INSPECTING THE INDIVIDUAL SEAL COMPONENTS FOR DAMAGE ST007
After the failure has occurred you will analyze the failed components. You are going to be looking for several things:
- Evidence of corrosion.
- Wear patterns on those parts that should be rubbing.
- Evidence of rubbing or wear on those components that should not be in contact.
- Discoloration of any of the seal components, especially the metal parts.
- Parts that are missing. Springs, set screws and drive lugs as an example.
- Loose hardware. Either a seal component or a foreign object.
- Product attaching to a rotating component. Carefully inspect the impeller and rotating part of the seal.
In the following paragraphs we will be inspecting the individual components and looking for evidence of the above. But before we get into that subject there are a couple of important points that you must keep in mind as you trouble shoot individual components:
Are you looking at a seal that has been rebuilt? Were the components cleaned before you looked at them? Troubleshooting a rebuilt seal is a frustrating experience. A trained troubleshooter is looking for evidence of rubbing, damage and corrosion. If those previous rubbing marks have not been removed from the rebuilt seal you can be led down a false path.
- A good rebuilding house would :
- Clean and polish the seal casing to remove any rub marks. If this was not done you may be trying to analyze a rub mark indication that happened several applications ago, in a different pump.
- Install a new carbon/ graphite molded face. Machined faces are not acceptable because they do not have the proper density. If the used face had only been relapped, the length of the carbon nosepiece will not be an indication of anticipated life in this application.
- Replace all the springs. Springs are made from corrosion resistant, austenitic materials that work harden over a period of time. Being a small cross section material that is under high stress, they are also sensitive to chemical attack.
- Replace the setscrews. They are made from austenitic metal also and should never be re-used.
- Replace all rubber parts (O-rings, rubber boots, etc.)
- Solid hard faces can be relapped if there are no significant chips or visible cracks. Plated hard faces should never be relapped.
- Be sure to identify the seal materials. It is impossible to troubleshoot mystery materials.
- If the metal is stainless steel, which grade is it? All stainless steels are not the same. There is a difference between Hastelloy C and Hastelloy B. Some people call Alloy 20 stainless steel, but it is a different product.
- There are a hundred different grades of carbon graphite used in mechanical seals. Which grade are you looking at? Is it filled or unfilled?
- Viton® is a trade name for E.I.Dupont. There are many grades of this product available. Some work in water, others do not. Which do you have?
- What is the spring material? It should be Hastelloy C, but is that what you have?