PIPE WALL THICKNESS CACULATION

Hi Sabir,

A couple of things to consider.

1) In your calculations, I only see stress from internal pressure. There are many other types of stress you need to consider, as listed in ASME B31.3, before you can specify a wall thickness.

2) "A672 Gr 60 class 22 or 32" In my 2007 version of ASTM Section One 'Iron and Steel Products', A672 only lists a pipe grade; there are no classes. It also lists the ASTM specification for the PLATE steel that the pipe is to be made from.

In the 2006 edition of ASME B31.3, Table A-1 starting on page 140 lists a number of different grades of A672, in the 'spec. no.' heading, which lists basic allowable stress in tension, with copious notes.

3) In practice you will not find pipe that diameter in that thin of a wall (0.05 inches); It would collapse under its own weight if you tried to handle it.

The thinnest wall on my schedule sheet for 24" is S10, at 0.250 inch thickness.

In practice, the thinnest you are likely to find stocked anywhere is standard wall at 0.375 inches.

Although this may be overkill in terms of its strength, its widespread availability may well make it the cheapest option.

In my field I see lots of requests for quotes on oddball size material, where it is obvious that someone has simple asked us to quote on the numbers their computer spits out, without any comprehension of what is available it the real world.

Some examples are 5" std wall pipe pipe, which due to its limited use and rarity is more expensive than 6" std wall. Or a 45 degree elbow to be machined to 44.99 degrees! Anyone who knows this stuff also knows that expecting 2 d.p accuracy on cutting an elbow has their head in the clouds

To summarize, ENSURE that you have accounted for ALL the stresses that will be applied to the pipe, including code requirements for safety factors, corrosion and erosion allowances etc and then spec the thinnest COMMON wall size (usually standard, S40, Extra heavy or S80) that EXCEEDS your calculated need. This will almost always result in a lower cost, in addition to having an extra safety margin.

Good luck!

A. The calculation is OK, but according to ASME B36.19: Stainless Steel Pipe (not B36.10M : Welded and Seamless Wrought Steel Pipe), Table 2, there are only two pipe Schedules (pipe wall thicknesses) for 24" NPS: Sch. 5S (0.218" = 5.54 mm) and Sch. 10S (0.25" = 6.35 mm).

B. So, the min. pipe schedule of SA358 Grade 321 (not TP321) shall be 5S (5.54 mm).

C. The material with a specification SA672 denotes to the procedure which used to produce a pipes from a pressure vessel plates like as SA285 Grades B and C, SA515 & SA516 Grades 55, 60, 65 and 70, … etc. with different grade designations (type of plate used) and class designation (type of heat treatment performed during manufacturer of the pipe).

So, at Table A-1 of ASME B31.3, at 2^nd column under title Spec. No., you will find the name of that procedure related to SA672.

D. Note. The both schedules 5S and 10S do not permit threads.

Dear Mr. Zaphod2Headed & Mr. Abdel Halim Galala

Thanks for your supports.

I have gone through your comments and accordingly I'm modifying my calculations. Based on your comments I would like to clarify couple of things.

1. In TABLE A-1, ASME B31.3

Material Spec No. Grade

A515 Gr.60 A672 B60

A516 Gr.60 A672 C60

The Basic Allowable Stress for both, at 400 F is 18.3

My doubt is, from the above list, which one I shall select,

A515 Gr.60 A672 B60 or A516 Gr.60 A672 C60

Thank you,

Regards,

Sabir

how to calculate thickness for vacuum condition in pipe

• Vacuum condition means that the external pressure Pe is more than the internal pressure Pi of pipe or vessel, and there is a difference in pressure equal to (Pe - Pi), to be taken into consideration.

• Full vacuum (FV) condition is that condition where the internal pressure in pipe (or vessel) is zero, while the outside pressure is atmospheric, hence the external pressure ≈15 PSI.

• Per ASME code, Section VIII, Div. 1, the Para. UG-28 Thickness of Shells and Tubes Under External Pressure, is clearly indicated at my post #7 of CR4 Thread: HOW TO CALCULATE PIPE THICKNESS FOR EXTERNAL PRESSURE.

Hello guys,

Currently I am working on piping of a Cryogenic plant.

While doing the calculation for the pipe wall thicknesses for the major sizes to be used in the project, using the formula given in ASME 31.3

[i.e. t = PD / 2(SEW + Py) ]

The thickness for a 16" pipe is coming out to be 0.4 mm (for parameters noted below)

Pipe size=16"

Design Temp= -105deg C = -157 F

Design Pressure= 3.5 kg/cm2 g = 49.78 psi

pipe material= A358 TP 304

My dilemma is:

1. Am I using right formula for thickness calculation?

2. Is there any modified formula for Cryogenic piping?

3. If I am using right formula, will it be practical to use a pipe of such a small thickness?

No, 0.4mm pipe wall won't be practical. Select the correct pipe with a larger wall thickness than this from published schedules of commercial pipe that are applicable to the process fluid, its temperature and its pressure.