DVS 2203: weld testing, requirements and documentation

What DVS 2203 covers

DVS 2203 describes how welds in thermoplastics are documented by tensile, bend or impact testing of specimens. Testing is performed on test bars cut from a joint, and the result serves as proof of how that specific joint or welding cycle behaved. This is the only method that demonstrates whether the material fuses properly in the weld seam.

The standard series is divided by method. Part 1 describes test methods and general requirements, Part 2 tensile testing, Part 3 tensile impact testing, Part 4 tensile testing at low temperatures, and Part 5 technological bend testing. Requirements for bend testing are also detailed in DVS 2203-1, Annex 3.

For semi-finished products, a parallel series, EN 12814, covers tensile, bend and peel testing of welded joints in thermoplastic sheets and pipes. The applicable standard series is specified in the contract or in the project specification.

Test methods and what they reveal

Select the test method according to the joint type and the properties to be verified. The tensile test provides information on strength, the bend test on ductility and the presence of brittle zones, and the tensile impact test on the joint's resistance to sudden impact loading.

Tensile testing and weld factor

During a tensile test, a test specimen is pulled from the joint until it breaks. The weld factor is calculated as the tensile strength of the welded test specimen divided by the tensile strength of an undamaged reference specimen of the same material. The factor thus expresses what proportion of the material's strength the joint has retained.

The fracture appearance is at least as important as the numerical value. A fracture within the weld seam, brittle fracture surfaces or visible pores indicate that the welding cycle was incorrect, even if the weld factor appears acceptable. A fracture outside the weld seam in the unaffected base material is the desired result.

The required factor depends on the material, joint type and contract specifications. For butt fusion welding of PE pipes, a requirement of at least 0,8 is common, whereas other applications require a documented fracture appearance rather than a specific numerical value. Check the requirements in the contract or standard applicable to the project before sending the test specimens away.

Bend testing in practice

The technological bend test is a rapid quality check used in daily operations. A test bar is cut transversely across the weld seam, bent around a mandrel or in a bend test fixture, and the seam is inspected for cracks and defects. This test requires no tensile testing equipment and can be performed on-site.

For butt fusion welding, the test bar is extracted so that the entire weld seam lies in the middle of the specimen. When the specimen is bent, a weak weld seam will open up as a crack, whereas a correct joint will bend continuously. Pores and inclusions become visible on the fracture surface and can be photographed for documentation purposes.

The number of test specimens is determined by the scope of the work and contract requirements. When starting with a new material, a new machine or a new welding programme, a test sample must always be produced and tested before production commences.

Sampling and frequency

Test samples must be taken from a joint produced using the same machine, the same programme and the same parameters as the production joints. If a sample is taken from a dedicated test joint, it must be produced as part of the routine workflow rather than as an exceptionally optimized joint.

For longer pipeline installations, it is standard practice to take test samples at start-up and subsequently at regular intervals, or when changing materials, dimensions or operators. The exact frequency is specified in the contract, the client's quality plan or the applicable standard.

Test samples must be marked with the weld number, date, dimension, material and machine number to ensure traceability back to the logged joint. Without traceability, the test result is worthless as documentation.

Reliable documentation

The test report must include the test method and standard, date, identity of the test operator, specimen dimensions and extraction location, results including tensile strength and calculated weld factor, fracture appearance and evaluation. Photographs of the fracture surface provide robust documentation at virtually no additional cost.

The report is compiled alongside the machine's joint log, the operator's name and any relevant operator certificates. In the event of a dispute, the overall package is decisive: a logged welding cycle, a traceable test sample, and a report detailing how the specimen was extracted and evaluated.

If testing is to be performed by an external laboratory, this must be agreed in advance with the client, and the samples must be dispatched with instructions regarding storage and transport. Read more about testing and documentation in testing and documentation.

Flaws detected by testing – and those that are not

Testing detects cold joints, insufficient pressure, incorrect temperature, contamination of the fusion faces, and incorrect drag/changeover time. It also identifies material defects that manifest as pores or brittle zones on the fracture surface.

Testing will not detect a joint welded with excessive pressure that otherwise appears sound, nor does it provide information on long-term durability. Long-term durability is documented through pressure testing and adherence to standard parameters, not through a single tensile test.

Therefore, use testing as part of an integrated chain: correct preparation, logged execution, visual inspection, destructive testing and, finally, pressure testing. See pipe preparation before welding and testing and documentation.