We carried out a series of investigative tests on the screw sample to find the cause of the failure. Here are our key findings:
Hardness surveys revealed that areas of the sample that has been welded were above the accepted maximum hardness levels, resulting in high hardness. This is a concern, as it can lead to the material being locally notch sensitive, brittle, and more susceptible to hydrogen cracking.
We also found that parts of the screw sample had been exposed to high temperatures in an oxidising environment. This meant that thermal fatigue was evident in the sample, propagating from the run welds.
The application of torsional loads/ cyclic bending resulted in stresses concentrated at the weld run ends, where high hardness, brittle and heat affected zones were present. This had resulted in fatigue fractures spreading from these regions.
With these intricate findings, our customer was able to determine whether this was an operational fault where the sample was misused, or if it was a supplier issue where the part was supplied as faulty.
Our investigation helped our customer to re-evaluate the material that this component was made from, and the components were then re-manufactured from new materials to minimise the risk of future damage to the equipment and improve design processes.