Pipe Wall Thickness Analysis

Learn more about PASS/START-PROF pipe stress analysis software

Steel Pipes

Required nominal wall thickness calculation:

S ≥ S_R + С

Where:

• S_R - Design wall thickness (minimum required for internal pressure per applicable codes)

• С - Total wall thickness allowance

Total Allowance, Mill Tolerance, and Corrosion Allowance

Total allowance C calculation:

С = С₁ + С₂

Where:

• С₁ - Manufacturing allowance (mill tolerance), combining negative wall thickness deviation C₁₁ and manufacturing process tolerance C₁₂. ASME codes use percentage values; Russian codes use millimeters.

• С₁₁ - Negative tolerance compensation allowance. Defined by code or specification requirements. Excludes design thickness rounding to standard values.

• С₁₂ - Manufacturing process allowance for wall thinning during forming operations (stretching, pressing, bending). Determined by fitting manufacturing specifications.

• С₂ - Corrosion and erosion allowance. Determined by design codes or industry standards based on projected service life. Increase for double-sided corrosion exposure.

Nominal wall thickness S must meet minimum values specified in applicable codes and round up to standard thickness values.

Design Pressure Wall Thickness Verification

During input data validation, PASS/START-PROF verifies wall thickness adequacy for design pressure using:

S - C ≥ S_R

Nominal thickness S and total allowance C are defined in element properties. Minimum design thickness S_R follows code requirements selected in Project Settings.

ASME code verification applies to straight pipes and bends only. Other fittings are excluded from wall thickness checks.

Test Pressure Wall Thickness Verification

When factory test pressure values are insufficient, system must withstand hydraulic testing to pressures producing equivalent stresses of:

• SNIP 2.05.06-85: 95% of specified yield strength σ = 0.95

• RD 10-249-98 (Tables 2,8): σ = /1.1 ≈ 0.9

• PB 03-585-03 [1]: 90% of yield strength at test pressure: σ = 0.9

PASS/START-PROF performs test pressure wall thickness verification using (GOST 32388-2013 sustained condition only):

S ≥ S_T

S_T - Minimum wall thickness for test pressure per Project Settings codes. Test temperature Т_test defined in Project Settings, test pressure P_test in element properties, material yield strength in materials database.

Per GOST 8731 and GOST 8733, carbon and low-alloy seamless pipes must withstand hydraulic pressure at 40% of tensile strength: σ = 0.4, which may not satisfy code requirements.

Pipes satisfy GOST 8731 and GOST 8733 only when:

Example - Steel 20: According to [2], tensile strength at 20°C = 460 MPa, yield strength = 250 MPa. Condition evaluation:

0.4 ∙ 460 < 0.9 ∙ 250 MPa

or

184 < 225 MPa

Condition not satisfied. Standard test pressure requirements are not met, requiring stricter factory testing at 225 MPa pressure (GOST documents include relevant notes).

Fiberglass Piping

Reinforced wall thickness calculation:

Where:

• - Nominal wall thickness

• - Internal protective layer thickness

• - External protective layer thickness

References

1. PB 03-585-03, Rules for Design and Safe Operation of Process Piping, Moscow, 2003

2. GOST 34233.1-2017 Boiler and Pressure Vessels Code