Steam turbine high-pressure casing repair-case history
- Inst. de Investigaciones Electricas, Cuernavaca (Mexico)
Many utility units approach 30 to 40 years of operating life. According to recent operation practice the units will be operated far beyond their 35-year economic life and are more likely to be used for cyclic duty. These two factors contribute to an increased potential for turbine casing problems in these units. The 158 MW steam turbine high pressure inner casing presented nozzle port bridge cracking and erosion. The cracks were caused by low cycle fatigue (LCF) due to thermal stress during rapid starting and loading. These stresses were relieved by axially slotting the bridges and fitting a dowel to seal the slot, but despite that the cracks occurred in the corners of the bridge slots and propagated very deeply into the nozzle ports. The casing material was Cr-Mo-V low alloyed steel. The dowels sealing the slots were removed partially or totally by erosion. Development of the in-situ crack repair welding technology and slot/hole machining methods are fully described. The cracks were removed and prepared for welding. The welding method was shielded metal arc welding process (SMAW), using buttering and two temperature-bead technique (two layer refinement technique). Also the peening of all the layers were carried out to reduce casing distortion. Special portable drilling and cutting heads were developed to machine the slots and holes for the dowels after welding. The slot retrofit was carried out to reduce the thermal stress concentration during start-up and load changes. The casing was put back into service after repair and nozzle block assembly.
- OSTI ID:
- 389917
- Report Number(s):
- CONF-960426-; TRN: IM9646%%202
- Resource Relation:
- Conference: 58. annual meeting of the American power conference, Chicago, IL (United States), 9-11 Apr 1996; Other Information: PBD: 1996; Related Information: Is Part Of Proceedings of the American Power Conference. Volume 58-II; McBride, A.E. [ed.]; PB: 886 p.
- Country of Publication:
- United States
- Language:
- English
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