Boiler Gaskets

Taking a boiler out of service is both expensive and disruptive. It can leave a building without heat, hot water, or steam for days, meaning lost production and unhappy customers or tenants. That’s why it pays to schedule boiler maintenance some time out, preferably for shutdowns or holiday periods. Many facilities make this an annual event, so the manhole and handhole boiler gaskets as well as the seals used in pipe flanges need to last at least that long.

1. Don’t assume any rubbery material will do the job. It won’t. Buy good quality boiler seals from a reputable supplier. (Look for those made from EPDM as they hold up well to steam.)
2. Clean the surfaces to be sealed thoroughly. The new seal should contact only the metal surfaces, not scale, corrosion, or scraps of old seal. Take care to avoid scratching the metal surfaces though as that will create a leak path.
3. Avoid using any adhesives, sealants or anti-seize compounds on the seal or flanges. These can lower friction and allow the seal to move as the joint is tightened.
4. Center the seal in the flange. This ensures clamping loads are distributed evenly across the surface. Not doing so creates areas of high and low load that reduce gasket life and let leaks form.
5. Minimize the surface area of the seal exposed to atmosphere. Hot air leads to oxidation of the seal material, quickly reducing it’s life. If necessary, add shields to protect against hot air.
6. Don’t overtighten the joint. This accelerates the process of the material taking a compression set and will lead to premature failure.
7. Excessive heat and pressure shorten seal life. Temperatures and pressure above 380°F and 180 Bar should be avoided.
8. Never reuse old gaskets. The material will have taken a compression set.

It’s worth investing time and money in buying quality boiler seals and fitting them carefully. When the job’s done properly the seals should function as intended for at least twelve months. That reduces the chance of premature failure, which would almost certainly require an unplanned, and expensive, shutdown.

Gaskets are part of every boiler and steam or hot water system. They’re used around the many handholes and manholes provided for access and inspection, to prevent leaks in exhaust ducting, and wherever pipes are joined. If a boiler gasket fails the consequences are usually serious. Hot water, steam, or exhaust gas leaks are dangerous and reduced efficiency increases operating costs. That’s why safety experts recommend boiler gaskets be inspected regularly and replaced every year.

Boiler Basics

Every boiler consists of a burner or heating element and some form of heat exchanger. Water, often chemically treated to prevent corrosion, enters the heat exchanger and is heated to a target temperature. In a steam-producing boiler temperatures and pressures can exceed 380°F and 180PSI.

Exhaust gases go up a flue and steam or hot water enter the piping system. In steam systems the vapor condenses as it cools and the condensate returns to the boiler to be reused. Condensing boilers tend to produce a corrosive condensate, (actually carbonic acid,) in the exhaust stack.

Boiler Maintenance

Shutting down a boiler is expensive and disruptive, so it’s always better done as part of scheduled maintenance rather than in response to a leak. Most boilers benefit from an annual inspection and clean. Removing accumulated soot and scale improves efficiency and components should be checked for correct operation. As that involves opening handholes and manholes, it’s also a good opportunity to replace gaskets, even if they show no sign of leaks. (And never reuse a gasket as that could lead to an unplanned shutdown!)

Boiler Gasket Materials

On the fire side of the boiler gasketing is usually done with fiberglass rope or tape. This can handle temperatures of more than 1,000°F. Another option is graphite foil, often formed into a spiral wound gasket for sealing flanges.

On the water side the primary consideration is tolerance to steam. Secondary requirements are good tensile strength, (to resist the internal pressures,) and resistance to corrosive acids and water treatment chemicals. Heat and oxygen tend to oxidize many elastomeric gasket materials, and this should also be considered when selecting boiler gaskets.

All-in-all, the water side environment usually leads to EPDM gaskets. They have a wide temperature range, good compressibility, and the excellent steam resistance that’s needed.

Boiler Gasket Selection

Downtime is expensive, so it’s important to ensure the new gaskets will provide at least 12 months of trouble-free service. Boiler gaskets should be selected based first on performance and secondly, on ease of installation and replacement. A well-made gasket will fit comfortably, providing good coverage of the mating surfaces. Contact a Hennig specialist today to ask what’s recommended for your boiler.