An LNG leak occurred at 2:00 p.m. while the driver for an independent contractor was unloading LNG from his road tanker at a chemical plant. The gas-leak detection alarm on the road tanker side was automatically activated, halting unloading and automatically shutting off the valves that control the supply to the LNG storage tank and the facilities that use it (steam production boilers). The gasket between the hose and the tank broke up. The driver replaced the gasket and resumed unloading at 9 bar of pressure at 2:50 p.m. At 3:15 p.m., unloading was again interrupted by another automatic gas-leak detection alarm, this time on the LNG storage tank side. Alerted by the boiler shutdown, the plant’s area manager went to investigate the problem. His portable gas detector was activated. He then implemented the internal emergency plan and ordered the workers to shelter in place.
As part of the internal emergency plan and after the operator and contractor in charge of the LNG facility had analysed the situation, unloading was resumed at 4:11 p.m. This time, the operation went smoothly because the pressure was reduced to 5 bar in accordance with the unloading procedure. The internal emergency plan was lifted at 4:20 p.m.
Causes of the LNG leaks
The break of the Teflon PTFE gasket and associated LNG leaks may have been caused by repeated mechanical stresses associated with incorrect positioning of the gasket on the facility’s hose connection by the driver. The use of a hammer to tighten the connection exacerbated these mechanical stresses. The contractor has seen three similar incidents of gasket deterioration in Spain over the last five years.
A change in pressure is believed to have caused the safety valve to open and led to an LNG leakage. Unloading operations are supposed to be carried out below 6.5 bar. To unload the LNG, the driver had used a pump on his road tanker. This pump, which was not originally designed for the facility, had allowed the pressure on the unloading line to reach the pressure setting of the valve at 13 bar.
Measures taken
After consulting with the contractor, he has provided a box full of gaskets to fit the different types of road tanker hoses and made it available in the unloading area. The use of these gaskets and their replacement frequency is traceably monitored. Preventive replacements have also been arranged at periodic intervals.
At the operator’s request, the contractor has also undertaken to stop making deliveries via road tankers equipped with unloading pumps. Tankers must be unloaded in compliance with pressure differential procedure, using an unloading heater and whilst maintaining the unloading pressure at 6.5 bar. The contractor has posted instructions reminding his drivers about the requirement to maintain safe unloading pressure of 6.5 bar and has improved his drivers’ training.
