Discover a Career: Cleaning Engineering—A Critical Role in Precommissioning
Have you ever wondered about the opportunities that exist in the precommissioning industry? It encompasses the activities undertaken to ensure smooth transition between the mechanical completion and commissioning/startup of process plants. Under the umbrella of precommissioning, electrical and mechanical instrumentation and control system testing may also be included, but this article will primarily focus on the cleaning aspects of process plants.
After a process plant is constructed, vessels and interconnected piping are left with construction debris, pressure-testing fluids, and sometimes even hard hats or hammers. It becomes critical to ensure these foreign materials are removed to avoid them being lodged into pumps, turbines, compressors, etc. For example, the lubrication system of pumps is flushed with compatible oil so that debris larger than 15 µm is filtered out and does not cause damage to the pump bearings.
Types of Cleaning
Cleaning methods may include cleaning by blowing (air, steam, or nitrogen), flushing (oil or water), chemical cleaning, and mechanical cleaning by using a “pig.” At times, a visual inspection of vessels or piping has to suffice if there is no economical way of cleaning the equipment or physical limitations to access exist. Improper cleaning operations can result in critical equipment malfunction and multimillion-dollar delays.
Cleaning by Blowing. Blowing is an effective cleaning method to remove construction debris, loose rust, liquids, and other contaminants from process piping. Three different media can be employed: air, steam, and nitrogen. Blowing generally is employed for cleaning systems such as utility and instrument air, natural gas, and fuel gas.
In this process, compressed, dry air is injected into process piping to blow out dirt and debris in an explosive manner. Air is typically compressed to 100 psi, then passed through an air dryer capable of dehydrating the air to a dewpoint of -40°C before being injected into the system. The dry air then expels moisture and construction debris into a receiver.
Steam blowing applications include
- Unseating mill-scale magnetite layer deposits and welding slag through thermal pipe shocking
- Purging high-, medium-, and low-pressure steam lines leading to end users, such as well pad injection points and steam traps
- Commissioning of steam supply and distribution piping, including lines originating from traditional boiler and once-through steam generator systems
- Cleaning of critical system piping leading to components, such as steam turbine generators on cogeneration units
Although air drying can achieve low dewpoints, it may take a significant amount of time to attain the dryness specifications. If low dewpoints are necessary, such as for refrigeration systems on liquefied natural gas (LNG) facilities, compressed nitrogen may instead be used. This allows dryness of -60°C in a timelier fashion but may be cost-prohibitive.
Cleaning by Flushing. Oil or water is used to flush equipment and vessels for wastewater, boiler feedwater and fire water systems. External pumps and filter systems can be used to circulate water at a high velocity that dislodges and removes debris and scale from piping walls and vessels.
Hydraulic and lubrication systems of rotating equipment are cleaned using oil-flushing techniques. Similar to water-flushing, hot oil is pumped and circulated through a filtration system to remove very fine construction material left post-welding.
Chemical Cleaning. Rust, grease, oil films, and scale are some of the byproducts of construction. Chemical cleaning addresses these concerns by degreasing, pickling, and passivating piping and vessels. Chemicals mixed with water are injected using a pumping unit and external filters to achieve cleaning specifications. Degreasing removes oily films and grease prior to the introduction of acid. Acid pickles the surface of piping and vessels to remove rust. Chemicals used for passivating are then injected to coat the cleaned surfaces with a thin oxidized layer thereby preventing additional rusting. Generally, systems that require chemical cleaning are upstream of sensitive equipment; for example, suction lines of boiler feedwater pumps.
Mechanical Cleaning. Mechanical and visual methods of cleaning are utilized for noncritical systems. Mechanical pigging moves larger materials from pipe work, while visual inspections are conducted to ascertain a minimum degree of cleanliness exists. If construction debris deemed detrimental to operations is encountered during visual inspections, vacuuming techniques may have to be used if the aforementioned cleaning techniques cannot be used.
The Importance of Cleaning During Precommissioning
When one thinks of precommissioning, brand new facilities come to mind. Often, however, plant expansions dictate that facilities that are operational, or brownfields, are in direct communication with the newbuilds, or greenfields. It is therefore crucial to gain an overall understanding of the systems that are being cleaned. For instance, H2S monitors are mandatory for areas that have sour gas operations. Proper lock-out/tag-out procedures must be followed to isolate live areas from newbuilds. Safety is key in these situations, where personnel are working in close proximity to rotating equipment, live steam headers, or high-pressure vessels.
As precommissioning is the step barring large facilities from becoming operational, it is often rushed or altogether skipped. What time and funds are saved before commissioning, therefore, is spent twice-over in maintenance or replacement of faulty equipment. Since startups or turnarounds are not everyday occurrences, it is advisable to take the time upfront to ensure precommissioning has been properly administered.
What happens when none of the cleaning methods achieve the results demanded? A particular foam plug refuses to dislodge after high-pressure air blows; rice paper, used during welding, remains stuck to process piping even after high-velocity water- flushing? A certain amount of ingenuity is required to engineer a cleaning solution. You may think becoming a professional cleaner is a piece of cake, but there are some intricacies involved.
Opportunities in Precommissioning
Among the myriad opportunities that are available in precommissioning, engineering plays a key role. In order to ensure effective cleaning operations are conducted, the engineer needs to decide the method that will be conducive once the plant becomes operational. An understanding of the overall process in essential. For instance, one would not clean an LNG facility in exactly the same manner as an oil sands upgrader. Back-to-the-basics of engineering is often required to recall how a cogeneration unit functions, for example. Looking to degrease a boiler unit? How much steam will be required to achieve temperatures of 700°C needed for the effective cleaning of the boilers? Interpretation of technical drawings is also required. You will become fluent in piping and instrumentation drawings and isometrics.
Once the engineering design for cleaning has been completed according to the specifications outlined by the plant owners, safe and efficient execution has to be undertaken, to turn over systems to operations in a timely fashion. At this stage, engineers can undertake a project management role to lead field staff in execution, while adhering to the project schedule and safety standards. Quality and documentation control; scheduling; health, safety and environment; and inspections are also some other milieu to be explored for career options.
When you hear the whirring of pumps as they kick into motion, or the whoosh of natural gas being fed to burners, remember to thank the cleaning engineer and all those associated with precommissioning.
|Did You Know?|
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29 July 2019
16 August 2019