Release without ignition from heat exchanger of a fertilisers production plant

In a fertilizer manufacturing plant, during his inspection round, an operator detected a hydrogen leak at a flange of an exchanger located between the conversion and decarbonisation stages of the ammonia processing unit. He alerted the control room.

A steam hose was installed blowing towards the flange to dilute the leak. Explosive gas measurements wer taken twice per shift to ensure that the consequences of the leak are under control. The area was placed under surveillance.


A few days later, 2 vapour rings were placed around the flange. A marker was also placed around the flange to indicate that access to the area was prohibited. Several control points are defined.

Three weeks later, a leak sealing system was put in place. Two weeks later, the injection of sealing paste into the collar did not seal the leak.


Two months after detection of the initial leak, an operator noticed short term changes in noise and direction at the leak. The operator finally decides to work on the leaking flange. The main process gas supply was shut down more than 9 weeks after the initial leak detection while maintaining a nitrogen flow. The gas flow stops in the pipe.

After the stop of the plant operation, inspection of the site revealed that the flange was loose at the time of the accident.

heat exchanger, hydrogen supply line

The normal operation of the plant continued all along the attempt to stop the hydrogen leakage.
A leak on a gasket due to a flange tightening defect had already occurred on site 2 months earlier

The consequence of a cold shut-down would have been 3 weeks of stop of the production. The need to guarantee production rate and the negative financial consequence in failing to do so are among the most common causes of incidents.
In this case, the company did not want to shut down the plant and decided for the alternative to control and possibly reduce the leak. It succeeded in avoiding ignition, but the event report does not assess the safety margin of the measures adopted.