MDMT Assessment per ASME UCS-66 and API 579
neqsim.process.safety.mdmt.MDMTCalculator evaluates whether a vessel’s
material selection is acceptable for the lowest temperature reached during
blowdown, autorefrigeration, or cold-vapour upset.
Method
ASME BPVC Section VIII Div. 1 UCS-66 maps material grade and thickness to an exemption temperature using one of four curves (A=carbon steel, B=normalized, C/D=fine grain / impact tested). UCS-66.1 allows a thickness-equivalent reduction when the actual stress is below the design stress:
\[\Delta T = -\,\ln\!\left(\frac{\sigma_{actual}}{\sigma_{design}}\right) \cdot 100\,^{\circ}\mathrm{F}\]If the curve-A/B/C/D temperature minus $\Delta T$ is ≤ the calculated MDMT, the vessel is exempt without impact testing.
Code pattern
MDMTCalculator calc = new MDMTCalculator();
calc.setMaterial("SA-516-70"); // selects Curve B
calc.setThicknessMM(38.0);
calc.setStressRatio(0.65); // actual / allowable
double mdmt = calc.computeUCS66(); // °C — required minimum metal T
boolean ok = blowdownTmin >= mdmt + 5.0; // 5 °C margin per operator practice
Applicable standards
| Standard | Scope |
|---|---|
| ASME BPVC VIII Div. 1 UCS-66 | Carbon and low-alloy steel exemption curves |
| ASME BPVC VIII Div. 1 UCS-66.1 | Stress-ratio thickness reduction |
| API 579-1 / ASME FFS-1 | Fitness-for-service brittle-fracture assessment |
| EN 13445-2 | European pressure-vessel material rules |
| NORSOK M-001 | Material selection for petroleum installations |