Risk-based maintenance within ISO 55001

Risk-based maintenance is a way to decide which assets you maintain or replace first. You look at the likelihood that something goes wrong and at the consequences if it does. The asset management standard from ISO asks you to identify and address risks in your asset management. This approach is a practical way to meet that requirement. More about the requirements is on the page about requirements per chapter.

The starting point is simple. You do not have enough money or people to maintain everything well at the same time. So you choose where the money delivers the most. The SAMP records the long-term choices you make in this.

Risk is likelihood times consequence. An asset that rarely fails but switches off a whole neighbourhood when it does can carry a higher risk than an asset that fails often with few consequences.

What is risk-based maintenance?

With risk-based maintenance, you ask two questions for each asset. How likely is it that this asset will fail? And what are the consequences if it fails? The consequence can concern safety, customers without power or water, fines or repair costs.

Likelihood times consequence gives the risk. This is the basis of most risk-based approaches. The difference from ordinary planned maintenance is that you do not spread maintenance evenly over all assets. You give the highest risks the most attention.

A related concept is criticality. Criticality shows how important an asset is to your organisation. Risk shows how likely it is that the asset fails to perform. An asset can be critical and still carry a low risk, if it is reliable.

How does this fit within ISO 55001?

ISO 55001 asks you to identify risks and opportunities that should affect your asset management system. This happens in planning. Risk-based maintenance is a way to make those risks concrete for each asset. The standard does not prescribe a matrix or formula. That leaves the choice to you, as long as you apply it consistently and record it.

What matters is the process. Who determines the risks? How often do you review them? And does the outcome lead to different choices in maintenance and investment? If that happens and you can show it, it fits the idea behind the standard.

Steps to set up risk-based maintenance

Make a list of your critical assets

Start with all the assets you manage. Then mark the assets that have serious consequences if they fail. This is usually a smaller part than you might think.

Determine the likelihood of failure

Use the fault history, the condition and the age. A recent condition assessment under NEN 2767 gives good input for this.

Determine the consequences of failure

Think about safety, customer impact, repair costs, the environment and reputation. Give each consequence a score on the same scale, so you can compare them.

Put likelihood and consequence in a matrix

Multiply or combine the two scores. An asset with a high risk gets a place at the top of your list.

Link the risk to a strategy

A high risk often means: preventive maintenance, condition monitoring or replacement. A low risk usually means: periodic maintenance or running the asset until it can no longer run. Record the choice in your plan.

Review the outcome

Repeat the assessment at fixed moments, and after every major failure. An asset that newly appears at the top needs a new decision.

Example: a risk matrix for a grid operator

This is a fictional example. Grid operator Netbeheer Oostdijk manages a high-voltage substation, an underground cable, a pumping station and a set of switchgear cabinets. The company gives the likelihood of failure and the consequences each a score from 1 to 5.

Asset	Likelihood of failure (1-5)	Consequence of failure (1-5)	Risk (likelihood x consequence)	Strategy
High-voltage substation	2	5	10	Annual thermography, replacement plan in the SAMP
Underground cable, Zuid neighbourhood	4	4	16	Preventive replacement within five years
Pumping station, polder	3	3	9	Condition assessment every two years
Switchgear cabinet, office	1	2	2	Periodic maintenance according to the manufacturer’s instructions

The cable in the Zuid neighbourhood has the highest risk, even though the substation is more expensive. That is why the cable comes first. This order only counts once you record the scores and justify them.

A 5 by 5 matrix is a common setup, but the standard does not prescribe a scale. Choose one scale and use it everywhere.

A matrix without justification is a guess dressed up in colours. Write down for each asset why you give it a score, and who assessed that score.

Common mistakes

Looking only at age. Old does not mean risky. An old asset in a quiet environment can score lower than a young asset in a busy area.
Weighting all assets equally. Then you spend attention on the lowest risks.
Making a matrix and not using it. If the outcome changes nothing in your budget or planning, the matrix does not work as a management tool.
Never reviewing it. A risk score from five years ago is usually no longer accurate.

Frequently asked questions

Is risk-based maintenance required by ISO 55001?

The standard asks you to identify and address risks. It does not prescribe how to do this. Risk-based maintenance is one of the common ways to do it, but not the only one.

Which software do I need?

A spreadsheet is enough to start. Many maintenance systems have a module for criticality. Choose something your team can keep up to date, because a system that nobody updates adds no value.

How do I know whether my approach is good enough?

Ask yourself whether the matrix led you to a different decision than last year. If the answer is no, the matrix does not yet work as a management tool. Discuss the outcome in your management review, as the standard requires.