Know Your Options
Welded End Ball Valves
Its time. The ball valve is leaking for the second time this year and needs service. The options can be replacing it with the same ball valve or consider choosing one with an extended-body using pup pieces and an estimated 15% increase in cost. The following discusses why the extended body option might be best, followed by a cost evaluation of valve life. Welding 3-piece resilient seated ball valves in line can be accomplished in three ways as follow.
· Assembled valve: The valve is prepared for welding using a wet rag to cool the center section and temperature stick. Cool-down time between welds is required. The downside associated with this method is additional cooling time as well as possible damage to the seats or seals due to excessive heat. Strictly following the IOM manual instructions should result in a good installation. Hydro test and/or commissioning will confirm if the seats or seals are sealing properly.
· Partially disassembled valve: This installation method requires the partial disassembly of the valve by removing all bolts except one that would hold the center piece and allow it to ‘swing away’ and hang from the remaining bolt, away from the tail pieces being welded. Manufacturers will generally recommend removal of seats and seals and the valve be loosely reassembled to maintain alignment prior to welding. After welding, the valve must be properly reassembled and torqued.
Another common practice is a variation of the above. Instead of removing the seats, the valve center section is swung away with the seats intact. Using a wet rag (this time to protect the seats from weld spatter) welding is performed without concern about heat ruining the seats or seals. After welding, the valve must be properly re-assembled and torqued.
A majority of manufacturers will insist that body seals be replaced for any disassembled 3-piece valve.
· Extended body valve: This method eliminates most of the concerns with installation, and for a reasonable cost. Use of wet rag to cool the center section is still required, but the risk of melting the seats or seals is reduced. The extended body pieces act as heat sinks during welding, decreasing the time for cooling between both tack welds and final fillet or butt welds and mitigating the risk of melting seats or seals. There is no need to buy replacement seals or to reassemble the valve. Concern about melted seats or seals is eliminated.
When considering the upfront increase cost of an extended body, you also need to consider the time saved and liability issues mitigated. Manufacturers have had much practice over the years limiting their liability for product failure due to incorrect installation practices and frankly, they are right to do so. If a welded, soft-seated ball valve fails upon initial energizing of the system, the cause most likely is failure of seats and/or seals due to the exposure of too much heat. If submitting a warranty claim for a failed 3-piece welded-in valve, chances are the claim is attributable to installation contrary to the manufacture’s installation procedure. The use of extended body tailpieces can be both a preventative measure against unnecessary system leaks, and a cost effective form of insurance.