Risks in power plant APPLYING ENGINEERING CONTRACTOR ...

Risks in power plant

OMMI (Vol. 1, Issue 3) December 2002

APPLYING ENGINEERING CONTRACTOR SKILLS TO MANAGE AND MITIGATE RISKS ON POWER PLANT D J Irving, Mitsui Babcock Energy Limited, Renfrew, UK

(Eur Ing) David Irving has over twenty years experience in the energy industry, the vast majority being spent with Mitsui Babcock, and with most of his work having been associated with mechanical integrity. In Mitsui Babcock he is mainly involved in the provision of specialist technical services, aimed at assisting energy plant operators plan and implement operations and maintenance strategies to maximise plant life, optimise reliability and comply with legislation (e.g. emissions, safety). He has also been involved in negotiations for plant rehabilitation and upgrade projects. His current position is Sales and Business Development Manager, with particular responsibility in a number of technology based business streams which address integrity issues throughout the thermal power, nuclear and oil/gas sectors.

ABSTRACT This paper describes how Mitsui Babcock, the UK based energy products, services and business solutions provider, is assisting asset owners and operators to reduce technical and commercial risks to their businesses. Examples are provided of work being carried out to mitigate the risk of plant failure using design assessment, risk based strategies, and physical testing. Information is included on how imaginative commercial arrangements (such as self financing schemes) between engineering contractors and asset owners/ operators, can contribute towards reducing business risk. 1. INTRODUCTION As commercial pressures on power plant operators increase, more attention is being focussed on the measures which can be taken to manage and mitigate technical and business risks. Technical risk management tends to concentrate on the prevention of plant failures, which can cause unscheduled downtime, safety incidents and loss of income. Actions to minimise such threats typically comprise development of risk based maintenance and inspection strategies, together with design and operation reviews, and analysis of the likelihood and consequences of failure. Such analysis is often backed up by detailed condition assessments and inspections, reviews of operation and maintenance histories, and design (code based or by analysis e.g. finite element). Full scale physical testing in controlled environments can also be appropriate when analytical design does not provide sufficient reassurance that plant will operate reliably and safely. The suitability of these strategies can vary depending on a number of factors



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including operating regimes and demands of licensing authorities and regulatory bodies. Business risks which may adversely affect profitability can be more difficult to identify and therefore more difficult to quantify and manage. Any aspect of an asset’s operation which limits output from design conditions is a business risk, but justification to devote resources to address such issues can be very difficult. The situation often demands a step out in faith to encourage those involved to explore where improvements could be made, without introducing additional risk. A constructive working relationship between the asset owner and other organisations with appropriate specialist skills can contribute greatly to improving the business performance and mitigating risks to mutual benefit. Historically, the suppliers of equipment, services and turnkey project capability have concentrated on protecting their own business interests when bidding and executing contracts. However, the development of closer working relationships between contractors and asset owner operators has increased in recent years, either through long term alliances or one off projects, to the point that contractors are encouraged to share risk and benefit from client success throughout the life cycle of the assets. 2. MINIMISING TECHNICAL RISKS 2.1 Thermal Plant Design and Operation Reducing the threat of unplanned plant failure is one of the main priorities of asset owners and new measurement techniques continue to be developed (Ref 1). Technologies which relate the mechanics of potential failures to risk analysis models have resulted in a number of tools being commercially available. To be effective, these tools must be able to accommodate variations in plant operation and maintenance strategies as well as the actual and predicted trading conditions which could influence plant reliability. Their success is also dependent on the correct fundamental engineering principles being applied. One particular threat to thermal power plant is a requirement to operate in cyclic modes, usually due to changes in electricity trading arrangements or fuel prices, when the plant was originally designed for base load operation. Many OEMs have standardised designs at the cost of flexibility in order to remain competitive, and market pressures are now testing their designs through gas turbine upgrades and cycling. Frequent start ups and shut downs lead to thermal transients which can damage pressure parts, casings and structural members, as well as creating process difficulties such as an increase in condensate formation during start up purges. The integrity of the plant can be further jeopardised depending on which design codes have been applied with, for example, the value of full header to tube welds as opposed to partial penetration welds now being taken more seriously. Figures 1 and 2 summarise the main issues which can be troublesome on CCGT plant. Potential difficulties on utility boilers can be similar in nature, especially where there are significant thermal gradients throughout the circulation paths, which are a typical cause of tube failures. The risk of lost availability, and the consequential penalties in certain trading markets, needs aggressive management.



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1. Pump life 2. Dew point corrosion 3. Common header dam plate bending 4. Inadequate drains, failure or control issues 5. Tube bank dry out/ vibration 6. Header cracking 7. Pipework Fatigue

1. GT ramp rates 2. EGT 3. Gas

S

1. Hot liner pin failures/ casing leaks 2. Hot casing leaks 3. Expansion Joint stiction / leaks

Figure 1: Horizontal Tube Bank/Assisted Circulation – Forced Outage Risks

1. Dew point corrosion 2. Common header dam plate bending

ST

1. Pipework Fatigue 2. Header cracking 3. Tube bank dry out/ vibration 4. Inadequate drains, failure or control issues

1. Hot liner pin failures/ casing leaks 2. Hot casing leaks 3. Expansion Joint stiction/leaks

Figure 2: Vertical Tube Bank/Natural Circulation Forced Outage Risks



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Mitsui Babcock has developed a risk based approach to identify the aspects of the plant which may require modification to ensure safe and reliable service during periods of cyclic operation (Ref 2). Optimisation of operational procedures especially during transients is also integrated into the assessment. Mitsui Babcock apply a health check approach, which comprises a combination of reviewing the design, the historical operating conditions, and the current condition. Table 1 shows a typical likelihood and consequence analysis and Figure 3 provides an overview on a typical power plant of how priorities can be presented, with certain issues being generic in nature and others more plant specific. This risk based approach has proved invaluable as a rationalisation and prioritisation tool, ensuring resource is devoted to the areas which really are at risk. Owner operators can use the results of this approach to plan their long term strategies for the asset, while also minimising difficulty gaining insurance cover.

Table 1: Typical likelihood and consequence analysis Likelihood (L) High

Medium

Low

Time L>70% Immediate Shutdown with up to 3 months lost availability 30%$100K

10%