Leak from a hydrogen compressor

This incident occurred on a high-pressure hydrogen compressor part of the hydrogen production and storage unit of a testing laboratory.
While in operation, a hydrogen gas detector installed above the compressor room detected a hydrogen concentration of 2,000 ppm, automatically shutting down the hydrogen compressor and closing the shutoff valve. When the concentration in the room was confirmed below 2000 ppm, an employee entered the room and identified the location of the leak on the leak port of the cylinder cap of the compressor.

An overhaul inspection had been conducted one month before, and in that occasion, O-rings had been replaced. The leak was caused by the corrosion caused by remnant of the soap used in the tightness test performed during the inspection.

The INITIATING CAUSE was the damaging of a O-ring and its seat, which could guarantee no more their sealing function.

After dismantling the compressor cylinder, the investigators found scratches on the upper inner surface of the cylinder and cracks in the cylinder cap O-ring.
These were attributed to the presence of the soap water used in tightness tests. The eight connecting joints between the cylinder and cylinder cap of the ultra-high-pressure hydrogen compressor were annually tested for airtightness using soapy water.
Because the soap water was retained in the structure, corrosion occurred near the O-ring grooves (atmospheric side) of the cylinder and cylinder cap.
The corrosion was not discovered before because the affected corroded area was not subject to periodic inspection. The same phenomenon was found in all eight cylinders opened after the accident, although variations occurred among the cylinders.
It is believed that corrosion of the O-ring grooves restricted the movement of the backup ring, causing the bias-cut portion of the backup ring to come into contact with the O-ring and damage it.

Therefore, the ROOT CAUSE can be attributed to some blind-spot of shortcoming of the maintenance procedures.

compressor cylinder, O-ring

same facility as HIAD_1199. Also this othe cylinder had been part of the same overhaul inspection one month before, as the previous incident.

No personal injury occurred. or property damage, beyond the costs incurred in replacing the cyinder of this compressor.

This is a case at the border between a minor incident and a near miss. The safety systems in place worked as designed with no consequence to human or installation, except the time lost during the shut-down and the investigation.
Some specific and technical lessons can be drawn:
(1) When using soapy water for airtightness testing, it is important to select an appropriate test method for each facility.
(2) When using soapy water for airtightness testing, corrosion may occur due to the application of soapy water. Therefore, it is necessary to confirm in advance that the structure does not allow soapy water to stagnate. If corrosion due to the application of soapy water is a concern, it is recommended to change the test method to measuring with a gas leak detector, etc.

The cylinder was replaced with a new one.
To prevent moisture from entering and accumulating in the corroded seal area (the atmospheric side near the O-ring groove), air was purged from the leak port during operation to protect the seal.
The airtightness test method was changed from applying soapy water to measuring with a gas leak detector.