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
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
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
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.
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