Extending Criticality Analysis in order to Consider Derating and Degradation Timót Veér, Olav Bolland Inst. for Energi- og Prosessteknologi, NTNU Naturgass Seminar, April 2003. Naturgass Seminar - 23. April 29/05/2019

Topics of this presentation Introduction, terms used herein Failure mode and effects analysis, FMEA Failure mode, effect and criticality analysis, FMECA Progressive loss of performance in FMECA Conclusions Naturgass Seminar - 23. April 29/05/2019

What is failure? Def: failure is the termination of the ability of a system/subsystem to fulfill its designed duties. Generally, the failure is considered the end effect of a failure mode resulting in outage. Naturgass Seminar - 23. April 29/05/2019

Brief regularity nomenclature Regularity is a term used to describe how a system is capable of meeting demand for deliveries or performance. Failure rate, the frequency of occurrence of the current failure mode. Failure mode, describes the way a failure occurs and its impact on equipment operation. Failure effect, consequence of failure upon operation, function or status of an item. Criticality is a relative measure of the consequences of a failure mode and its frequency of occurrence. Naturgass Seminar - 23. April 29/05/2019

What is FMEA/CA? FMEA – failure mode and effect analysis (EA) Maps the end effect of different possible failure modes of the subsystems FMECA – failure mode, effect and criticality analysis (CA) In addition to EA, it assesses the criticality of individual failure modes. Naturgass Seminar - 23. April 29/05/2019

Failure mode and effect analysis - FMEA Identifies the possible failure modes and the interrelationship between indenture levels – from cause to end effect. Naturgass Seminar - 23. April 29/05/2019

Failure mode, effect and criticality analysis – FMECA Criticality analysis intends to support the ranking of the failure modes. Qualitative as well as quantitative approaches are employed. Basic qualitative approach to criticality assessments Naturgass Seminar - 23. April 29/05/2019

Classical quantitative FMECA Inputs: lp [f/Mh] : part failure rate, number of failures of the part/subsystem during the considered time span a [%]: base failure rate, fraction of the part failure rate related to the particular failure mode under consideration. b [%]: conditional probability is probability that the failure effect will result in the identified criticality classification, given that the failure mode occurs. Criticality number: Cm = lp a b t ; whereas: Cm [f] : criticality number of the considered failure mode m, t [h]: time span. Naturgass Seminar - 23. April 29/05/2019

FMECA table – antisurge valve failure Criticality number: Cm = lp a b t ; Naturgass Seminar - 23. April 29/05/2019

What is derating/degradation? Derating and degradation are main causes of progressive performance loss (e.g. fouling, erosion, wearing, ambient effects, etc…) Base line is considered the performance of the regarded system in state definable as ”new and clean” Naturgass Seminar - 23. April 29/05/2019

FMEA – fouling, a typical case of derating The mechanism of fouling of a GT due to airborne particles: Naturgass Seminar - 23. April 29/05/2019

Quantitative CA in case of fouling Equivalent derated hours (EDH) Reflects the ratio of the derated energy amount and the current net capacity of the system plus the sum of the outages due to the considered derating cause: = = Naturgass Seminar - 23. April 29/05/2019

FMECA table – results Naturgass Seminar - 23. April 29/05/2019

Conclusions Extension of traditional FMECA to progressive performance loss was proposed Examples from GT operation are given for CA in both cases It is shown the relative importance of the progressive performance loss vs. traditional failure Naturgass Seminar - 23. April 29/05/2019