V. K. KHANNA, Engineering Consultant, Gurugram, India
The maintenance of industrial chemical plants is essential to protect and restore equipment, circuits and systems to enhance their function and provide efficient operations. Maintenance helps a plant remove deficiencies and malfunctions, improving its operational performance and life. Every design undertaken for such a plant requires well-thought-out maintenance requirements, accessibility, ease of equipment maintenance and tool options to be usable without limitations.
During the plant investment process, investors often raise questions about the allocation of maintenance funds and proper maintenance regimens that must be followed after the plant becomes operational. These guidelines help operators avoid mishaps or breakdowns that can affect the plant’s profitability, hurting their investment.
The author has been involved in implementing grassroots process plants and revamping oil and gas plants, with a significant focus on refineries. This article features inspection and maintenance requirements for refineries, which are also essential in other chemical and gas plants.
Types of maintenance. There are three types of maintenance, each with a unique methodology of approach and implementation:
For major maintenance, well-planned shutdowns may last weeks to months. Planned shutdowns are helpful to identify faults and should include an on-ground feedback report. Once the areas requiring maintenance are identified, suitable specialist teams are deployed after preparing a sequence chart of the faults individually, or collectively, as the situation and time permits.
In refinery and petrochemical plant maintenance, three additional terms are in use regarding equipment maintenance: preventive, predictive and corrective maintenance. Preventive maintenance includes cleaning, bolt tightening, oil changes, lubricating equipment and replacing small parts. Predictive maintenance helps predict likely failures using diagnostic instruments, which can be portable or permanently installed. Corrective maintenance involves necessary refurbishments and replacement.
Refinery maintenance core issues. Equipment is listed depending on maintenance essentials, and priority is fixed to carry out various works and activities as per related work-breakdown structure. The equipment in high-pressure areas and rotating equipment, compressors, turbines, pumps and agitators are critical, and repair and maintenance activities are undertaken carefully. The following are some maintenance points highlighted by experienced operations and maintenance specialists:
Maintenance prerequisites. The following prerequisites are important to consider for successful maintenance:
Inspection guidelines. Inspection paves the way to identifying problem areas and undertaking maintenance in a structured manner to achieve successful and timely completion. The following are some inspection guidelines:
Vulnerability issues. Leaks require the utmost care to avoid safety issues. The leakage points are pump glands, exchanger flanges, threaded joints, welds, valves, PRVs, corroded areas of equipment and pipes. Liquid leaks are visually noticeable, but gas and vapor leaks are measured with instruments. For underground pipes, operators use odorized test fluids passed into the pipe’s flow that seep into the soil at the leak point. The odor emitting from the soil confirms leakage.
Many refiners use mass-balance methods to detect leaks. Flow computers measure the mass of the liquids being transported through the piping network. If the difference in mass recorded at a point differs from that measured at another point, it indicates that leakage has occurred in between. If required, a physical inspection of flows can help locate leaks and discover the cause for each location.
In refineries, a H2 unit is involved. H2-induced crack points in components and various joints are the sources of leakage. H2 leakage is difficult to identify, and its flame is invisible during the day and feebly perceptible at night.2 Leak checks are done using a soap solution, but a more sophisticated method is to use a H2 leak detector. Leak repairs are done during shutdown. The Occupational Safety and Health Administration (OSHA) standard 1910.147 refers to the control of hazardous energy sources during equipment maintenance and must be followed.3
Leak repair requires skill and must be done as noted in the inspection report. For vapor and gases, options exist to repair it immediately or vent the gases to the atmosphere. For liquids, the inspection assesses the extent of leakage. If the leak is less than 3 drops/min, a temporary repair is undertaken within 1 yr. A temporary repair is undertaken if the rate exceeds 9 drops/min. Repair during the next shutdown must be conducted for bigger leaks, but should never be postponed beyond 1 yr.
Leak repairs are done by shutting off the system, clamping the affected area and filling the annular space with a sealant that hardens immediately. Threaded connections are sealed with sealants. Offline repair is done when the affected part is bypassed without shutting down the system. The system is drained, followed by nitrogen purging and steaming. Afterward, the cutting, repair, welding, inspection, radiography and stress relieving are completed. Mating flanges are provided with new gaskets, and bolt tightening is properly done using a torque wrench adopting parallelism sequencing in all earmarked areas, specifically in high-pressure lines.
Vibrations. Vibrations in piping and equipment caused primarily by imbalance, misalignment, looseness and wear are another critical issue requiring specialist groups to handle. An inspection group comprising in-house specialists with manufacturer representatives (in case the essential equipment causes vibrations) is deployed to study and diagnose the cause of vibrations to stop them. Vibration monitoring and diagnostic equipment can help to identify vibration locations. The maintenance team undertakes the physical implementation of measures suggested by the inspection group.
Instrument malfunctions, valves and guided drives are other critical areas. Instrument engineers and factory-trained specialists inspect this. They use various gadgets, including non-destructive evaluation (NDE) instruments, to monitor, diagnose and coordinate signals. Software engineers help resolve system problems, along with the inspection and maintenance groups. Instrument calibration is done before the work is completed. Flame and gas detection instruments and sensors must be serviced and confirmed as operational.
NDE. An NDE is another tool used to locate weak areas of high-pressure equipment that need repair and strengthening. It helps to assess the equipment’s balance of life, which is especially useful in older plants. Such a survey is conducted during long process plant maintenance periods.
DCS maintenance. DCS maintenance is carried out simultaneously during a process unit’s maintenance. The DCS supplier’s engineers, operations and maintenance teams carry out the maintenance. The proper functioning of field instruments is coordinated with DCS operators to achieve optimum process functioning, throughput and capacity results.
Laboratory equipment maintenance is done separately through annual contracts by engineers, testing specialists and equipment suppliers and is coordinated with process unit maintenance. In addition to mechanical maintenance, concerned engineers undertake maintenance on pavement, utility lines, sewage, buildings, structures and housing mechanical systems simultaneously.
Lastly, a complete maintenance team includes well-trained specialists from all disciplines and seasoned engineers with high interpersonal discipline to complete tasks without mishaps. Their completed work should achieve the desired operating results from the process unit’s operators. Experienced maintenance technicians deploy well-tried maintenance strategies that help in technically acceptable and cost-effective maintenance.
The process plant’s equipment, systems and components will develop regular faults in specific circuit areas over time. The operating team typically notices equipment, particularly rotating equipment, and will be ready to attend to these immediately.
Takeaway. Reliable maintenance is achievable with proper inspection, diagnosis, and leaks and vibration identification in affected circuits and requires timely repairs, corrections and replacements. An adequately maintained plant without spills performs at the expected level and standard. HP
LITERATURE CITED
VIJAY KHANNA has 26 yr of experience in the oil and gas sector, working with Engineers India Limited until March 2001. He has worked on numerous projects, including Sonatrach’s Jumbo LPG I plant in Algeria, the first hydrocracker plant in India, a grassroots refinery at Numaligarh, BPCL’s refinery expansion in Mumbai and several plant revamps. Khanna has published five articles/papers on structural engineering, articles on H2 generation in each Hydrocarbon Processing in 2001 and H2Tech in August 2023, and has reviewed maintenance essentials in the World Refining Journal in 2002, as well as hydrocracker projects and the Numaligarh refinery project implementation in the EIL Journal. Khanna earned a B. Eng degree and a PGD in management.