Case 1 – Parallel running of pumps to meet the designed throughput
A new mid-size refinery in the Middle East required parallel running of main condensate feed pumps (2x100%) during the commissioning phase to meet plant throughput, instead of having one on standby. The reason being that the motors driving the centrifugal pumps were getting tripped on high current overload when run individually at the designed throughput capacity. Running the plant on a single feed pump accounted for a 20 percent reduction in production. An early investigation by the project commissioning team and pump OEM recommendations (in absence of a reliability program) did not reveal the actual cause of the problem. Due to production pressures, it was mutually agreed to run both pumps in parallel to achieve the production targets until the problem was fixed. Both pumps ran in parallel for four years until a reliability section was established in the organization and conducted an investigation on parallel running pumps. The performance testing and design review of both pumps showed nothing significant. A second performance test was conducted to evalute the performance of automatic recirculation valves (ARVs) installed in the discharge lines of the pumps. It revealed extensive recycle flow across the ARVs, eventually shifting the system performance curve and causing the motors to trip at overload when run individually.
Figure 1: ARV brought to workshop for overhaul
Figure 2: A seized ARV bypass valve
The ARVs were overhauled during the next available shutdown and both were observed to have seized slide valves, allowing full flow bypass across the ARVs since commissioning. This raised questions regarding the execution of ARVs’ functionality checks prior to installation, as per vendor recommendations. After servicing, they were put back into operation and worked satisfactorily. Since then, one pump is now on standby.
Lifecycle cost savings of $800,000 was achieved by this defect elimination. The estimated production loss in the past four years due to the occasional downtime of one pump was estimated to be $350,000.
Similar problems were resolved on eight other pumps (with ARVs) that were running in parallel since commissioning with no standby, thereby saving millions in LCC costs in comparison to keeping them running in parallel for the lifecycle.
A reliability program in the early project phases could eliminate avoidable defects and deliver higher uptime performance at lower costs.
Emphasis should be given on proper acceptance testing and fixing equipment defects prior to the hand over to operations.
Always check the functionality of accessory items (e.g., ARVs, etc.) prior to installation as per OEM recommendations.
Case 2 – Fire pump bearing failure due to lack of lubrication
A newly commissioned fire water pump at a Middle East refinery repeatedly suffered high non drive end (NDE) bearing temperatures during periodic test runs and eventually caused a bearing failure. It was revealed that bearing failure was caused by a lack of lubrication since the failed bearing showed signs of lube oil starvation. However, the constant level oiler sight glass showed the oil level as full.
Figure 3: Constant level oiler orientation, before and after correction (Source: a Middle East refinery)
Figure 4: Correct orientation of constant level oiler (Source: vendor fire pump drawing)
This begged the question: Why was the bearing starved of oil? The answer: The wrong orientation and installation of piping for the constant level oiler during the construction phase.
After correct installation of the constant level oiler piping orientation, the problem was resolved. As this fire water pump was emergency duty equipment, it would have failed during a real-life scenario and could have burned down the whole plant.
Construction contractors should strictly follow vendor recommendations for equipment and piping installations.
Peer review of equipment and piping per vendor drawings should be part of construction audits to avoid these critical defects.
The need to review the piping of all other fire water pumps to identify possible installation errors was emphasized.
Case 3 – Low mean time between failures of mechanical seals
Since the commissioning of one Middle East refinery (nearly four years), mechanical seals of centrifugal pumps were observed to have an average mean time between failures (MTBF) of approximately six months. The reliability section conducted an investigation to identify and eliminate the causes of the fault to extend the life of the seals. A prelimanary review revealed that the majority of failures was associated with the failure of primary seals installed as per the American Petroleum Institute’s API 682 Mechanical Seal Plan 23/52.
The site survey revealed the wrong installation of seal flushing piping and incorrect orientation of seal oil cooler as per API 682 Plan 23/52 on the 14 pumps on critical duty. In addition, the piping between the seal, cooler and barrier reservoir was observed to have many elbows, sharp bends, long piping and vapor lock opportunities. Thermal IR imaging of the seal system further confirmed poor performance of the seal oil coolers. The mechanical seal vendor recommended correction of the seal piping arrangement and cooler orientation to achieve efficient operation of the seals. The use of elbows, long piping and sloping down from the seal to the cooler had to be avoided to minimize pressure drop and possible vapor locking/hampering of proper flush flow.
These avoidable installation errors of the seal system probably contributed to the resulting overheating of the primary seal faces and caused premature failure of seals.
If these installation defects had been rectified during the early phase of the project, it would have avoided the high maintenance cost of seal replacements estimated to be one million dollars since plant commissioning. In addition, the MTBF would have been a few years instead of six months.
Figure 5: As per API 682 Plan 23/52, the seal oil cooler should have be 18 to 24 inches above the pump to generate proper thermo siphon flow of flush oil. The flush out line from the seal should be connected to the top connection of the cooler, whereas the flush in line should be connected to the bottom connection of the cooler. (Source: API Standard 682)
If a reliability program had been in place in the early project phase, it would have eliminated these avoidable defects and delivered higher uptime performance at a lower cost.
Always check the functionality of the mechanical seal system during precommissioning activities as per seal vendor recommendations.
Figure 6: The wrong orientation of seal oil cooler installed below pump center line (Source: a Middle East refinery pump)
Figure 7: Elbows and long piping installed in seal flush circuit. The flush out line from the seal is connected to the bottom connection of the cooler, whereas the flush in line is connected to the top connection of the cooler, creating an incorrect installation. (Source: a Middle East refinery pump)
Case 4 – Live performance monitoring maximizes pump life and minimizes LCC
The key to achieving extended, trouble-free operating life of high energy (>500 kW) multistage centrifugal pumps is to operate them at best efficiency point (BEP). Operating away from BEP shortens pump life. Running a multistage pump (<3000 kW) at 30 percent BEP could reduce the pump life by up to 50 percent, as shown in Figure 8.
Figure 8: Influence on pump life of operating away from BEP (Source: Predictive Maintenance of Pumps Using Condition Monitoring by Raymond S. Beebe, Pub. Date: April 2004)
Fifteen high energy (>500 kW) critical pumps in an Exploration and Production (E&P) project in the Middle East as part of an engineering procurement construction (EPC) package were about to be installed in an online condition monitoring system based on bearing vibrations and temperatures. The reliability team decided to include pump live performance curve plots and motor current signature analysis into the online condition monitoring package at a minor cost difference.
The pumps’ performance data from the factory acceptance test (FAT) was used to extract the BEP and the actual performance curves were plotted as the reference input for the software. See Figure 9 of the actual reference curve for a variable speed pump, along with the pump operating point (green zone being ‘optimum,’ amber zone being ‘acceptable’ and red zone ‘avoid’). Monitoring pump performance during the operation phase and keeping it within the BEP optimum zone extends pump life and minimizes lifecycle cost (LCC).
Figure 9: Screenshot of actual reference curve for a variable speed pump, along with the pump operating point (Source: Bruel & Kjaer Vibro Compass 6000 Performance Monitoring module)
Live performance monitoring for critical pumps should be part of an online condition monitoring program implemented in new capital projects for achieving extended long-term reliable performance and reduced energy cost savings achieved by operating in the BEP optimum zone.
Case 5 – Lubricant rationalization avoided cross-contamination and reduced cost
An upstream E&P project in the Middle East had a list of 582 machines with 624 lubrication points having an initial list of 22 different lubricants (oils and greases) recommended by different equipment OEMs. A rationalization study was conducted to consolidate the list of lubricants. Based on strict quality criteria, a single lubricant supplier was finally selected and awarded the contract to supply all the lubricants required for the project. All major types of lubricants were covered by the selected supplier, in addition to lower delivery lead time, cost efficiency, a provision of minimum stock quantity at the supplier’s warehouse and training of staff on lubrication best practices. The outcome resulted in a reduction of the list to 17 lubricants with an initial lube purchase savings of $45,000.
Lubricant rationalization should be part of a reliability program for every new project to achieve long-term benefits, easier handling and reduced inventory cost, and avoid lubricant-related failures due to cross contaminations.
Implementing a reliability program in the early phases of a new capital project (engineering design, procurement, construction and commissioning) gives the greatest benefits. Reliability initiatives taken during the initial phases of the lifecycle of a project results in maximizing the intrinsic reliability of the assets, thereby delivering higher uptime performance, improved safety, and reduced operation and maintenance costs for the project’s life. Best-of-class organizations presently realize the impact of decisions made during the early development phases of a capital project, thereby investing in reliability programs in early project phases and minimizing the value leakage to retain the maximum net present value (NPV) possible.