The Importance of Pipe Support Inspections for Current Operations and Future Fitness-for-Service Assessments

Introduction

In the intricate web of industrial infrastructure, it is relatively easy for certain components to slip under the radar of routine maintenance. Pipe supports, once considered low-maintenance fixtures, have unfortunately fallen victim to this oversight in many plants. However, recent developments in standards and the evolving landscape of industrial operations are shedding light on the critical importance of regular pipe support inspections.

Historically, pipe supports may have been relegated to a lower priority status within plants. However, with the evolution of standards such as the ASME B31.1 “Power Piping,” overlooking pipe supports is no longer acceptable. This oversight not only poses operational risks but could also lead to significant liabilities for plants. Moreover, as global markets witness modest increases in oil and natural gas production, the demand for in-service uprates of existing facilities has surged, amplifying the importance of thorough pipe support inspections.

The consequences of neglecting pipe support inspections can be dire. Previous experience has shown that, without proper facility pipe walkdowns to confirm current support conditions (e.g., support clamp removed/added to provide flexibility/rigidity or support rigidity change due to damage), fitness-for-service assessment results can be out of concert with reality if only as-built data is used. This disconnect can result in either under- or over-prediction of stresses, putting the asset at risk, particularly if an up-rate in operating conditions is executed. In this article, we delve into why these inspections are crucial for both current operations and future fitness for service assessments.

ASME B31.1 Power Piping Code Chapter VII: Operation and Maintenance

ASME B31.1 now addresses the operation and maintenance of power piping and its supports. While inspection and evaluation methods are acknowledged, they are not detailed. This section of the code concentrates on creep exposed piping, like main steam and hot reheat [1]. Contributing factors to the need for more robust guidance on pipe supports include the fact that deregulation has reduced funds. Furthermore, with new faces in the industry and plants being bought and sold, common industry practice was to neglect pipe supports since they were considered low-risk. Throughout this time, there were many anecdotal stories about being “lucky” and closely avoiding an incident.

The Birth of ASME B31.1 Power Piping Appendix V

Appendix V was added to B31.1 after the Mohave Power Station incident. Mohave was a 1,580 MWe coal-fired power plant located in Laughlin, NV. On June 9, 1985, a 30-in (760 mm) hot reheat line at the Mohave station, carrying steam at 600 psi (4,100 kPa) and 1,000°F (538°C) ruptured, fatally scalding six workers and injuring ten others [2]. Most of the victims were in a nearby lunchroom during shift change. The accident report stated, among several factors, that the line was not routinely inspected, even though the pipe had shifted off supports and distorted because of thermal expansion due to operating temperatures above design specifications. It is implied that if a proper walkdown was conducted and the shifted piping properly noted, a fitness-for-service assessment could have been performed, subsequently flagging that section of pipe for repair or replacement. While nonmandatory, Appendix V does provide guidance on how to maintain critical piping, as it is clearly recognized in the Foreword of this section that B31.1 prescribes minimum requirements for the construction of power piping [1]. However, it does not provide rules or requirements for the determination of optimum function or useful life of the asset (i.e., inspection and fitness for service guidance).