Reverse engineering an obsolete face seal for a power station turbine
No spares, no OEM, and only water-damaged microfiche drawings to go on. A new turbine face seal, rebuilt from the original parts and drawings and back in service.
01Project description
A power station reliability study had found that a generator turbine face seal had no spares in stock and that the OEM had stopped trading 15 years previously. The partial 1960s OEM drawings had been extracted from an old microfiche that had suffered water damage. The drawings were in English Imperial and many dimensions were inferred from chords and other outdated drawing standards. Any new seals must be made to the original material specifications and be an exact match to the original parts.
02Solution
A site visit during a turbine shutdown allowed access to the seal assembly. Traditional measurement techniques, plus 3D scanning of the seals and surrounds allowed for the creation of an as-built CAD model of the seal assembly and the surrounding housings. PMI sampling was performed to identify the material composition.
The partial damaged drawings were then referred to for the creation of a nominal CAD model. A dimension and tolerance spreadsheet was created to identify where dimensions and tolerances were missing. The nominal model was compared to the as-built model to create a full set of dimensions, and any discrepancies were tracked with the dimension and tolerance spreadsheet.
In collaboration with the power station engineering team, the missing and contradictory information was compared with the old British Standards and agreement was made on the chosen dimensions and tolerances. A foundry in Belgium was found as the last producer of the old copper alloy needed for the seal body, whilst a local supplier that could centrifugally cast the white metal seal face was sourced.
03Outcome
A full set of modern manufacturing drawings, including the machining and white metal casting steps, was produced along with a Bill of Materials including supplier contacts. This has now been archived with the power station operators in hard-copy and digital formats.
A newly manufactured seal assembly was installed at the next power station shutdown with success. There are now stocks of the vital turbine face seal for future repairs and replacements.