The lack of a tight seal in a gasketed joint is a ticking time bomb. The timing of the issue presenting itself may vary, but unfortunately, you will have issues. The good news (for those of you that love troubleshooting) is that there are a variety of things that can contribute to the problem. In a perfect world, all of these things would be addressed during the design phase. Hopefully we can help some of you start to recognize these things sooner rather than later to get you out of the troubleshooting group!
We put together a short list of things that you should consider when it comes time to design or troubleshoot your gasketed joint.
Ways to Ensure a Tight Seal
1. Is the proper load applied?
Bolts not tightened to the proper torque values spell trouble for your application. If the load values defined in the development stages are not adhered to, you will most likely find a leaking gasket (and possibly further damage if it goes on for too long). What if you don’t know what the load should be? Start with the specified gasket material. You may be able to reverse engineer the values based on the recommended loads that the gasket material is designed for (you may need to talk with the materials supplier). You might also gather input from service instructions for similar applications. It will take some trial and error, but you can probably figure it out.
2. Can the gasket withstand the conditions it is under?
Sometimes conditions in the application are underestimated, and sometimes the robustness of a certain gasket material is overestimated. Whichever way it happens to go, there will most likely be problems. Is your gasket material designed to resist the effects of the fluid, pressure, and temperature of the joint? If it isn’t, you can count on having trouble maintaining a tight seal. However, this is generally an easy fix if you do a little research into materials that can withstand the specific conditions in your application and choose properly.
3. Is the bolt design sufficient?
This is probably the most expensive problem on this list. A redesign due to an incorrect bolt design can cost a lot of money, especially if you are too far down the design path. If your answer to this question is “no”, and you do have an insufficient bolt design, we can offer some advice on where to go from here. If there is any hopeful news in this scenario, it is that there are materials out there that are more forgiving than others that can help mask questionable design choices. Talk to your trusted gasket material supplier about some of the composite materials on the market. Three layer composites (or metal reinforced materials) can be manufactured to a specific thickness and they conform very well to flange surfaces – both of which can help compensate for bolt design issues. It isn’t always a magic bullet, but it’ll do the job in a lot of situations where nothing else will work.
4. Are the flanges appropriate for the gasket technology chosen?
Flange surface finish plays a huge role in the ability for certain gasket materials to adequately hold a tight seal. Gaskets made of stainless steel (MLS/SLS) require mirror-smooth surfaces, while metal reinforced graphite and certain fiber gaskets are more forgiving. If the flanges are not machined properly, or they wear over time, you will start to have sealing issues with MLS/SLS.
5. Are the leakage requirements met?
It is a common misconception that a gasket is expected to never leak. Leakage requirements are set during the design phase (you’ll commonly see mL/minute or mL/hour) and the load on the joint has a direct effect on whether or not these numbers are achieved. If you are exceeding your leakage requirements, that is a clear indication that your seal is not as tight as it needs to be.
6. Is a re-torque necessary?
What if you’re feeling pretty confident in everything above, and you’re still having issues with maintaining a tight seal? Maybe the solution is something as simple as a re-torque. If you have gaskets installed that are going through their first heat cycles, bolts loosen and a re-torque is often necessary. Without it, the tight seal you thought you had prior to running your application is long gone.
Maintaining the Seal
As you can see, there are definitely some things to consider if you are having trouble maintaining a tight seal. Some are always quick to blame the gasket, but a gasket is only as good as the conditions that it is designed for and the type of conditions it is placed under. It is important to have a full understanding of all of the things that can lead to the demise of a tight seal.