What is longitudinal stress in a pipeline?

Longitudinal stress acts along the pipe axis and consists of three components: Poisson stress from internal pressure (nu x S_H), thermal stress from temperature change (E x alpha x deltaT), and bending stress from pipe weight or soil loading (M/Z). These combine with hoop stress to determine the pipeline's structural adequacy per ASME B31.8.

How is combined equivalent stress calculated per ASME B31.8?

ASME B31.8 uses the von Mises (octahedral shear stress) criterion: S_eq = sqrt(S_H^2 + S_L^2 - S_H*S_L). The combined equivalent stress must not exceed k x S x T x SMYS, where k is the design factor (0.72 for Class 1), S is the temperature derating factor, and T is the joint factor.

What is the difference between von Mises and Tresca stress criteria?

Von Mises (octahedral shear) is used by ASME B31.8 for gas pipelines: S_eq = sqrt(S_H^2 + S_L^2 - S_H*S_L). Tresca (maximum shear stress) is more conservative: S_eq = max(|S_H - S_L|, |S_H|, |S_L|). Von Mises is generally 15% less conservative than Tresca for biaxial stress states in pipes.

Pipeline Stress (Longitudinal) Calculator | ASME B31.8 Combined Stress

Pipe Properties

Pipe Outside Diameter

Wall Thickness

Specified Minimum Yield Strength (SMYS)

psi

X42=42,000 | X52=52,000 | X60=60,000 | X65=65,000 | X70=70,000 | X80=80,000

Operating Conditions

Design/Operating Pressure

psig

Installation Temperature

°F

Operating Temperature

°F

Loading Parameters

Unsupported Span Length

Free span for bending stress (0 = buried/fully supported)

Fluid Density (contents)

lb/ft³

Gas ~3-8 | Oil ~50-55 | Water ~62.4 | Empty = 0

Soil Cover Depth (buried pipe)

0 = above-ground. Typical: 3-5 ft for buried pipelines.

Code Parameters

Design Factor (F)

Longitudinal Joint Factor (E)

Temperature Derating Factor (T)

Combined Stress Criterion

Understanding Pipeline Longitudinal Stress

Stress Components
Pipeline longitudinal stress combines pressure-induced Poisson stress, thermal contraction/expansion stress, and bending stress from weight or external loads.

ASME B31.8 Limit:
Combined equivalent stress must not exceed k × SMYS × T, where k = design factor and T = temperature derating. For Class 1 locations, the limit is 0.90 × SMYS.

When to Use:
Restrained buried pipelines, above-ground spans, pipeline crossings (road/river), elevated temperature service, and any B31.8/B31.4 code compliance evaluation.

📚 Learn the Theory

Understand longitudinal stress components, von Mises criterion, B31.8 combined stress limits, and restrained vs. unrestrained pipeline analysis

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Formulas

S_eq = √(S_H² + S_L² − S_H·S_L)

S_H = Hoop stress = P·D / 2t

S_L = Total longitudinal stress

S_LP = ν·S_H (Poisson effect)

S_LT = E·α·ΔT (thermal)

S_B = M/Z (bending)

Standards & References

ASME B31.8
Gas Transmission — Combined Stress §833
ASME B31.4
Liquid Transportation — Stress Limits
49 CFR 192
Federal gas pipeline safety regulations
API 5L
Line pipe specification and grades

Engineering Notes

Restrained pipe: Buried pipelines are restrained by soil friction, generating Poisson and thermal longitudinal stresses
Poisson ratio: ν = 0.3 for steel; converts hoop stress to axial compression
Thermal stress: Compressive when operating temp exceeds install temp (restrained pipe pushes against soil)
Bending: Significant for above-ground spans, river crossings, and areas of ground settlement
Von Mises: ASME B31.8 uses the octahedral shear stress theory for combined stress evaluation

Pipeline Stress (Longitudinal) Calculator

Pipe Properties

Operating Conditions

Loading Parameters

Code Parameters

Understanding Pipeline Longitudinal Stress

📚 Learn the Theory

Results

Formulas

Standards & References

Engineering Notes

Related Calculators

Hoop Stress

Expansion Loop

Bending Stress

%SMYS