The factor is used when calculating the required thickness of longitudinal and spiral welded pipe and fittings in pressure design. In the 2004 and 2006 edition, it was also used in evaluating longitudinal stress due to sustained loads at girth weld locations. In the 2008 edition, this was changed from a requirement, to stating that application of weld joint strength reduction factors to girth welds is the responsibility of the designer. This change was made as a compromise to avoid inconsistency between ASME B3I.3 and ASME B31.1; there was not general agreement that it should be required for girth welds.
The factor does not apply to the following conditions.
It is not used to reduce the allowable displacement stress range, SA, because these stresses are not sustained. The displacement stresses relax over time.
It is not used for evaluating stresses due to occasional loads, as such loads have short durations.
It is not used when considering the allowable stress for permissible variations, as provided in para. 302.2.4, as such loads have short durations.
It is not used to reduce the allowable displacement stress range, SA, because these stresses are not sustained. The displacement stresses relax over time.
It is not used for evaluating stresses due to occasional loads, as such loads have short durations.
It is not used when considering the allowable stress for permissible variations, as provided in para. 302.2.4, as such loads have short durations.
As mentioned above, the Code does not specify whether to use the factor or not when evaluating longitudinal stress due to sustained loads at girth welds.
The original background for development of the weld joint strength reduction factors in the 2004 edition is provided as Insert 3.2. In the 2008 edition, for most materials, the same slope was used for weld joint strength reduction factor versus temperature, but the starting temperature was changed to TCR which is material specific. TCR is 25°C (50°F) below the temperature at which point the allowable stress is governed by creep properties in the allowable stress tables. This is not yet indicated yet in the ASME B31.3 allowable stress tables, so the reference is made to the Section VTII, Div 1 allowable stress table. The material specific factors are provided in Table 302.3.5 (Table 3.1).
The original background for development of the weld joint strength reduction factors in the 2004 edition is provided as Insert 3.2. In the 2008 edition, for most materials, the same slope was used for weld joint strength reduction factor versus temperature, but the starting temperature was changed to TCR which is material specific. TCR is 25°C (50°F) below the temperature at which point the allowable stress is governed by creep properties in the allowable stress tables. This is not yet indicated yet in the ASME B31.3 allowable stress tables, so the reference is made to the Section VTII, Div 1 allowable stress table. The material specific factors are provided in Table 302.3.5 (Table 3.1).
A few highlights of the table follow:
Factors are provided for CrMo (through 9Cr-lMo), CSEF, and austenitic stainless grade 3xx, and N088xx nickel alloy steels. The prior ASME B31.3 factors are used for other materials, when required.
CSEF material weldment performance is highly dependent upon the heat treatment; if a subcritical PWHT is performed, the factor is dropped to 0.5 throughout the creep range.
Autogenous (i.e., no filler metal welds) austenitic stainless grade 3xx and N088xx and N066xx nickel alloys are assigned a W factor of 1.0 if they are solution annealed after welding.
Factors are not required for carbon steel.
Reference is made to permit use the Section HI, Subsection NH, Tables 1-14.10 A-xx, B-xx and C-xx factors specified for 100,000 hour duration. Observing Figure 3.3, and in particular the 304B line (304 welded with 316 weld metal), this can give higher factors for some combinations of base metal and weld metal.
Factors are provided for CrMo (through 9Cr-lMo), CSEF, and austenitic stainless grade 3xx, and N088xx nickel alloy steels. The prior ASME B31.3 factors are used for other materials, when required.
CSEF material weldment performance is highly dependent upon the heat treatment; if a subcritical PWHT is performed, the factor is dropped to 0.5 throughout the creep range.
Autogenous (i.e., no filler metal welds) austenitic stainless grade 3xx and N088xx and N066xx nickel alloys are assigned a W factor of 1.0 if they are solution annealed after welding.
Factors are not required for carbon steel.
Reference is made to permit use the Section HI, Subsection NH, Tables 1-14.10 A-xx, B-xx and C-xx factors specified for 100,000 hour duration. Observing Figure 3.3, and in particular the 304B line (304 welded with 316 weld metal), this can give higher factors for some combinations of base metal and weld metal.
Use of factors other than those provided in Table 302.3.5 are permitted based on use of creep test data for weldments other than Creep Strength Enhanced Ferritic (CSEF) materials, which can have significant issues in the heat alfected zone which require longer term testing to observe. Further, with the owner's approval, extensive successful service experience may be used to justify higher W factors. Succesful experience must include same or like material, weld metal composition, and welding process under equivalent, or more severe, sustained operating conditions.
In addition to changes to the weld joint factors, additional changes were made to the fabrication and examination rules for welds in elevated temperature piping.
Piping materials (this includes those in accordance with listed standards) with longitudinal or spiral welds in P-No. 4 or P-No. 5 materials are required to be examined by 100% radiography or 100% ultrasonic examination (para. 305.2.4).
Additional examination requirements are specified for elevated temperature piping in para. 341.4.4.
These include:
100% visual examination rather than random visual examination
Specific discussion of evaluating the installed system to ensure that movement of the piping under all conditions of startup, operation, and shutdown will be accommodated without undue binding or unanticipated constraint.
Longitudinal welds for P-No. 4 and P-No. 5 material made as a part of fabrication (welds made in the manufacturing process were covered by 1, above), also require 100% radiographic or ultrasonic examination.
Socket welds and branch connection welds for P-No. 4 and P-No. 5 materials that are not radiographed or ultrasonically examined are required to be examined by magnetic particle or liquid penetrant methods.
Weld metal requirements for CSEF materials are provided in note 3 of Table 302.3.5.
Required heat treatment conditions for use of the factors in Table 302.3.5 are specified for some materials therein.
Piping materials (this includes those in accordance with listed standards) with longitudinal or spiral welds in P-No. 4 or P-No. 5 materials are required to be examined by 100% radiography or 100% ultrasonic examination (para. 305.2.4).
Additional examination requirements are specified for elevated temperature piping in para. 341.4.4.
These include:
100% visual examination rather than random visual examination
Specific discussion of evaluating the installed system to ensure that movement of the piping under all conditions of startup, operation, and shutdown will be accommodated without undue binding or unanticipated constraint.
Longitudinal welds for P-No. 4 and P-No. 5 material made as a part of fabrication (welds made in the manufacturing process were covered by 1, above), also require 100% radiographic or ultrasonic examination.
Socket welds and branch connection welds for P-No. 4 and P-No. 5 materials that are not radiographed or ultrasonically examined are required to be examined by magnetic particle or liquid penetrant methods.
Weld metal requirements for CSEF materials are provided in note 3 of Table 302.3.5.
Required heat treatment conditions for use of the factors in Table 302.3.5 are specified for some materials therein.
Road Crossings
The pipeline model is a crossing of a 36″ potable water transport pipeline with a road. The road is 8 m wide with a roadside of 1 m on each side of the road and ditches alongside the road. The crossing is designed perpendicular to the road-axis and connected with two large radius bends R = 10*D and a angle of 60 degrees.
The pipeline model is a crossing of a 36″ potable water transport pipeline with a road. The road is 8 m wide with a roadside of 1 m on each side of the road and ditches alongside the road. The crossing is designed perpendicular to the road-axis and connected with two large radius bends R = 10*D and a angle of 60 degrees.
Pipe data
Pipe material API 5L X52 steel
Yield stress 52.000 psi = 358 N/mm2
Outer diameter 914.4 mm (36″)Wall thickness 9.52 mm
Corrosion allowance 2 mm
Minimum manufacturing tolerance 5%
Maximum operating pressure 1.0 MPa
Transported matterpotable water
Deadweight of filled pipe structure 1.854 kN/m
Pipe material API 5L X52 steel
Yield stress 52.000 psi = 358 N/mm2
Outer diameter 914.4 mm (36″)Wall thickness 9.52 mm
Corrosion allowance 2 mm
Minimum manufacturing tolerance 5%
Maximum operating pressure 1.0 MPa
Transported matterpotable water
Deadweight of filled pipe structure 1.854 kN/m
Pipeline geometry and side elevation are shown in the figures below.
Soil data
Soil is assumed to consist of a silty sand with a sub-layer of non-consolidated clay. Road construction will be done after the pipeline was laid, resulting in expected soil settlements of the road-earth body with a maximum of 200 mm at the road-axis location. (consolidation of sub-layer of clay due to increased vertical soil pressure)
Soil is assumed to consist of a silty sand with a sub-layer of non-consolidated clay. Road construction will be done after the pipeline was laid, resulting in expected soil settlements of the road-earth body with a maximum of 200 mm at the road-axis location. (consolidation of sub-layer of clay due to increased vertical soil pressure)
Loading data
Pressure 1.00 N/mm2
Deadweight 1.85 N/m
Settlements 200 mm
Pressure 1.00 N/mm2
Deadweight 1.85 N/m
Settlements 200 mm
1. The upper graph shows the surface level of the ground configuration with the water table. As may be seen, there is some water in the ditches.
The horizontal axis is the nodal axis projected on the longitudinal length along the pipe-axis. (various projection axes are possible)
The vertical utmost right axis (length dimension) shows the level and the zeropoint determines the position of the graph.
The horizontal axis is the nodal axis projected on the longitudinal length along the pipe-axis. (various projection axes are possible)
The vertical utmost right axis (length dimension) shows the level and the zeropoint determines the position of the graph.
2. The middle graph shows the soil settlement distribution. The horizontal axis is the same as above, the vertical axis (length dimension) is the middle axis as the scale and position of the graph differ from the first graph.
3. The lower graph shows the combined maximum stress distribution along the pipeline. Horizontal axis again as above, vertical utmost left axis (stress dimension) shows the stress scale. The red line above the graph is the allowable stress.
The overall maximum stress occurs at the middle of the roadcrossing due to pipe bending as a result of the maximum soil settlement
The overall maximum stress occurs at the middle of the roadcrossing due to pipe bending as a result of the maximum soil settlement
🆕 Keep pipe analysis records
Most people believe that a computer printout is a sufficient record of a pipe stress analysis. This a big mistake that can be avoided with little effort. Creating a record of your work is about more than keeping a hard copy or PDF of the computer-aided pipe stress analysis. It means documenting a trail of all inputs, not just the drawings used to create the piping geometry. Items that could be included are the piping and instrument diagrams, system parameters, load cases, and any corresponding external forces applied to the piping system, pipe-support locations, and type of pipe support used. Most pipe stress analysis records will fill a three-ring binder.
As most consulting engineers have internal quality assurance/quality control procedures, develop a standard list of the inputs commonly used and corresponding reference for the information. This would provide the checker of a calculation a place to sign off, indicating they concur with the input and acknowledge the source of the input. In the end, your documentation should tell a complete story.
Most people believe that a computer printout is a sufficient record of a pipe stress analysis. This a big mistake that can be avoided with little effort. Creating a record of your work is about more than keeping a hard copy or PDF of the computer-aided pipe stress analysis. It means documenting a trail of all inputs, not just the drawings used to create the piping geometry. Items that could be included are the piping and instrument diagrams, system parameters, load cases, and any corresponding external forces applied to the piping system, pipe-support locations, and type of pipe support used. Most pipe stress analysis records will fill a three-ring binder.
As most consulting engineers have internal quality assurance/quality control procedures, develop a standard list of the inputs commonly used and corresponding reference for the information. This would provide the checker of a calculation a place to sign off, indicating they concur with the input and acknowledge the source of the input. In the end, your documentation should tell a complete story.