08/29/2025
A couple of us in the shop crew are out burning the midnight oil doing a hydrotest on #7 in preparation for replumbing and reassembling it for operation again.
For those curious, a hydrotest is a water-based pressure test of the boiler in its entirety. Water itself is non-compressible, so when we fill the boiler to the brim and push all the air out, it doesn't take much to raise the pressure. Technically it's small amounts of air squeezing down to generate the pressure, plus the boiler itself stretching slightly since the water doesn't pressurize.
It therefore doesn't take long to get to our operating range of 100psi, but we then go to 1.5 times operating for the actual test. This has to do with Michigan state rules, where all boilers need to be tested to at least 1.5 or (sometimes) double operating pressure to ensure that absolutely nothing could come loose/fail when running at normal steam pressure later.
The other benefit of using water of course, is that if anything lets go on the boiler under pressure, the test pressure bleeds off instantly rather than violently like it would with air or steam.
Once up to pressure, it's simply a matter of waiting a certain length of time while watching for leaks or anything unusual. Each group has different wait periods, but a usual rule is a half hour at least without a major/rapid drop in pressure.
At this moment, 10:25pm, #7 has been holding for way past what was necessary, so it looks like we'll be moving on to replumbing in preparation for a steam test for our new injectors, and then another quick teardown so that we can properly reassemble everything and get #7 ready to run again.
Hopefully by Halloween time, she'll be up and ready once again.
