Boiler Tube Welding Repairs

Check out the boiler manufacturer and make contact with them first. If they don't exist anymore then find a reputable repairer to review your situation.

Boiler repairs must be carried out by welders carrying the requisite coded skill levels using the appropriate welding materials and techniques; otherwise you run the risk of nullifying any insurance you have on the plant.

Do not try to cut corners on this type of work.

Massey.

The repair is going to be done by certified welder.

as an engineer i have to check the work done is according to procedures

and this is the reason for my request. I was thinking if there is any book that can tell welding procedures for this material.

Hi,

I've been speaking to an expert in boiler repars and he would wish that you provide some further information to assist in determining the best course of action. Firstly the boiler manufacurer, model of boiler , working pressure and date of manufacture. With tube steels being produced all over ther world it is important to get as much info as possible because the durability of any repair will depend upon the compatibility of the materials being used.

Can you also expand on the spec of the tube material because depending on the pressure rating and diameter there are factors to be considered in the method of replacement to be adopted, ie in a tube bank the point of welding should be away from an area of highest temperature, this may therefore involve cutting back more tube element to achieve the optimum location .

You should also advise whether one end of the tube is presented to a header or tube plate because you will need to prep the opening and then expand the new piece into it.

Let me know as much as possible.

Massey.

below are the information i tried to collect and hope it will be helpful

Boiler make: NEI Power

Comissioning year: 1981

Design pressure: 58 bar

Working pressure: 28 bar

Details about the weld joint:

The leaking weld Joint is at final superheater which consist of 3 bottom headers.

the weld joint location is between the tube and seconnd header

(no access from both sides) .

Superheater tube material:

BS3059 grade 620 alloy steel

Dimensions:

tube: 44.4 OD X 3.2

header: 88.9 OD x 11

hope these information will be useful to provide technical advice on the above subject.

Also i will try to attach a sketch of the weld joint location.

Thank you I will pass on this info. Is the boier still in use with this tube element plugged off?

What if the exit steam temperature?

Massey.

The boiler in the present time is shutdown and in repair.

Regarding the steam temperature from the final superheater

its approximately 450 C.

Hi,

Thanks for the info. Can you advise on the tube spacing and the proposed method of accessing the defective weld? Is this at the site of an earlier repair? If so are there others in the same vicinity. Are you able to ultrasonically examine other welds. The reason for asking this is to determine the general health of the whole superheated bank; because this will suggest the most appropriate course of action.

Will it be possible to merely cut out the weld and shorten the element or are you proposing to add a short 'spool' piece? Given the small diameter it will not be possible to do a 'birds mouth' internal/external weld so access will be needed all round the tube.

Regards,

Massey.

The space between each tube row is very small.

i guess around 5 cm which means that no welder

can have acess to the weld joint.For the general

condition of tube banks its not possible to tell until

the particular weld joint is repaired and repeating the pressure test.

Can you please elaborate more on your proposal of adding spool piece and how it can be welded given that there is no space available?

Hi,

The problem seems a bit more of a challenge than I thought at first. I had thought that you probably had a divergent section to gain access but if as I now believe the fault to be at the entry to the header where the inter tube spacing is only 50mm then the 'spool piece' is a non-starter. It would have worked if you had had a plain piece of tube either side of the leak.

Were the tubes all stub ended into the headers as originally constructed? How many are there into this header? will this be the first time this repair has been required?

Massey.

Hi,

I've now had a detailed discussion with my boiler tube guru who has just returned from a spell off shore (in the North Sea).

Ater due consideration albeit without the benefit of the sketch you were going to provide we are of the opinion (subject to the approval of your boiler inspector that the quickest fix is the removal and sealing of the defective element at both headers. You are entitled to remove upto 10% of the tubes and still remain within the manufacturers spec in terms of performance. Therefore if you have not done so previously then this single tube removal would not materially affect performance etc.

Cut out using a sabre saw either immediately adjacent to the header or where-ever the minimum exposure to hot gases permits. The weld technique is then to creare a plug within the tube with a capping weld over the end.

Weld material and process TIG using 'A9' wire or higher spec. This is suitable for 450C working and your tube material spec, it is also readily available I am given to understand.

If you wish to retain the tube in action then a modified version of my previous suggestion about the spool piece is recommended. The defective section including the faulty weld is cut out using the sabre saw, make these cuts about 12" apart if possible. The end adjacent to the majority of the element will have enough flexibility to allow it to be displaced far enough to permit a normal prep and butt weld to be performed. The other end is to be prepped for a 'window weld' prior to the previous weld being carried. To achieve this you will make a cut across say 150 degrees of the circumference of the tube ,then cut longitudinally into the tube and remove the section. On returning the element into position and alignining with the remaining stub you perfom an internal weld through the aperture, The remaing peice of metal is then replaced and welded back into the wall as per normal. This technique is recognised as being a ' temporary repair' but some inspectors may not accept it as a permanent one. It all depends on issues such as the location (in the bank) and overall condition of the superheater.

Hope this has been of assistance and my apologies for the delay in responding.

Best regards,

Massey.

a window weld can be done. also a quick fix is to do a bypass

I recently finished lecturing a course of welding for boiler repairs addressed to engineers and supervisors at a sugar mill. Can you read spanish?

Reagards, William

I am a retired tube welder. Chromemoly is not too difficult to weld if your using a backing ring. However if u are welding open butt joints u need considerable skills . Most spec's require a specific amount of penetration flush, no suck back ; less than flush on inside tube,up to 3/32 inch buildup inside. The alloy of rod closely matches that of the tube. I could look in the garage and give you exact rod number. Fit of joint is critical proper bevel angle, landing or flat spot on sharp end of tube gap between tubes,1/16 to 1/8 depending whether welder feeds wire from inside or lays wire or filler rod against opening.heat is welders preference TIG root and hot pass and stick filler and cap. I hope this has been some help. I enjoyed welding Tubes more than any other job I've ever had, very challenging!!!! Testing is usually hydrostatic, filling boiler tubes with water and pressurizing one and one half of the operating pressure and holding it there for a specified time. Any further questions let me know. I was also an Instructor at Fla Comunity College. I love talking about this subject it brings back some fond memories.