(20 min.) Case Study: Important Design Considerations to Avoid Oil Coking in Lube Oil Reservoir

Ghulam Jillani, Lead Engineer Rotating Equipment , Dubai Natural Gas Company Limited


Frequent lube oil filters replacement on an API 614 special purpose lube oil system of centrifugal compressor train was reported. Two centrifugal refrigeration compressor trains were commissioned two years ago and one was having issue of high differential pressure on filters after few hours of operation. Oil analysis requested for three oil samples (both compressor train lube oils and new oil from barrel/drum).Unfortunately, results of oil analysis were not indicating an underlying problem. Overhead rundown tank was inspected and found clean.

It was observed in another test run of lube oil system that differential pressure across the filters and discharge pressure of lube oil pump both gradually increased after start and reached to a level, which was not acceptable for continued operation. Another set of oil samples requested and were taken while oil system was in operation. The sample collected from lube oil system return line to reservoir indicated very bad odor, dark color and suspended soft residue. It was immediately decided to drain the oil and open the many ways of lube oil reservoir. Severe oil coking found on immersed heater coils and residue at the bottom of reservoir.

Oil reservoir consisted of three compartments, separated by baffle walls having an opening. Immersed heater is installed in extreme right or left compartment whereas temperature control transmitter for this heater is installed in the central compartment of oil reservoir. The immersed heater did not have its own built in temperature control element. The immersed heater ON/OFF as found in control file was 90/ 130 F, which is different from control I/O list value of 90/110 F and compressor start permissive of 108F. Running hours of compressor, on which this lube oil problem occurred, was half of the other machine. It seemed that overheating of oil in compartment (temperature higher than sensing probe in center compartment) and insufficient circulation (baffles in reservoir and machine in standby for long time) of oil were the potential causes for this incident.


1- Understanding of an API 614 special purpose lube oil system design features
2- Design aspects to be corrected during engineering to avoid problems in future operation of equipment
3- Steps to be followed to bring a contaminated oil system back in service


A highly motivated, enthusiastic individual, who is confident in his approach, driven by the need to succeed and achieve a competitive market place. Enjoys working in a challenging environment that demands teamwork, initiative, creativity and sound analytical skills when making effective decisions and finding solution to problems. 18 years of experience in Engineering & EPC environment comprising of Feasibility Studies, FEED, Open Book Development, Detailed Engineering, Engineering & Procurement, PMC, Reimbursable, EPC projects specializing in rotating equipment design engineering, techno commercial evaluations, on site operational & maintenance support, commissioning, site completion activities, HSE, maintenance activities & their planning, quality assurance & control

Core Competencies

• Strong analytical and practical field engineering skills along with dynamic leadership qualities for effective contributions at a higher level for interaction with client, vendor and company management.

• Hands on work experience for detailed engineering of all rotating equipment i.e.; all pump types, steam turbines, fans & blowers, gas turbine, process centrifugal compressors, reciprocating compressors, utilities packages, refrigeration systems etc.

• Hands on experience in centrifugal compressors installation, start up, and commissioning activities.