Sealing devices play a vital role in ensuring that your plant performs at its best at all times. After all, a seal failure could mean leaking pumps or valves, or oil dripping from gearboxes and result in serious plant shutdowns and days of lost production.

Whether it’s gaskets, packings, expansion joints, or any other sealing device, selecting the right product that fi ts the application is crucial.

That process usually begins with defining the level of performance expected from the sealing solution and identifying the service conditions. Garlock Sealing Technologies uses a procedure called TAMPSS to make sure that nothing is missed when gathering information, says Jim Drago, Manager, Engineering. The acronym stands for Temperature, Application, Media, Pressure, Size and Speed.

“This kind of approach applies to gaskets, packings, expansion joints, hydraulic components, or any other sealing product,” says Drago. “You can use this template to walk through the selection process.

TAMPSS
With most processes, the Temperature of the fluid which contacts the seal is considered first. Knowing the temperature will quickly reduce the number of possible product materials.

Application defines the equipment in which the seal will be placed and also helps to determine the installation procedures that will optimize performance. This would include:

• Gaskets – flange type, flange material and bolting information to determine how much compressive force will be available
• Oil Seals – what type of equipment will the seal be used in – gearbox, machine spindle, etc.
• Valve Stem Packing – is it a reciprocating, helical or constantly-moving stem motion?
• Expansion Joints – what’s the joint’s function? Is it vibration isolation, linear or angular expansion, contraction or all? What type of equipment will it be attached to?
  

Media is used to determine the gas, solid or liquid media that will come into contact with the seal and its compatibility with the seal material. Other media that may be present intermittently, such as those used in cleaning processes, should also be considered. The aim here is to choose materials that are chemically compatible with the media. And, in the case of gases, there may be more concern in choosing products that have superior tightness and less permeability.

Pressure will include details on the internal pressure and whether there will be any pressure spikes or surges.

When dealing with pump packing, mechanical seals, oil seals or bearing isolators, it’s crucial to know the surface Speed at the seal shaft interface. Knowing the surface speed indicates the frictional heat which will be created. High surface speeds demand material which can stand up to and effectively dissipate heat.

Size comes into play with these products as there may be limitations on how big or how small they can be. For flanges, there are ASME standards that give standard dimensions for flanges and gaskets. However, some standard flanges may be more problematic than others, which an applications engineer would have to take note of when choosing the right sealing product.

Selecting the right product to fit the application
Once all the data has been collected, the next step is to select the right product to fit the application. Most manufacturers will provide at least two, if not three, recommendations, says Drago. It’s really a Good, Better, Best approach, with the customer weighing the advantages and disadvantages of the Good choice versus the Best choice. Multiple recommendations also allow the customer to deal with other pertinent issues, such as pricing or availability.

While price can be a factor in choosing the sealing product, it really depends on the application. For example, if standardization and emissions compliance is at the forefront, then sometimes price can fade into the background.

When selecting sealing devices, you should also consider the differences between the high-cost and low-cost solutions, including the raw materials used and the life expectancy of the product. Is the sealing solution reliable and will it minimize the possibility of unexpected shutdowns? Does it install and remove easily? How much will it cost if the product fails? These are all questions that need to be factored into the price equation.

Sealing products are very installation sensitive and even the best product the manufacturer offers can fail miserably if it’s not installed properly. Most manufacturers in the sealing industry provide the end-user with the proper tools and installation instructions, and training to perform proper installation. It’s vital that the manufacturer’s instructions are followed to ensure that the sealing product performs effectively.

In terms of preventive maintenance, regular inspection of fluid-handling systems will minimize downtime and allow corrective measures to be taken before failures occur. The correct identification, troubleshooting and gathering of information on sealing issues will lead to better sealing solutions for individual applications.

New Technologies
In the areas of gasketing, there are now products available that are tighter sealing – PTFE type products that creep even less than the previous best in class materials. Garlock, for example, has introduced its Sage GYLON Gasketing Material, which offers very good sealability and the lowest creep of any of the Gylon products which have been recognized as having the lowest creep as a general class for years.

Also on the gasket front, there’s the development of specialized compressed fibre gaskets, with specialized elastomers that will swell. While elastomers can be made to swell in all sorts of different fluids, the problem is that when they swell they degrade and lose all their strength, and lose all their integrity. The trick is compounding rubbers in such a way that you get the swell characteristics while still maintain integrity.

For example, drips coming off a leaky gearbox cover might not seem critical to some people. But when the oil drips on to the floor, it can produce big issues with worker safety. So putting a material like this that will swell up in the presence of oil but not break down, can easily solve the problem.

In the world of valve stem packing, maybe not so new but certainly noteworthy, are engineered packing sets. These are usually combinations of carbon graphite, spacers, flexible graphite braids, etc., which have simplified and changed the whole field of attaining low fugitive emissions for valve stems. In the process plant part of a refinery or a chemical plant valve stems are generally recognized as the biggest problem for fugitive emissions.

There have also been developments in the area of bearing isolators – dynamic seals designed to protect bearings from outside contaminants. Normally, bearing isolators are not expected to seal against positive pressure. They keep dirt and water from getting in and keep oil from getting out. Now there are bearing isolators that actually hold some pressure and handle gearbox oil levels that submerge the isolator.

As featured in Canadian Process Equipment & Control News