Wall Thickness — Companion Article
1. What this tool does
Wall Thickness evaluates ASME B31.3 Equation (3a) for straight pipe under internal pressure, from values the user types. The calculation runs in the browser. The tool does not contain a B36.10 table and it does not call out for one.
2. When to use it
Use it when a designer is checking a pressure thickness against a wall they already have. The result is preliminary. It is not a completed pipe specification.
Pipe Properties is a different page. This page does not look up a schedule wall.
3. Inputs
Enter P, D, S, E, W, Y, the corrosion allowance, and the mill undertolerance.
P is internal design gauge pressure. D is outside diameter. S is the allowable stress the user enters. E on this page is the quality factor, not the modulus. W is the weld joint strength reduction factor. Y is the coefficient from the code table. c is the corrosion and mechanical allowance the user adds.
W starts at 1.0. Y starts at 0.4. The mill field starts at 12.5%.
Enter a selected wall if the page should compare it.
4. How it works
The running tool is the calculation. The relations already written for version 1.0.0 are:
t = P × D / (2 × (S × E × W + P × Y))
tm = t + c
T = tm / (1 − mill undertolerance)
t is the pressure design thickness. tm adds the corrosion and mechanical allowance. T is the nominal thickness that still leaves tm after the mill undertolerance.
The page cites ASME B31.3 Equation (3a). It does not name a year of the code. This article does not add one.
W starts at 1.0. The page says that means no weld reduction, and that in the creep range the factor can be lower. Check ASME B31.3 paragraph 302.3.5 before keeping 1.0.
Y starts at 0.4. The page says that is the Table 304.1.1-1 value for ferritic steel when t < D/6 and the temperature is at or below 482°C (900°F). Check the table.
The mill field starts at 12.5%. The page calls that the usual pipe-wall undertolerance. Confirm the pipe specification.
If t is at least D/6, or P/(S×E) is greater than 0.385, the page warns that Equation (3a) is outside the limit stated for it. It does not switch to another equation.
A nearest-schedule suggestion is behind Settings, PD Wall Thickness, and defaults to off. Turning it on still shows nothing unless another integration passes rows through the pd_wt10_schedule_rows filter. Until then the page says to enter the selected wall to compare.
5. Understanding the result
Read t, tm, and the required nominal thickness T. A selected wall, if entered, is compared with T.
The 7.11 mm comparison in section 7 was typed. The page does not look it up from a B36.10 table.
6. Engineering considerations
Every material factor is typed. W = 1.0 and Y = 0.4 are starting values. Check paragraph 302.3.5 and Table 304.1.1-1 before keeping them.
The page does not change equation when Equation (3a) is outside the limit it states. It warns.
No schedule chart is shipped. A selected wall is one the user enters.
7. Example
Entered on the live page on 3 October 2026: P 2 MPa (20 bar g), D 168.3 mm, S 138 MPa, E 1.0, W 1.0, Y 0.4, corrosion allowance 3 mm, mill undertolerance 12.5%. The figures were hand-checked.
- t = 1.21254 mm
- tm = 4.21254 mm
- required nominal thickness = 4.81433 mm
Sch 40 wall 7.11 mm, entered for the comparison, passes. The 7.11 mm figure is the wall that was typed. The page does not look it up from a B36.10 table.
8. Standards/references (licensed vs interim)
Every material factor is typed. The equation and the paragraph and table names above are the ones printed on the page: ASME B31.3 Equation (3a), paragraph 302.3.5, and Table 304.1.1-1. No year of ASME B31.3 is stored in the tool. No B36.10 row is stored.
Interim pipe dimensions on this site follow ASME B36.10-2022 Table 2-1. This tool does not use that table.
9. Limitations/disclaimer
- The result is preliminary and needs engineering review. It is not a completed pipe specification.
- W = 1.0 and Y = 0.4 are starting values. Check paragraph 302.3.5 and Table 304.1.1-1 before keeping them.
- The page does not change equation when Equation (3a) is outside the limit it states. It warns.
- No schedule chart is shipped. A selected wall is one the user enters.
A member check is not an engineering fact.
10. Use the tool
Calculate now: Wall Thickness
Related tools
No peer calculation is named on this page. Pipe Properties is a different directory page. This page does not read it. A nearest schedule appears only when another integration passes rows through pd_wt10_schedule_rows. That filter is off by default and this tool does not ship the rows.