Testing and Weld Analysis
Carrs are able to offer customers a wide variety of testing methods, depending on the application involved, the operating environment, and the gravity attached to different potential failure modes.
Macro analysis is a destructive testing method of inspecting the quality of the welds. This procedure entails the close visual inspection of cut and polished weld samples. Acid etching these samples highlights the structure of the weld and the surrounding substrate and identifies issues concerning penetration depth, fusion, cracks, linear shrinkage, and porosity. Carrs have the facility to record results using macro photography at up to 50x optical magnification.
Micro analysis is another destructive method of assessing critical weld parameters and it is, usually, employed at the weld development stage. The process is similar to the macro analysis, however, in this case, the surface finish of the weld samples requires additional polishing steps. Using an Optimax Live Camera, Carrs has the ability to perform micro analysis at optical magnifications ranging from x50 to x400 which reveals possible failure modes and provides the detailed information required to fine-tune weld parameters.
Dye testing is an economical and non-destructive method used for evaluating cracking and porosity of metals at surface level, and for verifying effective sealing. Dye is applied to the assembly (or just the weld) which seeks out cracks or imperfections. The dye is cleaned off and the area developed, any residual dye will then re-emerge revealing any surface flaw. This is a common and useful test for checking welds on materials which exhibit a high cracking propensity such as aluminium and titanium.
Leak testing is employed to verify the integrity of production parts or assemblies. This may entail 100% testing or sample testing depending on the individual circumstances of the production job and assessment of the risk of leaks. If a product is designed not to leak air or fluid, it is important to test, locate any faults and re-work or reject.
Gross leak testing
Pressure testing is a practical, economical and non-destructive method of assessing an assembly for leaks. This is a simple test where a sealed volume is immersed in hot water or another non-conductive medium (such as perfluorocarbon liquid) and checked for air escape as evidence of a leak. Carrs conduct tests up to 5 bar with air pressure and, for high-pressure applications such as cooling circuits, oil ways, and hydraulics, with a stirrup pump up to 50 bar.
This non-destructive test regime is used for aerospace and automotive applications, equipment working in a vacuum, and assemblies which contain pressurised liquid. In this case, welded components are coupled to a vacuum pump, evacuated and a particle detector determines the air leak rate.
Fine (Helium) leak testing
Fine leak testing follows the same vacuum testing principles, but helium gas is introduced either inside or outside the assembly. Helium is used for fine leak testing because its minute molecules will seek out the tiniest of leaks (sub-micron), it is also inert which means it will not react with materials. It is hundreds of times more sensitive when compared to pressure decay techniques.
Through this method (leak testing), any leaks are pinpointed and repaired. After repair, the assembly is retested until no leaks are detected. In some critical cases where multiple overlying welds are involved, we may have to test the quality of the initial welds for defects before proceeding with sequential welds.