Testing proves that the completed pressure parts hold the test pressure without leakage or visible deformation, and that welds selected by the ITP meet the NDT acceptance criteria. Ohm's standard shop tests on heat exchangers are hydrostatic testing of pressure parts and NDT as specified. Other leak-detection methods exist in industry; they are not implied by an ISO 9001:2015 certificate or by 'ASME design'.
Hydrostatic test of pressure parts
Each pressure chamber (shell side, tube side) is filled with water, vented of air, and pressurised to the test pressure required by the named construction code or the purchaser specification. ASME VIII-1, when that code is specified, uses a hydrostatic test based on MAWP and allowable-stress ratios (commonly discussed as 1.3 × MAWP when temperatures align). IS 2825, when specified, has its own test-pressure rules. The hold is long enough to inspect joints; acceptance is no leakage and no visible permanent distortion.
Gaskets used for shop hydro may not be the service gaskets. Stainless equipment may need control of test-water chlorides. Expansion joints must be protected from over-extension during the test as the procedure requires.
What the hydro is for — and what it is not
- It is a strength and tightness test of the pressure boundary at the shop.
- It is not a substitute for correct gasket selection in service.
- It does not prove tube-side to shell-side isolation at a sensitivity tighter than visual water tightness unless a specific differential or complementary test is specified.
- It does not qualify the unit for a design pressure higher than calculated — do not 'test extra' to uprate.
NDT as the ITP — not a hidden menu
Visual testing is baseline. Additional NDT (radiography, ultrasonic, dye-penetrant / PT) is performed where the ITP and the construction code joint efficiency require it. Full RT, spot RT, or VT-only are different commercial scopes. PMI, hardness after PWHT, and ferrite checks are likewise specified items. Requesting 'all NDT' without naming methods and extent is not an ITP.
| Method | Typical use on exchangers | Standard on every Ohm unit? |
|---|---|---|
| VT | Weld workmanship, dimensions as visual | Yes — shop practice |
| PT / DPT | Surface-breaking indications on specified welds (e.g. tube-to-tubesheet, nozzles) | When the ITP says so |
| RT | Butt welds to support joint efficiency or purchaser hold | When the ITP / code extent says so |
| UT | Thickness, specified welds, or as RT alternative | When the ITP says so |
| Hydro | Pressure parts | Yes — pressure parts |
Tests that are not standard Ohm shop tests
Pneumatic testing stores far more energy than hydro and is used in industry only when liquid fill is impractical, with barricades and a lower test multiplier under the code. Helium (or halogen) mass-spectrometer leak testing is a specialised tightness demonstration for some vacuum or hazardous services. Neither pneumatic nor helium testing is a standard Ohm heat-exchanger shop test. If your specification requires them, they must be written on the RFQ and ITP so method, acceptance, and safety provisions can be planned — or declined if they cannot be executed.
Do not assume a pneumatic 'air test' after hydro as routine. If the PO does not name it, it is not in the shop's standard sequence.
Records and witnessing
The hydro record should state which side, test pressure, medium, duration, gauge identification, and result. NDT reports should identify the welds (map) and the procedure. Purchaser or TPI witness is a hold point on the agreed ITP, not an automatic calendar event. Gauge calibration status should be current for the test that was performed.
RFQ: name the tests
On /rfq?product=heat-exchangers, state the construction code, required hydro basis if it differs from the code default, NDT extent, and any extra leak test. Attach your ITP. Ohm will test what is agreed — hydrostatic pressure parts and specified NDT — at Vadodara, and will not pad the quotation with helium or pneumatic tests that were never requested.
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