As the pipe temperature changes from the installation condition to the operating condition, it expands or contracts. In the general term, both cases are called thermal expansion. When a pipe expands it has the potential of generating enormous force and stress in the system. However, if the piping is flexible enough, the expansion can be absorbed without creating undue force or stress. Providing the proper flexibility is one of the major tasks in the design of piping systems.
Piping is used to convey a certain amount of fluid from one point to another. It is obvious that the shorter the pipe is used the lesser the capital expenditure is required. Long pipe runs may also generate excessive pressure drop making it unsuitable for the proper operation. However, the direct shortest layout generally is not acceptable for absorbing the thermal expansion. Flexibility analysis is done on the piping system to study its behaviour when its temperature changes from ambient to operating, so as to arrive to the most economical layout with adequate safety. Piping flexibility is provided in many different ways.
Pipes bend, even under their own weight. The longer the pipe, the easier it is to bend. If a pipe is bent within its elastic limit (no permanent deformation), it will behave like a spring and return to its original shape after the load is removed. If the elbows and anchors on a pipe system are arranged to allow movement, the forces will be much less than a straight run. Also, the turns and offsets needed for running the pipe from one point to another provides some flexibility as well. This inherent flexibility may or may not be sufficient depending on the individual cases.
✏️Piping Stress Analysis Engineering Specification
This content provides you with sample piping stress analysis Engineering Specification that is used in industrial plant construction works.
This content provides you with sample piping stress analysis Engineering Specification that is used in industrial plant construction works.
1. Piping Stress Analysis - Scope
This specification prescribes the basic requirements for stress analysis of the piping systems to be performed during the piping design work for use in industrial plant.
This specification prescribes the basic requirements for stress analysis of the piping systems to be performed during the piping design work for use in industrial plant.
2. References
The latest edition / version of the following codes, standards and specifications shall form a part of the requirements of this specifications.
2.1. Piping Stress Analysis - Codes and Standards
⬇️ASME B31.3
Process Piping
⬇️ASME section VIII div 1
Boiler and Pressure Vessel Code
⬇️ASME section VIII div 2
Rule for Construction of Pressure Vessels
⬇️API 610
Centrifugal pumps for petroleum, heavy duty chemical, and gas industry services
⬇️API 617
Centrifugal compressors for petroleum, chemical, and gas service industries
⬇️API 618
Reciprocating compressors for petroleum, chemical, and gas service industries
⬇️API 560
Fired heaters for general refinery services
⬇️API 650
Welded steel tanks for oil storage
⬇️API 660
Shell and tube type heat exchangers for general refinery services
⬇️API 661
Air-Cooled heat exchangers for general refinery services
⬇️API RP520
Sizing, selection and installation of pressure – relieving device in refineries
⬇️NEMA SM23
Steam turbine for mechanical drive service
⬇️EJMA
Standard of expansion joint manufacturers association – ASME 16.9, ASME 16.25
⬇️WRC 107
Local stresses in spherical and cylindrical shells due to external loading
⬇️WRC 297
Supplement for WRC 107
The latest edition / version of the following codes, standards and specifications shall form a part of the requirements of this specifications.
2.1. Piping Stress Analysis - Codes and Standards
⬇️ASME B31.3
Process Piping
⬇️ASME section VIII div 1
Boiler and Pressure Vessel Code
⬇️ASME section VIII div 2
Rule for Construction of Pressure Vessels
⬇️API 610
Centrifugal pumps for petroleum, heavy duty chemical, and gas industry services
⬇️API 617
Centrifugal compressors for petroleum, chemical, and gas service industries
⬇️API 618
Reciprocating compressors for petroleum, chemical, and gas service industries
⬇️API 560
Fired heaters for general refinery services
⬇️API 650
Welded steel tanks for oil storage
⬇️API 660
Shell and tube type heat exchangers for general refinery services
⬇️API 661
Air-Cooled heat exchangers for general refinery services
⬇️API RP520
Sizing, selection and installation of pressure – relieving device in refineries
⬇️NEMA SM23
Steam turbine for mechanical drive service
⬇️EJMA
Standard of expansion joint manufacturers association – ASME 16.9, ASME 16.25
⬇️WRC 107
Local stresses in spherical and cylindrical shells due to external loading
⬇️WRC 297
Supplement for WRC 107
2.2. Piping Stress Analysis - Related Specifications and References
⬇️Engineering specification for Piping Hanging & Support
⬇️Engineering specification for Piping Design
⬇️Engineering specification for Thermal Insulation (HOT)
⬇️Engineering specification for Thermal Insulation (COLD)
⬇️Engineering specification for Piping Material
⬇️Engineering specification for Piping Hanging & Support
⬇️Engineering specification for Piping Design
⬇️Engineering specification for Thermal Insulation (HOT)
⬇️Engineering specification for Thermal Insulation (COLD)
⬇️Engineering specification for Piping Material
3. Piping Stress Analysis -Design Conditions
The piping stress analysis shall include the following loading effects as applicable.
The piping stress analysis shall include the following loading effects as applicable.
3.1. Piping Stress Analysis - Weight Effects
The weight load shall include the pipe weight, weight of content, insulation weight and weight of fittings and any inline equipment. For piping systems, which are tested hydraulically and have content with specific gravity less than 1.0, a hydro-test run shall be performed assuming a specific gravity of 1.0 to establish the structural design loads.
The weight load shall include the pipe weight, weight of content, insulation weight and weight of fittings and any inline equipment. For piping systems, which are tested hydraulically and have content with specific gravity less than 1.0, a hydro-test run shall be performed assuming a specific gravity of 1.0 to establish the structural design loads.
3.2. Piping Stress Analysis - Thermal Effects
Temperature to be used in the piping flexibility analysis shall be the maximum differential temperature between any of the following applicable conditions.
3.2.1. Piping Stress Analysis - Installation Temperature
1) Maximum dry bulb temperature of 48°C shall be taken as the installation temperature for cold insulated piping service.
2) Minimum dry bulb temperature of 5°C shall be taken as the installation temperature for bare/hot insulated piping service.
3.2.2. Piping Stress Analysis - Calculation Temperature
1) Operating temperature as stipulated in the line list.
2) In addition, the following temperature condition shall be considered in the calculation when lines are specified in the line index.
⬇️ Start-up / shutdown temperature
⬇️Steam out temperature: Normal steam out temperature should not exceed 120°C for saturated steam. This steam out temperature shall be considered only for flexibility purposes of hydrocarbon serviced lines.
⬇️Decoking temperature
⬇️Regeneration temperature
3) For piping which normally have no flow (such as drains, start-up lines, etc.) the flow calculation temperature shall be determined as follows.
For insulated piping, 75% of operating temperature shall be taken.
For un-insulated piping, 25% of operating temperature shall be taken.
For section between stand-by equipment and cut-off valve, installation temperature shall be taken.
For piping which have warming-up by-pass, operating temperature shall be taken for all section.
Temperature to be used in the piping flexibility analysis shall be the maximum differential temperature between any of the following applicable conditions.
3.2.1. Piping Stress Analysis - Installation Temperature
1) Maximum dry bulb temperature of 48°C shall be taken as the installation temperature for cold insulated piping service.
2) Minimum dry bulb temperature of 5°C shall be taken as the installation temperature for bare/hot insulated piping service.
3.2.2. Piping Stress Analysis - Calculation Temperature
1) Operating temperature as stipulated in the line list.
2) In addition, the following temperature condition shall be considered in the calculation when lines are specified in the line index.
⬇️ Start-up / shutdown temperature
⬇️Steam out temperature: Normal steam out temperature should not exceed 120°C for saturated steam. This steam out temperature shall be considered only for flexibility purposes of hydrocarbon serviced lines.
⬇️Decoking temperature
⬇️Regeneration temperature
3) For piping which normally have no flow (such as drains, start-up lines, etc.) the flow calculation temperature shall be determined as follows.
For insulated piping, 75% of operating temperature shall be taken.
For un-insulated piping, 25% of operating temperature shall be taken.
For section between stand-by equipment and cut-off valve, installation temperature shall be taken.
For piping which have warming-up by-pass, operating temperature shall be taken for all section.
3.3. Piping Stress Analysis - Pressure Effect
Maximum operating pressure and minimum vacuum pressure shall be taken as the calculation pressure as per ASME B31.3, unless otherwise specified.
Maximum operating pressure and minimum vacuum pressure shall be taken as the calculation pressure as per ASME B31.3, unless otherwise specified.
3.4. Piping Stress Analysis - Friction Effects
3.4.1 Friction effects shall be considered in the design of anchor on horizontally long run piping system with OD larger than 8 inch.
3.4.2 Following friction factor shall be used for computing the frictional resistance.
Surface Friction Factor
Steel to Steel = 0.3
Steel to Teflon = 0.1
Teflon to Teflon = 0.06
Steel to Concrete = 0.5
3.4.1 Friction effects shall be considered in the design of anchor on horizontally long run piping system with OD larger than 8 inch.
3.4.2 Following friction factor shall be used for computing the frictional resistance.
Surface Friction Factor
Steel to Steel = 0.3
Steel to Teflon = 0.1
Teflon to Teflon = 0.06
Steel to Concrete = 0.5
3.5. Piping Stress Analysis - Wind and Earthquake Effects
3.5.1. Wind and earthquake effects shall be checked in formal computer analysis, if experienced stress engineers decide it necessary. Wind loading shall be considered for sizes 24NB and over, for heights more than 10 m above grade where not shielded. For earthquake loading the equivalent static force analysis method shall be applied. The wind load and Earthquake as acting separately in two lateral condition 90º apart. 2.
3.5.1. Wind and earthquake effects shall be checked in formal computer analysis, if experienced stress engineers decide it necessary. Wind loading shall be considered for sizes 24NB and over, for heights more than 10 m above grade where not shielded. For earthquake loading the equivalent static force analysis method shall be applied. The wind load and Earthquake as acting separately in two lateral condition 90º apart. 2.
4.0 Piping Stress Analysis - Design and Analysis Requirements for Flexibility
4.1. Piping to purged vessels that cannot be disconnected during purging shall be designed with sufficient flexibility to accommodate the thermal displacement of the vessel.
4.2. The use of cold spring in piping, which connects to rotating equipment, is prohibited.
4.3. If temperature, resulting in short term loading as those stated in Para. 3.2.2.2) is specified in the line list, thermal effect by this temperature shall also be considered in the analysis. However, the reaction loads at equipment shall not be taken from this alternate analysis case.
4.1. Piping to purged vessels that cannot be disconnected during purging shall be designed with sufficient flexibility to accommodate the thermal displacement of the vessel.
4.2. The use of cold spring in piping, which connects to rotating equipment, is prohibited.
4.3. If temperature, resulting in short term loading as those stated in Para. 3.2.2.2) is specified in the line list, thermal effect by this temperature shall also be considered in the analysis. However, the reaction loads at equipment shall not be taken from this alternate analysis case.
4.4. Flexibility
1) The required flexibility of the piping shall be achieved by a suitable layout configuration without the need for expansion joints, first. Expansion joints shall be used only where bends, offsets or expansion loops are not deemed feasible. In this case, the stiffness of expansion joint shall be considered in any flexibility analysis. And, the destabilizing effects of unbalanced pressure thrusts shall be accounted for in the piping design.
2) Expansion joints shall be used only with adequate guides and anchors and when the fluid plugging properties cannot make the expansion joint ineffective.
3) Bellows type expansion joints shall be avoided in services that cooking can occur. If a suitable piping configuration can not be designed to eliminate the joint, connections shall be provided to enable flushing of the area between bellows and liner to be carried out in a non-coking medium.
4) Torsional rotation of the bellows shall be avoided. This twisting generally produces extremely high shear stresses in the bellows so where torsional rotation cannot be avoided; special hardware shall be used to limit the amount of torsional shear stress in the bellows.
5) The maximum, minimum and installation temperatures shall be accurately stated in data sheet to be prepared by the designer. Where the ambient temperature can vary significantly during pipeline construction, pre-positioning of the Expansion Joint at installation may be required.
6) The Expansion joint manufacture shall be advised if the Expansion joint will be insulated and the manner by which the Expansion joint will be insulated in order to properly design the component parts.
7) The movements to be absorbed by the expansion joint shall include not only piping elongation or contraction, but also movement of attached vessels, anchors, etc. and the possibility of misalignment during installation. Unless included in the design requirements, misalignment of the Expansion joint shall be avoided.
8) Where movements are cyclic, the number of cycles expected shall be specified. As in the case of pressure, the movement specified shall be realistic. An excessive safety factor can result in an Expansion joint, which is unnecessarily flexible; thus its stability under pressure is unnecessarily reduced.
9) If the flowing medium can pack or solidify, provisions shall be made to prevent entrapment or solidification of the material in the convolutions, which could result in damage to the Expansion joint or pipe line.
10) The predicted amplitude and frequency of external mechanical vibrations to be imposed on the bellows, such as caused by reciprocating or pulsating machinery, shall be specified. A resonant condition in the bellows will result in a grossly reduced fatigue life and shall be avoided.
1) The required flexibility of the piping shall be achieved by a suitable layout configuration without the need for expansion joints, first. Expansion joints shall be used only where bends, offsets or expansion loops are not deemed feasible. In this case, the stiffness of expansion joint shall be considered in any flexibility analysis. And, the destabilizing effects of unbalanced pressure thrusts shall be accounted for in the piping design.
2) Expansion joints shall be used only with adequate guides and anchors and when the fluid plugging properties cannot make the expansion joint ineffective.
3) Bellows type expansion joints shall be avoided in services that cooking can occur. If a suitable piping configuration can not be designed to eliminate the joint, connections shall be provided to enable flushing of the area between bellows and liner to be carried out in a non-coking medium.
4) Torsional rotation of the bellows shall be avoided. This twisting generally produces extremely high shear stresses in the bellows so where torsional rotation cannot be avoided; special hardware shall be used to limit the amount of torsional shear stress in the bellows.
5) The maximum, minimum and installation temperatures shall be accurately stated in data sheet to be prepared by the designer. Where the ambient temperature can vary significantly during pipeline construction, pre-positioning of the Expansion Joint at installation may be required.
6) The Expansion joint manufacture shall be advised if the Expansion joint will be insulated and the manner by which the Expansion joint will be insulated in order to properly design the component parts.
7) The movements to be absorbed by the expansion joint shall include not only piping elongation or contraction, but also movement of attached vessels, anchors, etc. and the possibility of misalignment during installation. Unless included in the design requirements, misalignment of the Expansion joint shall be avoided.
8) Where movements are cyclic, the number of cycles expected shall be specified. As in the case of pressure, the movement specified shall be realistic. An excessive safety factor can result in an Expansion joint, which is unnecessarily flexible; thus its stability under pressure is unnecessarily reduced.
9) If the flowing medium can pack or solidify, provisions shall be made to prevent entrapment or solidification of the material in the convolutions, which could result in damage to the Expansion joint or pipe line.
10) The predicted amplitude and frequency of external mechanical vibrations to be imposed on the bellows, such as caused by reciprocating or pulsating machinery, shall be specified. A resonant condition in the bellows will result in a grossly reduced fatigue life and shall be avoided.
4.5. The flexibility analysis shall be in accordance with ASME B31.3 and shall be based upon the total displacement strain imposed upon piping system including the effects of equipment settlement or anchor movement, if applicable.
4.6.. The computed stress range shall be less than allowable stress range as defined in ASME B31.3 unless otherwise specified.
4.7. Thermal movements shall be limited to 300mm between anchors and to 100mm at pipe bends or turns. However, greater movements will be considered if the availability of space and the capacity of the anchorage to accept the incremental loads are confirmed.
4.8. Start-up, shut-down and steam-out where applicable and upset conditions including short-term excursions to higher temperature or pressure as well as normal operating conditions, shall be considered in flexibility analysis. This is particularly pertinent to loads applied to connecting equipment. The effect of vibration from machinery on connecting piping shall also be assessed.
4.9. Flare system piping shall be designed to take care of expansion, movement or vibration caused by the most severe operating or emergency conditions. Pipe shoes or saddles shall be furnished on the main flare header at all supports.
4.10. Cold spring shall be used as much as practical to reduce forces on equipment nozzles and to prevent interference from expanding lines.
4.11. The use of cold spring for piping systems, which connected to rotating equipment, is prohibited.
4.12. The combinations of the loads shall conform to the applicable piping code.
4.13. Impact loads caused pressure relief through a safety valve shall also be calculated in accordance With " API PR 520 ".
4.6.. The computed stress range shall be less than allowable stress range as defined in ASME B31.3 unless otherwise specified.
4.7. Thermal movements shall be limited to 300mm between anchors and to 100mm at pipe bends or turns. However, greater movements will be considered if the availability of space and the capacity of the anchorage to accept the incremental loads are confirmed.
4.8. Start-up, shut-down and steam-out where applicable and upset conditions including short-term excursions to higher temperature or pressure as well as normal operating conditions, shall be considered in flexibility analysis. This is particularly pertinent to loads applied to connecting equipment. The effect of vibration from machinery on connecting piping shall also be assessed.
4.9. Flare system piping shall be designed to take care of expansion, movement or vibration caused by the most severe operating or emergency conditions. Pipe shoes or saddles shall be furnished on the main flare header at all supports.
4.10. Cold spring shall be used as much as practical to reduce forces on equipment nozzles and to prevent interference from expanding lines.
4.11. The use of cold spring for piping systems, which connected to rotating equipment, is prohibited.
4.12. The combinations of the loads shall conform to the applicable piping code.
4.13. Impact loads caused pressure relief through a safety valve shall also be calculated in accordance With " API PR 520 ".
5.0 Piping Stress Analysis - Line Classifications
5.1.Each piping system shall be classified as grade “A”, “B” and “C” according to the severity of its design condition and need for special design. Each grade requires the following methods for stress analysis.
Grade “A”: Judgment based on the experience of stress engineer.
Grade “B”: The simplified method according to Para.319.4 of ASME B31.3.
Grade “C”: Formal computer analysis.
5.1.Each piping system shall be classified as grade “A”, “B” and “C” according to the severity of its design condition and need for special design. Each grade requires the following methods for stress analysis.
Grade “A”: Judgment based on the experience of stress engineer.
Grade “B”: The simplified method according to Para.319.4 of ASME B31.3.
Grade “C”: Formal computer analysis.
5.2. For the following 3” and larger lines, formal computer stress analysis method is required:
1.Process, regeneration and decoking lines to and from Fired Heaters and Steam Generators.
2. Process lines to and from Blowers.
3. Steam lines to and from Turbines.
4. Suction and discharge line of Pumps.
5. Suction and discharge line of Compressors.
1.Process, regeneration and decoking lines to and from Fired Heaters and Steam Generators.
2. Process lines to and from Blowers.
3. Steam lines to and from Turbines.
4. Suction and discharge line of Pumps.
5. Suction and discharge line of Compressors.
5.3. The judgment of grade for all piping except that connected to rotating equipment shall be in accordance with the criteria shown on fig.1.
5.4. The judgment of grade for all piping connected to rotating equipment including air fin cooler and fired heater shall be in accordance with the criteria shown on fig.2.
5.4. The judgment of grade for all piping connected to rotating equipment including air fin cooler and fired heater shall be in accordance with the criteria shown on fig.2.
6.0. External Load Limits on Equipment
6.1. Rotating Equipment
The allowable nozzle loads for rotating equipments shall be limited to those specified in their governing Engineering specifications and standards to which the equipment is designed, unless otherwise specified by applicable vendors.
For ANSI and ISO pumps, allowable nozzle loads shall be those as other stated in table 2 of API 610 unless otherwise specified by vendors.
6.1. Rotating Equipment
The allowable nozzle loads for rotating equipments shall be limited to those specified in their governing Engineering specifications and standards to which the equipment is designed, unless otherwise specified by applicable vendors.
For ANSI and ISO pumps, allowable nozzle loads shall be those as other stated in table 2 of API 610 unless otherwise specified by vendors.
6.2. Air Fin-Cooled Exchangers
The allowable nozzle loads for air fin cooled exchanger shall be limited to those specified in Engineering specifications and vendor recommendation and API 661. Piping to air fin cooled exchanger shall be designed to take into account clearances between the frame and the header box of each bundle. And, thrust blocks between tube bundles shall be used whenever possible to minimize friction loads at piping takeoffs and anchors, and to meet allowable loads at the nozzles.
The allowable nozzle loads for air fin cooled exchanger shall be limited to those specified in Engineering specifications and vendor recommendation and API 661. Piping to air fin cooled exchanger shall be designed to take into account clearances between the frame and the header box of each bundle. And, thrust blocks between tube bundles shall be used whenever possible to minimize friction loads at piping takeoffs and anchors, and to meet allowable loads at the nozzles.