CASE STUDY: Development of a Spreadsheet Tool for ALARP Assessment and Cost Benefit Analysis of Boiler Tube Inspections

Risk Assessment Consultancy

Client: E.ON

Following a cold formed bend (CFB) boiler failure which led to a high pressure steam release at UK’s Ratcliffe Power Station in 2006, the UK Health and Safety Executive required that a minimum of 25% of cold formed bends should be inspected at all coal fired power stations. However, this policy did not take into account the variations in design and operating experience between power stations and could potentially lead to widely differing inspection costs as well as differences in probabilities of CFB failure.

In 2013 GENSIP1 sought to explore the impact of inspection costs and CFB failure probabilities by funding a project to develop a tool for the CFB ALARP Assessment and Cost Benefit Analysis in accordance with GENSIP Good Practice Guidance. Egerton Consulting was commissioned to produce a simple spreadsheet tool to help optimise CFB inspection strategies at each power station.

Power Station with Pylon

Egerton Consulting liaised closely with specialists at E.ON and RWE nPower to establish those factors that have a significant impact on the probability or consequence of a CFB failure. These factors were then incorporated as data inputs into a spreadsheet model designed to calculate whether or not the inspection of a defined population of Cold Formed Bends (CFBs) justified, within the context of ALARP, the costs given the risk reduction that were likely to be achieved.

The CFB population considered within the spreadsheet could be as large or as small as the analyst chose. Similarly, the data set on which the assessment was based could be general (e.g. sampled from the entire population of CFBs across all coal fired power stations in the UK) or focussed (e.g. sampled from an individual boiler or area within a boiler).

Factors taken into account within the spreadsheet model included:

  • Any commercial benefits that could be expected from actions taken primarily to manage safety
  • The benefits through inspection of averting significant interruptions of production by detecting potential CFB failures and preventing their occurrence
  • The on-going costs of continued engineering actions that could be introduced to reduce the risk of CFB failures.

The CFB spreadsheet model enabled Coal Generators to better understand which coal fired boilers were at greatest risk of CFB failure and to estimate on a unit by unit basis the probability of such failures and the cost of their occurrence. As a result, station managers became better informed as to the risks to which they were exposed and whether those risks were cost effective and ALARP compliant.

GENSIP (Generators Safety and Integrity Programme) is funded by the Coal Generators Forum to address generic plant safety and integrity risks associated with ageing UK Coal Fired Power Stations through the development and implementation of appropriate good practice solutions. This is achieved by sharing awareness and expertise across the industry, and through the commissioning of specific R&D projects and initiatives.