![]() This may slightly temper the underlying bead. Then weld another pass overlapping 1/2 of the prior bead. ![]() One idea to reduce residual stress at the heat affected zone at the drum side is to run a 2 or 3 pass weld with the 1st or 2nd bead favoriing the drum side. Some of thes scale is impossible to weld to but in my experience has always been removed with a grinder. ![]() As mentioned above, cleaning is needed to remove the scale from the surface around the tubes. I have seal welded a few tubes in Recovery Boilers and Garbage Burners with few problems. RE: steam drum repairs GenB (Mechanical) 22 Apr 04 00:18 Seal welded plugs from the outside of a drum (this happens on small drums, headers, etc.) are considered strength welds and the calculations must be performed to show the welds are sufficient to hold pressure and to hold the plugs into place.Īll the above must be accepted by your friendly, neighborhood Authorized Inspector prior to the repair. The welds are not holding the tubes in place and the pressure is actually working to try and force the weld into the leak. Seal welds from inside a drum are not considered strength welds. All adjacent tubes are given a very light roll as well. The tube is then rerolled (unless there is a plug installed). The completed weld area is examined with MT or PT. The seal welds cannot be larger than 0.5" or else problems with PWHT requirements occur. The area should be examined with MT or PT prior to welding Preheat temperature control is essential, normally 200 F, maintained during welding and the area allowed to slow cool. There is more to this story than davefitz has written). ![]() It is not normal to have such a high pH in the boiler water. In this case the options again are to replace or seal weld.įor seal welding it is important to ensure the area to be welded is clean (the Fort McMurray case was unusual and unique. Either the tube has to be cut out, the tubesheet seating surface repaired and then a new tube installed or the tube is seal welded.Įven if a tube has been plugged it is still possible for the tube seal to leak. If a tube has been leaking for a while and the tubesheet seating surface has been steam/water cut, no amount of rolling is going to create a seal. The only options in this case are to replace the tube or seal weld. If a tube roll is leaking and it has been rerolled and rerolled until finally the tube material is past it's modulus of elasticity, no amount of rolling is going to create a seal. We do it fairly often but it is always considered a last resort. Seal welding boiler tubes is not such a big deal as long as, as deanc puts it, all the ducks are in a row. RE: steam drum repairs metengr (Materials) 20 Apr 04 19:30 I'm not sure of any retubing done before then. It was partially retubed (d-tubes) over the past two years. It was moved from one area of the site to another, years ago. It is a package 1200# boiler that dates back to the late-60's. Bringing it back online has been one headache after the other. The boiler has been down for 2yrs, getting a partial retube and a new low-NOx burner. We are under a serious time constaint, due to emissions testing that has already been postponed twice. The air test held this time, and we will be performing a hydro tonight. I have just been notified that they went back in and re-welded. I'm not sure if there was just no way to get it out, or if they decided to go with the seal weld due to time constraints. Problem is that we couldn't get the old piece out due to the old plug being driven in so tight. knock out the old piece, install a new piece, re-roll, and plug. We were planning to do just what you mentioned.
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