Difference between ASME B 31.3 and B 31.1 (B31.3 vs B31.1)

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 NoParameterASME B 31.3-Process PipingASME B 31.1-Power Piping
1ScopeProvides rules for Process or Chemical PlantsProvides rules for Power Plants
2Basic Allowable Material StressBasic 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 31.1)
3Allowable 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.
4SIF on ReducersProcess Piping Code ASME B 31.3 does not use SIF (SIF=1.0) for reducer stress calculationPower Piping code ASME B 31.1 uses a maximum SIF of 2.0 for reducers while stress calculation.
5Factor of SafetyASME 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
6SIF for Butt Welded JointsB 31.3 uses a SIF of 1.0 for butt welded jointsB 31.1 uses a SIF of upto 1.9 max in stress calculation.
7Approach towards SIFASME B 31.3 uses a complex in-plane, out-of-plane SIF approach.ASME B 31.1 uses a simplified single SIF Approach.
8Maximum values of Sc and ShAs 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.
9Allowable Stress for Occasional StressesAllowable value of occasional stress is 1.33 times ShAs per ASME B 31.1, the allowable value of occasional stress is 1.15 to 1.20  times Sh
10Equation for Pipe Wall Thickness CalculationThe equation for pipe wall thickness calculation is valid for t<D/6There is no such limitation in Power piping wall thickness calculation. However, they add a limitation on maximum design pressure.
11Section Modulus, Z for Sustained and Occasional StressesWhile 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.
12Rules for material usage below -29 Deg. CB 31.3 provides extensive rules for use of materials below -29 Deg CPower piping code does not provide any such rules for pipe materials below -29 deg C.
13Maximum Value of Cyclic Stress Range FactorMaximum value of cyclic stress range factor f is 1.2Maximum value of is 1.0
14Allowance for Pressure Temperature VariationAs 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
15Design LifeProcess Piping is normally designed for 20 to 30 years of service lifePower Piping is generally designed for 40 years or more of service life.
16PSV reaction forceB 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.
Differences between process piping and power piping codes

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:

Stress values for the same system with code change
Fig. 1: Stress values for the same system with code change

Few other useful differences for you.

Differences between ASME B 31.4 and ASME B 31.8
13 major differences between Seamless and Welded Pipe
10 Differences between Pressure and Stress
Difference between Tee and Barred Tee
Difference between Stub-in and Stub-on Piping Connection
Difference between Centrifugal and Reciprocating Compressor
Difference between PDMS and PDS
Difference between Piping and Pipeline
Difference between Pipe and Tube
Difference between Primary load and Secondary load
Difference between Caesar II and Start-Prof
Difference between API and ANSI Pump

Print Friendly, PDF & Email

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

9 thoughts on “Difference between ASME B 31.3 and B 31.1 (B31.3 vs B31.1)

  1. your contents are always useful and valuable. please continue, such that it will be helpful for lot of freshers and entry level engineers.

    1. In case of power piping operating pressure and temperature is high as compared to process piping , so to add extra safety factor we generally go for conservative design in case of power piping

  2. Anup Sir please Explain why sustain and expansion stresses they have different allowable limits in codes. Is there any derivation for that
    ? Please Explain in brief.

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent Content

Enable Notifications    Ok No thanks