Boiler Tube Leak Study

7/31/2019 Boiler Tube Leak Study

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World Energy Council Performance of Generating Plant 2004 Section 6: CASOM 1

CASOM 23: BOILER TUBE LEAK STUDY

PART 2

Robert R. Richwine

Reliability Management Consultant

LAST MONTH

In last months case study we summarised part of a study performed by NERCs GeneratingAvailability Trend Evaluation (GATE) Working Group in which we demonstrated that the

reduced unavailability due to boiler tube leaks experienced in newer power plants was due to

vintage effects rather than aging of the older plants and was strongly correlated to learningcurve theory. This month we will continue summarising that study by considering possible

areas where learning could have been incorporated into the design, construction plus the

operations and maintenance programmes of the newer plants that could have contributed to

their improved performance. In addition we will examine statistical evidence that suggeststhat although the older plants might have more difficult challenges, nevertheless some are

meeting those challenges and are achieving performances that are close to the top performers

in the recent vintage class.

LEARNING

If learning explains the superior reliability of recent vintage plants what changes in design,

construction or Operations and Maintenance might be responsible? Discussions with

knowledgeable industry experts identified severalpossible areas:

DESIGN

Newer units have had much larger volume boilers with lower heat release rates; Specifications for older units were made during times when utility emphasis was on

lowest initial cost;

Older units had operational problems when using lower quality coal that originallydesigned to burn;

Design of the older, first generation large units was scaled up from versions of smallerunits;

High load growth during years when older vintage units were being designed meant shortcuts were used during the design process;

Old sub critical units had circulation problems that have largely been eliminated in morerecent designs;

Boiler tube metallurgy has been improved; Increased involvement and influence by operations and maintenance staff during the

design and procurement stage;

Improved steam condition control systems.

Section 6: CASOM 23 Pg. 1


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CONSTRUCTION

Newer units have benefited from:

Better construction management; Increased quality assurance/control; Reduced site welds and total welds; Greater involvement and control by owners/operators on boiler construction techniques.OPERATIONS AND MAINTENANCE*

Newer units have also benefited from:

Improved operator training and procedures; Increased monitoring of boiler tube metal temperatures and adherence to design limits; Earlier detection of potential areas for failures; Better water chemistry control; Clearer understanding of root causes of failures; Reduction in operating boiler in overpressure condition to increase output; Improvement in welding techniques and weld verification; Better communication throughout industry on problems and cost-effective solutions.*Although most Operations and Maintenance improvement techniques can be applied to

older units, damage already incurred through poor practices in their early years may havealready reduced the long-term potential reliabilities of these units.

CONCLUSIONS

In last months case study we reached the conclusion that vintage effects were more likely to

explain the superior reliability of newer plants than aging effects of the older plants. Does

this result mean that we must be satisfied with poor performance of older plants? Absolutelynot!!! Some interesting statistics support this answer.

There is a very large variation in the performance of the older units such that even though theaverage older unit is much worse that the average newer unit there are still a large

percentage of older units with very good performance. Figures 1 and 2 display the

cumulative probability distribution of boiler tube unavailability for the older and newer units.



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One striking statistic stands out: more than 1 out of 5 (21%) of the older units are performingbetter than the average value for newer units! This indicates that older units can be good

performers if the necessary steps are understood and taken. A survey of companies with older

units in the good performer category revealed that their units good performance was noaccident. Rather it was only through commitment and consistent application of resources

(money, time, manpower) that these results were achieved (see our case studies for Jan April 2003 for a detailed discussion of this successful process).

Another important factor contributing to superior performance of top units is application of

the work that the Electric Power Research Institute (EPRI) has done to identify the root cause

and possible solutions for almost all boiler tube failure modes. Case studies of some of theapplications of this work have shown that a company can be successful if they are persistent

in their pursuit of good performance andrefuse to accept less.

References:

Richwine, R.R., Lofe, J.J., Mills J.B.,Boiler Tube Failure Trends.

Boiler Tube Leak Study

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