How Neglected Maintenance Led to Catastrophic Engine Failure and What It Teaches Us About H₂S Management

Background

Hydrogen sulfide (H₂S) is one of the most challenging contaminants found in biogas produced through anaerobic digestion. It’s highly corrosive, toxic, and can be devastating to engine performance if not properly managed. For operators, keeping H₂S levels under control isn’t just about compliance, it’s about protecting valuable assets and ensuring reliable energy generation.

Recently, MPE was called to investigate a catastrophic engine failure at an anaerobic digestion site. The incident serves as a clear reminder of why routine maintenance, professional oversight, and proactive monitoring are essential for biogas systems.

The Situation

The customer operated and maintained their anaerobic digestion plant independently, without a maintenance contract in place. While day-to-day operations continued, essential preventive checks were being overlooked.

Three critical issues were later identified:

1. The carbon filter had not been replaced on schedule.
   The activated carbon filter plays a vital role in removing hydrogen sulfide from biogas before it enters the engine. Once saturated, it can no longer capture H₂S, allowing high concentrations of the gas to pass downstream.
2. Oil testing was being carried out, but it failed to detect H₂S presence.
   Although regular oil sampling was performed, the testing process did not reveal that hydrogen sulfide levels were increasing. This gave a false sense of security and delayed intervention, allowing corrosive compounds to build up in the system undetected.
3. The oil grade being used was unsuitable for the site’s high H₂S levels.
   Although the lubricant was OEM-approved, it was not designed to handle the elevated sulfur content present in the biogas. The customer was also conducting their own gas sampling and provided MPE with the data. The results showed minor fluctuations in H₂S levels but nothing alarming, at least on paper. However, when MPE carried out independent testing, an H₂S concentration of 378 ppm was recorded. For the oil grade in use, the safe threshold should have been no higher than 50 ppm.
   This meant that, even though the system appeared to be operating within acceptable limits, the oil’s protective capacity had been exceeded many times over, leaving key components exposed to rapid corrosion.

Together, these issues created the conditions for severe internal corrosion and premature mechanical failure.

The Failure

When the engine eventually failed, the damage was extensive. Corrosion had affected multiple core components:

As corrosion weakened critical components, internal stress increased. Ultimately, a conrod (connecting rod) seized, snapped and punched through the side of the engine block, causing catastrophic mechanical failure.

The combination of high H₂S levels, acid corrosion, and oil breakdown created a perfect storm, one that no amount of reactive repair could reverse. The engine was written off and required complete replacement.

However, through MPE’s partnership with PowerUP GmbH, we were able to source, supply, install and commissions a replacement long block quickly, helping the customer return to operation and minimise further downtime.

By the time MPE engineers were called in, the damage was irreparable, the cost of replacement and downtime far exceeded what proactive maintenance and proper monitoring would have cost over the same period.

Further Investigation and Preventive Action

Following the replacement, MPE engineers carried out detailed inspections on the site’s other engines. Evidence of late-stage H₂S-related corrosion was discovered on multiple units, including damage to valves, liners, and turbo components. Recognising the risk of further failures, MPE performed major overhauls on the affected engines, using precision-engineered parts sourced through our trusted supplier network.

During these works, the customer had been repeatedly assured by the OEM, their oil sampling company (who also supplied the oil), and other operators in the industry that there was no H₂S issue. However, MPE’s experienced engineers knew something wasn’t right. The wear patterns, corrosion signatures, and component condition all pointed toward sulfur-related damage.

Standing by our technical judgment and independent gas sample, we encouraged the customer to test again using a different testing company and this time, elevated H₂S levels were confirmed. The new readings aligned with our earlier findings of 378 ppm, proving that the oil and maintenance regime in place were not sufficient for the gas quality being produced.

By trusting MPE’s expertise and acting on our recommendations, the customer avoided further catastrophic failures. The subsequent overhauls and preventive measures restored reliability across the entire engine fleet. With MPE’s ongoing support, the site has now implemented an enhanced maintenance and monitoring plan to ensure H₂S levels and oil condition remain tightly controlled.

The Consequences

This failure led to:

• Prolonged downtime, with the plant offline for several weeks.
• High replacement costs, including new components and lost production.
• Reduced biogas utilisation, resulting in economic losses and wasted feedstock.

It also underscored a critical lesson: unmonitored H₂S levels, incorrect oil selection, and missed maintenance can quickly turn a profitable energy system into an expensive liability.

Lessons Learned

The incident highlights several key takeaways for biogas operators:

• H₂S control is essential, not optional.
  Filters and scrubbers must be maintained and replaced at manufacturer recommended intervals.
• Oil testing must be accurate and properly interpreted.
  Regular lab analysis of lubricants should include checks for sulfur contamination to detect rising H₂S levels early.
• Choosing the correct oil grade is critical.
  Even OEM-approved lubricants may not be suitable for every application. Engines running on high-H₂S biogas require oils with enhanced acid-neutralising properties.
• Maintenance should not just be data-driven.
  Relying solely on visual inspections, fixed schedules or incomplete analysis leaves too much to chance.
• Professional service contracts protect your investment.
  Trained technicians understand the subtle warning signs that non-specialists can overlook.

The MPE Difference

At MPE, our service philosophy is built around experience. We specify maintenance contracts that combine regular inspections, oil analysis, and filter management with condition-based servicing and remote monitoring to ensure that problems are caught before they become failures.

For customers, this means:

• Longer engine life and improved reliability
• Lower long-term maintenance costs
• Optimised performance, even under variable gas quality
• Expert support from engineers who specialise in biogas systems
• Access to replacement engines and components through trusted partners like PowerUP

When MPE manages a system, operators don’t just get maintenance, they get predictive protection and responsive support when it matters most.

Conclusion

This case serves as a reminder that even the best engineered systems are only as reliable as their maintenance. Hydrogen sulfide may be invisible, but its impact on engines is anything but.

By working with trained professionals and maintaining regular service agreements, operators can safeguard their investment, protect their energy output, and keep their anaerobic digestion plants running efficiently for years to come.

With MPE and our partners at PowerUP, operators gain the confidence of knowing their systems are supported by expertise, technology, and a rapid response network built to keep them running.