Quality of maintenance

Many accidents have occurred because maintenance work was not cai -ried out in accordance with the (often unwritten) rules of good engineering practice, as the following incidents and Section 10.4.5 show. 

The correct way to break a joint is to slacken the nuts farthest away from you and then spring the joint faces apart, using a wedge if necessary. If any liquid or gas is present under pressure, then the pressure can be allowed to blow off slowly or the joint can be retightened. 

It was not a good idea to use a crane for a job like this on a line full of process material. Fortunately the leaking vapor did not ignite, although 

Section 2.11.1 describes an explosion caused by the failure of nuts that had been tightened with excessive force. 

Nobody knows why this had been done. Probably one nut was tighter than the other, and in attempting to tighten this nut, the whole stud was screwed through the second nut. Whatever the reason, it produced a dangerous situation because the pressure on different parts of the flange was not the same. 

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Number of call-backs (or percentage of craft rework) Measures the quality of maintenance repair work and provides one key indicator for maintenance customer service. It helps focus on doing the repair right the first time. 

A subtle, but very important, common cause effect concerns the availability and quality of maintenance personnel and of replacement parts. If a facility has only one crew that can repair pumps and both P-IOIA and P-IOIB were to fail at the same time, then the repair times provided in the example would be overly optimistic. 

Deterministic analysis is basically quite simple either an equipment item operates as required, or it does not. Yet real-world actual equipment performance is usually much more complex. For example, it may be found that the availability of Pumps, P-101 A/B in the example depends on the service in which they are operating. Factors such as the viscosity of the fluids being pumped, ambient temperatures, and the quality of maintenance will affect the performance of the pumps, often in ways that are difficult to model mathematically. 

Visit a location where the culture demands good safety practice and immediately, from the appearance of the exterior premises, you will get a feel for the quality of maintenance. That isn t necessarily an absolute indicator, but the opposite is almost always tme if the exterior of the premises is shabby, safety maintenance will likely be inadequate. In the best operations, cleanliness is truly a virtue, maintenance schedules are adhered to, and personnel are encouraged to report on and seek elimination of hazards. 

Warning signs, labels, and instmctions have been partially effective. Warning systems are reactionary. They alert persons only after the development of a situation for which a hazard s potential is in the process of being realized (e.g., the smoke alarm in a house). Warning system effectiveness relies considerably on training, the quality of maintenance, and people reactions. 

It is extremely difficult to determine frequencies of occurrence for the loss of containment (leaks and ruptures). These frequencies depend on the size and length of pipes, the number of valves, the design of vessels and other medium containing components (e.g. pump casings). An important part is also played by the number of elbows, flanges, pipe branches, instrumentation ports etc. The properties of the medium involved, the pressures and temperatures just as their variations with time are of relevance, too. The frequency and quality of maintenance should also not be forgotten. 

The PFDo is influenced by a number of assumptions about the future operating and environmental conditions, the quality of maintenance, test coverage and efficiency of testing, and deterioration mechanisms of the SIS components (Limdteigen and Rausand 2007 Limdteigen 2009). 

Quality of maintenance of the tool (sufficient V-ring height and force, correct radius on die plate, correct punch and die clearance)... 

Equipment failure rates, and the quantity and quality of maintenance (e.g., the level of expenditures on preventive maintenance) ... 

Equipment failure rates and the quality of maintenance, including their relationship to accident rates. 

Materials of construction/quality of maintenance materials and parts... 

Key issues in determining the achieved life of equipment are the quality of maintenance, and environmental issues. Furlheimore, the age of equipment at which it changes from exhibiting random failure rates (i.e., the flat portion of the bathtub) to accelerating (or aging) failure rates will differ for different types of elecirical and I C equipment. 

CP systems, and so forth, the factors which affect pipeline life include nature of the product, nature of the external environment, operating conditions, and quality of maintenance. Regular inspections to assess the rate of change in physical condition provide a more accurate assessment of how much longer a pipeline can be expected to operate safely and productively. These inspections may also provide the essential information to plan for remedial action if the estimated life is below requirement [6]. 

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