One of our customers discovered that a
compressor was leaking gas into the cooling
water, and we brought the cylinder into the
HTC service repair shop for investigation.
Following our standard practice, we carried
out a thorough condition analysis and issued
a full report before carrying out any repairs.
We removed the valves and the liner then
subjected the cylinder’s cooling water space
to water and helium leakage testing.
Unfortunately, this did not locate the exact
position of the leak. However, when the gas
side of the cylinder was pressurised to 50 bar,
a leakage path between the gas and the
cooling water sides was clearly seen.
Normally, it is essential to find the precise site
and nature of the leakage before starting
repairs, but when it is hard to find the
investigation can take several days or even
weeks. The HTC engineers realised that there
was a faster and more cost-effective way to
rectify the problem, and it would require
precision engineering of the highest quality.
Because our engineers knew they could trust the skills and experience of the repair shop staff at every stage, they decided that it would be possible to eliminate the problem by grinding out the cylinder bore all the way down to the point where the end of leakage path was seen. This would ensure that the whole of the pathway was removed. It would also, however, mean that the structures and surfaces would have to be restored.
The whole process required a complex sequence of reheating, welding, pre-grinding work. Studs had to be removed, and grit blasting of the cylinder was carried out.
The risk of deformation associated with heat treatment after welding was anticipated and dealt with using a proven Thomassen stress relieving treatment. This action saved an enormous amount of time and money, as it kept most of the machined surfaces intact.
Due to the extensive heat the cylinder was exposed to during welding, the inner bore of the cylinder showed some deformation.
We machined it to an oversize, then applied a coating to the outer circumference of the liner, increasing its diameter to match the new dimension of the bore.
All of the necessary procedures including
welding, grinding, grit blasting, heat treatment,
Non Destructive Testing (NDT) and machining
were completed in just four weeks. At the end,
we carried out the programme of cleaning and
inspection procedures that we use on new
build compressors. This included pressure
testing and further NDT exercises.
To ensure that any inconvenience at the
customer’s site was kept to a minimum, we
carried out all the painting and pre-assembly
activities in the HTC repair shop. The entire
operation was carried out in close co-operation
with the customer, who also asked to witness
some of the work being carried out. We were
pleased to grant their request.
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