Pressure testing and quality control of plastic welds
How to document that a joint holds
A plastic weld can look perfect and still be leaky or weak. That's why control is a fixed part of the trade especially on piping and tanks where a flawed joint can have major consequences. The control ranges from what the eye can see to destructive tests that determine the joint's strength.
§Visual control — the first and cheapest step
Any weld is first assessed visually: is the weld bead even and uniform are there signs of underfill, porosity, burning or lack of fusion? Visual inspection cannot stand alone but it catches many of the errors that occur along the way and costs nothing extra to perform because it happens as a natural part of the work.
§DS/EN 12814 series: destructive testing of welded joints
To test the actual strength of a weld on semi-finished thermoplastic parts, there is a series of Danish/European standards, DS/EN 12814. The standards describe different types of destructive testing, where a test piece of the weld is loaded until it breaks or deforms, so that the quality of the weld can be assessed.
| Part of the journeyman's test | What it tests |
|---|---|
| DS/EN 12814-2 | Tensile testing — how much tensile force the joint can withstand before it breaks |
| DS/EN 12814-4 | Peel test (peel test) — how well a lap weld resists being peeled apart |
| Other parts of the series | Including bend testing and tensile testing at low temperature, depending on task requirements |
§Pressure testing: inspection of the pipe system itself
Where destructive tests tell something about the weld's material strength, pressure testing is used to control the finished pipeline itself: the pipe section is placed under pressure, and you check that the pressure remains stable without drops that would reveal a leak. Pressure testing is particularly widespread in PE welding of pipelines, where tightness is the entire purpose of the joint.
§Documentation ties it all together
Inspection only has value if it is documented. Welding parameters, who performed the welding, the result of the visual inspection and any test and pressure test results are recorded so the work can be traced and approved afterwards — especially important on piping where faults only show when the pipe is dug down or hidden in a structure.
“A weld that no one has checked is not a good weld — it is just a weld nobody yet knows how good it is.”