Calculators

Pipe wall thickness calculator

Minimum wall thickness of straight pipe under internal pressure to EN 13480-3 or ASME B31.3 – and the ordered thickness that results once corrosion allowance and negative tolerance are added.

Input

Code Outside diameter Design pressure Internal gauge pressure. The calculation uses MPa – 1 bar equals 0.1 MPa. Allowable stress EN 13480-3: design stress f at calculation temperature – for non-austenitic steels the lower of elevated-temperature yield strength ÷ 1.5 and tensile strength ÷ 2.4. ASME B31.3: S from the code tables. Weld joint factor EN 13480-3: joint coefficient z (1 · 0.85 · 0.7 depending on the extent of testing, seamless 1). ASME B31.3: quality factor E.

ASME B31.3 only

Factor W Weld joint strength reduction at elevated temperature; 1 below that. Coefficient Y 0.4 for ductile steels up to 482 °C; at higher temperatures from the code table.

Allowances

Corrosion allowance Fabrication allowance Thinning caused by bending or threading. Negative tolerance given Negative tolerance From the dimensional standard of the pipe – per cent or millimetres as selected above.

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Result for the example

Design pressure: 4.00N/mm²
Minimum thickness without allowances: 2.55mm
with corrosion and fabrication allowance: 3.55mm
Required ordered thickness: 4.06mm

Limits of the calculator. The calculator applies to straight pipe under internal pressure. It checks neither external pressure nor bends, branches or flanges and does not replace a code calculation. You must take the allowable stress for material and design temperature from the material standard.

How the calculator works

For EN 13480-3 and straight pipe with a diameter ratio up to 1.7 the equation is e = pc · Do / (2 · f · z + pc). For ASME B31.3 it is t = P · D / (2 · (S · E · W + P · Y)). Pressure is converted from bar to MPa so that it matches the stress.

Corrosion and fabrication allowances are added to the minimum thickness. If the negative tolerance of the pipe is a percentage of the ordered thickness, the result is divided by (1 − tolerance) – the tolerance is not added. This gives the thickness that must at least be ordered; the next larger standard thickness is selected.

Where the allowable stress comes from

The calculator asks for the allowable stress instead of taking it from a material list – on purpose. It depends on material, wall thickness, delivery condition and design temperature, and it is only binding as stated in the material standard or the code tables.

Under EN 13480-3, for non-austenitic steels in the time-independent range, it is the lower of the yield strength at calculation temperature divided by 1.5 and the tensile strength at room temperature divided by 2.4. Different rules apply to austenitic steels and to the creep range.

What follows the wall thickness

Wall thickness is the first step of a piping class. It is followed by the pressure-temperature rating of the flanges, the selection of gaskets, bolting and valves – and, depending on temperature, size and connected equipment, the pipe stress analysis verifying loads from weight and thermal expansion.

Frequently asked questions

Frequently asked questions about Pipe wall thickness

Why is the ordered thickness considerably larger than the minimum thickness?

Because the pipe supplied may be thinner than ordered and loses material to corrosion over its life. Both are added in advance so that the minimum thickness is still present at the end of the service life.

Can I use the result as a code calculation?

No. It is an estimate for straight pipe. A code calculation covers all components of the line, the correct material values and the documentation of the assumptions.

What is the negative tolerance of a pipe?

It is set by the dimensional standard of the pipe and depends on manufacturing method, diameter and wall thickness. For seamless steel pipe 12.5 per cent is a common value – the standard to which the pipe is ordered is binding.

When an estimate is not enough

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Pipe wall thickness calculator

How the calculator works

Where the allowable stress comes from

What follows the wall thickness

Frequently asked questions about Pipe wall thickness

Why is the ordered thickness considerably larger than the minimum thickness?

Can I use the result as a code calculation?

What is the negative tolerance of a pipe?

When an estimate is not enough

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