Monday, May 26, 2008

When the Steam Doesn't Stay in the Tube: Day 3

It is a little after 5 am and I am at work. Checked in and almost ready to get into the boiler. The night shift has just gone home. They welded in 6 tubes (12 welds) which is very good. It always buoys everyones spirits a little when we stop cutting things apart and start putting them back together.

Annie wondered in her comment on the Day 2 pictures what caused this in the first place. It might take a minute, but I think we have the answer.
Coal is a dirty fuel.... compared to refined oil products, or natural gas. It is a solid fuel, and has dirt in it, basically. To keep all the tubes clean we have air driven lances that blow the ash off the tubes at regular intervals with hot, dry steam. Well, it should be hot and dry, but it takes a bit to warm up the lance and all the connecting piping, so when it gets to the sootblower, some of it has cooled and condensed and when it blows into the tube bundle there is water that mixes with the ash, and steam. This mixture, and to a lesser extent dry steam is like a fine sandblasting mixture, and over time it erodes the tube wall.

In the early days of operation the sootblowers were set to run at about 300# of steam. So some areas got a lot of erosion. This particular sootblower hole is short, and the lance is close to the top tubes. Erosion is always worst above, rather than below the blower. So these tubes took a beating. If nothing is done, pretty soon there isn't any metal between the steam and the metal, and you have a leak. There are thee things that can be done to keep the steam in the tubes:

1. Pad weld the tube. Put more metal on the thin places with lots of weld beads. This can work pretty well, but in this area you have to do a lot of out-of-position welding and the tubes are always somewhat dirty. These two things contribute to POROSITY. Yikes!

2. Put a stainless steel shield around the bottom of the tube. This also works well, and during the last outage we pad welded and shielded hundreds of tubes. More than the usual amount, but we do a lot each year.

3. Put in a dutchman. This is a short segment of new pipe. This is by far the best solution, but the most expensive, the most labor intensive and the slowest. But that is what we are doing now in the boiler in the section that was damaged.

Back to POROSITY. If your tube is dirty or your arc gets long the molten metal get impurities dissolved into it, and they form little gas bubbles. When the metal freezes, they are trapped. You never get rid of it.... well, you can grind it all out and start over, but it is amazing how hard it is to grind it all out. So, for practical purposes, you can't really get rid of it.


All those little bubbles can line up and form a crack, or a passage for the steam to follow to get out of the tube. Once a little steam can get through, it isn't long before the hole is bigger, and you have a leak. Because the tubes are so close together, it isn't long before you have worn a hole in a tube nearby, which send a jet of erosive steam over to another tube, and pretty soon there are holes all over and it looks like there was a Mafia gun battle that went on. You pull all the poor dead bodies out and line them up and look for what could have caused the problem to begin with. This is a picture of the tube that started it all. It was thin, the welder blew through the thin tube wall and a pocket of porosity formed, the welder tried to get rid of it, but it remained, and a crack formed.Then a leak formed and this tube started to leak up at about a 45 degree angle, blasting one of the tubes in yesterday's post that opened up.

That tube failed, and blasted right across. Both tubes opened up at about the same time, blasting each other sideways and getting everyone's attention.


Here are some new tubes, with the end's prepped, cut to length and ready to be welded in.








Home Sweet Home.









Making chill rings.










Chill rings are little devices that help to align and space the tubes so that they are welded just right. Those of higher ideals and purer hearts prefer the more elegant TIG root. This is where you use a tungsten arc with inert shielding gas to weld in the first pass between the tubes. There is normally a 1/8" gap between the tubes, and you delicately fill this with a thin film of molten metal. If conditions are good, then you get the very best weld. But if they are not so good, you just think you get the best weld. These little guys help fix that. You just put them in both tubes and use a normal stick weld. For all intents and purposes, these are the root weld. The ones that you buy commercially are kind of thick and clunky, but we make our own out of the same tube material, and they work very well.

Sunday, May 25, 2008

When the Steam Doesn't Stay in the Tube: Day 2


Here are a few more pictures.

As of last night they had removed 16 tubes. Two tubes were blown out, and three had some holes worn in them, the other 11 tubes were cut out just to get access to the tubes in the bundle.


Here you can see the two blown tubes, one bent to the right, one to the left. We are still trying to determine what was the original cause of the failure.





And a close up of the two blow tubes after they have been cut from the bundle.







The tubes in this section of the boiler are 2.0" dia. and have a wall thickness of about 0.203". And they are all bound together. So, to have them open up like this, and get bent as badly as they did shows the tremendous force involved in life steam.

Saturday, May 24, 2008

When the Steam Doesn't Stay in the Tube: Day 1



We have a tube leak in Unit 2, in the primary superheat section of the boiler. This is an area where the tube bundles are very close together, and the tubes are very close together. And there is a lot of pressure (~2500 psi) so when a tube fails it starts to cut it's friends nearby, and they cut their friends and it is a mess. To fix it you have to cut out a lot of tubes to get to in to the ones that have failed, and then weld your way back out again. We are looking at a minimum of 12 tubes that will need to be removed and replaced, and possibly as many as 20. So there goes the weekend.


Posted by Picasa

Sunday, May 18, 2008

The Starvation Messabout

If you filtered out all of the people who have much interest in -ball sports, then filtered out everyone who if interested in the rest of the competitive sports that are left, and then filtered for people who like to experiment, and make things with their hands, you would be left with a pretty small group of people. Then you have to filter out anyone who is influenced much by trends, fads, or conspicuous consumption. Among the people you would have left are the boat builders.

This isn't to say that boat builders are especially virtuous or anything, just that they are fairly rare. So when you get a bunch of them together, they are pretty interesting. And if you, like me, don't fit into the the world of competitive sports or conspicuous consumption, you sometimes wonder just how weird you are. So it is a lot of fun to go a 'messabout' and just kind of hang out and enjoy the sun and the water. I didn't bring along a boat (too cheap to drag Picara over for a day, and I have given away all my other boats) so I brought my dutch ovens and did some visiting. I even got a little sunburn. But it was fun, and the people are nice.

I particularly wanted to visit with Jim Thayer a little. Jim is in his 70's someplace, and has been sailing and building boats for years and years. He owns Grand Mesa Boatworks, and sells fiberglass hulls that they make. His heart isn't so good, and so he is on oxygen, but he is a trooper, and still goes on extended expeditions on Lake Powell. He has a special box on the front of his boat (Nina) that he keeps his oxygen in.

Anyway, here are a few clips of my afternoon there. I didn't get all the boats. There was an amazing rowing boat that I really wished that I had a shot of.


The Lighter Side

Here are a couple of videos that you might enjoy. The Man with the Mask is fun. Shooting sports are very relaxing if you have a Class 3 permit. Judge not, that ye be not judged..... More shooting sports.... well not really sports... Rube Goldberg has way too much time on his hands. So does Red Green. Then there is an example of enforced cell phone etiquette.


Well, nothing very profound here. Hope you have a good one and a maybe a laugh or two.

Monday, May 5, 2008

Scripture Guys: King Benjamins Words Reported Live

Gospel Doctrine was interesting this last Sunday. We have a great teacher, and he always leads us to the point of the lesson. But rather like a goat that wanders hither the thither, when I read the key text, I somehow see things other than the point of the lesson.

We were reading about King Benjamin's Sermon in Mosiah 4: 1

1 And now, it came to pass that when king Benjamin had made an end of speaking the words which had been delivered unto him by the angel of the Lord, that he cast his eyes round about on the multitude, and behold they had fallen to the earth, for the fear of the Lord had come upon them.

So everyone is keying in on their on the spiritual aspect of this scene, and I am thinking 'Holy Cow' what did this really look like! So we are at conference, and maybe you had to go to the restroom or something - you miss some of President Monson's talk and come back to find twenty or thirty thousand people senseless on the ground. The news guys are there from Channel X and they are equally puzzled "This is an incredible scene Marsha, you would have to be here to believe it. People are dazed, laying on the ground as you can see. Many are moaning or sobbing and none of them have the strength to even sit up. It is like a bomb went off in here. We missed the call to repentance that was given by President Monson, as we were stuck in traffic, and only saw the aftermath of his talk. Back to you Rolland".

My purpose isn't to make lite of this scene, but to look at it a little closer, and maybe from the lens of the news reports we hear today. We read so much in the scriptures and I think that sometimes the enormity of what we read, the incredible scenes that are recounted with almost no elaboration zip right by us. I guess I like to stop sometimes and try to feel what it might have been like in some small way.

Anyway, that is all for tonight. Read your scriptures and what ever story or event you are reading about, slow down, and try to put yourself there. It is surprising what pops out sometimes.