Contact person
Peter Eriksson
Forskare
Contact PeterDetermination of stress corrosion resistance of copper alloys
Stress corrosion cracking (SCC) of a material can occur in certain environments specific for the material. Cracks can be induced either by applied stresses, for example by mounting of a component, or by residual stresses from manufacturing and machining. Brass fittings and valves are often used in water piping systems. Failure due to stress corrosion cracking can result in extensive and expensive water damage. Use of components that are resistant to stress corrosion cracking in the environment they are intended for reduces the risk of this type of failure.
Purpose
Testing in an ammoniacal atmosphere according to ISO 6957 detects if applied or residual stresses in copper alloy products can cause failure of the material, due to stress corrosion cracking, in service or storage. The severity of the test can be regulated by changing the pH value of the solution producing the ammoniacal atmosphere. Recommendations for the choice of pH values are given in the standard for some frequently occurring applications.
RISE is accredited by SWEDAC for determination of stress corrosion resistance according to ISO 6957.
Method
Determination of resistance to stress corrosion cracking according to ISO 6957 involves degreasing, pickling and mounting of the test objects, e.g. with copper or plastic pipes, according to the mounting instructions for the product. The assembly is then exposed to an ammoniacal atmosphere, given by a solution with adjusted pH value (corresponding to different types of corrosive environments) at room temperature for 24 hours.
Any cracking caused by stress corrosion is evaluated after exposure using optical microscopy. If cracks are observed during evaluation, and if criteria for approval shall be based on crack depth, cross sections of the material around the crack (s) will be prepared and crack depth will be measured using optical microscopy.
For example, assessment can be made based on the approval criteria found in NKB (Nordic Committee for Building Regulations) Product rules. No approval criteria are specified in standard ISO 6957.
Deliveries
Results will be delivered as a report.
