ESC Risk & Lifetime Calculator — Environmental Stress Cracking Safety Factor
Calculate ηESC, estimated time to failure, and ESC safety factor using applied stress, yield strength, chemical factor, material resistance, and temperature.
Enter the known values and review the calculated result
Input parameters
Use consistent values and select the intended engineering units.
Stress state
Chemical & material resistance
Temperature
Exposure time
Design criteria
Results
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Method, application and limitations
Review the calculation method, intended application and engineering assumptions before using the result in a design decision.
Formula and calculation method
ηESC formula:
σ ratio = σ / σy
ΔT = T – Tref
Tf = exp(0.025 · ΔT)
Chemical severity = Kchem / Cmat
ηESC = IESC = (σ / σy) · (Kchem / Cmat) · exp(0.025 · (T – Tref))
tfail formula:
tfail = texp · exp(-ηESC)
SFESC formula:
SFESC = 1 / (ηESC + 1e-9)
Additional calculated values:
- Margin to yield = 1 – σ / σy
- Lifetime ratio = tfail / texp
- log lifetime = log10(tfail)
where:
- σ — applied stress
- σy — yield strength
- Kchem — chemical factor [-]
- Cmat — material resistance factor [-]
- T — operating temperature [K]
- Tref — reference temperature [K]
- texp — exposure time
- SFreq — required safety factor [-]
- ηESC — ESC risk index [-]
- tfail — estimated time to failure
- SFESC — safety factor against ESC [-]
When to use this calculator
When to use this calculator:
- To estimate environmental stress cracking risk for a polymer part under sustained applied stress.
- To compare the applied stress against yield strength before ESC lifetime estimation.
- To include chemical aggressiveness and material resistance in one combined ESC driving index.
- To evaluate how operating temperature relative to reference temperature changes ESC acceleration.
- To compare the calculated ESC safety factor with the required safety factor.
How to interpret the result
ηESC is defined as the combined ESC driving index from stress ratio, chemical severity, and temperature acceleration.
Estimated time to failure depends on exposure time and ηESC. Increasing ηESC decreases the estimated time to failure because tfail = texp · exp(-ηESC).
The ESC safety factor depends inversely on ηESC. Increasing ηESC decreases SFESC.
- Safe — ηESC < 0.3 and SFESC ≥ SFreq.
- Warning — ηESC ≥ 0.3 and < 0.6, or SFESC < SFreq when ηESC is not already unsafe.
- Limit — ηESC ≥ 0.6 and < 1.0 when SFESC is not below the required safety factor.
- Unsafe — ηESC ≥ 1.0.
- Invalid — input or model condition is outside the allowed calculation range.
The result is used to evaluate whether the selected polymer, chemical environment, stress level, and temperature produce an acceptable ESC safety margin.
Calculation example
Example:
A user wants to estimate ESC risk for a polymer component exposed to a chemical environment while operating below yield strength.
- Applied stress: 20 MPa
- Yield strength: 100 MPa
- Chemical factor: 0.30
- Material resistance factor: 0.60
- Operating temperature: 313 K
- Reference temperature: 293 K
- Exposure time: 1000 h
- Required safety factor: 2.0
The calculated ESC risk index is ηESC = 0.165, the estimated time to failure is tfail = 848 h, and the ESC safety factor is SFESC = 6.065.
Assumptions and limitations
- Applied stress must be greater than 0 and lower than yield strength.
- The stress ratio must stay within 0.02–0.75.
- Chemical factor and material resistance factor must be within (0, 1].
- Exposure time must be greater than 0 and within 0.01–100000000 h.
- Required safety factor must be within 1–5.
- Operating temperature and reference temperature must be within 230–450 K.
- The temperature difference between operating and reference temperature must not exceed ±80 K.
- The chemical severity factor must be greater than 0 and not exceed 50.