ASME B31.3 steel pipe pressure and wall thickness calculation

What determines steel pipe wall thickness?

Steel pipe wall thickness is determined by internal pressure, pipe diameter, allowable stress, temperature, weld efficiency, and corrosion allowance.

It is calculated using standardized formulas rather than simple proportional relationships.

1. ASME B31.3 Wall Thickness Formula

ASME B31.3

Formula

t=P×D/2SE+2PY

Simplified formula (low pressure)

t=P×D/2S

Key meaning

Used for chemical and process piping systems

Weld efficiency and temperature correction are included in the full formula

Applicable to industrial pressure piping design

2. GB/T 20801 Wall Thickness Formula

GB/T 20801

t=P×D/2[σ]tφ+2PY

Key meaning

Chinese industrial piping design standard

Same mechanical principle as ASME B31.3

Uses allowable stress based on temperature

3. Key Parameters (Core Engineering Logic)

Allowable Stress (Most important factor)

Decreases as temperature increases

Controls final wall thickness requirement

Example: A106 Gr.B drops from ~138 MPa to ~70 MPa at high temperature

Weld Efficiency

Seamless pipe: 1.0

ERW pipe: 0.85

LSAW pipe: 0.85–1.0

Corrosion Allowance

Normal service: 1.5 mm

Corrosive media: 2.0–3.0 mm

Clean service: 0 mm

4. Material Impact on Wall Thickness

Carbon steel (e.g., A106): higher thickness needed at high temperature

Alloy steel (e.g., A335): better high-temperature strength → thinner wall possible

Stainless steel (304/316): corrosion-resistant, stable over wide temperature range

5. Quick Selection Logic

Higher pressure → thicker wall

Higher temperature → lower allowable stress → thicker wall

Welded pipe → higher safety margin required

Corrosive medium → add corrosion allowance

6. Simple Example Result

Given:

P = 1.6 MPa

D = 219 mm

S = 130 MPa

Result:

Calculated thickness ≈ 1.34 mm

corrosion allowance 1.5 mm

Final design ≈ 2.84 mm

Standard pipe schedule (Sch 20 / Sch 40) is selected in practice.

FAQ

1. What is steel pipe wall thickness based on?

It is based on pressure, diameter, allowable stress, temperature, weld efficiency, and corrosion allowance.

2. Which standard is used for pipe thickness calculation?

Common standards include ASME B31.3 and GB/T 20801.

3. Does higher pressure always mean thicker pipe?

Generally yes, but temperature and material strength also strongly affect final thickness.

4. Why is allowable stress important?

Because it decreases at high temperature and directly controls required wall thickness.

5. Do welded pipes need thicker walls than seamless pipes?

Yes, because weld efficiency is lower than seamless pipe strength.

Conclusion

Steel pipe wall thickness is calculated using standardized engineering formulas rather than simple proportional rules. Both ASME and GB systems follow the same mechanical principle, with differences in coefficients and safety definitions. Proper selection ensures safe operation, cost efficiency, and long-term reliability in piping systems.