Compressor replacement keeps ethylene supply on tap
6 Apr 2020
No compressor, no ethylene: when the reliability of one piece of equipment determines a process can go ahead, you can’t take chances with who overhauls it...
Ethylene is the most widely used and produced petrochemical, due to its versatile physicochemical properties. The organic compound is generally obtained as a gas, but it is turned into a cryogenic liquid for optimal storage before undergoing any subsequent processes, such as polymerization to form polyethylene.
The condensation of ethylene involves cooling and pressurisation stages. Therefore, compressors are fundamental machines, whose correct functioning is vital, and any failure can heavily affect the entire processing line, as well as downstream plants. Regular inspection and maintenance of the compressors help manufacturers to ensure reliability in their production and meet demand.
This was the case for a large petrochemical company, which schedules routine maintenance on its key pieces of equipment. Located in North East England it is responsible for ethylene production and relies on four three-stage reciprocating compressors. These are used to liquefy the chemical and obtain cryogenic ethylene, which is then stored in a warehouse nearby.
Tried and tested
Every year, one of the reciprocating compressors is scheduled for maintenance. Components that generally require attention include parts made of white metal, or babbit alloy, such as bearings. This material is often used in large pieces of rotating equipment as it provides a low friction surface when combined with lubrication. As such, white metal bearings need to be inspected for wear regularly to ensure continued performance.
The plant was able to reduce the frequency of regular maintenance on its reciprocating compressors
Leading provider of maintenance solutions for rotating equipment, Sulzer, had already assisted the company with the inspection and maintenance of one of the four reciprocating compressors before it was contracted again for the scheduled maintenance of a second compressor.
This was found to be cracked around the water jacket of the stage-two cylinder, causing leakages. A temporary repair was performed by plant operators, in order for it to continue running before the plant shutdown. However, a permanent solution was required and a replacement cylinder was necessary.
Dale Jarvis, business development engineer for turbomachinery at Sulzer’s Leeds Service Center, explains: “Due to the dimensions of the large compressor, which weighed approximately 10 tonnes (22,000 lbs), any maintenance work had to be conducted at the customer’s location. Therefore, predicting which equipment was likely to have failed was important to ensure that the correct replacement parts were readily available on-site, and we could perform maintenance operations effectively.”
Expecting the unexpected
To identify worn out components and prevent future failures, the specialized team inspected the integrity of all the parts containing white metal and carried out non-destructive testing using fluorescent penetrant. The analysis confirmed the presence of damage to a number of bolts, big and little end bearings, as well as the compressor crossheads.
Also, unexpected defects on the two main bearings on the crankshaft were identified. The on-site team identified a need to replace four pistons, four piston rods, four connecting rods, oil wipers, sealing gas packings as well as the temporarily repaired stage-two cylinder.
Also a malfunctioning stage-one cylinder needed a replacement liner that required adjustment in order to fit. This was transferred to the Leeds Service Centre, equipped with specialist machining facilities.
Service specialists were able to complete the project ahead of schedule in 19 days, two days ahead of the timeframe, further reducing plant downtime.
As a result, the plant was able to reduce the frequency of regular maintenance on its reciprocating compressors, which will take place every other year and involve all four machines.