Mechanical failure of a hydrogen compressor

At a hydrogen production facility, the hydrogen compressor used to store hydrogen at approximately 20 MPa failed due to the rupture of the casing (spacer) connecting the hydraulic drive unit and low-pressure compression unit. While there was no hydrogen in the damaged casing, the rupture caused an excessive load on the two compressor supports, with consequent deformation of the hydrogen gas piping connected to the low-pressure compression unit. The hydrogen gas leaked from the piping joints.
A stationary hydrogen gas detector installed in the ventilation opening above the hydrogen compressor room detected a hydrogen leak of 2,000 ppm or more, automatically shutting down the hydrogen compressor and closing the shutoff valve.

The INITIATING CAUSE was a material failure.
The breaking of the compressor casing was induced by an error when the producer of compressor components performed a modification of the casing. When drilling a hole in the casing connecting the low-pressure compression section and the hydraulic drive section, the manufacturer mistakenly machined a deep circumferential groove. The groove was repaired by welding.
After the accident, inspection of the repaired welded area revealed multiple voids (defects) on the machined surface and inside the inner diameter. Very probably, a crack started from a void at the boundary between the repaired and unrepaired section of the drilled groove. This crack then propagated outward leading to fracture. The results of the fractographic analysis of the failed surface is compatible with this scenario. Crack onset and propagation was probably assisted or driven by residual stress induced during when welding, as well las difference in material strength.

The ROOT CAUSE is related to the management of the contractors along the compressor supply chain.
The producer of the damaged compressor subcomponent did not report the machining error to the compressor manufacturer, and the weld repair was performed without the manufacturer's approval. The equipment manufacturer was prohibiting weld repairs and there were no welds in the whole hydrogen compressor.
The fact that the drill had been performed erroneously could be attributed to a human error cause component. However, nothing is known about the reasons for the drilling and the condition this happened, so that it is impossible to be able to attribute it to procedures, local management or real human error.

casing, compressor, piping, joint

The compressor failed after 8,501 hours of operation and 6.1 x 106 cycles.

DESCRIPTION OF THE FACILITY
The data provided for the hydrogen production facility has two production flows:
417,844.8 m3/day (Business)
2520.0 m3/day (facility )
The compressor was used to store hydrogen at 19.5 MPa in buffer tanks (250 L, 4 tanks), after which the hydrogen is refined and used hfor performing testing activities. The compressor operated at a gas flow rate of 75 m3/h and a discharge pressure of 19.5 MPa.

The compressor had to be repaired. Costs are not provided

[management related]
(1) The establishment of and the agreement on clear work specifications with contractors and subcontractors before the start of the works is an essential and critical condition to guarantee quality control of materials, components and equipment. It is also important to review regularly on-site contractors’ and subcontractors’ work. This is because the management of equipment (their fabrication, repair, etc.) by (sub-)contractors differs from the in-house management.
(2) It is also important to establish a reliable communication system in advance so that contractors can promptly report deviations from the work specifications to the equipment manufacturer.
While the control of the supply chain is important in all industrial area, it is even more important in the case of the hydrogen supply chains, because the hydrogen technologies are still developing and improving. Therefore, the supply chains are affected by weakness such as lack of hydrogen-specific experience and knowledge and lack of stability, what translate in additional costs in respect to already established technologies.
[Technical level]
(3) Before correcting manufacturing errors with simple solution such as welding repairs, an analysis of the consequences of various repairing solutions is needed, considering also their impact on the lifetime performance of the equipment. For example, in the case of high tensile strength materials, a repairing weld can introduce additional defects and residual stress, and the welded area may become a source of fatigue cracks.

[actions taken by the plant]
(1) The owner of the plant required the equipment manufacturer to implement a thorough quality control.
(2) Non-destructive testing (penetration testing, ultrasonic testing, and radiological testing) was conducted on another hydrogen compressor of the same model, confirming the absence of cracks in the casing. After which it was reassembled and resumed operation. The casing of this hydrogen compressor had no welded repairs, as the holes had been drilled by a different contractor than the one that performed the unauthorised welding repairs.
[actions taken by the equipment manufacturer]
All subcontractors were re-notified that welding repairs were prohibited.