The skilled millwright and pump specialist has experienced multiple breakdowns with a centrifugal pump. The pump has been rebuilt multiple times but it keeps breaking down with 4-6 months interval. The symptom of the failure was a catastrophic failure of the seal, each time.
The pump broke down and the millwright carefully examined every part as done previously. At this time the shaft sleeve was welded to the shaft and could not be removed. It appeared that the sleeve was coming loose.
See picture below, part of the shaft was cut off with the sleeve still welded to the shaft.
The materials used in the mechanical seal were as follows: Shaft - 400 series SS Sleeve - Titanium Setscrews - Carbon steel The Cause: The dissimilar metals in this case were corroding away the setscrews. Basically the setscrews become the sacrificial anodes between the shaft and the sleeve. The Solution: The carbon steel setscrews where replaced with hastaloy C. The pump has now been running for over two years.