The operating risk controls you use, or do not use, directly impact your equipment reliability, plant maintenance costs and consequently your operating costs and profits
A Physics of Failure Reliability Strategy Analysis is the structured methodology used in Plant Wellness Way EAM to select and place successful risk elimination and risk controls into the equipment life cycle
IONICS PROCESS 3 is selecting and planning the risk controls to be used throughout an asset’s life cycle to eliminate the many causes of equipment failure during operation.
PEW/PWW EAM Course Day 2 – Plant Wellness Way Processes Session 11 – Risk Controls Planning
Plant Wellness Process 3 – Risk Controls
Risk Reduction – Reduce Chance or Reduce Consequence? #1
This slide categorises many of the maintenance and reliability strategies into either Chance Reduction Strategies or Consequence Reduction Strategies. For example, Maintenance Planning and Scheduling is a proactive chance reduction strategy because it aims to control maintenance work so that it reduces the possibility of defects and errors being introduced by the maintainers into the plant and equipment.
Risk Reduction – Reduce Chance or Reduce Consequence? #2
Maintenance Strategy for Risk Management
Maintenance is a risk management strategy. When used as a chance reduction tool, maintenance is an investment spent proactively to prevent failure. As a result it delivers low-cost operation because few things go wrong. When maintenance is used as a consequence management tool it is applied after failure, and so it is wrongly seen as an expense to be minimised. Maintenance used to prevent failures is cheap; when used to repair failures it is expensive. The Figure shows the process used in the Plant and Equipment Wellness Way Methodology to match maintenance strategy for an equipment asset to its business-wide risks.
PEW SOLUTION: Apply Chance Reduction by Proactive Risk Management
The Figure lists some of the current methods available to address risk. The various methods are classified by the Author into chance reduction and consequence reduction strategies. Several observations are possible when viewing the two risk management philosophies. Consequence reduction strategies expect failure to happen and then they manage it so least time, money and effort is lost. The consequence reduction strategies tolerate failure and loss as normal. They accept that it is only a matter of time before problems severely affect the operation. They come into play late in the life cycle when few risk reduction options are left.
In comparison, the chance reduction strategies focus on identification of problems and making business system changes to prevent or remove the opportunity for failure. The chance reduction strategies view failure as avoidable and preventable. These methodologies rely heavily on improving business processes rather than improving failure detection methods. They expend time, money and effort early in the life cycle to identify and stop problems so the chance of failure is minimised.
Both risk reduction philosophies are necessary for optimal protection. But a business with chance reduction focus will proactively prevent defects, unlike one with consequence reduction focus that will remove defects. Those organisations that primarily apply chance reduction strategies truly have set-up their business to ensure decreasing numbers of failures, and as a consequence they get high equipment reliability, and reap all the wonderful business performance it brings.
Equipment Reliability Strategies
Since reliability can only be improved if failure is prevented, the diagram asks what can be done at the various stages of equipment life to deduce the chance of failure occurring. By selecting the right strategies and practices we can mould the chance of failure curve to what we want.
Match Maintenance Strategies to Risk
The maintenance strategies we use need to be matched to operating risk so that by doing them the risk falls.
Where risk is high, proactive strategies to remove problems reduce the likelihood of failure and so lower the maintenance costs from breakdowns. Where risk is low, consequence reduction strategies that happen after failure starts can be applied because the cost of failure is low. Chance reduction strategies are viable in all situations, but consequence reduction strategies must be carefully chosen because they do not prevent failure, rather they only minimize the extent of the losses. Hence using condition monitoring in high risk conditions must be accompanied with rapid response capability to address the failure before it goes to failure.
Maintenance Strategies Matched to Risk Levels
Use a Risk Matrix to Model Impact of Choices | Example: Risk Cost Calculation for Roller Bearing
Putting your risk boundary onto a risk matrix turns a difficult concept like risk, which involves ever-changing chance and consequences, into a simple visual representation of the current risk situation from a failure scenario in a company.
In this slide the conveyor return roller failed long ago and now the conveyor belt running over it is wearing away the tube wall at the right hand side of the roller. Once that happens the edge of the hole that appears in the tube becomes a knife edge. The knife edge is always in contact with the moving belt. Once the knife edge appears it creates an opportunity for the belt to be ripped its full length. As the hole gets bigger in the tube it grows both circumferentially and toward the centre of the roller. The opportunity to catch the underside of the belt with the knife edge and rip it full length continually rises. A ripped belt would lose the company $200,000 DAFT Cost.
But much worse than a ripped belt is the possibility for the knife edge to become a peeler and scrape the rubber belt into a large volume of rubber shavings. The thin rubber shavings are taken by the moving belt to the conveyor drive where they build-up around the motor. As the motor gets hotter and hotter from lack of ventilation the rubber shavings catch fire and the entire conveyor system and its drive is completely burnt. To replace the damage of a conveyor system fire would be $2,000,000 DAFT Cost.
The consequence and chance of each scenario is easily plotted on the risk matrix. From doing regular maintenance for $1,000 per year, to the $12,000 cost to replace a failed roller, to the $200,000 loss of a ripped belt and finally the $2,000,000 rebuild of a burnt system the risk situation is clear to see on the matrix. It is now up to Production and Maintenance to decide how to handle the risk.
Developing Equipment Risk Reduction Strategy
Developing a maintenance strategy to prevent failure of a centrifugal pump-set would start by drawing the process map for the equipment. The pump-set could fail for many reasons, as could any of its parts. The wet end could fail, the shaft bearings, the shaft coupling, the motor internal parts, the power supply to the motor, and the mounting frame or foundation plinth may fail. Each of these assemblies must be analysed. From the analysis a maintenance strategy that delivers high reliability for each of them is developed. An example of an operational and maintenance risk reduction strategy for the pump bearings is shown in Table.
If the proposed operational and maintenance strategy in Table is carried out properly it will ensure the pump bearings have a long failure-free life. The precision maintenance laser alignment removes the chance of overstressing parts and the inspections remove the risk of unknown environmental and operational degradation. The likelihood of a bearing failure event on the risk matrix has gone from ‘likely’ to ‘very rare’ and the criticality from High to Low.
Identify the New Risk Level
The Risk Matrix connects the risk levels a business WILL NOT accept with the action to be taken to reduce the risks TO ACCEPTABLE LEVELS. When calculating risk (Risk = DAFT Cost consequence x No. failures in the period x chance of failure) we use the DAFT Costs and the historical frequency of failure occurrence in the operation, or if that is not available then the common frequency for that industry. From the table where consequence meets frequency we get a risk rating, those that are Extreme or High will need to be reduced by using one or more Consequence Reduction or Chance Reduction strategies.
Use Low Cost Ways to Monitor Low Risks
The trap many operations fall into is to focus much condition monitoring effort on the critical plant and discount the importance of monitoring the remaining equipment. In reality, the key equipment is naturally high in priority, and people are well aware of the consequences of failure. This focus tends to help keep reliability and availability high by applying condition monitoring to detect impending failures. As a result it is possible that the rest of the plant will end up suffering more downtime from lack of attention.
It becomes necessary to find methods to also condition monitor all the ‘less important’ items of plant and equipment. One method is to use the human senses of operators and maintainers and supplement them with simple monitoring tools to conduct regular inspections of all equipments’ condition.
WORKED EXAMPLE – Physics of Failure Reliability Growth Cause Analysis
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