It’s the little things that get you the worst

Don’t worry. For a change from what seems to be normal day-to-day fodder at the moment, I’m not going to talk about viruses. Rather, it’s a tale about a plumbing fitting, a missing support and a very large hole in a roof.

Let’s set the scene.

Ian earlier part of my life I was often called upon to run around the country, commissioning, repairing and generally trouble-shooting all sorts of industrial control equipment. On the whole, the people “on the ground” were a good crowd to know. Often when they realised an outsider was genuinely interested in what they did, they opened up.

I’d been a regular visitor to a UK power station (long since closed down) and in one of those post-job chats over a cuppa, “The Scrapbook” came out. I don’t recall what prompted it but the book was opened at a scene of devastation and the tale recounted.

You need to know a little how the station worked. There were several steam turbine driven generators, each churning out 500-600MW. In each one, steam came from the boiler and blasted first through three sections of the turbine: high pressure then intermediate pressure and finally low pressure. The exhaust steam then went to a big condenser that was like a saddle over the top half of the turbine. Condensed water then ran into a small catching tank and was whipped back to the boiler by a steam turbine driven pump.

Now, as the turbines were whipping round at 3000rpm, the blades on the 8ft (2.4m) diameter low pressure section were moving almost supersonically. Even a tiny bit of water running back into the low pressure turbine would definitely be A VERY BAD THING TO HAPPEN, so there was a backup electric pump, just in case the turbine pump broke.

For ages the operators had been annoyed by random high level alarms from a sensor on that catching tank. The problem had been investigated but as there was never an actual high level and no real cause found the problem had become “one of those things to be fixed at the next service outage”. To stop any more nuisance alarms in the meantime, someone had bypassed the trip. (You can begin to see where this is going, can’t you?).

Well, the inevitable happened: The standby electric pump was running one day while the turbine pump was undergoing maintenance. The electric pump failed and, with no turbine pump running, condensate stopped being pumped from the catching tank. The level in the tank rose.

And rose.

And rose.

Eventually (quite quickly actually) water backwashed, through the condenser and into the turbine.

Now, a few gallons of water suddenly getting in the way of the low pressure turbine blades – which, remember, were travelling almost supersonically – had much the same effect on the blades as would hitting a brick wall.

Most of the low pressure turbine left the turbine hall via the roof. The main shaft, a 22 inch (55cm) diameter chunk of chrome molybdenum steel, simply bent and the 35mm bolts holding down the bearing caps, failed in perfect textbook tensile fractures. A man working up a ladder in the turbine hall slid down, broke both ankles but managed to run out of the building.

There was consternation.

Eventually, piece by piece, the cause emerged. The level sensor on the catching tank was mounted remotely. It was connected to the tank by some copper piping, described to me as “pretty much like your central heating pipe at home”. The pipe ran from the tank, to a wall, along the wall and round a corner to the sensor. Whoever installed the pipe hadn’t put in enough supports. The pipe had simply sagged a bit and a joint had cracked after a while. Not much: just enough to cause spurious trips.

So, from a missing support on a small pipe and a cracked joint, there was a chain of events that led to the turbine disappearing through the roof and the National Spare having to be mobilised.

Like I said: It’s the little things that get you the worst.

Bays can pull out granular detail from all sorts of data. Whilst we may not be able to cover dodgy pipework installation, if there’s detail in your data, we certainly can go after that.

By John Kirkwood
Categorized as blog

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