strap analysis.pdf

7/29/2019 STRAP analysis.pdf

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STEAM TURBINE RISK ASSESSMENT

PROJECT: Inspection and OverhaulsOptimization of Steam Turbines

John W. BiggsSenior Project Manager

Stone Container Corporation1979 Lakeside Pkwy, Suite 300Tucker, GA 30084U.S.A.

G. Mark Tanner, P.E.Senior EngineerRadian International LLC8501 N. Mopac BlvdAustin, TX 78759U.S.A.

ABSTRACT

John A. Latcovich, Jr.Fleet Mgr - Rot. Equip.

Hartford Steam BoilerInsp. & Insurance Co.One State StreetHartford, CT 06102U.S.A.

There is a trend in the pulp and paper industry, as well asin other heavy industries, to increase the time betweenoverhauls of machinery, particularly steam turbines. The

primary driving force behind this tendency is the desire toreduce direct overhauling and inspection costs. The basisfor justifying additional overhaul and inspection work issometimes expressed by machinery engineers as a risk offailure. This risk is not easily quantified and may not beunderstood by managers responsible for these budgets. TheSteam Turbine Risk Assessment Project (STRAP) wasinitiated to develop a methodology and model for

addressing the optimization of overhauls by identifying andquantifying the risk of failure associated withmaintenance, operation, and engineering practices appliedto steam turbines. The process is an adaptation of theASME Risk-Based Inspection Guidelines and has beenused previously on a project for utility steamturbine/generators. This paper details development of theSTRAP model, demonstrates the application of this modelin evaluating a turbine, and displays the results achievedthrough testing of the analysis. The STRAP model isincorporated into a computer program that allows what ifscenarios for individual turbines to be evaluated on acost-risk-benefit basis. These results are then used to

optimize the overhaul and inspection process.

INTRODUCTION

Most engineers in manufacturing are now used to hearingphrases like profit and loss statement, stockholdersdemand for return, time value of money, data driven,just in time, return on investment, etc. Engineers in

the pulp and paper industry have also had to become usedto working in an industry that experiences large swings inthe market that over the past few years has become evenfaster and more severe. Business and accounting factorsare now a major part of the machinery operation andmaintenance business as a result of the need to reduce thecosts of operating manufacturing facilities while,

maximizing production and minimizing productioninterruptions (increasing availability). All of these factorscoupled with the capital intensity of the pulp and paperindustry, demand that the industrys manufacturing capitalassets be managed using the best engineering andmanagement practices.

Planning and justification of maintenance overhauls ofsteam turbines in the pulp and paper industry is a goodexample of these new concerns. An overhaul of a largeturbine (greater than 20,000 horsepower) may cost severalhundred thousand dollars. There is also a considerable costin lost paper production since most mills must shut down at

least a portion of the manufacturing process during atypical 15-to-20-day turbine turnaround. The alternativeof maintaining full production during a major turbineoverhaul requires purchased power. Many mills, however,do not have an adequate utility tie to offset the lost power;even if they do have the utility tie, the purchased power costis considerably higher than self-generated power.

On the other hand, failure to perform a scheduledinspection and overhaul in time, it can lead to unexpecteddeterioration of the turbine and the need to extend theduration of the turbines planned overhaul to completerepairs or even to turbine failure and an unexpected outage.Both of these scenarios present the possibility of greatlyincreased expenses, running from hundreds of thousands tomillions of dollars.

Thus, regardless of whether a turbine is driving apowerhouse generator, a paper machine line shaft or otherpieces of critical equipment, the maintenance engineermust employ the best available practices in prioritizing,scheduling and justifying turbine maintenancerequirements.

PROBLEM

There are currently no, or at best very limited, industryguidelines on which to base turbine inspection and overhauintervals. Vendor recommendations are available but areoften very conservative because they fail to fully considerthe economic consequences of an inspection and overhaul.There is a trend to extend the intervals based on costconsiderations.

1997 Engineering & Papermakers Conference /9


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strap analysis.pdf

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