What is B 31.3 or Process piping Code?
ASME B 31.3 or Process Piping Code provides rules for piping design for petroleum refineries; onshore and offshore petroleum and natural gas production facilities; chemical, pharmaceutical, textile, paper, ore processing, semiconductor, and cryogenic plants; food and beverage processing facilities; and related processing plants and terminals. This code is known as The Bible for Process Piping Professionals. So this code dictates the design considerations of process plants.
What is B 31.1 or Power Piping Code?
ASME B 31.1 or Power Piping Code provides rules for piping typically found in electric power generating stations, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems. This code is very important for Power piping Professionals as this code governs the design rules for power generation plants.
Difference Between ASME B 31.3 and ASME B 31.1 (B 31.3 vs B 31.1)
From the above discussions, it is clear that both ASME B 31.3 and ASME B 31.1 codes i.e Process Piping Code and Power Piping code are different. Both are related to piping design aspects but different in design considerations. In this article we will tabulate the major differences as prescribed in these codes.
|Sr No||Parameter||ASME B 31.3-Process Piping||ASME B 31.1-Power Piping|
|1||Scope||Provides rules for Process or Chemical Plants||Provides rules for Power Plants|
|2||Basic Allowable Material Stress||Basic allowable material stress value is higher (For example the allowable stress value for A 106 B material at 250 Deg C is 132117.328 Kpa as per ASME B 31.3)||Basic allowable material stress value is lower (For example the allowable stress value for A 106 B material at 250 Deg C is 117900.344 Kpa as per ASME B 31.3)|
|3||Allowable Sagging (Sustained)||ASME B 31.3 code does not specifically says about any limit of allowable sagging. An allowable sagging of upto 15 mm is acceptable in general. B 31.3 does not provide suggested support span.||ASME B 31.1 clearly specifies the allowable sagging value as 2.5 mm. Table 121.5-1 of ASME B 31.1 provides suggested support span.|
|4||SIF on Reducers||Process Piping Code ASME B 31.3 does not use SIF (SIF=1.0) for reducer stress calculation||Power Piping code ASME B 31.1 uses a maximum SIF of 2.0 for reducers while stress calculation.|
|5||Factor of Safety||ASME B31.3 uses a factor of safety of 3; relatively lower than ASME B 31.1.||ASME B 31.1 uses a safety factor of 4 to have higher reliability as compared to Process plants|
|6||SIF for Butt Welded Joints||B 31.3 uses a SIF of 1.0 for butt welded joints||B 31.1 uses a SIF of upto 1.9 max in stress calculation.|
|7||Approach towards SIF||ASME B 31.1 uses a complex inplane, out-of-plane SIF approach.||ASME B 31.1 uses a simplified single SIF Approach.|
|8||Maximum values of Sc and Sh||As per the Process Piping code, the maximum value of Sc and Sh are limited to 138 Mpa or 20 ksi.||For Power piping code, the maximum Value of Sc and Sh are 138 Mpa only if the minimum tensile strength of the material is 70 ksi (480|
Mpa) otherwise it is dependent on the values provided in the mandatory appedix A as per temperature.
|9||Allowable Stress for Occasional Stresses||Allowable value of occasional stress is 1.33 times Sh||As per ASME B 31.1, the allowable value of occasional stress is 1.15 to 1.20 times Sh|
|10||Equation for Pipe Wall Thickness Calculation||The equation for pipe wall thickness calculation is valid for t<D/6||There is no such limitation in Power piping wall thickness calculation. However, they add a limitation on maximum design pressure.|
|11||Section Modulus, Z for Sustained and Occasional Stresses||While Sustained and Occasional stress calculation the Process Piping code reduces the thickness by corrosion and other allowances.||B 31.1 calculates the section modulus using nominal thickness. Thickness is not reduced by corrosion and other allowances.|
|12||Rules for material usage below -29 Deg. C||B 31.3 provides extensive rules for use of materials below -29 Deg C||Power piping code does not provide any such rules for pipe materials below -29 deg C.|
|13||Maximum Value of Cyclic Stress Range Factor||Maximum value of cyclic stress range factor f is 1.2||Maximum value of is 1.0|
|14||Allowance for Pressure Temperature Variation||As per clause 302.2.4 of ASME B 31.3, occasional pressure temperature vaiation can exceed the allowable by (a) 33% for no more than 10 hour at any one time and no more than 100 hour/year, or (b) 20% for no more than 50 hour at any one time and no more than 500 hour/year.||As per clause 102.2.4 of ASME B 31.1, occasional pressure temperature vaiation can exceed the allowable by (a) 15% if the event duration occurs for no more than 8 hour at any one time and not more than 800 hour/year, or (b) 20% if the event duration occurs for not more than 1 hour at any one time and not more than 80 hour/year|
|15||Design Life||Process Piping is normally designed for 20 to 30 years of service life||Power Piping is generally designed for 40 years or more of service life.|
|16||PSV reaction force||B 31.3 provides does not provide specific equations for PSV reaction force calculation.||ASME B 31.1 provides specific equations for PSV reaction force calculation.|
The following image (Fig. 1 ) shows a rough estimate of different stress values of the same system with code change in Caesar II-2018 software:
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