 = (3ED / 144 Sa) ^ ½ Therefore, L2 = (3*29*10^6*12*5.4 / 144*20000) ^ ½
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Piping Stress Analysis Part-II – G.Palani L2 = 44 ft The estimated loop size is shown in fig. 5.13 below.
Example 2:
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Piping Stress Analysis Part-II – G.Palani Kellogg Charts C-11 & C12 for Symmetrical Expansion Loop sizing and Calculating Forces & Moments
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Piping Stress Analysis Part-II – G.Palani Example 3: Determining which of the lines requiring loops need the
largest loop, second largest, etc., by the following process:
Multiply the total expansion of each line between its proposed anchors by the pipe’s moment of inertia (E). (The stiffness of a line is measured by its “Moment of inertia”) The line with the largest of these calculated numbers will require the largest loop, the next the smaller number, the next smaller loop etc.
The above calculation shows that the 16” line should be berthed where the 6” line is, the 10” line should be where the 16” is, and the 6” line should be where the 2” line is. Note, on longer than normal span, loop bowing may cause the pipe to lift off intermediate support causing overspan.
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Piping Stress Analysis Part-II – G.Palani 5
Thermal Expansion
The thermal loads that arise when free thermal expansion or contraction is prevented by supports or anchors, loads due to temperature gradients in thick pipe walls, and loads due to difference in thermal coefficient of materials as in jacketed piping. The coefficient of linear expansion of a solid is defined as the increment of length in a unit length for a change in temperature of one degree. The unit is 10E-06in/in/°F. The unit for mean coefficient of thermal expansion between 70°F (installation temp.) and the given temperature is given as in/100ft of pipe length. To convert from 10E-06in/in/°F to in/100ft of pipe length, the following relation may be used: e, in/100ft = (coefficient) * 12 * 100 (Design temp. – install temp.)
5.1
Equipment – Anchors:
Most equipment is anchored to a foundation. Therefore equipment nozzles are also anchors. Generally they are full anchors. The anchors are mechanically rigid but may have additional expansion when the equipment is hot. Even if the equipment is not bolted down, the weight may be great enough to make the equipment an anchor point.
5.2
Using coordinates to find free expansion:
The algebraic combination of lengths in any direction is the same as the difference in anchor coordinates (In all three dimensions, i.e. north, east and elevation). The above condition satisfies only when the piping system temperature is uniform or same throughout the configuration considered for finding free thermal expansion.
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Piping Stress Analysis Part-II – G.Palani The fastest way to find the free thermal expansion is to multiply the difference between the anchor coordinates times the coefficient of expansion. This is where the method has its greatest advantage. Example 4:
Carbon Steel @ 300°F, e = 0.0182 in/ft. North Expansion = 190’ * 0.0182 = 3.46” East Expansion = 65’ * 0.0182 = 1.18”
5.3
Expansion influencing Vessel Anchor End: Points to Remember:
When finalizing the layout and plot plan the location of anchor needs to be considered in relation to the major piping systems (large diameter pipe, pipe coming from underground, etc). The free thermal expansion does not depend on the piping arrangement. The free thermal expansion depends only on the relative location of the Page 27 of 40
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anchor points. It is very useful for the layout man who is locating equipment. Stretching a pipe even a small amount takes a very large force. Preventing pipe from expanding thermally takes an equally large force. In other words, the force required to prevent the pipe from expanding is the same as the force required to stretch it an equal amount. The force found using the Nomograph-A can differ greatly from a computer output, but is good enough for piping study purposes. The following are the examples for the above points, Example-5: (Fig. 1-11 & Fig. 1-12) Case-1: Note that the Anchor End is at the right side of Horizontal Vessel.
Answer:
In N-S direction the expansion to be absorbed is: = eL (Coefficient of expansion * Length) = 0.046 * 30’ = 1.38” Page 28 of 40
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Piping Stress Analysis Part-II – G.Palani In E-W direction: = eL = 0.046 * 20’ = 0.92” Case-2: Change the anchor end of the drum as shown in figure below, (i.e.) the anchor is shifted to left side of Vessel
Answer:
In N-S direction the expansion to be absorbed is: = eL (Coefficient of expansion * Length) = 0.046 * 10’ = 0.46”
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Piping Stress Analysis Part-II – G.Palani In E-W direction: = eL = 0.046 * 20’ = 0.92” Conclusion: The E-W expansion did not change from the previous
example. The N-S expansion was reduced considerably by just shifting the anchor end of the drum. Thus the case-2 requires less flexibility and has the potential of saving pipe and fittings. Example-6: (Fig. 1-19)
Both vessel and pipe CS at 300 F – 8” Sch. 40. Calculate the thermal forces at A & B as shown below, Case-1: Let the Anchor end of Horizontal Vessel shall be as shown in Fig. 1-19 below, Note: Radial expansion of vertical vessel must be added for horizontal
expansion.
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Piping Stress Analysis Part-II – G.Palani Case-2: If the anchor end and slotted end were reversed, then T.F.A would be:
Conclusion: Reversal of anchor end of horizontal vessel (Case-2)
causes an increase in anchor force, (i.e.) as the expansion increases, the force required to restrain the expansion will also be increased. Example-7: (Fig. 1-20)
SS material @ 350 F, 10” Sch. 20, with I = 114 calculate the thermal force at A & B as shown in figure below,
Note: In this example, the guide acts as an anchor for forces in “B”
direction, but not in “A” direction. Example-8: (Fig. 1-22)
Refer to the Fig. 1-22 below; find the horizontal and vertical thermal forces.
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5.4
Different expansion coefficients have an effect in the piping expansion calculation:
Taking the difference between anchor coordinates does not work when portion of the system are different temperature and/or of materials with different expansion coefficients. Example-9: (Fig. 1-25)
Find the N-S and E-W thermal forces for the fig. 1-25 as shown below,
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5.5
Line Spacing Requirement:
When there are no flanges between the corner and first guide/anchor on the two adjacent lines, line spacing may be based on O.D of pipe or insulation to O.D. of insulation plus expansion plus 1” clearance (Refer Fig. 1-32) below. = (D1+D2)/2 + thermal expansion + 1” (Clearance) + (Insu thk D1 + Insu thk D2 (if applicable)) Where, D1 & D2 are the O.D of two adjacent pipes. Page 33 of 40
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Piping Stress Analysis Part-II – G.Palani In expansion case, usually spacing is calculated with one line hot (operating) and one line cold (not operating).
Example-10: (Fig. 1-34)
Determine which line requires loops, based on the line spacing at the east end of the pipeway under consideration. Assuming no extra space is available for thermal expansion.
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Answer: Case-1: without considering the expansion,
Refer to the Fig. 1-35 below,
A = 2.375” + 2” + 1” + 3” + 7” = 15.375” 16” B = 7” + 3” + 1” + 2.25” = 13.25” 14” C = Using Standard pipe spacing table = 12” D = Using Standard pipe spacing table = 19”
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Piping Stress Analysis Part-II – G.Palani Without considering the expansion, the total line spacing required for distance A, B, C & D, Total = 15.5 + 13.5 + 12 + 19 = 62” Case-2: Considering the expansion:
After the need for a loop has been established, locate the loop anchors
Let us locate the anchor for 4” SS @ 500 F – 2” IH line, The coefficient of thermal expansion is 0.0501 in/ft. Page 36 of 40
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Piping Stress Analysis Part-II – G.Palani Allowable expansion at the right end, without increasing line spacing is = 16” – 7” – 3” - 1” – 2” – 2.25” = 0.75” The maximum distance the anchor may be from the corner on both ends is found by dividing the allowable movement by the coefficient of expansion. Left End L = 6 / 0.0501 = 120 ft Right End L = 0.75 / 0.0501 = 15 ft Referring to the figure 1-36, the expansion that the loop must absorb is given as, =700 ft – 120 ft – 15ft = 565 ft, Total expansion = 565 * 0.0501 = 28.3” of expansion. Since the maximum expansion that the loop can absorb is only 12”, which is less than 28.3”, so multiple loops is required. 5.6
Locating Friction Balance: Locating the friction balance of liquid headers that change size:
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Piping Stress Analysis Part-II – G.Palani The anchor is placed at the lines “Center of Gravity”. The calculation is as follows, find the total weight and divide by two:
Locating the friction balance of vapour headers that change size:
Steam headers and flare headers should have their anchors located without considering water in the line. Include insulation, however if present. The method of calculating is same as above,
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Piping Stress Analysis Part-II – G.Palani 6.0
Attachments:
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