HOT TAP FILLET WELD

Date 02-09-2009 00:52

YVAN,

Yes, I have done that type of work. I have welded hot tap fittings onto Natural Gas lines with product flowing. They were probably about your 3.2mm (1/8" for me). Have done same on water, jet fuel, High Octane aviation fuel, etc. These were all on existing systems doing additional runs for supply or repair.

The first object for me was to know my material. Important to know how thick and what grade before you strike an arc. Many times we would get to an underground line right as it was being uncovered and find it was not steel though that is what all the info on the lines said it was.

Second, is to check the condition of the line. If it has been underground for any time, even coated, this can be a major consideration. Rust spots, especially on natural gas, can be very hazardous.

If your lines are water (just a comparison, I know you are talking natural gas), you have fewer concerns though you might get wet if you hit a rust spot and don't handle it correctly.

Now, I'm not sure what you are trying to accomplish and what you mean by "a welding strategy". The thicknesses (or thinness) of the materials is not really a problem. These can be welded easily with SMAW, GMAW, GTAW. If in a field situation, there would obviously be other considerations. A good, certified, pipe welder is a must. Even many of them are out of their element on used pipe with product flowing through it (no offense to many who are able here on this site). There is a big difference between rusty material that stays really cool because there is water flowing through it and new pipe with no cooling agent.

I would then proceed to make sure, because of liabilities and other factors, that I had a proper WPS in place and that the welder was capable of working to that spec. Then he needs to be tested on mock ups with no product in the line. Make him do it in all kinds of awkward positions. Be unusual to be able to weld from a comfortable position all the time. How many tests do you give this type of person before you let him weld for real? Assuming you are talking about doing this work on live lines. One mistake and it can be all over for several people.

There are many ways to check the then attached fitting before hot tapping to be sure there are no leaks in the weld just applied.

Don't know how else I can, hopefully there will be others here with more info for you.

Have a Great Day, Brent

By YVAN

Date 02-09-2009 02:56

Brent,

Main concern is, when the wall thickness is very thin (5 mm or thinner wall thickness), and you have high pressure (1000 psi) natural gas inside the pipe, you may come to a point that the pressurized gas blow through the weld puddle.

I'm working on the development of a welding strategy for those situations.

Using of low heat input in vertical down welding position;

Lowering the gas pressure;

Etc...

Thanks for helping me with that development.

By dbigkahunna (****)

Date 02-09-2009 04:13 Edited 02-09-2009 04:16

[deleted]

By PlasmaHead2 (***)

Date 02-09-2009 23:07

It is a very good thing that company exists because thinking of trying to weld on an active system with a very large amount of flammable liquid under pressure is Not creating a happy feeling for me... more like one of terror.

The only comforting thought is that if you F- it up it would be over pretty quick, heck if the pressure is high enough you might not even know you screwed it up. Everyone else in a few mile radius would know, but you and the unfortunate few that were close to where you were working wouldn't.

All that being said, I'm not a pipe welder, I'm a shop minion and I enjoy it. I respect any of you who are crazy and skillful enough to do such things, and you will never have to worry about me trying to take your job. :)

-Clif

By welderbrent (*****)

Date 02-09-2009 04:22

YVAN,

The pressure is a very critical point of info. dbigkuhuna has given you good sources to go to.

Have a Great Day, Brent

By YVAN

Date 02-10-2009 00:27

Brent,

I already know API 1104. We have done many hot tap. When the pipe wall thickness is over 5 mm it's no problem.

Now I need to develop a welding procedure to use down to 3.2 mm wall thickness.

I know that pressure and heat input are critical.

I'm looking for some work done that may help me to deptermine maximun heat input for a given wall thickness and pressure, or a maximum pressure for a given heat input and wall thickness.

I already have some information but I wonder if someone may have something more.

Regards,

Yvan

By welderbrent (*****)

Date 02-10-2009 19:46

YVAN,

Did you check out the sources listed above for that? I did not go through it, only scanned.

I personally can't direct you to that and it has been too many years since I was doing those. Pressures we were working to, heat, etc are not something I try to memorize. It is too critical. Besides, my mind is too crowded with totally useless info, if I tried to put something important in there I would really be confused.

Sounds to me like you want advice from more of an engineering type person, not the grunt-labor doing the work. There should be some of those types on this site. Give them some time, hopefully one will read this and respond. Also, some of the others on here who are current in all the high pressure piping may be of some help (Inspectors, contractors), but currently that is an area I don't deal with.

Have a Great Day, Brent

By Robert Turney (*)

Date 02-11-2009 01:00

YVAN,

I work in the natural gas distribution industry and I am somewhat famailiar with your question, although not enough to answer your question. You might want to check out T. D. Williamson, inc. on thier website. We use a lot of their equipment from 2" inch up and weld a lot of their fittings, I.e... shortstops, three way tees, sphyrical tees........... You should be able to e mail them with your question.

By YVAN

Date 02-14-2009 19:48

Thanks Robert,

I'm already talking with TD Williamson but still looking for informations, like tests results, to held me with that development.

Regards,

Yvan