Failure of a high pressure synthesis feed pipe in an ammonia plant.

A high pressure feed line carrying hydrogen-base synthesis gas (syngas) to the ammonia converter experienced an explosion followed by a severe fire. One of the operators was fatally injured. The failure of the high-pressure feed line was characterised by a sudden rupture without previous leakage.
Portions of the piping shattered in a brittle fracture, which was produced due to a severe hydrogen attack. Extensive blisters were observed on the inside surface which failed.
The initial crack probably originated at one of two small nozzles provided for temperature measurements. These small nozzles acted as stress raisers.

The INITIATING CAUSE was failure of a high pressure synthesis pipe due to internal hydrogen attack, which induced steel decarbonisation and brittle fracture.

Probably the possibility of the hydrogen attack was not taken into consideration in the design and the maintenance phases, or the regular inspection procedures were not designed to detect this type of degradation, characterised by a brittle fracture.

syngas pipeline, ammonia reactor

DESCRIPTION OF THE COMPONENT
The failed pipe had a diameter of 323.9 mm and a wall thickness of 36 mm .

This is a case of road crash involving a liquid hydrogen carrier without release, despite its roll-over. The protective structure designed for avoiding damage to the pressure control system worked as expected. Because of the long-term aspects of a failure of the type of this event, in 1986 Prescott et al. (see references) was recommending all operators of ammonia plants to check the alloy content of components and welds, and to check alloys operating limits for in hydrogen service to avoid decarburization and cracking.