Natural gas pipeline failure due to hydrogen attack

[NOTE of the EVENT VALIDATOR: this is a natural gas event, related to the NG supply chain. It may be however of interest for hydrogen-NG mixture transportation in pipeline.]
A 30-inch natural gas transmission pipeline ruptured, releasing about 101.5 million cubic feet of natural gas, which ignited.
The fire fighters were almost immediately on site, 3 hours later all fire suppression activities had concluded.
The pipeline failed by a combination of a manufacturing defect, a degraded coating and ineffective cathodic protection, all resulting in hydrogen-induced cracking at the outer surface of the pipeline.
The accident resulted in 1 fatality, 6 injuries, and the evacuation of over 75 people. Five residences were destroyed by resulting structure fires, and an additional 14 were damaged. A nearby railroad track was also damaged, and over 30 acres of land were burned.

The INITIATING cause was the failure of a natural gas pipeline due to hydrogen cracking at a weak spot.
The NTSB investigation identified the root cause in shortcoming of the company integrity management program. It did not accurately assess the condition of the pipeline and/or estimate the risk from combined threats. The company underestimated the risk posed by hard spots because its processes and procedures were inconsistent with PHMSA guidance and industry knowledge of hard spot threat interaction.
In details, the contributing causes were:
(1) Incomplete evaluation of the risks caused by a change of gas flow direction;
(2) Limitations in data analysis related to in-line inspection tool usage;
(3) Incomplete assessment of threats and threat interactions;
(4) Missed opportunities in training and requalification practices.

NG pipeline

Two years before, the operation of the pipeline was modified. From one directional natural gas transportation, to bi-directional operation. Since this modification could induce increase in the temperature of pipeline sections triggered by compressors, and this can accelerate external corrosion, a risk analysis had been performed. Gas coolers were installed. The compressor directly related to the failed section started to be used in two years before the incident, inducing a 70 F (20 C) degree increase in that section.
In May 2019, a shutdown in the compressor station, which caused indirectly a pressure build-up in that section. In that occasion, wrong diagnosis reveal a lack of understanding of the operator.

The accident resulted in 1 fatality, 6 injuries, and the evacuation of over 75 people. Five residences were destroyed by resulting structure fires, and an additional 14 were damaged. A nearby railroad track was also damaged, and over 30 acres of land were burned.

A. AVAILABLE KNOWLEDGE
Buried steel pipelines corrode due the presence of moisture and ground water in the soil. Cathodic protection is an electrochemical method used to prevent corrosion on buried pipelines where the applied coating has been damaged, exposing bare pipeline metal to the soil. This protection has to be optimised considering the local soil characteristics and the expected operative conditions.

B. RECOMMENDATIONS
The authors of the investigation (see References) made the following recommendations to US Pipeline and Hazardous Materials Safety Administration (PHMSA):
(1) to revise the regulations regarding potential impact radius methodology. This methodology is based on old data, and its review must be based on data from recent natural gas pipeline ruptures and human response considerations.
(2) To advise natural gas transmission operators on the circumstances of this accident, the need to evaluate the risks associated with flow reversal projects, the impacts of such projects on hydrogen-induced cracking, the possible data limitations associated with the use of in-line inspection tools and analysis used in hard spot management programs, and the need to follow industry best practices when conducting in-line inspection data analysis.

The following recommendations were addressed to the affected pipeline operator:
(3) to evaluate the effectiveness of its corrosion control equipment and infrastructure following a major change in operations, like a gas flow reversal.
(4) To modify its integrity management program to better address threats and threat interactions.
(5) To require disqualification, remedial training, and/or requalification of covered tasks whenever an employee does not follow procedures when responding to an emergency shutdown, rupture, or other abnormal operation.