18  Prakt. Met. Sonderband 50 (2016) 
In fuel gas piping systems of stationary gas turbine engines, corrosive loads, e.g. by aqueous 
solutions from condensation, can never be completely ruled out. That said, one must concede that 
the material selection intended by design in this case is not well suited for this particular 
application. If corrosive environments could be avoided during manufacture, e.g. through proper 
drying after wet cleaning, they might still destroy the retaining rings in service by aqueous elec- 
trolvtes that accumulate in the piping system during standstill. 
The fact that the material actually selected in the case at hand, X39Crl3, 1.4031, violated 
specification requirements, was no more than a contributing factor at best. 
First, the corrosive agent must be removed to prevent this kind of failure from recurring. In the 
subject case, causative chemicals apparently originated from wet cleaning residues. It is therefore 
recommended to dry components thoroughly after cleaning, prior to shipping. Second, the material 
selection should be altered. An austenitic spring steel should be selected for this particular applica- 
tion. Generally, they are less prone to sensitisation since no post-solutioning heat treatments are 
required to obtain appropriate mechanical properties. What is more, they are not sensitive to contact 
corrosion like a pairing between martensitic retaining ring and austenitic piping. 
$ mm 
Fig. 4: Fractured retaining rings in as-received condition. Note local surface corrosion Fig. 7: Scanni 
3 Ther 
A particular 
feed pipe. 
component 
conditions w 
pipe was pic 
melting (SL 
freedom. It : 
| | | | . | . pipe failed t 
Fig. 5: Planar section (surface polish) perpendicular to fracture surface (right). Note intergranular corrosion