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Instrumentation to Plant is what Central Nervous System is to Human Body
Drastic reduction in maintenance cost, achieving unity uptime, reduction in overtime from 5000 to 2000 hours at BPCL refi nery are few of the accomplishments of
PLN Murthy, CHMM, Maintenance Head BPCL. In an exclusive interview with CEW he shares his opinion on critical role of instrumentation to ensure uninterrupted plant operations and personnel and plant safety. Excerpts from the interview.

Please apprise us about the safety practices in context to the chemical industry in the country. How have the safety practices changed over the years, typically in the refining sector?
Like all the other standards, safety standards and practices are evolving and modified with time. The working conditions, awareness of health hazards especially in abnormal conditions like plant or unit start up and shutdown, made the safety regulations more and more detailed and specific. After every incident - like BHOPAL tragedy and Jaipur incident - the safety regulations were revised. On the other hand, in earlier days the chemical plants were located away from populated locations. But over the time, the townships have come around old plants and with cities growing the units are surrounded by dense inhabitant.

Again the environmental criteria have been constantly demanding less pollutants release both in atmosphere and liquid effluent. It is possible for new units to be designed according to new guidelines. However continuous efforts are needed to modify the existing units to suit the revised safety guidelines. Not only CAPEX, but also space and technical limitations come in way to run or modify the units safely.

We at BPCL follow all the statutory guidelines, of PESSO for safety. Like all the other Oil Companies, we are guided by Oil India Safety Directorate (OISD) standards. We have continuous Internal Safety Audits, biannual external audits (like DNV), and surprise audits from OISD. There is an external audit once in 3 years by OISD. We dilute / mitigate all the points raised in the above audits, in timely manner, so that the same stand for scrutiny by next audit team.

What are the major considerations that need to be factored in at the time of design, keeping in mind upgrading to future technologies to ensure plant performance and safety?
At the time of design, various factors are considered and factored in to the plant design and selection. The first factor is selection of a process technology, which gives an optimum performance and process safety.

Simply putting a renowned process licensor can fulfill such a requirement. But the catch lies in bringing different (Technique) licensors on to a common level for comparison purpose. Many a time, performance criteria are fulfilled by all licensors. There will be variations in requirement of utilities, both in quality and quantity. Sometimes the criteria is on space requirement, in other cases it will be maintenance factors and ease of operation. In all cases process safety is ensured, but the risk factors and levels vary. Some of these cannot be quantified, which makes it complicated to compare two process technologies.

All the above factors are for only process selection. At design stage, many more considerations come into play, such as area availability for the plant or unit. If the space available is limited then, one has to go vertically (up) for construction. If inter equipment distances and free spaces are limited, it is more difficult and less safe for maintenance working. Sometimes, due to space constraint, a particular equipment selection may become different and that may lead to non-optimum performance or more prone to maintenance.

The other factor at design stage is capital, as any investment is considered, based on return on capital (except in case of safety requirements). The limitation on capital will tell on quality and finish of the work done. Capital limitation leads to cut corners in many a place, which will leave tell tale on every aspect of the unit. Sometimes additional facilities (in each individual equipment and also overall) may be dropped which may not be possible to add later. This may curtail the optimum utilisation of the equipment or any data utilisation.

Actually, once a process technology or equipment is selected, later on the upgrading is only dependent on the OEM. The technology may be improved at a regular interval, but to adopt the new technology and make a new hardware changes, it may take few years as the factors such as procurement of technology, time for approvals and preparing for a hardware change and next available opportunity (of plant turnaround) may take some time. A meaningful up gradation happens say after 10 to 12 years. As mentioned above, process safety is assured all the time. The plant safety conditions can be and shall be upgraded at the earliest without any time limits (upper or lower).

From the maintenance perspective, what are the major parameters that one needs to look out for to ensure safe and uninterrupted plant operations?
For ensuring both safety and uninterrupted plant operation, the prime parameters are quality, quality and quality. Quality in work, quality of selected equipment, quality (reputed) vendor, quality in design are important for achieving safety and uninterrupted plant operations.

Quality at design stage ensures reliable equipment specifications such as correct metallurgies. Suitable API specifications increase the availability of equipment with high efficiency. Where as quality in work reduces, frequent failures and avoids rework. Rework cost, or say cost of poor quality of work, is the single most avoidable cost of maintenance. Rework (failure) causes interruption in plant operation and has many folds cost implication. Apart from the cost aspect, it gives rise to avoidable efforts from operator for isolating, handing over, commissioning of the equipment, and maintenance efforts for attending the equipment.

The equipment like pump is to be installed with proper care. Any piping stress, alignment, foundation, anomalies will have impact on performance of bearings, seals and result in interruptions in availability of equipment. The availability of spares is another major factor to deliver the quality work, so that mean time between failures can be increased (and hence, more availability of plants). Purchasing spares from OEM, other material from standard manufacturers (not from traders) through third party inspection will increase the quality of spares. Instrumentation plays a critical role to ensure uninterrupted and safe plant performance and avoid unprecedented downtimes. What is the lifespan of

Instruments typically in refineries and how frequently these need to be upgraded? The instrumentation in plant performance is like central nervous system to the human body. The instrumentation in safe plant performance is broadly categorised into three categories.

One is for safe start up and one is for safe shutdown. Though the popular belief is to avoid spurious trips, in terms of safety of the plant, spurious trip is still acceptable rather not tripping the plant, when required, as it is unsafe and not at all acceptable. In that case, the damage/ loss to both the plants and human cannot be quantified.

The third category of Instrument is used while plant is running. This category is considered to be very important for uninterrupted and safe plant performance. Under this category, the indications/ controllers are more found.

The transmitters, barriers, relays and SOV form major part in the nervous system apart from cables, terminals, terminations, electronic cards and JBs. The strength of the chain is determined by the weakest link. In this case of requirement of uninterrupted plant running (in terms of instrumentation), all the above have to provide robust, uninterrupted service.

Hence the quality, which we talked earlier, is of utmost important. The quality of each instrument, the quality of installation, quality of design of logic, the Proven Track Record (PTR) of equipment and use of standard software is essential. The SOV considered being the last control element (assuming the shutdown valve is designed fail safe), which has to trip when required, shall be reliable.

At BPCL the SOV is designed (as a default practice, as is in many other refineries) to be ¬ON  (energised) condition while the plant is running. The ¬DC  power is supplied through battery back up so that even in power failure conditions the control is possible.

The other regular troublemaker is ¬relay . By design the relay is ¬ON  while plant is running. The relay through DC power is in energised condition, so that in all situations, logic will have control on the safety of the plant. We had experienced that the other key contribution to interruptions is (high pressure) tube fittings. We have restricted vendor list for all the above, SOV, relay and tube fittings. This along with dedicated teamwork, I believe, has given us the uninterrupted and safe running of our units with a 100 per cent up time.

Apart from above, all those instruments, which form part of interlocks, say vibration switches, bearing temperature elements etc. give raise to unwanted trips. These can be regularised at design stage, in consultation with OEM, may be made 2 out of 3 logic, or 2 out of 2 or making 2 or 3 separate groups.

Yes, when we talk about the uninterrupted performance of equipment (instruments), there comes a question of Ąhow long?Č That is the life span of instruments. Now a days the Meantime Between Failures (MTBF) of instrument, is very high, as the electronics life as well as quality of material is improved.

However, the reliability of RT type of thermocouples and vibration probe life is still uncertain. Hence we change them in single equipments like compressors, at every turnaround. All other instruments, as we ensure quality of material and quality of work and check at every turnaround, we did not find necessary of changing yet. We do upgrade the DCS software, and man machine interface, (operation stations) at 8 to 10 year interval.

May we have your comment on forward thinking in CAPEX considering the real economic life and changes in product design? The point in your question, though has a vast implications and coverage, I will answer in Maintenance perspective. Normally at design stage, some margins are included for quality improvements. But if the product or feed specifications change then, material of construction need to be looked into.

That is where CAPEX in maintenance come into the lime light. If the severity of the damage, is manageable, i.e., if the wetted parts repair is less costly and less frequent that is advisable to continue, without any changes (no capital cost). If otherwise, spend CAPEX to increase the reliable and uninterrupted plant running, by upgrading the wetted parts to higher metallurgy.

The forward thinking in CAPEX, it is always ¬postpone  CAPEX, if not possible reduce the CAPEX to bare minimum. In any case, without full economic calculations no CAPEX shall be taken up.