We always could cut in a new valve, but then we would have to buy and install a spool piece, weld on flanges to the exiting line, and have all the welds x-rayed and pressure tested. If we could find someone who could make a valve of the same dimensions as the ones we are replacing, it would be more expensive than an off-the-shelf part, but overall cheaper and easier.
And as for the type, everyone here has been calling it a wafer check, and with the 36" one just 4 1/16" thick, they definately aren't full body.
They are used in a natural gas environment, so water hammer isn't a factor. The reason it failed is because the flapper plate (as we have come to call it) was attached to the pivoting bar by 4 bolts. For whatever reason, the bolts weren't welded, lock washered or even loctited in place, so they backed out over the last 7 years. Once one on the end wiggled itself out, the two in the middle sheared at the interface, and the last one bolt put up a good fight before failing.
The new design from Wheatley has a one-piece internal assembly. While this undoubtedly makes for a more reliable valve, it is thicker than the original and this proposes a problem.
Repairing was considered, but since the only logical explanation for this check valve is backup protection for an expander, we opted to replace it in the line without the flapper in order to start up the plant sooner. At the moment it is an orifice plate. At the turnaround this fall we are going to replace it with a functional wafer check, whether we have to cut the pipe or not.
