Charpy Arrest Energy Calculator (Battelle CVN Requirement) — Sample Report

1 · Design inputs

An NPS 12 gas transmission line: 12.75 in OD (6.375 in outside radius) with a 0.375 in wall, operating at a hoop stress of 40 ksi. The mill certificates for the heat report a full-size Charpy energy of 30 ft·lbf at the minimum design temperature.

2 · Method

The Battelle/AGA correlation for the minimum full-size Charpy energy required to arrest a propagating ductile fracture in conventional line pipe:

CVN_req = 0.0108 · σ_h² · ( R · t )^1/3

ratio = CVN_available / CVN_req → PASS when ratio ≥ 1

Units are fixed by the coefficient and are not interchangeable: σ_h in ksi (not psi), R the outside radius in inches (not the diameter), t the wall thickness in inches, and the result in ft·lbf. The 0.0108 constant carries the unit system inside it — it is a published empirical coefficient fitted to full-scale burst test data, not a code table value, which is why it is implemented here rather than left as an input.

The shape of the equation is worth reading before the number is. The requirement rises with the square of hoop stress and only with the cube root of the R·t product. That asymmetry is the whole engineering story: operating pressure dominates, and geometry barely moves the answer. Doubling R·t — a much larger, much heavier pipe — raises the toughness requirement by only 26%, while a 25% increase in hoop stress raises it by 56%.

The engine validates that σ_h, R and t are positive and that the available CVN is non-negative, then reports the requirement, the ratio to five decimals, and the verdict. Every run carries a standing warning that the correlation is calibrated for conventional-strength line pipe: rich gas, high grades from X80 upward, and low design temperatures all sit outside the data the fit was built on and need the governing code's correction factors or a full two-curve assessment.

3 · Calculation

1. Geometry term: R·t = 6.375 · 0.375 = 2.390625 in².
2. Cube root of the geometry term: (2.390625)^1/3 = 1.33712.
3. Stress term: σ_h² = 40² = 1,600 ksi², and 0.0108 · 1,600 = 17.28.
4. Required arrest energy: CVN_req = 17.28 · 1.33712 = 23.105 ft·lbf.
5. Compare against what the pipe has: ratio = 30 / 23.105 = 1.2984.
6. The available toughness exceeds the requirement by about 30%, so the verdict is PASS — a fracture in this pipe at this operating stress is predicted to arrest.

4 · Results PASS

5 · Verification statement

The result values above are locked as fixture charpy-arrest.json, case “σh=40 ksi, NPS 12 t=0.375, 30 ft·lb available — passes”, tolerance 0.001, in the calc-core continuous verification gate (see https://pipingtoolset.com/trust/validation.html). Allowable-stress and factor data are user-supplied inputs; citations: ASME B31.8, Gas Transmission and Distribution Piping Systems — ¶841.1.2, fracture control and arrest toughness requirements for steel pipe. · W. A. Maxey et al., Battelle Memorial Institute / American Gas Association — full-scale burst test programme and the ductile fracture arrest correlation, including the two-curve model this screening form derives from. · API 5L, Line Pipe — source of the supplementary Charpy impact requirements and the pipe body test regime; the certified CVN value is user-supplied from the material test report. · ASTM E23, Notched Bar Impact Testing of Metallic Materials — full-size (10 × 10 mm) specimen basis the 0.0108 coefficient is calibrated to; sub-size results require conversion before use. · The 0.0108 coefficient is a published empirical constant of the correlation, not a code table value.