Page 442 - Failure Analysis Case Studies II

Failure Analysis Case Studies II
D.R.H. Jones (Editor)
0 2001 Elsevier Science Ltd. All rights reserved 425

Failure analysis of a condensate pump shaft

A.M. Lancha", M. Serrano, D. G6mez Briceiio

Materials Programme, DFN, CIEMA T, Avda. Comphtense 22,28040 Madrid, Spain
Received 19 October 1998; accepted 6 November 1998

Abstract
This paper presents the failure analysis of a condensate pump from a nuclear power plant. The failed
components were the martensitic stainless steel shaft and a chromium-plated sleeve in the first stage sealed
area. The fake occurred during normal operation of the plant after a service of 8 years. The cause of the
fracture was found to be quench cracking due to overheating. Taking into account the results obtained in
the destructive examination of the shaft and the sleeve, and the low operation temperature of the pump
(-100"F), it was deduced that the heat source was the friction between the shaft (or the associated
components) and the casing. 0 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Pump failures; Metallurgical failure analysis; Overheating; Quench cracks

1. Introduction

This paper describes the failure analysis of a condensate pump shaft from a nuclear power plant
(NPP). The catastrophic failure of the pump shaft occurred during normal operation of the plant,
after a service for 8 years.
In a secondary cooling system of a NPP (which includes the main steam system and the
condensate-feedwater systems), cooler water is pumped from the condenser, by the condensate
pumps, through the feedwater system to the steam generator tubes where it is heated by the primary
water from the reactor pressure vessel and converted to steam. The steam then passes through the
main steam line to the turbine, which is connected to the electric generator. The steam from the
turbine condenses in a condenser to close the cycle.
The failed condensate pump is a vertical six stage enclosed impeller unit with double suction in
the first stage. The liquid pumped is condensate at 100°F and the nominal flow is 1180 m3/h. The
shaft failure is located in the sealed area of the first stage. The shaft was made of martensitic
stainless steel AIS1 410 and has a diameter of 4.5 in.
In the original design. the first stage sealing was performed by a bronze bearing. It is well known

* Corresponding author. Tel.: + 34-9 1-346-6000; fax: + 34-91-346-6005; e-mail: martasg@,ciemat.es

Reprinted from Engineering Failure Analysis 6 (5), 337-353 (1 999)