On-Site retubing of surface condenser 2

[starfarooq]

We have a small surface condenser consisting of 600 tubes (tube diameter 25 mm). After 25 years of its service life, we are planning to re-tube it as 12 % of its existing tubes have already been plugged. For this activity we want to hire a contractor. I am interested to know about the steps involved in the re-tubing process and the estimated time taken. A detailed reply (specially about the steps involved in the process) will be highly appreciated.

 

[chicopee]

Several things for sure: several good tubes will be sacrificed to remove the bad ones; the sacrificed and bad tubes will be flamme cut inside at both ends where attached to the tube sheets; extra caution will be needed to remove the projected ends into the tube sheets so as not to damage or enlarge the holes in the tube sheets; replacement tubes and espacially the ends should be free of debris and scale. The tube ends will be expanded with rollers and either beaded or flared unless they are seal welded on the tube sheets; hydro test the condenser to ensure no leakes.

 

[rmw]

Wow, I learn so much. I have been to several dozen condenser re-tubings and haven't seen a flame cut tube yet.

The contractors I have worked with have the specialty tubes necessary to go into the tube, cut the tube right behind the tubesheet with a knife like mechanical cutting tool. This is after they pull out the (12%) of plugs out of the plugged tubes first. They do that on both ends of the tube. Then they use another specialty tube to grab (grip) the portion of the cut off tube that remains in the tubeshee and pull it out. Now they reach through the empty tubesheet hole with a tool that can grab the tube and they pull it out and feed the end of it into a machine that pulls the tube, smashes it and cuts it into ~6" pieces and flings it into a hopper so it can be hauled off for junk.

Then they clean all the holes in the tubesheets as well as all (each and every one) of the holes in the support plates with flapper wheels and ball burr tools. The also set up alignment equipment and line up the tubesheets to the extent they are movable and the support plates, making sure to align the support plates to the tubesheets.

With that all lined up, they then begin to feed new tubes into the condenser from the end that is accessable. On a good job, where the holes are cleaned well, and the tubesheets and support plates line up I have seen workers walk up to 5 tubes at a time into the tube bundle. and that was tubes almost 40 feet long. On difficult jobs I have seen them fight each and every tube into place each and every foot of its length. Not fun.

The tubes will normally be bought just a little longer than necessary so the next step is to line up the tube ends at one tube shet and roll those tubes into place. The the other end of the tubes are trimmed to the proper length and those tubes are rolled. People who know their business will select a rolling pattern that minimizes tubesheet distortion due to tube growth caused by tube wall reduction during rolling.

Make sure that your contractor does not roll the tubes past the inner edges of the tubesheets. Best if they leave about 1/8" of unrolled tube rather than take the chance of rolling out past the end of the tubesheet. Watch them close here.

Now I have seen tubes that are so worn out and so thin that it was necessary to go into the hotwell with chop saws and saw the tubes in a gang sawing fashion and then shovel or rake the short tube sections out of the hotwell. If they know their business, they will write a contract with you that accounts for the extra expense of doing it this way rather than with the normal tube pullers.

You didn't state whether or not your tubes were welded or just rolled, so if welded, factor in the steps to (1) first cut the welds before doing any of the steps above, and (2) weld the new tubes after intallation.

Google "condenser tube pulling equipment" and see what you find. Some sites have some informative videos of this type of equipment in use. Also go to

http://www.retubco.com

and look all through their site. I have never worked with them, but I have often used their photos to show people the process. They used to have some videos of the chopper machinery too.

rmw

 

[starfarooq]

Thanks rmw for the detailed reply. You are always so helpful.
The tubes are rolled only (not welded with tube sheet) and the the tubesheet holes for tubes don't have grooves inside. I have attached the joint detail(Actually its an old design of 1967 and the grooves are not there)
According to the method statement submitted by the contractor, they will first ream (remove material) the inside of the tube portion that is rolled inside the tubesheet to make it thin and loose its grip (they will do it by reamer). Then they will cut the tube immediately inside tube-sheet. After removing the reamed portion inside tube-sheet, they will pull the tubes with the threaded tool (a rod with threads on its end just like tape that will go inside tube and the threads will then grip the tube.
Kindly provide (if possible) following additional info:
1. From your reply I have understood that all the tubes should be removed first (not pulling and replacing tubes one by one?).
2. After that clean all the holes. and then align the tube-sheet with support plates (baffles?). But here the point is that that baffles lie inside the shell. How to get access there for aligning with tube sheet.
3. How to remove any broken tube pieces from inside (for example hot well). The only option in this case is to cut window from the hot well to get access and restore the window by welding after removing the tube pieces.
4. What is the average time of replacing the tubes (in our case the tube length is 8 meters and diameter is 25 mm). Is the shutdown of 10 days is sufficient for replacing 600 tubes?
5. How to remove the plugs?
5. What should be the removal sequence (from bottom to top OR from periphery to center?) and similarly what should be the installation sequence.

 

[rmw]

Starfarooq,

First, I am surprised at your contractor's approach of reaming the tubes out of the tubesheet when there are tools available that will grip and pull them much faster without the danger of a reamer slip or mistake damaging the tubesheet - especially if the tubesheet is soft metal.

Now to your questions:

1. Yes, all the tubes should be removed first to allow full access to the support plates (baffles) to clean those holes. Not mandatory, but much faster.

#2 & 3. I would consider cutting a window (or maybe multiple windows) to gain access a normal operation if access is not otherwise provided into this hotwell. Make sure your contractor has a procedure for removing and replacing this window(s) including testing for leaks after replacement.

#4. I have no way to guage the compentency or abilities of the contractor, access to the work or even the work ethic of the work crew. In our country, some jobs done in 10 days by non-union workers may take twice to three times that if done with union labor. In other cases I have seen union workers who could work circles around non-union workers, but they were out of a different local. For 600 tubes, I would think that 10 days would be OK if as much pre-work, scaffolding, removing non-essential equipment, staging tube pulling/chopping equipment, staging new tubes, etc. is done and in place ahead of time. I would work it on a two shift basis. Better to work two sifts and finish in 6 days than to work one shift and finish in 12 days on a 10 day turnaround.

The plugs, depending on what type they are are typically drilled out or drilled and tapped and then pulled out with a puller. This assumes all are pounded in and none are welded in. If welded, the weld has to be ground off.

#5. I would remove from the bottom and work up. This allows "stuff" from the tubes being removed to fall free to the floor of the hotwell rather than onto tubes that haven't been removed yet. If your only access into the shell is via the hotwell below, I'd install tubes from the top so that someone can get into the condenser to aid stubborn tubes through the baffles if needed. Likewise, if there is access from the top (through the turbine hoods) then I'd start from the bottom and work up. If there is trouble with a tube and it gets hung up (or the bullet nose that guides the tube through the baffle holes comes out and gets loose, for example) you have to have access to get in and remedy the situation. If your access is from the hotwell, then that bullet nose can fall into the hotwell rather than onto already installed tubes.

You never did state what the tube and tubesheet materials are.

Good luck with this work.

 

[starfarooq]

Thanks a lot RMW.
The material of both the tubes and tube-sheets is carbon steel.
Your inputs helped us a lot.

Regards

 

[chicopee]

Pulling the tubes thru the tube sheet holes could damage the holes if the tubes are scaled or crusted.

 

[MJCronin]

farooq,

Consider the purchase of this fine book:

http://www.amazon.com/Tubular-Heat-...3408815&sr=1-1&keywords=heat+exchanger+yokell

rmw, as always, provides clear... correct and concise advice.

Regards

 

[starfarooq]

Thanks MJCronin for advising such a good book. i have checked its limited preview on Amazon and it seems that it provides answer to every question related to heat exchangers.

 

[rmw]

Carl Andreone and Stan Yokell are among the most knowledgeable Hx experts out there. You might also visit Stan's website.

http://www.mgt-inc.com/

I am not going to tell you I agree with them 100%, but I do wonder who will replace them as industry experts as both are getting up in age now, but then again so am I.

rmw