Safety Incident Topic: Check Valve Counterweight Failure
Location of Incident: Compressor Building Cooper River, America
Date of Incident: 20 July, 2007
Brief Account of Incident
While commissioning the gas expander, an operator was hit in the leg by a falling weighted lever from a check valve. The check valve was located approximately 20ft above the operator’s position at the time of failure. The weighted lever, weighing 15-20 pounds, hit the ground and then grazed the operator’s leg. There was no damage to equipment, no one was injured, and there was no harm to the environment.
What Went Wrong
1. The check valve counterweight assembly is held together with setscrews which can work loose over time and allow the weight to fall from the valve.
2. The check valve is installed high overhead in an area where there is operations activity.
Summary of Immediate Causes
Inadequate guards or protective devices – The swing check valve did not have a secondary means of securing the counterweight balance assembly from falling due to vibration or fatigue.
Summary of System Causes
Inadequate preventative Maintenance – This check valve does not have a PM in SAP to check for functionality or proper operation of the counterbalance assembly.
Summary of Local Actions
Upon investigation of this check valve, it was determined that the external counterweight assembly is an optional accessory that assists the operation of the valve. In this application, the counterweight was deemed not necessary and removed. The counterweight is primarily used in check valve applications where increased closing speed is necessary.
The following actions were taken:
1. All check valve installations were checked to identify any potential risk to personnel from falling object/counterweight.; Those check valves w/counterweights not in applications requiring increased closing speed will have the counterweights removed to prevent future incidents.
2. In areas where the counterweight assembly would not cause a danger; the assembly was left in place and verified to be secure (tack welded) and operating as designed.
All check valves that have external counter weights that upon failure or fatigue could cause a potential falling object hazard will need a PM frequency that will mitigate the hazard. These same check valves will need an additional means of securing the counter weight to prevent a future failure (tack welding is an option).