SEDL / STP / STP918-EB / STP19329S

Choosing a Steel for Hydroelectric Penstocks

Reid, CN
Professor, The Open University, Milton Keynes,

Baikie, BL
Research officer, Central Electricity Generating Board, Manchester,

Pages: 20    Published: Jan 1986

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Abstract

This case history concerns the design of the high pressure water pipes (penstocks) of the Dinorwig pumped storage power station. The first part describes an Open University teaching exercise which is based on the original assessment performed by Milne of the Central Electricity Generating Board. It involves the consideration of two contending steels, “A” and “B,” and the selection and justification of a preferred choice. Since the hydraulic loading contains cycles of changing pressure, the fatigue lives of the penstock designs were compared. The possible presence of longitudinal surface cracks was considered, with a depth equal to the limit of ultrasonic detection (taken to be 6 mm). The Paris-Erdogan equation was used to calculate the length of time required to grow a fatigue crack from this depth up to the critical size. Comparing designs of equal cost, that in Steel B achieved a much longer “crack growth lifetime” and was the preferred choice. Finally, defect acceptance standards were drawn up for this design.