Case Study 1305 - Root Cause Identification

Again this case study was also based on a group of four variants of similar parts developed by the customer else­ where and transferred to CRP. They are cylinder heads of the compressors and needed to be 100% leak tested.
The parts started to fail by breakage of the flanges (Figure 5.1) while just fastening before leak testing as well as during leak testing.

Figure 5.1 - Leak testing setup and the failure.

The failures happened only in the case of Variants 1, 2 and 4 whereas the Variant 3 never failed. Upon detailed study, the Variant 3 had fillet radius between 3mm and 4 mm whereas the other variants had between 1mm and 2mm (Figure 5.2).

Hence it was decided to simulate the fastening and leak testing. (Figure 5.3 and Figure 5.5) The simulation results correlated exactly with the failure of the flange. Also, the effect of various fillet radiuses in terms of Von Mises Stress was simulated using the parametric capabilities of the tool and results obtained (Figure 5.4 and Figure 5.6).

Figure 5.3 - Simulation of Fastening before Leak Testing

Figure 5.4- Result Effect of various Fillet Radius while Fastening

Figure 5.5- Simulation of Leak Testing.

Figure 5.6 - Results: Effect of various fillet radius while leak testing.

The results justified the radius of 3 mm to be the opti­mum, and hence all the variants are modified to this effect with the due approval from the customer. No failure has been reported since then.

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