Hydrogen leak at a refinery

A gas release occurred on a pipe located between two hydrogenation units of a steam cracker. The gaseous mixture transported through this line was composed of 95% hydrogen, 4% methane and 1% nitrogen. The pipe was located in a rack within the cold sector, at a height of 6 m.

The personnel shut down the steam cracker and isolated the sector and the gases of the hydrogenation units were sent to the flare system. The leak was successfully sealed at noon, while the steam cracker remained down for a full 24 hours.

INITIATING cause of the leak was the weakening of the pipe due to external corrosion by water drop, followed by a mechanical shock during operation.

According to ARIA, the ROOT CAUSE was the inadequate inspection and consequent failure of damage detection and repair.

pipeline, steam cracker

Diameter of the pipe: 2''

The direct cause of the pipe rupture was a water runoff due to vapour condensation on a cold pipe above the perforated piping assembly. This drop-by-drop action had weakened the pipeline by corrosion which thinned the upper part of the pipe. The perforation had resulted from a pressure shock during operation.
The authority responsible for the inspection of the classified facilities that the pipeline was lacking the paint protecting against corrosion. This pipe section had been repainted in 1990 and verified during previous inspections, in 2000 and 2007. During this last inspection, the inspectors noticed water runoff on the pipe, along with a major degradation of pipe paint, which in some cases had totally disappeared. Since an expansion layer formed by corrosion/erosion, the integrity of the section could not be assessed. No specific guideline was issued for the restoration of this section (as a minimum, the repainting of the section would have been necessary).
As consequence of the leak, the authority required the plant operator to put in place an effective plan for an effective regular inspection and actions guaranteeing the integrity of the components.