Can anyone tell me the material of choice for bolting dual laminate (teflon/fiberglass) pipe flanges both flange to flange pipe and flange to steel(glass lined) vessel nozzle. Operating conditions are 100 psig, @ ambient, outdoors exposed to weather, pumping 100% bromine in the line. Currently using and ASTM 193 B7 but expeiencing rapid corrosion due to permeation of Br throught the teflon gasket.
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Bolts for Bromine
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Have you tried Xylan coated A193-B7 bolts? Xylan is a very thin PTFE based coating than only increases the fastener pricing slightly. It is used a lot in general chemical industry environments. I cannot comment on specific experience with bromine.
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We haven't tried it but considered it. We had some concern that because the bromine readily permeates the teflon and may mask a corrosion problem. Since the PTFE is thin it may not be a problem and may be worth a shot. How about the effect on torgue? Any idea regarding changes we currently torque bare unlubed to 25 ft-lbs?
ElderX,
Coated carbon steel bolts may not work for you. The coating may not stop the Br, and it can be abraded during assembly leaving no protection. I would recommend using more resistant material such as stainless steel or titanium. I have no direct experience with Br, so I will assume it behaves similarly to Cl. Titanium alloys are nearly impervious to Cl corrosion, so I would consider them first.
If you do choose to coat the existing bolts, then you need to change the torque based upon the friction coefficient. The preload developed from a given input torque is directly proportional to friction coefficient. I would estimate the bare friction coefficient at 0.20-0.25, and PTFE would be around 0.10. Therefore, you should use about 1/2 the original torque. If this is a critical application, I would perform testing to confirm the friction coefficient levels.
Cory
cpadfield@omnimetalslab.com
Coated carbon steel bolts may not work for you. The coating may not stop the Br, and it can be abraded during assembly leaving no protection. I would recommend using more resistant material such as stainless steel or titanium. I have no direct experience with Br, so I will assume it behaves similarly to Cl. Titanium alloys are nearly impervious to Cl corrosion, so I would consider them first.
If you do choose to coat the existing bolts, then you need to change the torque based upon the friction coefficient. The preload developed from a given input torque is directly proportional to friction coefficient. I would estimate the bare friction coefficient at 0.20-0.25, and PTFE would be around 0.10. Therefore, you should use about 1/2 the original torque. If this is a critical application, I would perform testing to confirm the friction coefficient levels.
Cory
cpadfield@omnimetalslab.com
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