A free, browser-based engineering calculator for shell-and-tube heat exchanger tube rupture relief analysis. Estimate the relief load from a ruptured tube, screen whether a dedicated relief device is required under the API 521 10/13 rule, and size the pressure safety valve (PSV) and API 526 orifice — all in one place.
Engineering screening tool. Results are preliminary and educational. Final relief-device design must be performed and verified by a qualified Professional Engineer using validated software and complete fluid property data per API 520, API 521, and ASME Section VIII.
What this calculator does
The suite covers the full preliminary workflow for heat exchanger overpressure protection when a high-pressure tube fails into a lower-pressure shell:
- Tube rupture relief load for gas/vapor (choked and subcritical flow) and liquid cases, using the API 520 critical-flow relations.
- API 521 exemption screening via the 10/13th rule, comparing high-pressure design pressure against the low-pressure side’s hydrotest envelope.
- PSV / PRV sizing per API 520 Part I, with automatic API 526 orifice selection (D through T).
- Two-phase relief analysis using the DIERS Omega method and a Homogeneous Equilibrium Model (HEM).
- Transient surge analysis with a Method-of-Characteristics solver to flag millisecond pressure peaks that can occur before a valve opens.
- Cubic equation-of-state thermodynamics (Peng–Robinson / SRK) for real-gas compressibility and Joule–Thomson cooling.
- Multi-scenario governing-case comparison (tube rupture, external fire, blocked outlet, thermal expansion).
How tube rupture relief sizing works
When a heat exchanger tube fails, the high-pressure fluid discharges into the shell. If the shell-side equipment cannot contain the resulting pressure, a relief device is required. This calculator estimates the rupture release rate from the tube bore, pressure differential, and fluid properties, then determines the required relief area and the nearest standard API 526 orifice.
The API 521 10/13 exemption rule
API 521 allows a tube rupture relief device to be omitted when the low-pressure side can safely contain the surge — broadly, when the high-pressure design pressure does not exceed the low-pressure side’s hydrotest pressure (about 1.3 × MAWP). The calculator screens this automatically and returns one of three outcomes: relief required, conditional review, or candidate for exemption. A passing screen is a starting point only and still requires full API 521 §5.19 review.
Who it’s for
Process safety engineers, mechanical and EPC engineers, and students working on relief valve sizing, heat exchanger tube rupture analysis, and pressure relief system design for refineries, LNG plants, offshore facilities, and chemical processing.
Standards referenced
API 520 Part I & II, API 521, API 526, ASME Section VIII Division 1, ISO 4126, and DIERS methodology.
Frequently asked questions
Is this tube rupture calculator free to use?
Yes — it runs entirely in your browser at no cost.
Does it replace HYSYS or Farris Sizemaster?
No. It’s a transparent screening and educational tool. Final designs must be verified by a licensed PE using validated commercial software.
What is the 10/13 rule in API 521?
A screening criterion: a dedicated tube-rupture relief device may be unnecessary when the low-pressure side can momentarily withstand the high-pressure source up to its test envelope (~1.3 × MAWP).
Which relief scenarios does it model? Gas/vapor and liquid tube rupture, two-phase flashing flow, plus a governing-case comparison against fire, blocked outlet, and thermal expansion.
