The cooling water pump has been running reliably for years. Until one Friday afternoon the mechanical seal fails, water runs into the motor and half the plant is down. Afterwards someone says: \u201cIt was obvious that the seal would start leaking at some point.\u201d It was obvious \u2013 but nobody had thought systematically beforehand about what would happen then.<\/p>\n
That\u2019s exactly what FMEA is for. The method forces a team to ask in advance: what can fail on this equipment? What are the consequences? And how likely is it that we will notice the fault in time?<\/p>\n
In this article you will learn how an FMEA works in maintenance, how to assess risks using the RPN or action priority, and what a concrete FMEA example looks like. You will also read which mistakes turn an FMEA into a mere paper exercise.<\/p>\n
FMEA stands for \u201cfailure mode and effects analysis\u201d. It is a structured, preventive method. A team breaks a product, a process or a piece of equipment down into functions and components and examines for each element:<\/p>\n
Internationally, the standard IEC 60812<\/strong> describes how to carry out an FMEA. In the automotive industry, the joint AIAG\/VDA FMEA Handbook<\/strong> is widespread, and its approach is often used as a template outside the sector too.<\/p>\n In maintenance, the FMEA mainly answers one question: which failures are so critical that we need to take preventive action \u2013 through inspection, servicing, condition monitoring or spare parts stocking?<\/p>\n The AIAG\/VDA Handbook divides the FMEA into seven steps. This structure transfers well to equipment:<\/p>\n For each combination of failure mode, effect and cause, the team assigns three ratings, usually on a scale from 1 to 10:<\/p>\n Important: for detection, a low<\/em> value is good. A 10 means that the fault goes unnoticed until the effect occurs.<\/p>\n Traditionally, the three values are multiplied: RPN = S \u00d7 O \u00d7 D<\/strong>. The RPN therefore lies between 1 and 1,000. The higher it is, the more urgent the actions.<\/p>\n The RPN is simple but has a well-known weakness: identical numbers can mean very different risks. A cause with S = 10, O = 2, D = 5 gives an RPN of 100 \u2013 exactly the same as S = 2, O = 10, D = 5. In the first case a serious effect is looming, in the second a frequent but harmless fault. If you sort by RPN alone, you can overlook a serious risk.<\/p>\n The AIAG\/VDA FMEA Handbook therefore replaces the RPN with action priority<\/strong> (AP). Instead of multiplying, a table assigns each combination of S, O and D to one of three levels: high<\/strong>, medium<\/strong> or low<\/strong>. Severity carries the most weight, followed by occurrence, then detection.<\/p>\n IEC 60812 also describes other ways of prioritising risks besides the RPN, such as a criticality matrix of severity and occurrence. Decide in advance which method you will use and apply it consistently across the whole site. Whatever the method: failure effects of very high severity, for example for safety or the environment, always deserve separate consideration.<\/p>\n The following fictitious example shows an extract from an equipment FMEA for a centrifugal pump in the cooling circuit. The ratings are illustrative and in practice depend on your equipment and your rating catalogues.<\/p>\n The mechanical seal stands out: serious effect, moderate frequency and hardly any way of noticing the fault in time. Possible actions are:<\/p>\n After implementation, the team reassesses. If, for example, detection drops from 7 to 3, the RPN falls from 280 to 120. If you work with action priorities, you reclassify the new combination according to the AP table.<\/p>\n A good FMEA doesn\u2019t end on the form. Its results feed directly into day-to-day work:<\/p>\n Many companies shy away from FMEA because it sounds like weeks of work. To get started, a manageable framework is enough:<\/p>\n After the first round you will have a prioritised list of actions. Implement the three most important ones first and reassess after a few months whether the failures have changed.<\/p>\n The FMEA often shows that the biggest risk isn\u2019t the failure itself but the time until a replacement arrives. On older equipment in particular, some parts are discontinued or only available with difficulty. In that case you should look for alternatives early \u2013 not once the plant is already down.<\/p>\n KTB Europe is a family business from Hamburg and has been sourcing spare parts of all brands worldwide since 1976. You can send us an enquiry with a part number, nameplate photo or description. For discontinued parts, we look for suitable alternatives. Find out more on our pages about spare parts management<\/a> and discontinued parts<\/a>. Related reading: how to measure failures with MTBF and MTTR<\/a> and how to transfer the FMEA results into a maintenance plan<\/a> .<\/p>\nWhat types of FMEA are there?<\/h2>\n
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FMEA in maintenance: the process in 7 steps<\/h2>\n
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Assessing risk: severity, occurrence, detection<\/h2>\n
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\n \nCriterion<\/th>\n Question<\/th>\n 1 means<\/th>\n 10 means<\/th>\n<\/tr>\n<\/thead>\n \n Severity (S)<\/td>\n How serious is the effect?<\/td>\n barely noticeable<\/td>\n danger to people or the environment<\/td>\n<\/tr>\n \n Occurrence (O)<\/td>\n How likely is the cause to occur?<\/td>\n practically never<\/td>\n very often<\/td>\n<\/tr>\n \n Detection (D)<\/td>\n How reliably is the fault detected before the effect?<\/td>\n reliably detected<\/td>\n practically undetectable<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n The risk priority number (RPN)<\/h3>\n
Action priority (AP)<\/h3>\n
FMEA example: cooling water pump<\/h2>\n
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\n \nComponent<\/th>\n Failure mode<\/th>\n Effect<\/th>\n Cause<\/th>\n S<\/th>\n O<\/th>\n D<\/th>\n RPN<\/th>\n<\/tr>\n<\/thead>\n \n Mechanical seal<\/td>\n leaking<\/td>\n water in the motor, cooling down<\/td>\n dry running at start-up<\/td>\n 8<\/td>\n 5<\/td>\n 7<\/td>\n 280<\/td>\n<\/tr>\n \n Pump rolling bearing<\/td>\n bearing damage<\/td>\n noise, later seizure<\/td>\n insufficient lubrication<\/td>\n 7<\/td>\n 4<\/td>\n 4<\/td>\n 112<\/td>\n<\/tr>\n \n Motor<\/td>\n overheating<\/td>\n motor protection trips, downtime<\/td>\n fan cowl dirty<\/td>\n 6<\/td>\n 3<\/td>\n 3<\/td>\n 54<\/td>\n<\/tr>\n \n Coupling<\/td>\n wear on the spider\/gear ring<\/td>\n impacts, consequential damage to bearings<\/td>\n misalignment<\/td>\n 6<\/td>\n 4<\/td>\n 6<\/td>\n 144<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
What the FMEA brings for maintenance and spare parts<\/h2>\n
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How to start your first FMEA without a lot of effort<\/h2>\n
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Typical FMEA mistakes<\/h2>\n
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When critical parts are hard to get<\/h2>\n