process risk reliability book chapter 7 reliability availability maintainability

7/30/2019 Process Risk Reliability Book Chapter 7 Reliability Availability Maintainability

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Relia bility, Ava ila bilityand MaintainabilityCONTENTS

.............347of a RAM program....... ................34gand safety.... ...............3sl....352Modes .....35sRates" ...........356Distribution. . . . . . . . . . . . . . .35gailure Rate Data........ .............364Probability/Bayes' Theorem. .....364

Availability, and Maintainability (RAID pfogfams are anintegral part of anymanagement system. -RAM techniques possess many similarities to those used forthat were discussed in chaptet" < ^ia 5. However, ,rr.t.f difference betweenand safery analyses is that itls possible to talk about optimum reliabiliry i.e., theat which a dollar spent on improving reliability leaos to less than a cost-avefagedin benefits, as ilrustrated k nig.rr."7.t. \rith safety, however, there is no realyalue; all incidents are unacceptable.Figure 7.1 shows that as funds are initiaily expended on improved reliab'ity, thefevenue is greater than the money spent (when factored over the normalinvestment period). However, there is an optimum point, above which a d,ollaron improved reliability generates less than a dollar ir, iir" cycle incremental(i.e. the srope of the curwe becomes lessthan uniry). r" f.u.rr.., there is rarerydata to be abre to develop a curye such as Figure 7.1 with precision. Never_it is usefur to keep in mind that a reliabirity prog.um is not, in and of itserf, itsjustification' It has to demonstfate that an investment in reliability will lead to anin profits.Figure 7'2 shows three causes for losses. The first is that the sales of the product areEven though the facility can make product, the market is not buying it, so ratesto be cut back' The second cause in nlgure 7.2 is todo with scheduled turnaroundswhich equipment that cannot be mlintained while it is operating is workecl on.asset integrity program may help reduce the amount oiri-. needed for suchRisk and Reliability ManaeementO 2010, Ian Surton. publishecl by Elsevier Inc. AII righrs resened. 347


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CHAPTER 7 Reliability, Availability and Maintainability

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FIGURE 7.1Reliability Payoutturnarounds but they are not usually part of the RAM process.) Non-sc:.,:the third element in Figure 7.2, are the focus of this chapter.Naturally, it is not possible to identify and correct all possible cau:.: ,,:loss. Therefore it is suggested that the pareto principle (described in ch,::- *to flnd and correct the major problem areas, as shown in Figure 7 .3. The r ,crs {on flnding and correcting the important few factors that contribure :scheduled downtime, and ignoring the unimportant many.BENEFITS OF A RAM PROGRAMThe benefits of an effective RAM program include the following:I Increased Production

A reliable facility will make more money because it will operate for lr-::.Er:of time . The extra production will increase revenlles (assuming that the i:r.-ii

FIGURE 7.2Loss Categories

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Benefits of a RAM program 349

FilTURE 7.3

sell all that it makes). Furthermore, the incremental production is very profltabrebecause all of the fixed and semi-fixed costs of production such as rents andsalaries will have been covered by the base-line production.I Increased profitabilityFigure 7.4 shows a faclity where the first 9O% of theproduction covers fixed andsemi-fixed costs such as payro', taxes, equipm.nt d.pr..iation, and rent4easepayments' It is in the range go% to roo% that the profits are made. Therefore, ifavailability can be increased by ,,only,, l%, frombSy" ,o 9G%, profitability willincrease by 2O%.

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7.4and Profitabiliiy


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350 CHAPTER 7 Reliabitity, Availabitity and Maintainabitityr Increased ProductivityAn unreliable facility will experience increased losses, most of *-i::i ,.shutdown and re-start, for reasons such as flaring of waste gases :: -- ..spec products, and reduced reactor selectivities. such situations 1 . , r:rL i:a loss of materials but also create an increase in energy consumpti,::_ :,:-.].equipment items will have to be cooled down and then re-heare : JlLuitems such as pumps, compfessors, and fired heatefs have to "r..:even thoLrgh they are on total recycle.r Minimal InvestmentProductivity improvements can often be achieved with minimal ;.;1.q;example, a pump in production-critical service may fail once eref-. --:-::-:If each pump failure leads to production losses of $ 15,000 then the --- uii"this problem is $60,000. Investigation into the pump failures shos s ::; urr!,,..down rate could be greatly reduced if a preventive maintenance S1'Sir:: ir, 111,1yimplemented, so that problems can be addressed before the pump ".- . ilii,is predicted that the new failure rate will be once per year, equi\-alr:: iji$15,000 per year. Hence the annual savings that flow from thi pre\--:.,, :

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nance pfogfam ate $45,000. If the preventive maintenance system .i, : -r;iilcosts say $10,000 to implement and $5,000 per year to run, then trr ::.over a period of five years is $190,000 (ignoring the discounted r-al::and the return on investment is very high indeed.Reduced Maintenance CostsW.hen a facility operates smoothly, the cost of maintenancefewer spare parts will have to be purchased, and labor coststime - will be reduced.

goes i -;, lReduced InventoriesThe response to reliability problems is often to increase the number ,-,and the qlrantify of raw materials. As reliability improves, these invenireduced.

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production frc,:plans to builc t:,_: ;Reduced Capital CostsIf the RAM program is effective at squeezing moreequipment, it may be possible to postpone or cancelfacilities.Customer SatisfactionA facility that operates reliably will have more satisfied customers bec._..:will be fewer problems with off-spec products and missed deliven- dart:Personal RecognitionManagers recognize that a smoothly operating facility makes them look g,-, ,_ iT :ltilr]r,eyes of their bosses, whereas frequent upsets and shutdowns reflect neg:=, : i 111tithe perception of a manager's competence. This insight was recognize : :, ,r*il,rr,,facility manager when he was evaluating some reliability software. Hi r,-r,r rfiri,,the software salesperson, "I see what yoll're selling - you're selling job se _--,.*:r,Moreover, when a facility is running smoothly, a manager has time to der-e1 .: r{r,${{and positive programs that develop both his or her own career and the cer..:*. ittrrj

process risk reliability book chapter 7 reliability availability maintainability

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