At a glance
- For vessels: the higher of 1.25 × the pressure corresponding to the maximum in-service loading (given PS and TS) and 1.43 × PS — Annex I point 7.4, literally and with no stress ratio in it.
- The usual way of filling in the first term, 1.25 × PS × ftest/fdesign, comes from the standard (for unfired vessels EN 13445-5 §10.2.3.3.1). The module labels each step as law or standard.
- At ambient temperature 1.43 × PS almost always governs; the temperature term takes over once the stress ratio exceeds 1.144 (= 1.43 / 1.25).
- The static liquid column, the test condition as its own load case, and the option of another recognised test (3.2.2) all come on top.
The calculator
Only PS is required. Without material data you get the floor of 1.43 × PS. Same rule engine as the Dutch site, 47 test cases against OJ L 189, Annex I points 7.4 and 7.1.2.
Material data — optional, but needed for the temperature term of point 7.4
Indicative floor; it does not replace a strength calculation or a notified body's decision. Values are rounded up, because point 7.4 gives a minimum. Your input stays in your browser and is not stored.
The two terms of point 7.4
Annex I point 7.4 requires, for pressure vessels, that the hydrostatic test pressure of point 3.2.2 is no less than the higher of two values: the pressure corresponding to the maximum loading the equipment may be subjected to in service, given its maximum allowable pressure and temperature, multiplied by 1.25 — and the maximum allowable pressure multiplied by 1.43.
Note what the first indent does and does not say. The directive names no stress ratio; it says only “given its maximum allowable pressure and temperature”. Filling that in as 1.25 × PS × ftest/fdesign comes from the standard — for unfired pressure vessels EN 13445-5 §10.2.3.3.1 — not from point 7.4. The module therefore labels each step with its source: law for 1.43 × PS, standard for the temperature term. Point 7.1.2 belongs to the design: it caps the allowable general membrane stress per material type and is no part of the formula in point 7.4; the module uses those caps to test the stresses you enter.
When does which term govern?
The crossover is exact: once the stress ratio ftest/fdesign exceeds 1.144 (that is 1.43 divided by 1.25), the temperature term wins. Below it, 1.43 × PS always governs. Practically: a vessel designed at ambient temperature nearly always tests at 1.43 × PS; a hot vessel tips over.
Does this also cover piping, boilers and accessories?
Not directly, and the answer differs per type. Point 7.4 opens with "for pressure vessels"; point 3.2.2 extends the value to all pressure equipment "where appropriate". What the harmonised standards then make of it:
- Pressure vessels — point 7.4 applies directly. EN 13445-5:2021+A1:2024 §10.2.3.3.1 gives the same two terms, but calculates the first with the design pressure Pd (higher than PS, so a higher outcome than this calculator gives), takes the smallest stress ratio over the main pressure-bearing parts, and lets the 1.25 rise as far as 2.2 for certain single-side-welded governing joints and testing group 4.
- Piping — EN 13480-5:2017+A1:2019+A2:2021 §9.3.2.2.1 prescribes exactly the same two terms, so the outcome here is the normative value. The standard does add: the smallest ftest/f across all main parts, a stress ceiling from EN 13480-3:2017 §5.2.1.2 (ferritic 95 % ReH), and the rule that the liquid column counts once it adds more than 5 % anywhere — this calculator works that percentage out.
- Boilers — EN 12952-3:2022 §5.7.4.3 (water-tube) and EN 12953-3:2016 §5.7.4 (shell): the same two terms, but with the bare yield ratio Rp0,2(20 °C)/Rp0,2(tc) and without the caps of point 7.1.2 — at higher temperatures the boiler value therefore comes out higher than the vessel formula. Water-tube: lowest ratio, PS or the higher calculation pressure pc; shell: highest ratio over shell and tube plates, always pc; exclusively expanded smoke tubes: 1.43 × pc without exception.
- Accessories — the product standard and the manufacturer's specification.
The failure mode is always the same: taking the number without walking through the accompanying normative conditions, and a test protocol ends up too low or impermissibly high.
The standard-specific conditions above are referenced by clause in the full report; standard texts themselves are copyrighted and are not reproduced here.
Running the test: where it goes wrong in practice
Calculating the pressure is the easy part. This is what a notified body or a Dutch inspection body actually looks at during the test.
Choosing the gauge and the 10-to-2 rule
Choose a range of one and a half to two times the test pressure. On the shop floor you check that with the 10-to-2 rule: at the test pressure the needle of an analogue gauge should sit between the 10 o’clock and 2 o’clock positions, that is between 28 % and 72 % of full scale. Lower down the reading error is too large; higher up there is no margin against overshoot.
The range rule is the stricter of the two: a full scale at one and a half to two times the pressure puts the needle between 1:30 and 12 o’clock, which satisfies 10-to-2 automatically. The reverse does not hold — 10-to-2 permits full scales up to about 3.6 times the pressure. The gauge serial number belongs in the report.
Four points on which test reports founder
- Calibration chain — calibrated within twelve months before the test, traceable to an ISO/IEC 17025 accredited laboratory. Ask for the parent certificate of the reference gauge as well; without that link the traceability cannot be shown.
- Test water — keep it between roughly +10 and +50 °C. With austenitic stainless steel the chloride content is critical: demineralised water, and drain and dry after the test, or you risk stress corrosion in the welds you have just approved.
- Hold time — topping up during the hold time is not allowed; if you do it anyway, the hold time starts again. Record the temperature too, or a pressure drop cannot be explained afterwards.
- Attachments — a test report without calibration certificates and without a pressure-time record is an empty shell in a file review.
The full PED report covers the whole execution — filling and venting, staged pressurisation, safety distance and overpressure protection, the standpipe method at a design pressure of 0 bar, and the split between the notified body and the Dutch inspection body at the hold points — plus a fill-in test protocol as an annex.
What else counts at the test
- The static liquid column of a tall or standing item adds to the test pressure at the lowest point.
- The test condition is its own load case in the strength calculation; the structure must carry the test pressure, which is not self-evident if you raise it.
- Point 3.2.2 permits another recognised test where the hydrostatic test is harmful or impracticable, provided additional measures such as non-destructive testing are applied first.
How reliable is this calculator?
The material limits and the factors 1.25 and 1.43 come straight from the text of the directive (OJ L 189 of 27-6-2014, pp. 213–214), not from a secondary source; the stress ratio and the standard-specific departures come from the standards named above and are labelled as such, and are covered by a suite of 47 test cases: the six calculation cases of point 7.1.2 (five material types, austenitic steel in two variants), the 1.144 crossover, and a grid check over more than 4,000 combinations. Pressures are rounded up, because point 7.4 is a minimum. The outcome is an indicative floor and replaces neither a strength calculation nor a decision by a notified body.
Frequently asked questions
What is the minimum test pressure under the PED?
For pressure vessels: the higher of 1.25 times the pressure corresponding to the maximum in-service loading, given PS and TS, and 1.43 times the maximum allowable pressure PS (Annex I point 7.4). Point 3.2.2 extends that value to other equipment where appropriate.
When does the temperature term govern instead of 1.43 × PS?
Once the ratio of the allowable stress at test temperature to that at design temperature exceeds 1.144, which is 1.43 divided by 1.25. Below that ratio, 1.43 × PS always gives the higher value.
Does the liquid column count in the test pressure?
Yes, at the lowest point of a standing or tall item the static column adds to the pressure. Point 7.4 does not regulate it; the product standard and your procedure do — and ignoring it is a common finding at witnessed tests.
May I test pneumatically instead of hydrostatically?
Point 3.2.2 permits another recognised test where the hydrostatic test is harmful or impracticable, provided additional measures such as non-destructive testing are applied beforehand. It is the exception, not the default, and it needs agreement with the body involved.
Is a higher test pressure always safer?
No. The test condition is a load case of its own: the structure must be shown to carry the test pressure. Raising the test pressure without checking that case can damage the equipment you are trying to prove sound.
Want the number for your equipment?
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