Cylinder repair time drastically reduced

Casestudies | Reciprocating compressor cylinder repair

Compressors are at the heart of the refining process and their reliability is critical to the operation of the entire refinery. Effective compressor maintenance and high quality repairs are vital to ensure continuous production.

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.

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Testing in water - reciprocating compressor

Our solution

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.

 

The outcome and benefits

 

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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