Probabilistic life assessment of GT vanes

Plant:

  • Four heavy duty, 6-stage expansion GTs driving compressors at a UK chemical plant; installed in the 1960s with 112,000 hours service on the current set of vanes

Objective:

  • To reduce maintenance costs by extending vane life from 100,000 to 130,000h, prior to retirement of the units

Approach:

  • Inspection
  • Flow, thermal and stress analysis
  • Probabilistic creep life calculation, allowing for local hot-spots

Benefits:

  • Inspection revealed no cracking and little degradation or oxidation
  • One row demonstrated to be of a different material to that specified
  • Analysis showed life to be limited by creep under flow-induced bending
  • Risk calculated to increase by a factor of 5 from 112,000 to 130,000 h
  • Absolute risk level during extended life deemed tolerable by the operator
Predicted failure probability for GT vanes, individually and as a row, under two operating scenarios

Published:

Wood, M.I., Lant, R.P.D. and Brear, J.M., “Quantitative Risk Assessment and its Role in Plant Maintenance Decisions”, IMechE Conf ‘Power Station Maintenance 2000’, St. Catherine’s College, Oxford, September 2000

Plant Integrity