Fire from a hydrogen pipeline

A leak occurred at an underground steel pipeline (6 inch) transporting pressurised hydrogen (75 bar). The leakage lasted for at least several hours, but it cannot be excluded that the leakage started weeks or even months prior to the discovery of the leak.
The leakage occurred at a location at which the pipeline entered a building and contained a so called “CP coupling” (a device to interrupt the cathodic protection). This is a specific “weak spot” in a pipeline in which tensions could mount, and resulted in the partial failure of “CP coupling”.
The escaping hydrogen gas was ignited by welding activities which at that time were taking place in the vicinity of the leak as part of a construction project to add another pipeline in the corridor. The ignition resulted in a small fire on top of the soil. In the surroundings there were several additional pipelines transporting other gases.
Because of this, police and the fire brigade took severe precautionary measures, by confining at home the inhabitant of a near village, and stopping the waterborne and road traffic for several hours.
At least 8.4 kilograms of hydrogen have escaped since the leak was noticed, for approximately 7 hours. It is very possible that the leakage had started much earlier. This suggested that the hydrogen released was probably in excess of 50 kg.

INITIATING CAUSES
The leakage was caused by a mix of several tension factors acting on the pipeline:
(i) The main stressing factor was the gradual settlement of the pipeline and the earth surrounding it. The settlement took place over a time span of several years and resulted in the bending of the pipeline at a spot where the pipeline got stuck on a fixed structure, e.g. a feed through in which the pipeline enters a building. The bending forces caused tensions on the CP coupling nearby in the pipeline, which eventually started to leak.
(ii) Other possible stressing factors were un-allowed heavy traffic and
(iii) the placement of heavy equipment on the soil covering the pipeline.

CONTRIBUTING & ROOT CAUSE
The investigation identified a lack of coordination between at least four supervising bodies responsible for safety inspections. This resulted in a situation in which each body was not assuming responsibility for overall safety, assuming that the other would do the inspections they were not doing.

Hydrogen underground pipeline

The leakage lasted for several hours but it can not be excluded that it started weeks or even months prior to the discovery of the leak.

Nobody was injured.
No serious estimate about the cost of the property damage has been made by anyone but the damage can be estimates at least 1 million Euros.

The accident caused a lot of concern under the people living nearby the pipeline corridor and generated discussions in the local and national parliaments.
No environmental impact.

Specific, mostly of a technical nature:
1. Criteria had to be established for the quality of CP couplings in pipelines and the installation and maintenance conditions associated with them in order to safeguard that the couplings are not exposed to any type of stress during their operational lifetime.
2. Policies with regard to the measurement and interpretation of ground settlement had to be reassessed.
3. A strict surveillance policy had to be developed to prevent infringements on rules regulating activities on top of pipelines in order to prevent the possible damage of these pipelines.

General, of a organisational nature:
4. An abundant series of supervisors and inspectors on a project does not necessarily mean that the essential requirements to safeguard a safe environment are met. On the contrary.
5. All parties involved in the management of the pipeline corridor (the management of the foundation as well as all individual pipeline operators) had to redefine supervision and inspection policies in order to get a clear division between each other’s tasks and responsibilities, particularly during construction activities in the pipeline corridor. The additional supervisory role of external parties, like “notified bodies” and “independent supervisors” had to be included in this survey of responsibilities.

Immediate actions: Repairing the pipeline, checking pipelines with similar constructions and tightening supervision during activities in the pipeline corridor.
Long term actions: Revising technical and procedural safeguards against the stressing of pipelines.