Fire - hydrogen

This incident occurred at an aromatics manufacturing plant.
A staff member patrolling the plant heard a strange noise and rushed to the site, where he discovered a hole in a pipe, from which hydrogen and the catalysts were ejected, causing a fire.
The plant was immediately shut down and the catalyst regeneration system was depressurised and replaced with nitrogen.

In this plant, the hydro-de-sulphurised naphtha was heated to a specified temperature together with recycled hydrogen and then fed to the reactor, where the de-hydro-cyclization and de-hydro-isomerization reactions were carried out by the catalyst continuously fed into the reactor. The final product was a reformate with a high aromatic content. The catalyst used in the reaction was continuously extracted and transferred using hydrogen for regeneration.
The failed pipe had the purpose to transfer the regenerated catalysts for the continuous feed into the reactor. The damage occurred at a bent section (angle of about 30 degrees). The causes of the failure were:
(1) Corrosion: a small amount of catalyst activity modifier (DMDS) added to suppress catalyst activity and its thermal decomposition products remained in the transfer pipe, causing high-temperature sulphide corrosion under operating conditions,
(2) Abrasion: the metal surface was worn away when the granular catalyst was transferred with hydrogen
The damage was the results of a synergistic effect (erosion-corrosion) of the metal surface wearing away when it hits the bent part.

The INITIATING CAUSE was the failing of a pipe carrying hydrogen and catalyst due to corrosion-abrasion of the internal surface.

The KHK report does not identify a ROOT CAUSE. It reports nevertheless, that the system to transport the catalysts had been considerably changed one year before the incident. This suggests a shortcoming or total lack of Management of Change approach. Also the inspection routines wer not designed in suc ha way to detect internal deterioration processes.

hydrogen pipe, catalyst regeneration

The operating conditions were significantly changed one year before the accident occurred.
(a) The injection location of the catalyst activity regulator was changed from the catalyst reservoir at the top of the reactor to the regenerated catalyst transfer pot.
(b) The injection method of the catalyst activity regulator was changed from continuous to injection only during transfer.

In the year of occurrence of this incident, the need for a management of change culture and approaches were not yet understood and broadly adopted.
Although it is not demonstrated that the changes to the process executed one year before to the process were at the origin of the failure, it is plausible and even probable that they plaid a part, if not the major one.
The new route for the catalysts and the switch from a continuous to a cycling process changed the way that the pipe was stressed.