Pipe Wall Thickness for Recip Applications
Pipe Wall Thickness for Recip Applications
(OP)
I am a junior engineer in this field and just want to get more understanding behind piping specifications.
To determine the pipe wall thickness to be used, the minimum wall for internal pressure can be calculated using B31.3, than most books ask to use the next pipe wall schedule. I noticed that for smaller diameter pipe, sometimes heavier wall are specified (e.g. for NPS 2, sch 160 may be used instead of sch 80). Is this because we want to avoid buckling during pipe handling and installation?
I was also advised to use two schedule up (from the min wall calculated) for recip applications. I was reading some books but did not find a direct answer for the reason behind this. Is "2-wall schedule up" an industrial practice for vibration/fatigue consideration? (B31.3 addresses "low cycle, high load" fatigue calculations, but vibration is a "high cycle, low load" situation and guideline was not provided in detail).
I am wondering if someone can advise where I can look for the reasoning behind the above (thanks ahead for the help).
To determine the pipe wall thickness to be used, the minimum wall for internal pressure can be calculated using B31.3, than most books ask to use the next pipe wall schedule. I noticed that for smaller diameter pipe, sometimes heavier wall are specified (e.g. for NPS 2, sch 160 may be used instead of sch 80). Is this because we want to avoid buckling during pipe handling and installation?
I was also advised to use two schedule up (from the min wall calculated) for recip applications. I was reading some books but did not find a direct answer for the reason behind this. Is "2-wall schedule up" an industrial practice for vibration/fatigue consideration? (B31.3 addresses "low cycle, high load" fatigue calculations, but vibration is a "high cycle, low load" situation and guideline was not provided in detail).
I am wondering if someone can advise where I can look for the reasoning behind the above (thanks ahead for the help).





RE: Pipe Wall Thickness for Recip Applications
RE: Pipe Wall Thickness for Recip Applications
I was not clear in my original question - The application is for process fluid (natural gas, produced water and hydrocarbon liquids). When I calculate the min WT required per B31.3, corrosion allowance of 1/8" was included in the wall thickness calculation for sour applications (< 2% H2S); and for sweet applications, 1/16" was used.
RE: Pipe Wall Thickness for Recip Applications
For large piping in recip service a dynamic analysis should be used. The rule of thumb for two sizes up is to stiffen up the pipe so that the dynamic forces don't cause the pipe to flex such that it exceeds the yield stress. If this happens it just a crapshoot on how many cycles it create stress cracks. Like "how many licks does it take to get to the center of a tootsie roll pop"..
Think of it in terms of bending a wire. If you bend it easily back and forth you can break it.. If you make the wire so thick that the applied forces
never cause it to exceed yield then it will last..
The supports are very important. Every thing between the recip equip and the first pressure vessel need to be restrained as much as possible.
RE: Pipe Wall Thickness for Recip Applications
For recip piping, sometimes thicker walls are specified in an often vain attempt to limit vibration stresses, or to at least move the natural resonant frequencies of the pipe lower down in the spectrum to keep it away from compressor operating range rpms, but a better approach I think is to change the spacing of supports and do not use equal spans between supports, or do both.
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RE: Pipe Wall Thickness for Recip Applications