Equipment Overview and Its Role in the Process Unit
The equipment under review is a recycle compressor, configured as a package unit, operating in a process unit within the energy industry. This compressor returns process gas to the main circuit and plays a critical role in maintaining operational stability and controlling process conditions.
The compressor operates continuously and is part of a production train. Unstable performance of this equipment can disrupt process balance, increase operating pressure on upstream and downstream equipment, and ultimately raise the risk of unplanned unit shutdowns.
The Signal That Kept Reappearing
Shortly after each oil change, the compressor crankcase oil would turn unusually dark and black. At first glance, this signal was attributed to issues such as oil quality, incidental contamination, or temporary operating conditions – issues that are typically resolved by draining, flushing, and replacing the oil.
However, a few weeks later, without any noticeable change in operating conditions, the same signal appeared again, and the oil darkened once more. This pattern repeated several times, and each time the corrective action was limited to the same approach: replacing the oil and returning the equipment to service as quickly as possible.
Since no production downtime occurred and there was no immediate or visible risk, the issue was treated as a minor maintenance concern rather than an early warning of a failure that was gradually taking shape.
What Made This Issue Impossible to Ignore
As repeated oil changes continued, a critical field observation fundamentally shifted the technical team’s perspective. Unusual corrosion was observed on the compressor shelter structure. Although this corrosion occurred outside the lubrication system, it appeared at the same time as the abnormal oil darkening. This coincidence strengthened the suspicion that a corrosive source – most likely acidic process gases – was escaping from the system and simultaneously affecting both the surrounding environment and the oil inside the equipment.
When the steel around the compressor started corroding at the same time the oil kept turning black, coincidence was no longer a credible explanation.
At this point, it became clear that continuing with the previous approach was no longer defensible. The recurring behavior pointed to an escalating failure mechanism that, if left unaddressed, could lead to more serious internal damage, increase the risk of sudden failure, and ultimately result in an unplanned unit shutdown. Taken together, these observations made the decision to perform a structured Root Cause Analysis (RCA) a technical necessity.
What the Root Cause Analysis Showed
The root cause analysis revealed that the primary source of the problem was neither the oil itself nor the oil change process, but the gradual entry of corrosive materials into the compressor crankcase. A review of the relevant process paths and mechanical components showed that failures in certain control components and return paths – particularly check valves in the drain and return lines – allowed corrosive process gases to enter the system.
Once inside the crankcase, these corrosive gases increased the corrosive nature of the internal environment and gradually led to chemical changes in the oil, accelerated oil darkening, and a reduction in the oil’s effective service life. At the same time, the release of some of these gases into the surrounding area explained the unusual corrosion observed on the compressor shelter structure. In this way, the internal and external evidence supported the same conclusion.
The internal and external evidence pointed to the same conclusion – corrosive process gases were attacking the oil from the inside and the structure from the outside.
The analysis also showed that this failure mechanism was not simply the result of a single mechanical defect. Changes in process conditions – including modifications to catalyst design or performance and increased generation of corrosive gases – combined with procedures that had not been updated to reflect the changed conditions, played a significant role in sustaining this abnormal behavior.
The Actions That Effectively Stopped the Failure Mechanism
The first step was to identify and fully correct the defective components in the drain and return paths of the process stream. The failed check valves were taken out of service and, following detailed inspection, were repaired or replaced to fully eliminate the possibility of corrosive gas flowing back into the system.
At the same time, the condition of the crankcase sealing elements was reviewed to prevent potential gas leakage into the enclosure. This action not only prevented further ingress of corrosive materials but also provided a more stable operating environment for the lubrication system.
Finally, at the process level, changes implemented in the unit – including increased generation of corrosive gases – were reviewed. Close coordination between the process and maintenance teams led to updates in operating and maintenance procedures to reflect the updated process conditions.
Evaluating the Effectiveness of the Root Cause Analysis and Implemented Actions
Following the implementation of the actions defined in the root cause analysis, the compressor and lubrication system behavior were continuously monitored in a focused manner, in line with the updated routine. The abnormal oil darkening stopped, and corrosion in the surrounding area – particularly on the shelter structure – also stopped. These were the first clear indications that the primary failure driver had been removed and that the system had moved out of its recurring failure behavior.
The oil stopped turning black. The shelter stopped corroding. The failure mechanism was finally broken.
The results showed that the effectiveness of root cause analysis was not achieved solely by executing corrective actions, but by correcting the failure path and aligning maintenance decisions with the actual process conditions. This experience clearly demonstrated that breaking a recurring failure behavior is not achieved by increasing maintenance frequency or replacing consumables more often, but by understanding the failure mechanism and acting on it.
The Principle That Broke the Cycle
This case study showed that many recurring failures persist not because of equipment or CMMS tool limitations, but because attention remains focused on visible signs rather than the failure mechanism. In this case, repeated oil changes only removed the visible sign of the problem for a short time, while the underlying failure path remained active in the background.
What ultimately stopped the recurring failure pattern was a clear understanding of the relationships among process conditions, leakage paths, and lubrication system behavior, and turning that understanding into effective operational decisions. Root cause analysis becomes meaningful only when its effectiveness is evident in the equipment’s actual behavior, not just in completed forms or one-time corrective actions.
This experience highlights a key principle in maintenance and reliability: success begins when organizations move beyond reacting to early signs and focus on managing failure paths, where making the right decision before a failure occurs becomes the most effective maintenance tool available.
