How is allowable stress calculated per ASME?

ASME BPVC Section VIII Div.1 uses σ_allow = min(Rp0.2/1.5, Rm/2.4) for austenitic stainless, or min(Rp0.2/1.5, Rm/3.5) for carbon and low-alloy steels at room temperature. This provides a safety margin against both yielding and fracture.

What is the fatigue endurance limit?

For steels with Rm < 1400 MPa, the endurance limit Se ≈ 0.5 × Rm (unnotched, polished specimen). For Rm ≥ 1400 MPa, Se ≈ 700 MPa. Actual fatigue strength depends on surface finish, size, stress concentration, and environment.

What safety factors are used for different load types?

Typical: Static loads n=1.5-2.0 against yield. Alternating/fatigue loads n=2.0-4.0 against endurance limit. Pulsating loads n=1.5-2.5. Impact loads n=3.0-5.0. Factors depend on consequence of failure and load uncertainty.

What is yield strength Rp0.2?

Rp0.2 (or proof stress) is the stress at which 0.2% permanent (plastic) deformation occurs. Below this stress, deformation is elastic and recoverable. It is the primary design parameter for pressure vessels and structural components.

Do properties change with heat treatment?

Yes, significantly. Values shown are typical for standard delivery condition. Q&T (quench and temper) generally increases strength but decreases ductility. Actual properties depend on section size, austenitizing temperature, and tempering conditions.

Free Engineering Tool

Steel Properties & Allowable Stress Calculator

Select a steel grade to view mechanical properties. Calculates ASME allowable stress, fatigue endurance limit, and safety factors for different load types.

ASME BPVC Rp0.2 / Rm Fatigue Se

Properties & Allowable Stress

ASME Allowable Stress σ_allow

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Yield Strength Rp0.2

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Ultimate Tensile Strength Rm

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Fatigue Endurance Limit Se

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Elongation A%

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Hardness HB

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Density

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Safety Factors (n)

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ASME Allowable Stress

Per ASME BPVC Section VIII Division 1, the allowable stress at room temperature is:

For austenitic stainless steels (which have significant work hardening), ASME uses Rm/2.4 instead of Rm/3.5.

Fatigue Endurance Limit

For unnotched, polished steel specimens under rotating bending:

Actual fatigue strength requires modification factors for surface finish (ka), size (kb), reliability (kc), etc.:

Safety Factors by Load Type

Load Type	Factor n	Design Stress
Static (yield)	1.5	Rp0.2 / 1.5
Static (fracture)	2.4–3.5	Rm / 2.4 or Rm / 3.5
Pulsating fatigue	2.0	Se / 2.0
Fully reversed fatigue	2.5	Se / 2.5
Impact / shock	3.0–5.0	Rp0.2 / n

Practical Example

Example — 42CrMo4 Q&T

Properties: Rp0.2 = 900 MPa, Rm = 1100 MPa

σ_allow (ASME) = min(900/1.5, 1100/3.5) = min(600, 314) = 314 MPa

Se = 0.5 × 1100 = 550 MPa (unmodified)

Pulsating fatigue: 550/2.0 = 275 MPa

⚠️ Note: Properties shown are typical values. Actual properties depend on heat treatment, section size, and material test certificate. Always use certified values for design calculations.

Steel Allowable Stress Calculator | Free ASME Tool | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Properties & Allowable Stress

ASME Allowable Stress

Fatigue Endurance Limit

Safety Factors by Load Type

Practical Example