Flange Gaskets

Gaskets exist to seal joints or interfaces. They’re either keeping something in or keeping something from getting in, and if they do their job no one notices them. That’s probably why some gasket buyers find themselves under pressure to go with the cheapest. Only later do they find that a very expensive mistake.

Gasket failure is expensive

The consequences of a leaking joint range from the trivial to the fatal. At one end of the spectrum, if a pipe flange gasket lets a trace of toxic chemical into the environment the results can be unthinkable, and will probably incur the wrath of the EPA. Fines and clean-up costs could sink the most successful company. Or consider other less serious but still expensive examples. Water penetrating an electrical enclosure gasket could damage equipment inside, causing lengthy unplanned downtime. Failed boiler seals might shut down a heating system, sending employees home. Even when the impact is minor, a lot of time might be spent cleaning up, and a lot of product wasted.

Gasket replacement is expensive

There’s the time and materials to do the job and perhaps other expenses involved in accessing the gasket location, but these pale next to the cost of lost production. A single leaking pipe can bring an entire plant to a halt while a new gasket is installed. Planned replacement is always preferable to reacting to a leak, but either way takes equipment out of service for a period of time.

Lifetime reliability

The price of the gasket is a very small part of the cost of a sealing problem. Logically then, anything that extends the life of the gasket is worth doing.

There are many options for sealing a joint or interface. Gasket materials come with long lists of specifications. Interpreting these and selecting the optimal combination takes in-depth product knowledge and understanding. Gasket experts might find what they need in a catalog, but for most buyers the best option is to ask their supplier. They’ll be happy to explain the characteristics of each gasket material

Preparation is everything they say, and that’s certainly true for flanged pipe connections. As flanges are brought together and the bolts tightened, the flange gasket compresses and flows into surface irregularities. If those are too severe for the gasket material to fill, the joint will leak. Here’s some advice on flange preparation.

Step 1: Inspection

Examine both flange faces carefully for damage like cracks, dings, burrs and radial scoring. Scoring is the worst problem as this will almost certainly create a leak path. Also check for alignment and verify that the faces are flat and parallel. (It’s possible for flanges to warp if the bolts are tightened in the wrong sequence.) Some softer gaskets will tolerate flanges being slightly out of parallel, but this does depend on the material being used.

Also check bolts, nuts and washers for signs of damage or corrosion. If in doubt as to fitness for purpose, opt to replace.

Step 2: Clean the Mating Faces

It’s common for traces of the old gasket to remain on the flange surfaces. These can be removed with a wire brush or scraper. However, to avoid damaging the flange face, this must be made from a softer material. Brass is usually a good choice. Always brush in a circumferential direction and not radially.

Step 3: Preparation

Inspect the new gasket for damage and ensure that it’s the correct size for the joint. Don’t use any kind of sealant on the gasket or sealing faces unless specifically advised to do so by the gasket manufacturer.

Proper torque tightness is essential to deform the gasket and seal the joint. If there’s excessive friction bolts will seem to be at their torque limit when they’re not, resulting in leaks. This can be avoided by lubricating the threads and under the heads of the bolts. (Ensure the lubricant is compatible with expected service conditions.)

Do it once

Inspection and cleaning may seem time-consuming, but doing a job once is better than having to fix a leak. That’s why thorough preparation of flange surfaces is so important.  Contact Hennig Gasket & Seals for custom manufacturing of flange gaskets to your exact specifications.

A gasketed joint is rarely static. Changes in temperature can cause mating flanges to move apart or closer together, creating a variable gap that the gasket has to fill. That’s why understanding the influence of temperature helps when selecting the gasket material for flange gaskets.

Flanged joint dynamics

In service a gasket is compressed between two flanges. Sufficient load must then be applied to hold the joint closed, regardless of how conditions change.

Fluid moving through the pipe creates hydrostatic end thrust that opens up the joint. Internal pressure also creates side loading on the gasket, trying to extrude it out between the flanges. And changes in temperature result in expansion and contraction of both the piping and the fastening bolts.

Temperature influences

Temperature changes have two sources: the temperature of the fluid being transported, and the environment through which the pipe runs. In a continuous process media temperature may vary very little, but a pipe exposed to hot desert sun could experience a range of 80 deg F or more over a twelve hour period.

The influence of media temperature changes, (perhaps at start-up or shut-down,) will depend on the details of the pipework installation. However, most likely higher temps will act to close the gap between mating flanges.

Higher temperatures will make the flange bolts grow, so reducing the clamping force. Tightening to recommended torque levels creates some elongation that compensates for expansion, which is why proper jointing procedures should always be followed.

Of lesser importance, gasket materials and piping usually have different coefficients of thermal expansion. This may cause differential movement between flange and gasket which could, in marginal situations, open up a leak path.

Material selection impact

The ideal gasket possesses both good compressibility and good recovery or resilience, enabling it to maintain a seal as the gap between flanges changes and the compressive load varies. Natural rubber is one of the most effective materials, but is not always suitable.

The prudent approach is to discuss the application with the gasket vendor, being sure to make them aware of the various temperatures to which the joint will be exposed.  Contact Hennig Gasket & Seals today to discuss your flange gasket application.