Under Compression can be caused by not tightening the the bolt enough or possibly due to gasket relaxation. As you begin to tighten the material it will start to “creep” due to the compressive load being applied. As the gasket thickness decreases, the originally applied load on the bolts will lessen. This is due to the thickness change resulting in a lower gasket stress or compression and can cause a leak due to permeation through the gasket or tangential between the gasket and the flange sealing surface. Additionally, unloading of the gasket can occur due to temperature or pressure cycling which can have the same effect.
Over Compression is caused by too much load on the gasket. This can be caused by not using the correct torque value or perhaps using a tightening tool that you cannot measure the torque, for example an impact gun or cheater bar extension. Over compression reduces the contact area of the gasket and crushes the gasket towards the ID allowing fluid to penetrate the gasket ID thus leading to deterioration of the gasket, damaged flanges and can result in leakage or gasket failure ‑ a huge problem.
Using the Wrong Product can become a serious safety issue. The material selected must be capable for the temperature, pressure and media that it is being installed into. If the gasket material is not rated for either the pressure or temperature of the application, this can cause very serious issues such as worker injury or plant down time. Additionally, the gasket must be chemically compatible with the media or the chemical can attack the gasket; causing it to prematurely break down which may cause leakage or even failure.
Other could be several things, such as using the incorrect gasket size, poor method of cutting, or quite simply, it is somewhat of anomaly and couldn’t be grouped into one of the three categories above.
In sum, 96% of failures can be avoided by following these key guidelines:
- Pick the correct material, verify the pressure, temperature and media that you will be installing the gasket into.
- Use the proper tightening procedure noted in ASME PCCC-1.
- Lubrication is key, friction is robbing and can account from more than 50% of the required torque.
- Always use the manufacturers recommended torque values. If you are unsure, give them a call as they will be happy you did.
- Use a proper tightening tool, such as torque wrench.
- Gasket creep and bolt relaxation happens, be sure to eliminate this by always remembering to re-torque within 4-24 hrs.