Free Engineering Tool
Allowable Stress by Material
Calculate design allowable stress per ASME VIII Div.1 or EN 13445-3. Temperature-dependent properties, creep rupture check, weld joint efficiency factor. 12+ material grades.
Design Allowable Stress
EN 13445-3 (Ferritic Steels)
ASME VIII Div.1
Temperature Derating
Both yield and UTS decrease with temperature. This calculator uses linearized derating curves based on EN 10028 / ASME II-D data:
- Below 100°C: properties are at room-temperature values
- 100–400°C: gradual reduction (yield drops faster than UTS)
- Above 400°C: significant reduction; creep may govern
Creep Regime
When the design temperature exceeds the creep onset temperature, time-dependent rupture stress governs. Typical creep onset:
| Material Type | Creep Onset (°C) | Typical Max Design T |
|---|---|---|
| Carbon steel (S235, S355) | ~350 | 400°C |
| C-Mn pressure (P265GH, P355GH) | ~380 | 450°C |
| Mo steel (16Mo3) | ~400 | 500°C |
| CrMo steel (13CrMo4-5) | ~450 | 550°C |
| 2¼Cr-1Mo (10CrMo9-10) | ~470 | 600°C |
| Austenitic SS (304, 316L) | ~500 | 700°C |
Practical Example
Given: P265GH, Rp(20)=265 MPa, Rm=410 MPa, T=250°C, weld E=1.0
Rp(250°C) ≈ 265 × 0.85 = 225.3 MPa (derating for temperature)
f_yield = 225.3 / 1.5 = 150.2 MPa
f_UTS = 410 / 2.4 = 170.8 MPa
f = min(150.2, 170.8) = 150.2 MPa (yield governs)
With E=1.0: σ_allow = 150.2 MPa
Material Comparison at Room Temperature
| Material | Rp0.2 | Rm | f (EN) | S (ASME) |
|---|---|---|---|---|
| S235JR | 235 | 360 | 150 | 103 |
| S355JR | 355 | 510 | 213 | 146 |
| P265GH | 265 | 410 | 171 | 117 |
| P355GH | 355 | 490 | 204 | 140 |
| 16Mo3 | 280 | 450 | 187 | 129 |
| 13CrMo4-5 | 295 | 460 | 192 | 131 |
| 10CrMo9-10 | 275 | 450 | 183 | 129 |
| 304 SS | 210 | 520 | 140 | 138 |
| 316L SS | 200 | 500 | 133 | 133 |
| 2205 Duplex | 450 | 620 | 258 | 177 |
⚠️ Note: This calculator provides approximate values for preliminary design. Always verify with the actual code tables (ASME II-D, EN 10028, EN 10222) for your specific material grade, product form, thickness, and temperature.
Allowable stress is the maximum stress permitted in a design component. It is the material strength divided by a code-defined safety factor. Using it ensures the component won’t fail under normal (or abnormal) loading with an adequate safety margin.
Different codes use different safety factors, leading to different allowable stresses for the same material.
ASME VIII uses a UTS safety factor of 3.5 (was 4.0 before 2007), while EN 13445 uses 2.4. This means ASME is more conservative on the UTS criterion. However, both use 1.5 on yield.
For high-strength materials where yield governs (e.g. S355, 2205), both codes give similar results. For lower-strength materials where UTS governs, ASME is significantly more conservative.
Both yield strength and UTS decrease with temperature. The yield strength decreases faster. Above the creep onset temperature, time-dependent rupture stress may become the governing criterion.
Example: S355 at 400°C has Rp ≈ 297 MPa (vs 355 at RT), so allowable drops from 213 to ~173 MPa (EN).
Creep is significant above: ~350°C for carbon steel, ~400°C for Mo steel, ~450°C for CrMo, ~500°C for austenitic SS. Above these temperatures, the 100,000h creep rupture stress divided by its safety factor may be lower than the yield-based allowable.
Weld joint efficiency (E or z) accounts for potential weld defects:
- E=1.0: Full radiographic or ultrasonic examination of all welds
- E=0.85: Spot (partial) radiographic examination
- E=0.7: No volumetric NDE (visual only)
The effective allowable = σ_allow × E. Using E=1.0 requires more NDE but allows thinner walls.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field instruments. Used in 50+ countries.
