January 2017

The Role of Gaskets in Minimizing Fugitive Emissions

Fugitive emissions are a serious matter for chemical plants and petrochemical facilities. First, the EPA is focused on reducing unplanned releases of VOC’s into the atmosphere, and second, it’s a cost-saving opportunity. Studies blame valves for the bulk of these emissions, but flanged joints and their associated gaskets play a part too.

Hunting Fugitives

Defined as “… unanticipated or spurious emissions from any part of the process plant,” in 2014 the Fluid Sealing Association estimated fugitive emissions amounted to some 300,000 tons annually. Furthermore, it’s thought a high proportion are hydrocarbon gasses like methane believed to be environmentally harmful.

Plants handling such chemicals are expected to implement Leak Detection And Repair (LDAR) protocols, preferably on a monthly basis. “Sniffing” technology is the method most commonly employed, although IR camera technology is increasingly available.

Prevention First

Should a LDAR survey reveal a leak the next step is usually to shutdown the affected equipment for valve repair or gasket replacement. Unplanned shutdowns are disruptive and expensive, making it essential to avoid such events. While leak-free performance can never be guaranteed, buying different types of quality gasket materials and following good sealing disciplines will reduce the likelihood of problems.

Three Principles to Follow

  • Select material appropriate to the media, pressure and temperature. Nitrile gasket material for instance is generally compatible with hydrocarbons like gasoline but should not be taken above 250°F. A neoprene gasket will perform better against ammonia, alcohols and mild acids while high temperature applications may need a fluorocarbon or PTFE gasket. In particularly arduous conditions a spiral wound gasket might be needed.
  • Analyze the joint to determine material thickness and hardness needed. The general rule for gasket materials is “as thin and soft as possible.” The goal is always to ensure the gasket compresses sufficiently to seal the gap when the joint is bolted up. High bolt loads risk deforming the flange, potentially causing leaks.
  • Follow good gasket replacement disciplines. Clean flanges thoroughly and verify mating surfaces are undamaged. Tighten bolts following the recommended sequence to avoid uneven compression and the risk of gasket extrusion.

Gasket Swell Isn’t Always Bad

If gasket material isn’t chosen to suit the fluid being sealed, problems are almost inevitable. One reason is that some fluids will make the gasket grow thicker. This is an effect called swell. It increases bolt loads and can lead to material extruding out of the joint. Almost every gasket material has a fluid that will make it swell to some degree.

Bad Combinations

To give one example, an Acrylonitrile Butadiene Rubber (NBR) gasket swells significantly when exposed to acetone or methyl ethyl ketone yet shows almost no growth in the presence of vegetable or mineral oils. Hydrocarbons and petroleum products are a particular problem because they will cause swelling in several widely used gasket materials. EPDM, Styrene Butadiene Rubber (SBR) and Neoprene gaskets are prime examples and should not be used to seal these fluids.

Information on susceptibility to oil swelling is given in the ASTM D2000 classifications for elastomeric materials. This was addressed in “Buna-N (Nitrile) Gaskets and Oil” and “ASTM and Gaskets.”  Rubber gasket material sheet properties are essential to know.

Some Exceptions Apply

There are times when a gasket installer might use swell to his advantage. This would be when it’s difficult to get the required level of compression. To give two examples:

  • Thinner flanges not meeting ASME/ANSI standards may distort as bolts are torqued, resulting in a variable gap.
  • Bolts may lack the thickness or strength to take the necessary loads.

Faced with these problems, choosing a gasket material prone to swelling can be the solution. When exposed to fluid in the pipe the inner region of the gasket will swell, increasing the loading achieved.

Buy the Right Gasket Material!

Harnessing the swell effect doesn’t just mean deliberating selecting the wrong material. This would swell unpredictably, possibly with catastrophic results. However, some gasket material manufacturers produce so-called “controlled swell” material. Often employing Styrene Butadiene Rubber (SBR) binders, these provide predictable growth. (“Controlled swell” material is available for fluids other than hydrocarbons, even water!)

Ask About the Material

If you have a hard-to-seal joint “controlled swell” gasket material might be worth considering. Discuss what’s available with the material specialists at Hennig Gasket & Seals.

Custom Gasket Cutting

One of the challenges with replacing gaskets is that you don’t always know what kind of replacement is needed until you get the joint apart. If you’re lucky it takes a standard gasket that you can collect or have shipped out. If you’re unlucky though you’ll need a fabricator who provides custom gasket cutting — FAST.

The Cost of Downtime

When a gasket starts failing prompt replacement is essential: product is being lost, yields are falling, and profits suffering. Worse still, you might be risking both ground contamination and fugitive emissions from pipeline leaks, which could lead to legal action and fines.

Unfortunately, gaskets can’t be replaced without taking joints apart. That means shutting down production so that pipes are cool and empty. Once the new gasket is in place, start-up may take several hours. Lost production means lost sales, and that money may never be recovered.

Gaskets and Inventory Costs

Few maintenance departments have the luxury of keeping in stock every gasket that might ever be needed. Even if there was enough space and Accounting would tolerate the costs, the material ages and eventually becomes unusable.

Just-in-Time Delivery

Many maintenance operations have adopted a different approach. Instead of carrying a large gasket inventory, they’ve aligned themselves with custom gasket suppliers capable of rapid delivery.

Configuring a business to cut and deliver custom gaskets in just hours takes a significant commitment of time and money. A large inventory of gasket material is essential, as are flexible cutting processes that don’t demand long lead-time tooling.

With an extensive range of material on-hand, plus computer-controlled cutting machines, Hennig is positioned to provide the fastest possible turnaround. To save time, new gaskets are often reverse-engineered from the one that’s been removed, and it’s not uncommon to work from photocopies of gaskets and even hand-drawn sketches.

Gaskets Aren’t Expensive, Downtime Is

When you need a gasket in a hurry, think of Hennig. A massive inventory of gasket material, combined with flexible cutting/manufacturing processes means we can produce a custom gasket in just hours. That means less downtime, which goes straight to your bottom line. Contact us today for fast and accurate custom cut parts.