Risk Management - Taking the pressure01 February 2005

Before 1989, the Factories Act 1961 detailed the requirements for the examination of, and reporting on, steam and air plant within the power industry by the Competent Person (often the insurance company). Where water tube boilers were concerned, the Competent Person typically reported on three main components: the economiser, the boiler and the superheater. Inspections carried out to certify a boiler would include advice from technical bodies - in-service specialist bodies. Examples of these bodies today include E.ON's Power Technology division and RWE Innogy's specialist staff, based at Swindon.

1989 saw the introduction in the UK of the Pressure Systems and Transportable Gas Containers Regulations. These brought about major changes concerning the inspection and certification of pressure plant, and came about following the major failure of a pressure system at Flixborough in 1974, which resulted in 28 deaths, 36 injuries and damage to 2,000 buildings.

The Regulations describe the process of 'authoritative review', which presents all the facts relevant to a specific system. A system's history, operation and maintenance, combined with an examination of all the potential failure mechanisms, are reviewed together. In this way, the decision to increase the periods between inspections can be safely taken, but only at the time of the Thorough Examination.

Following authoritative reviews, many coal-fired power stations were able to extend the intervals between Thorough Examinations from 38 months to 50 months. When deciding which parts of the plant should be inspected, the Competent Person was supported by the technical body.

On 28 December 1996, an event occurred that was to cause concern within the power industry: the header on a sixth stage superheater failed at one of the power stations insured by Royal & SunAlliance: the end plate became detached from the shell.

The superheater had been constructed from a relatively new material to the industry - F91 steel (forged modified 9Cr steel) - which had also been used in plant that was running at other power stations. While the header in question had been designed for a minimum of 150,000 hours' operation, it had failed after only 36,500 hours.

The material was known to be susceptible to Type IV cracking - cracking located in the finegrained or intercritical heat-affected zone next to a weld - and so this was thought to be the likely mode of failure. However, only short-term creep tests had been carried out on the header before installation.

After investigation by a number of bodies, it became clear that the failure was due to a number of factors:
- A mixture of elements from UK and US design codes had been used
- The header had a flat end instead of a domed end
- Heat treatment - which was known to be a critical factor in determining the alloy's performance - had been poor
- Commercial pressure to procure a replacement header at minimum cost had contributed to these factors.

As a result, a number of recommendations were drawn up: installed 9Cr steel headers should be tested at outage, and their design reviewed if necessary; and for new headers, care should be taken over heat treatment and the nitrogen to aluminium ratio, and domed ends should be used if possible.

Looking across its power station portfolio, Royal & SunAlliance also recognised that, although a number of components within water tube boilers had been changed over the years because of fatigue and creep problems, this had not always been noted in the Competent Person's examination reports. This made it difficult to track and ensure accurate calculations of creep life.

In addition, Royal & SunAlliance noted other causes for concern within the UK power industry as a whole:
- Recent safety cases showed some power plant was operating above design specifications
- Changes of ownership within the power industry meant a company could operate just one power station, and not have access to the technical support that had been available previously
- Many experienced people within the industry had left. Operators at the power stations did not have the same experience as those who had been employed prior to industry privatisation.
- The technical bodies were now commercial operations, and power stations were comparing their rates and switching technical bodies on cost grounds. One station did this on four occasions within five years.
- The quality of some Competent Persons' inspection reports could be called into question. Some engineer surveyors were reporting on the whole unit in a single examination report.

All these factors caused Royal & Sun Alliance to reconsider the inspection criteria and the reporting of plant at a power station. This coincided with the introduction in 2000 of the Pressure Systems Safety Regulations (PSSR), to ensure compliance with the Pressure Equipment Directive. These replaced the 1989 regulations.

Regulation 7 of the PSSR is entitled 'Safe Operating Limits'. It clearly indicates that a complex system needs a wide range of conditions for safe operation: as well as pressure, these may also include, time, temperature, volumes, flow rates and other parameters, depending on the pressure vessel and how it is operated. In all cases, however, a suitable margin of safety must be included.

Regulation 8 of the PSSR, entitled 'Written Scheme of Examination', states that the Competent Person should use his judgement and experience, based on relevant information, to determine the maximum interval between plant examinations. This relevant information can include safety records, previous history, current condition corrosion, erosion, expected operation, quality of fluids, standard of technical supervision, operation, maintenance, inspection in the user's organisation and the applicability of any on-stream monitoring.

Fortunately, all of this information had already been collected in the authoritative reviews. By bringing the authoritative review up to date, the Competent Person would now have access to all the necessary information and the power station owners could comply with PSSR.

In 2000 Royal & Sun Alliance visited the main technical bodies within the power industry and convinced them of the need to update the authoritative reviews at all stations where Royal & Sun Alliance was the Competent Person. This took place from the outage year 2001.

In the authoritative review process, a power station now provides the technical body with the predicted hours and starts for the next operating period. The technical body will use this information, taking into account previous recommendations, to produce a draft provisional technical review, which will indicate the inspections required. The resulting report clearly highlights safe operating limits, the failure mechanisms and the recommended work to be done at the outage.

Pre-outage meeting

To ensure all parties agree on the level of inspection, the Competent Person, the power station and the technical body meet approximately three months before a main outage. All three parties bring their experience of power station plant to the meeting. The authoritative review is updated after this meeting, ensuring that only inspections that are required are actually carried out. This keeps the cost of inspection, preparation and scaffolding to a minimum.

Under PSSR Regulation 9 'Examination in Accordance with the Written Scheme', the Competent Person is responsible for the examination of the plant and also any other work carried out to ensure the plant is safe to operate. These may be non-destructive tests, metallurgical examination or examinations by technical bodies.

To ensure all information about the results of examinations is captured, the same parties convene a post-outage meeting within 28 days of the float of the boiler safety valves. Any restrictions on plant operation can then be discussed in detail, so that when the examination reports are received by the power station from the Competent Person they are clearly understood.

A very brief document is produced as a result of this meeting, but it covers all the relevant information. The water tube boiler report is divided into sections covering the economiser, drum, water walls and distribution headers, superheater by stages and the reheater by stages. Each stage clearly indicates the Safe Operating Limits. Another benefit of this reporting system is that all the changes in headers within the units are clearly shown. The Competent Person now knows when the headers have been changed due to creep expiry or excessive cracking and when they next require inspection.

This new process has numerous benefits for the owners of power stations:

- They can demonstrate compliance with PSSR. The process also clearly follows the HSE guidance paper Best Practice for Risk Based Inspections as a Part of Plant Integrity Management.
- In the event of a visit by the Health and Safety Executive, the inspector can be shown all the information clearly recorded in the technical review.
- If a change in operation is required - such as more starts or more hours' running - the document can be easily revisited and if necessary further inspections can be arranged. As an additional check, all stations are being reviewed at the midterm point to confirm that no overshoot in starts or running hours will occur. If it looks as if this may happen, the authoritative review is revisited and if necessary additional examinations are completed.
- If an examination needs to be postponed, the technical body, in conjunction with the power station, must make a safety case to the Competent Person. The information needed for this is now clearly documented with issues highlighted in the post-outage meeting report.
- Carrying out the review before an outage enables the correct labour skills and numbers to be resourced.
- The Competent Person's examination reports are understood by all parties - which was not always the case previously.
- The process of the technical review, preoutage and post-outage meetings would clearly highlight to the Royal & Sun Alliance risk engineer that a station is being managed and operated safely. This could therefore contribute to a reduction in premium and excess levels.
- The improved management and safe operation of the pressure plant is likely to reduce the number of accidents. This may result in the reduction of other insurance cover, such as liability insurance.

Recently, the Health and Safety Executive has been investigating a power station. The technical review described above has been shown to be a benefit during this process. Additional comments from the HSE arising from its investigation will be taken into account to improve the process still further.

This article is based on a presentation given by Alan Fitzpatrick of Royal & SunAlliance at the SOE IPlantE seminar 'Maintenance Matters - How Good is Your Strategy?' on 8 December 2004. Alan Fitzpatrick would like to acknowledge the support of RWE Innogy technical staff at Swindon and E.ON Power Technology staff, without which none of this work would have been possible.

SOE

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