Due to the high requirements on output and efficiency of the gas turbines, the design stresses on these components are considerable. Resulting from this, a tight quality assurance process is necessary to ensure a maximum reliability and performance. This requires an appropriate specification system, a strict predevelopment phase and last but not least a straight inspection procedure for the series batches.
The specification system covers a general specification, a material specification and a specific component specification. In the general specification, the requirements on the foundiry and their quality assurance system, the investment casting process, and the inspection steps to be performed, are defined. The material specification gives the chemical composition, the heat treatment and the mechanical properties of the alloy. The component specification refers to the part itself and defines the non-destructive requirements depending on the design stresses. The latter specifies also microstructural features as grain size and microporosity.
The predevelopment on each new component ("first article") takes place in close cooperation between the turbine manufacturer and the acting foundry. It comprises a small production batch, on which all relevant process parameters will be established. During this phase also the feedback of the foundry to the castability of the part is obtained, and if necessary an optimization of the design respectively the specifications will be done. On the parts themselves, as well destructive as non-destructive steps are performed. Destructive inspections are carried out with respect to microstructural and mechanical properties. Non-destructive inspections on a 100 % basis consisting of visual and fluorescent penetrant inspection and radiographic/ultrasonic inspection have to prove the requirements on maximum permissible external and internal defects. Also the procedures for the dimensional inspection are fixed. At the end of the predevelopment, all results are documented in the validation brochure signed by both parties. With this brochure the entire casting process will be frozen. Attached to this brochure are the inspection procedures, and if applicable the welding procedures.
The first production batches are inspected at the foundry site in the frame of a source inspection. The detailed procedure for this will follow the above mentioned specifications and the agreements fixed in the validation brochure. Later, if a general quality assurance agreement was established with the foundry, the scope of this will be enlarged by the new part.
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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