LT Leak testing
Leak testing · Inspección y ensayos · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Helium leak test 5×10⁻⁶ mbar·l/s at 6 bar” states a leak testing requirement.
What controls
Test that checks that a vessel, circuit or joint does not leak fluid above an established limit. The requirement is only verifiable if the drawing gives three pieces of information: the method (pressure decay, bubble, helium tracer or other), the conditions (pressure, time, temperature) and the acceptance criterion, expressed as an allowable leak rate or as no indications. Without them, “must be leak-tight” is not a testable requirement, because every joint leaks something if measured with enough sensitivity.
How to verify
Depending on the method: pressurize and monitor the pressure decay with a gauge or transducer for the specified time; immerse and inspect for bubbles; or pressurize with helium and detect with a mass spectrometer, which is the sensitive method when the criterion is a small leak rate. Pressure, time, temperature, method and result are recorded. When the criterion is demanding, check the setup with a calibrated reference leak to show that the system would have detected a real leak.
Common mistakes when interpreting it
- Requiring leak-tightness without defining method, conditions and allowable leak rate criterion.
- Using a method less sensitive than required and declaring the part leak-tight.
- Blaming the part for a pressure drop caused by the test fixture or by a temperature change.
How to get it in the workshop / if it comes out of tolerance
Make sure the part is in the right condition before testing: clean and dry, with the specified seals and plugs, and with threads in good condition. The methods have very different sensitivities, and using one less sensitive than required gives a false pass. Mind safety: a pneumatic pressure test stores energy and requires different precautions from a hydrostatic one.
Leak detected: locate it before repairing (soapy water, tracer or detector), because the leak is often in the test fixture itself and not in the part. Pressure drop with no locatable leak: this may be a temperature effect, especially in long tests with air; stabilize before starting the clock. Recurring leaks in welds are usually through-porosity, which is ground out and rewelded, not sealed with a compound.
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