"Withdraw into yourself, as far as you can.
Associate with those who will make a better man of you.
Welcome those whom you yourself can improve.
The process is mutual; for men learn while they teach." - Lucius Annaeus Seneca
We are currently in the middle of a steam turbine outage. The High Pressure Control and Stop valve and both Reheat Intercept and Stop valves are being overhauled. It's a difficult process, as many of the fasteners are breaking off, leaving the millwrights to deal with drilling out and tapping threads in the holes. It's adding time to the outage that was not planned for. A couple of the steam seals are also damaged, and this is very likely due to the thrust bearing clearances opening up.
Below: Looking down at the Left side Intercept/Stop valve, with the hydraulic actuator on top of it. The insulating blankets have been removed to allow the metal to cool more quickly. These valves are a bit funky. There is another hydraulic actuator underneath. The combined valve is actually two valves in one body. The upper valve does throttling, and the lower valve is positive sealing and acts as a stop valve.
Below: The single High Pressure Stop/Control valve with actuator still installed. Same arrangement on this one. It also has a lower actuator for the stop valve. Note the size is slightly smaller, but the bolting is spaced more closely and the bolts are larger in diameter.
Below: The left and right reheat control valves and stems.
Below: Top-down image of the reheat valve body on the left, and the high pressure steam valve body on the right. Reheat steam pressure is lower than high pressure steam, so it requires a larger diameter pipe and valve body so as not to restrict the flow.
Below: One of the millwrights working on the bolting for the valve bonnet. This guy is over six feet tall (188cm for my metric-unit readers).
Below: The High Pressure steam valve body. The upper part of the valve is called the "bonnet". Four of the bolts that hold the bonnet in place are broken and will have to be drilled out. The more difficult issue is that while trying to replace the valve seat down inside, every single one of the bolt heads snapped off. Each will need to be precisely drilled down the center with a magnetic-base drill - so as not to damage threads in the valve body.
Below is the rupture disc (disk?) for the main condenser. This is a thin round sheet of aluminum that in the event of a steam overpressure condition in the condenser of about 5 psi, the sheet will flex outward. It will then contact an installed circular knife, and split open, allowing steam to escape safely upwards - to prevent the main condenser splitting open at a seam. Main condensers are internally braced against vacuum, but cannot withstand much internal pressure.
Below: A close-up of the circular knife, once the assembly was flipped over and the rupture disk removed.
Below: Looking down from where the above rupture disk is normally installed - The steam turbine exhaust. There are a few deposits, nothing major or abnormal. The pipe at the right is venting for the aft steam turbine support bearing. All of this stuff gets inspected each year for signs of failure.
Below: Yes the seals are looking a bit rough.
Very rough indeed. Chunks of seal are brittle and coming off. Possible heating issue due to steam leak-by. Which came first? The chicken or the egg? Did the damaged seal allow too much heat to escape, or did the heat escape damage the seal?
Below: Interesting spring weather!
4 comments:
Hi Spud, interesting article. A couple of questions, did the seal damage result in an oil leak?
Do you perform a 'partial stroke test ' on your stop valve when the Turbine is in operation?
Hi Johnny,
We didn't see any oil leakage, nor steam leakage, for that matter. We were experiencing some vibrations and unusual noises shortly before the outage arrived. It was a bit unnerving. Hopefully the thrust collar machining and replacement thrust bearing holds the shaft in place a bit better. I think we are also getting a balance shot afterwards, which should also help.
Yes we do online stop valve testing daily. The High Pressure and Low Pressure stop valves get a partial stroke. The Reheat valves get a full open and shut cycle, because the steam can still flow through the valve not under test.
I hope to get a post up soon with some of this stuff coming back together.
Thanks Spud, yes we do the same on the stop valve using a manual lever, although the overspeed test is electronic. And yes strange noises are always unnerving ,especially as the control room with us is right beside the Turbine, even a 'growl' on a stormy day. Mind you I'm thinking a strange noise on a Neuclear Submarine might be a bit more worrying.
Hi Johnny,
I didn't realize you also worked in a power plant! Cool deal! If you are inclined, sent along some pictures to the email address in the side-bar. I'm always interested in other plants!
Our stop valve testing is done with a mouse click, and same for the overspeed test, although other places I've worked, the overspeed test was done from the front standard with a plunger and a lock-out lever. It was a very long time ago, and I'd forgotten about that until you mentioned it.
Funny noises: Fortunately we never had any in the power train or turbine generators. That said, every time when we dove deep there was a huge shuddering pop in the engine room as we passed a certain depth. It probably had to do with the floating deck getting briefly stuck as the hull compressed, but until you got used to it, it was absolutely hair-raising and bowel-loosening :)
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