Release from a hydrogen line to the desulphurization unit of a refinery

Event

Event ID: 840
Quality: 3
Description: A sudden failure occured on a hydrogen line of a refinery desulphurisation unit. The equipment was located between a hydrogen compressor and its overpressure protection valve. It was equipped with an automatical isolation system, however, the failed pipe, located at the bottom of the system, was without self-draining mechanism. .
The bursting of the pipe was due to its corrosion: a large loss of thickness extended over 300 mm. The presence of a bend at a low point on a line without circulation led to the accumulation of deposits initiating a corrosion mechanism.
Event Initiating system: Non-Hydrogen system initiating event
Classification of the physical effects: Unignited Hydrogen Release
Nature of the consequences: leak no ignition
Macro-region: Europe
Country: France
Date: 01/04/2006
Component involved: pipe (bend)
Failure mode: rupture, no ignition
Initiating cause: material degradation (internal corrosion / erosion)
Root CAUSE analysis: INITIATING CAUSE was corrosion which reduced the stress-bearing wall thickness of the pipe.
The ROOT CAUSE was found in a non-optimal design, failing to identify and taking care of weak points on the line.
Root causes: System design error
Date entry in HIAD: 01/01/2020

Lesson Learnt: The valve inlet lines were similar to dead arms and should have been considered as such when establishing inspection plans. They must be the subject of the corresponding enhanced controls;
2. The lines should be as short as possible and self-draining.
Corrective Measures: The operator modified the layout of the piping to avoid low points. It performed thickness checks on lines identified as sensitive.