minimum recommended pipe thickness B31.3

[mrmyagi]

Suppose I have a 1'' schedule 80 pipe with a corrosion allowance (CA) of 0.126'', factoring in a 12.5% mill tolerance and using A106GrB, which leaves me with a remaining thickness of 0.0224''. While this thickness is acceptable from a pressure standpoint, I am concerned about the structural integrity of the pipe. Is there a recommended minimum thickness for piping? For instance, should one avoid using pipes with a thickness less than 0.02''?

 

[Louisiana Inspector]

API 574 Table 7 shows an example of alert thicknesses for carbon and low-alloy steel pipe that could be used in conjunction with the default minimum structural thicknesses.

 

[LittleInch]

Yeh, that's one reason I hate these "global" CA - 3.2mm on a 4.55mm pipe is just bonkers. If it corroded that badly you would replace it. Yes, 0.5mm is rather thin, but then how likely is 3mm of corrosion? How do you get to that thickness though?

When it gets down to 1" pipe the usual D/t or min thicknesses don't work so well. If in doubt use sch 160

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GBTorpenhow]

That's just the amount of the wall thickness that the code is relying on to support the hoop stress in the pipe. Put another way, the min. pressure design thickness is just the design margin left over when all the code required worst case scenarios in the calculation pile up.

There is no realistic scenario where installed 1" S/80 piping would actually end up being a uniform 0.02" thick.

 

[hacksaw]

"Suppose I have a 1'' schedule 80 pipe with a corrosion allowance (CA) of 0.126'', factoring in a 12.5% mill tolerance and using A106GrB, which leaves me with a remaining thickness of 0.0224''. While this thickness is acceptable from a pressure standpoint, I am concerned about the structural integrity of the pipe. Is there a recommended minimum thickness for piping? For instance, should one avoid using pipes with a thickness less than 0.02''?"

It all depends on the service conditions, pressure, temperature, fluid, fluid velocity, environment conditions, and whether the pipe is supported or not.

 

[EdStainless]

Ask the question this way, If you used a corrosion resistant alloy (CA=0) would I feel fine building this in 1"x0.024" mw?
Considering that the stiffness and support requirements are vastly different, and that your chances of uniform corrosion are zero I would suggest that you look at this a bit more.
You either need to start with more wall or a lower CA.
I would question the CA first.


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P.E. Metallurgy, consulting work welcomed

 

[1503-44]

My advice is NEVER place a 1" pipe anywhere that structural dependency must be assured.
Find a different solution, either larger diameter, or carry the structural loads with other member(s). As an example, a very common standard practice amongst many companies is to not even use anything less than a 2" pipe with XXS Wall.

Keeping in mind that minimal handrail diameter is 1.5" and that's with no internal pressure at all.
A 1"pipe is just not suitable for any serious structural load, including sole support of itself in most cases, never mind if it has internal pressure.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[mrmyagi]

Thank you, appreciate the input.

 

[KevinNZ]

All our projects use min XS for small CS piping. Think about all the loads that could be applied to your corroded thin DN25 pipe. Even tightening a flange stud would be a worry.