Pipe welding connected to Machinery

Date 06-08-2009 19:22 Edited 06-08-2009 19:27

Piping flanges should not pose any stress to rotating equipment flanges. Back in my days of erector engineer I've did the job like this:

1. The piping flanges are bolted to the equipment flanges. The piping flanges aren't loose, they're attached to the pipe by means of strongbacks.
2. The piping flanges are tackwelded to the pipe.
3. The flanges are unbolted, the strongbacks are removed and by means of feeler gages it is checked whether the pipe flanges are paralell to the equipment flanges.
4. If they are, they're bolted again and the first pass is completed.
5. They're are unbolted and the paralelism is checked again. If everything is OK, then the flanges are once again bolted and the weld is completed.
6. After it's cooled down, unbolt again the flanges and align the rotating equipment within tolerances.
7. Bolt again the flanges and check the alignment. It should be always within tolerances.

A heck of a time consuming job? No, because the time spent in welding the flange with such precautions is saved afterwards when aligning the equipment.
Of course, this procedure applies to large rotating equipment, you won't do that for a 2 inches discharge nozzle pump.
Giovanni S. Crisi
Sao Paulo - Brazil

By Richman (**)

Date 06-09-2009 04:54

Since in our project specs states that the piping flanges are bolted to the equipment flanges are not allowed in all rotating equipment during welding, just to make things clear as per your response,you mean even if both flanges it is tightly bolted during and after welding there is no EFFECT on this to rotating machinery equipment, is that correct Sir?Kindly correct incase I misunderstand what you said.

Thanks

By G.S.Crisi (****)

Date 06-09-2009 16:24 Edited 06-09-2009 16:29

Richman,
I havn't understood the first phrase of your question. What exactly the project specification states? What does "flanges are not allowed in all rotating equipment during welding" means?
Read again paragraph 6 of my answer: after the weld is complete and cool, loosen the piping flanges (there's no need to take the bolts away, they just need to be loose, i.e., you can move them freely with your hands, so they will pose no stress on the equipment flanges) and align the equipment. In this manner, the equipment will be aligned with no stress from the piping.
Now read paragraph 7. After alignment is complete, you must make sure that the piping poses no stress on the equipment, and that's why you must tighten the flanges again and check the alignment. If it's out of tolerance, it means that the piping is putting stress on the equipment, and the situation must be corrected. How? Usually, working on the piping supports, in order not to cut the weld and have to remake it. This is the last remedy, used when all of the others have failed.
Now, if you follow the apparently time consuming procedure I've described, you'll never have to cut and remake the weld.
Again, this is done on large rotating equipment, like a boiler feed pump, a cooling water circuit recirculation pump, a petrochemical compressor or a refinery API 610 pump. You won't do that in a small pump with 2 inches discharge nozzle.
Giovanni S. Crisi

By Richman (**)

Date 06-10-2009 07:57

Our project specs states; No alignment of piping is allowed while connected to machinery and no connection of piping to machinery is allowed until machinery alignment is complete unless the ground connector directly connected to the pipe being welded.

It didn't specifically says for small or large rotating equipment. In-case for small pump what was the effect on the pump.

By G.S.Crisi (****)

Date 06-10-2009 15:23 Edited 06-10-2009 15:26

Who wrote the project specification? I'm curious to know. It appears to me that's too much (and unnecessarily) stringent.
In any case, the specification is there and there's nothing we can do except following it.
So, my suggestion is the following:

1. Erect the piping leaving the connecting flange (i.e., the piping flange that will be bolted to the equipment flange) tackwelded. Four tacks 1 centimeter (3/8 inches) long are sufficient, don't make them longer than that. Until now, of course, the piping hasn't been in contact with the equipment.
2. Now, approximate the piping to the equipment until both flanges are, say, 1 millimeter or so (1/16 inches) apart. Both flanges are very close to each other but they aren't in contact. With a feeler gage, check if both flanges are parallel to each other. Case nº 1: they aren't. Cut the tack welds and make the necessary corrections. Usually, it's sufficient to cut two tacks, leaving the other two untouched, that's why the tacks should be short. Case nº 2: the flanges are parallel. Give another four tacks, this time longer than the first four. In this manner, the flange will be attached to the pipe end by means of eight tacks and it will be very unlikely for it to move from its original position when completing the first pass.
3. When the first pass is complete and cool, check again the parallelism between both flanges. It should be OK.
4. Complete the weld. After it's cooled down, bolt both flanges together. There's a technique for tightening flanges bolts, and you should follow it. In the meantime, the equipment has been aligned, BUT IT'S IMPERATIVE (no matter what the project specifications says) THAT THE ALIGNMENT BE CHECKED AFTER THE PIPING HAS BEEN CONNECTED TO THE EQUIPMENT.

Regarding your question on the difference between small and large rotating equipment, it's a matter of common sense: therer's a big difference between a 600 kW boiler feed pump and a domestic swimming pool water recirculating pump.
Giovanni S. Crisi

By Shane Feder (****)

Date 06-10-2009 23:30

Richman / Giovanni,
I am reading the project specs a bit differently.

"Our project specs states; No alignment of piping is allowed while connected to machinery and no connection of piping to machinery is allowed until machinery alignment is complete unless the ground connector directly connected to the pipe being welded."

"No alignment of piping is allowed while connected to machinery" - I take this to mean that the weldneck flange closest to the machinery is already welded and bolted and you are not allowed to perform any alignment on the other end of the spool. (If you are forcing the pipe around to align it you will be putting stress on the flange connection at the machinery.)

" no connection of piping to machinery is allowed until machinery alignment is complete unless the ground connector directly connected to the pipe being welded."

The machinery must be aligned before you can perform final fit up and weld, that is understandable.

"........unless the ground connector directly connected to the pipe being welded." - this is simply stating your earth connection must be directly on the pipe being welded and not arcing through some machinery.

I cannot see anywhere that the specs are prohibiting what Gionvanni initially recommended.

In my experience we bolt the weldneck flange to the machinery (that has been previously aligned), bring the pipe to meet the flange (putting no lateral or vertical pressure on the pipe), put four good strong tacks, unbolt and check the alignment of the two flanges. If they are within acceptable tolerances remove the spool, complete the weld and reinstall the spool.
Hope that helps,
Regards,
Shane

By G.S.Crisi (****)

Date 06-11-2009 01:11

Shane's opinion deserves to be considered. Richman, why don't you print this sheet with your question and our (Shane's and mine) answers, show it to the project engineer and ask his opinion? You may save time and manhours by doing that.
Giovanni S. Crisi

By Richman (**)

Date 06-11-2009 05:24

Thanks for all your opinions on the above topic. I think I will follow what you guys advise to show to the engineer the copy and answer to our project engineer.

Thanks guys.

By 3.2 Inspector (***)

Date 08-14-2009 10:30

Richman,

Is this ----> "Our project specs states; No alignment of piping is allowed while connected to machinery and no connection of piping to machinery is allowed until machinery alignment is complete unless the ground connector directly connected to the pipe being welded" <---- Copy and paste from your specs? Or did you re-write it with your own wording?

The way I read it is that you are allowed to do all of the above IF you connect the ground clamp directly on the pipe you are welding. Maybe I just misunderstand it, but it seem a little strange way to word it.

3.2

By Richman (**)

Date 08-22-2009 04:07

This is what our specs states;

Welding on piping connected to machinery is not allowed unless the welding machine ground lead DIRECTLY to the part being welded. No alignment of piping is allowed while connected to machinery and NO connection of piping to machinery is allowed until machinery alignment is complete. Spring type alligator clamps shall not be used.

Ground leads shall be directly to the part being welded.No ground welding clamps shall be allowed on any part of the machine skid.

By cremx

Date 07-31-2009 12:25

Check the ASME B31.3 interpretation 15-07

By Richman (**)

Date 08-01-2009 04:19

cremx,

I don't have a copy of that interpretation 15-07; can you attach that when you make a post or kindly explain to me what is written in there?

Thanks so much

By cremx