Reciprocating compressors within the natural gas industry may leak natural gas during regular operation. Some identified areas with high leak frequency include valves, flanges, and fittings on the equipment. But the highest volume of gas loss is linked to seal packing systems.
Leaks cost a lot of money through the value of the lost gas and the nitrogen purge that is sometimes needed to ensure safe operation. Leaks also have regulatory and environmental consequences. For instance, methane is an incredibly powerful greenhouse gas, and it is also not uncommon for some natural gas to contain toxic components.
This article covers compressor seal packing and how it prevents leakages when utilized.
What is a Compressor Packing?
Compressor seal packing is the sealing device in mechanical equipment. Its primary function is sealing, which helps control gas or fluid leakage. Compression seal packing is mostly available as relatively pliant, soft materials consisting of several rings. These rings can be inserted into the stuffing box or annular space between the reciprocating or rotating member and the body of the valve or pump.
Then a packing or follower gland is tightened against the top ring, allowing pressure to be transmitted to the packing set and radially expanding the rings against the side of the stuffing box as the rotating or reciprocating member, engendering the seal.
A seal packing set generally consists of a series of sealing units. Compressor packing is not generally bottle-tight, but its effect is that the leakage is extremely small, i.e., usually within tolerable limits and a fraction of 1 percent of the machine’s capacity.
In the event of the danger of explosion, the toxicity of the gas, or corrosion, leakage can be vented to a safe place.
Compressor packings are used extensively in the process industries such as paper and steel mills and petrochemicals, as well as in service industries like water, marine, sewage, nuclear, utilities, and food.
They are used for sealing all types of fluids, including acids, solvents, caustics, steam, gasoline, gases, oil, and other chemicals across a wide range of pressure and temperature conditions. Compressor packings are also used in reciprocating, centrifugal, and rotary pumps, expansion joints, valves, soot blowers, and several other types of mechanical equipment.
Installing and maintaining compressor seal packing is relatively easy. All that is required is adequate attention, and you will record an extremely high degree of several successful operations.
Factors That Affect Successful Sealing with Compressor Seal Packing
Highly successful sealing using compressor packings is a function of more than a few vital factors, such as:
- High standards of equipment maintenance.
- A meticulous selection of packing materials that meet specific application requirements.
- Exhaustive consideration of pressures, surface speeds, temperatures, and medium handled.
- Appropriate attention to break-in procedures and excellent installation.
When compressor packings are used during reciprocating or rotating service, i.e., in pumps, they tend to depend heavily on a fluid film between the packing and the surface of the moving member of the equipment for lubrication. Primary sources of this fluid film include built-in lubricants (solid, liquid, or a combination of the two), an external lubricant supply, or the leakage of the medium handled.
Lubricants can be released from packings by gland pressure – on equipment start-up – in order to provide initial sealing and lubrication. During break-in periods, the lubricants bridge the gap between introducing normal lubricating systems and dry operation.
By gradually adjusting the gland pressure, the external lubricating source or the pumped medium takes on the lubricating function by providing an uninterrupted source of fluid film.
The gland pressure is regulated to provide optimal lubrication and prevent overheating and subsequent damage to the rod or shaft. The volume of leakage increases with the increase in the differential pressure across the rings. The leakage will also increase according to the time that the differential pressure exists.
In other words, the longer the differential pressure exists, and the higher the differential pressure, the greater the volume of leakage.
During the operation of the equipment, built-in lubricants are expended gradually. But this action is compensated for by further adjusting the gland pressure.
What Causes Compressor Seal Packing to Lose Its Effectiveness?
When the volume loss of the lubricated packing approximately equals the initial or original amount of built-in lubricant, the overall effectiveness of the compressor packing is eventually lost, and replacement will be required.
Built-in lubricants can also serve vital functions of blocking the passage of the pumped fluids. This action prevents excessive leakages.
Compressor packings used in static operations and valves with infrequent or slow motion are required to seal completely with zero leakage. Several tools are used to assist this crucial function.
Some compressor packings are even designed with unique, non-migrating stable lubricants for excellent operation under extreme temperatures and pressures.
Compressor Seal Packing Failure
One of the most common mistakes engineers make is the tendency to increase the compressor packing’s time in service to a perceived point of failure before replacement is required. This should not be the case.
Signs that the compressor packing of equipment has failed include:
- Smoke at the stuffing box
- Increased leakage
- Uncontrolled leakage at the gland.
Therefore, every safety-conscious operator must regularly service the pump and replace the seal packing. However, no common criteria for determining the frequency of replacement exist.
Nevertheless, an acceptable replacement cycle time depends heavily on the application, the compressor packing itself, and the equipment.
This confusion often occurs due to the compression packing’s forgiving nature. Pump operation is never impaired until there is a compressor packing failure. Therefore, it should be replaced long before this incident occurs.
Reciprocating compressors in the natural gas industry function like perpetual motion machines. This may result in methane emissions to the atmosphere caused by leakages around valves, flanges, and fittings. This is where compressor packings come in.
Compressor packings are excellent seals composed of durable materials that help prevent or minimize leakage or natural gas emissions. They are used extensively in several industries, such as oil and gas, paper and steel mills, and service industries like sewage, marine, food, nuclear, and utilities. Contact us for your needs and equipment. We carry legacy components like packing, wiper cases, and more that you can count on.
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