Piping Minimum Thickness
Piping Minimum Thickness
(OP)
When calculating minimum thickness for a pipeline using ASME 31.3 equations and values I come up with a value that is too small for wall thickness (~0.002") because of small internal pressure (150psig). Is there an absolute minimum thickness requirement, which says if you calculate a value smaller than this - use this value?
I am using ASTM A106 Grade B Sch 80 carbon steel seamless with a diameter of 1/2".
Thanks in advance.
I am using ASTM A106 Grade B Sch 80 carbon steel seamless with a diameter of 1/2".
Thanks in advance.





RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
We should not consider only internal pressure for the design especially for this small bore piping...
Your selection of carbon steel pipe diameter 1/2" Sch. 80 may come from additional stiffness to withstand external loads plus corrosion allowance...
RE: Piping Minimum Thickness
@PAN- Thank you too for your response. I will make sure to take into account external load and corrosion before I go about using the smallest standard wall thickness as BigInch suggested.
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
welding the little stuff is difficult... threading the thin stuff is impossible. Generally go with the cheapest to fabricate, labor is usually more expensive than materials. Unless you get into the stainless or exotic materials you will most likely be limited to Sch40 or heavier for pipe less than 8"nps.
RE: Piping Minimum Thickness
I need to be able to reference a standard in order to justify the replacement of the pipe, a reference to a drawing that nobody can tell me anything about does not seem right. Thank you again for your help!
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
You should consider the detail of API 570...
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
150 psig would "normally" be a Sch40, so the heavier original wall had to be something else: corrosion (outside and inside?), long span distance needed between pipe supports? Some unusual bending requirement where the heavier wall made minimum thickness after bending easier to meet?
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
B31.3 para 304.1.2 gives D/6 = 0.140 therefore equation 3b applies. (Sch 80 would not as the wall thickness is greater that D/6, I am not going there).
t = (P*D)/(2*S*E) = (150psi*0.84")/(2*16ksi*1) = 0.004"
I personally have not encountered 3/4" A106 in lighter than sch 40.
This is only looking into internal stress....
probably sch 80 was selected for environmental reasons, i.e. corrosion, external loads, etc. BTW hat is in the pipe? Is it hazardous?
any further analysis into whether sch 40 or 80 should be used is most likely not economically justified.
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
All ant-flow could be in only one direction.
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
NO! Stainless is the shiney one.
If it was from a mill order, it might be any WT. There are standard wall thicknesses and an infinite number of others. You can special fab any WT you want.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
You're 87.5% SMWT isn't the right limit for this discussion. You're talking about the manufacturing tolerance for a specific requested wall thickness pipe (SMWT) on some purchase order, which is SMWT - 12.5% SMWT. It has nothing to do with the wall thickness required for guaranteeing adequate wall thickness for pressure or handling needs.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
@BigInch; if NStamp was referring to fittings has right, isnt he?
RE: Piping Minimum Thickness
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Piping Minimum Thickness
RE: Piping Minimum Thickness
@ohman10: I don't think there are any ASTM/ANSI/ASME specs that dictate a replacement thickness (beside the thickness required for pressure, which, as you noted from the beginning, is extremely light).
For small bore lines like you have (which I would consider anything under 2", for certain), the wall required for pressure is often a non-issue. As BigInch noted above, structural integrity will generally limit the minimum wall thickness. You don't want some operator walking down the line, tripping and tearing a hole in the process because he grabbed a pressure gauge to steady himself and the 1/2" pipe that connects it to the header rips off due to a .002" wall thickness.
In most specs I run across in refinery service, particularly for cheap carbon steel, using a wall lighter than Schedule 80 is rare and Schedule 160 is not uncommon.
Now, regarding your original question about where the replacement wall thickness came from - likely some experienced guys 50 years ago figured out that when your 1/2" line corrodes to a specific thickness it is in much greater danger of failure due to accident and therefore should be replaced at the next turnaround. Odds are good that the guys are long since retired, or probably got laid off in the 80's and the company never bothered to save the knowledge that went into developing the spec you are now trying to live with.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
RE: Piping Minimum Thickness
Another reason for using thicker pipes is the "Bubba climbing factor" -- where a plant operator has to reach a valve (or a guage or whatever) and decides to use an instrument line to rest his foot." While they probably would avoid a 1/2" tube, I've seen where 1" on up is fair game for climbing.
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Piping Minimum Thickness
vpl, Right. This is one of those topics like "how much straight pipe in front of a pump" that everyone has some kind of an opinion on, right or wrong, and that is apparently very difficult to keep to one's self.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus