Motor-Operated Valve Incident Investigation: A Lesson in Maintenance and Torque Adjustment

Introduction: Importance of Motor-Operated Valves (MOVs)

Motor-operated valves (MOVs) are essential components in pipelines that require high torque, often found in large-diameter or high-flow systems. These valves, typically designed as butterfly or gate valves, manage the flow of critical applications. However, if MOVs are not properly maintained or adjusted, they can fail mechanically, leading to significant operational disruptions and costly repairs.

The Incident: Stuck MOV and Strange Noises

A recent incident involved an MOV that frequently jammed, prompting intervention by the Instrument team. After their maintenance, the MOV began to function smoothly, and the issue seemed resolved. However, 20 days later, abnormal noises began to emanate from the valve, particularly when it was opening and closing. The valve also exhibited jerks during operation. This raised concerns, prompting a full inspection of the MOV.

Maintenance Actions: Initial Diagnosis and Solution

Upon investigation, the Instrument team discovered that the stroke was restricted during opening, causing the MOV to fail to open properly at times. The handwheel, crucial for manual operation, was also found to be defective. As a temporary fix, the team increased the opening torque from 60% to 70%. This adjustment initially seemed to resolve the issue, and the MOV operated without further problems for a short period.

The Problem: Damage from Over-Torque Condition

After 20 days, the noises returned, signaling that something was still wrong. During inspection, the team found that both the valve’s disc and seat were damaged. These damages were directly linked to the higher torque setting. MOVs are typically designed to operate within a torque range of 40% to 60%. Exceeding this torque range, as in this case, subjected the valve components to undue stress, leading to failure.

Key Lessons: Importance of Proper Torque Settings and Inspection

The key lesson from this incident is the critical importance of adhering to the proper torque settings for MOVs. Exceeding the recommended torque can cause permanent damage to the valve components, resulting in costly repairs and prolonged downtime. Before adjusting torque settings, it’s crucial to inspect the MOV thoroughly and identify the root cause of any resistance. If the valve requires more than 60% torque to operate, further investigation into the cause should be conducted rather than simply increasing the torque.

Conclusion: Best Practices in MOV Maintenance

To avoid similar incidents, always follow the manufacturer’s recommended torque settings for MOVs. In cases where problems arise, never adjust torque settings without first diagnosing the underlying issue. Regular maintenance and thorough inspections are vital for ensuring the long-term reliability of MOVs and preventing costly damage.