Gaskets in flanged joints fail in two ways. Either they allow a very slow leak or they blow out. A blowout can be quite spectacular, but also dangerous and expensive. As it’s something to be avoided, here’s an explanation of what causes it and some ways of making sure it doesn’t happen.
Recognizing a Blowout
A blowout occurs when the gasket material fails catastrophically. This can happen when the gasket is resisting significant internal load. A steam system might be one example but it could be any application where the media being sealed against is under pressure. When this pressure exceeds the strength of the gasket the material is likely to fail fast, forming a hole that releases the media.
In a steam system, this results in a dangerously hot jet. In other situations, it could be acid or a flammable fluid that escapes.
One factor is the tensile strength of the gasket material, but a flange system is more complex than that. The gasket is held in place by the clamping force. This creates friction between the flange surfaces and the gasket, and that resists movement.
Analysis of the forces in a flanged joint shows that clamping force is a bigger factor in blowout prevention than material tensile strength. (The full analysis is available on the Fluid Sealing website.) Thus anything that reduces clamping force can cause a blowout. Here are six tips to prevent that happening.
- Follow best practices when bolting flanged joints together. Use the recommended tightening pattern.
- Don’t overtighten. This makes the flanges rotate, compressing the gasket at its outer edge while there’s little or no contact on the inside. It can even crush the material, guaranteeing a failure.
- Minimize vibration through the joint.
- Choose gasket materials with low creep. (Silicone and nitrile rubber are particularly good.)
- Consider the effect of temperature. High temperatures will lengthen bolts, (which reduces clamping load,) and let gasket material creep. Conical spring washers may help.
- Use the thinnest gasket possible that handles unevenness in the flange faces.