REGULATIONS & COMPLIANCE


IDENTIFYING DEFECTS AND THEIR CAUSE


Five hydrocarbon leaks at Fife Ethylene Plant were ultimately traced to the same deterioration mechanism. Josh McNicholas, Evalu-8 EHS, explains how the case shows why repairing a defect, and understanding what it means for the rest of a plant, are not the same job


T


he Health and Safety Executive recently prosecuted ExxonMobil Chemical Limited after five leaks of highly flammable hydrocarbons at its former Fife Ethylene Plant between February 2018


and September 2019. All five were attributed to corrosion under insulation (CUI), and the company was fined £267,000.


In February 2018, a pinhole leak developed on a high-pressure DMS and ethane line operating at 115°C and continued for around four months before it was repaired. Later that year, a worker carrying out unrelated work noticed a haze coming through insulation on different pipework. That leak lasted around six weeks, and HSE estimated that 82 tonnes of hydrocarbons escaped. During a routine visit in May 2019, HSE inspectors then detected a strong smell of dimethyl sulphide. The leak was on the same DMS line involved in the first incident, but at a different point. It had been detected by the company in January and had been leaking for around four and a half months. By the end of the investigation, five CUI-related leaks had been identified, and HSE was looking beyond individual sections of pipework at how CUI risk was being managed across the site.


Repairing the defect is only part of the response


HSE found that visual “scoping” inspections were being used alongside information about the pipe and its operating conditions to produce a risk score. Further investigation was generally directed towards higher-rated pipework. The strength of any risk-based inspection system depends on the evidence behind it. HSE found that overhead lines were often viewed from ground level, sometimes from several metres away; visibility could be restricted, and insulation was not always removed.


Once a defect is found, the immediate priority is clear: make the equipment safe, arrange the necessary repair and decide what is needed before it can return to service.


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But closing the repair should not automatically close the wider question.


If the defect has been caused by corrosion, fatigue, repeated seal failure or another deterioration mechanism, there may be similar assets elsewhere that deserve a closer look.


At Fife, the same line leaked again, separate pipework showed the same form of corrosion and further defects were identified as the investigation widened. A new defect can change the meaning of previous findings.


Six questions after a significant finding: Not every defect calls for a wider inspection programme, but it should reach someone who can decide whether the current inspection strategy still makes sense in light of what has been found. 1. What deterioration or failure mechanism has been identified? Record the underlying cause of the defect, not just the repair that was carried out.


2. Which other assets could be exposed to the same problem?


Look at similarities in material, age, temperature, operating conditions, insulation and maintenance history.


3. What does the previous inspection history show?


Review earlier defects, repairs, unusual readings and outstanding actions across comparable equipment. Findings that once looked isolated may appear differently when a second or third issue emerges.


4. Does the finding affect the current inspection strategy? The scope, frequency, technique or risk ranking may need to change. That decision should sit with competent inspection and engineering specialists.


PROCESS & CONTROL ENGINEERING | OCTOBER 2026 5. Are there actions still open beyond the repair?


The equipment may be back in service while wider inspection or engineering work is still underway. Closing the repair should not make those actions disappear.


6. What evidence is needed before the wider


review can be closed? There should be a clear record of what was


considered, what action followed and why the wider review was signed off.


Keep the wider review visible One of the practical problems for operators is making sure the wider issue stays visible once the immediate fault has been dealt with. A repair can be complete, and the maintenance job closed while the engineering work prompted by that defect is still ongoing. Evalu-8 EHS can help keep those records connected by linking asset information, inspections, incidents, supporting documents and follow-up actions in one place. That gives teams a clearer view of what has been completed and what still needs attention after the original repair is closed. The software is there to support the record and the follow-up, not to make engineering judgements. Decisions about inspection methods, corrosion, equipment condition and whether an asset is safe to operate remain with the competent specialists responsible for the plant. The individual repair solves the immediate


problem. The bigger question is whether that defect has told you something about other equipment that has not failed yet.


Evalu-8 EHS evalu-8.com


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