Welding Tips and Tricks

I don't often get to do much pipe welding in the shop, it's almost always on site and usually no cameras allowed. I just got the chance to spool up a control column for a pressure vessel level sensor (80"). Nothing bionic but its an opportunity to post up a job at least.

The column is a 3" sched 40 pipe about 80" long with end caps and socket weld flanged branch pipes. End caps have 3000# sockets cut in.

First job, cut socket holes with mag base roto-broach and prep.
Now to cope the branch pipe ends, prep and tack into flanges
Next cut branch holes in 3" pipe and prep for welding
Now weld im up.

Root pass 105amps 3/32" tungsten and wire (ER70S-4)
Fill pass 110amps
Here comes the cap cap 125amps
Sorry I thought I took pics of the branch welds but not there now.

Here is the finished column ready to go to site for installation. If I can sneek a pic I will.

Nice work.

coldman
did you make all the cuts with plasma?
craig

No only the two branch holes. My plasma is a cheap Chinese job and mostly the results are not pleasing. All other cuts were pipe wrap marked and 1mm x 125mm wafer disc cut. I find it fast and accurate for bevel prep. The end caps were done with mag base.

coldman
thats a great way to do it. I've
done a few with a die grinder and file.
i give it a try
thanks for the info
craig

Sweet!

I know how it feels to not be able to take pics of your work. I have and do take them anyway, but have to be very careful to stick to close-ups and keep out identifying marks, emblems, color schemes, and the like.

I was slightly surprised to see Gra-Loc fittings on the branches since the material is shd. 40. I gather the working pressure is high enough that standard flanges would be unhandy at that size?

Steve S

Application is refrigeration ammonia. Industry standard for ammonia is that all flanges must have captive gaskets to guard against blowout.
These flanges are a true lump of steel to weld onto 1-1/4" sched 40 pipe. I think I cranked up about 160-170amps on the pedal for the second pass.
Most pipe welders on site would stick weld these because mostly they use lightweight scratch start dc power sources good for 140-150amps only. I got the 200dx because I tig all pressure welds only. The extra weight does not bother me, hell the steel argon bottles are worse to carry up stairs and roof access ladders.

Design pressure is 2.1MPa. (300psi)

Coldman,

That makes complete sense. I've not done ammonia piping, so I was not aware of the captured gasket requirement. I typically use these gra-loc style fittings for extreme pressures, but I can see the benefit in toxic fluid applications.

Steve S

It's no surprise to me that our industry flanges are originally from another industry segment although I have not heard the name "gra-loc" before. We only know them as ammonia flanges and there are several manufacturers around the world that I know of off the top of my head so there probably are more. These particular ones come from good ol Uncle Sam. Company I used to work for in my gangly youth used to turn them up from bar stock on an nc lathe. (reminds me of the bugs bunny cartoon where the lumber mill grinds down a whole log to make a tooth pick)
1" and under these flanges are two bolters which is why I went to 1-1/4" for this job. I've never understood why a body would squeeze two pipe ends together with 2 bolts only when a body could easy die if one comes loose or snaps - S@#* happens as we all know....

Coldman,

I misspoke. Grayloc (not gra-lock) fittings are captured-gasket fittings, but the design is a bit different.

Here's a sample.

http://www.oceaneering.com/wp-content/u ... ctor-2.jpg

The principle of the captive gasket is the same.

Steve S

Steve, that looks like a very good flange system and probably good for hydraulics although it leaves you with butt weld joints. Not that it bothers me, I have done 4000psi sched160 butts before with no problems. I have seen hydraulic companies that manufacture power packs and cylinders that refuse to do butt welds - socket welds only. I could never figure out why and they wouldn't tell me.

But welds leave a bit more room for error maybe.

Sure, but if it's done right it must be good. I did speak to a welding inspector about it who suggested they were worried about pulse but even he would not say whether or not I should proceed with the butt weld. I know I'm missing something here but my welds have been in service for 18 months now.

I've welded sch. 160 3/4" 304SS (with those Graylocs) that were x-rayed and then pressure tested to 9680 PSI. Our client won't allow socket-welds for those pressures. Butt-welds only.

Steve S

Exactly my point. If the butt weld has been done right it must be good. We've all heard stories of socket weld joints blowing out due to lack of fillet throat.
Maybe these guys who refused to butt weld just weren't certified and running a fillet on a flange is relatively easy as long as you deposit enough throat.

Steve I just looked up 3/4" xxs. I think it ends up with a 3/8" bore. You wouldn't want to have much root reinforcement would you? Did you get a chance to see the x-rays to see how it turned out?

Coldman wrote:Steve I just looked up 3/4" xxs. I think it ends up with a 3/8" bore. You wouldn't want to have much root reinforcement would you? Did you get a chance to see the x-rays to see how it turned out?

Not xxs... Sch. 160. About 7/16 bore? I'd have to look it up again. Not much difference, though. Root penetration was limited to 1/32 (average) if I recall.

Yes, I got to see all the shots. Nice validation. They actually came and did it on site on a Saturday (I got overtime for showing up and drinking coffee while they worked), and I was the first one (other than the techs) to see the film.

Steve S

Here's a crazy one for you. They want me to butt weld a 2" long piece of Sch.80 4" to a 90* elbow to be able to socket weld it into a flange. I suggested we just use a butt weld flange to eliminate one weld and they said it has to be socket welded per the engineer. I called the engineer and he said the standard calls for a back welded socket weld so I have to do 3 welds instead of one and it still has the butt weld right next to the flange. This is for a gravity fed pump inlet with 130" WC pressure on it. I told them that I'll make sure I don't get to it until I'm on overtime.

I checked out on the rack and Sch. 160 x 3/4 is .614 ID and XXH (XXS) is .439 in boiler tube. Didn't have either in stainless to check only 1".

Len

You gotta laugh[GRINNING FACE WITH SMILING EYES]

Update:
Finally got around to welding in the control column on site. Sneaked a pic.
OK the tie-in was 1-1/4" to 2-1/2" vertical.
Holes cut with 32mm bi-metal hole saw (now stuffed).
All sched 40.
2 passes. 1st pass 155amps. 2nd pass 165amps.
New column held in place with chain block and stronghand magnets which worked really well.
Just managed to get around the inside bottom corners without a mirror. (yay)
Pressure tested with nitrogen to 1800kPa
Relief valve setting 1200kPa
Standing pressure 800kPa.

Took 2hrs to get all the paperwork in place prior to starting:
-Hot work permit
-Smoke detector isolation permit from off site management and insurance company
-Work method statement - hot work
-Job safety analysis
-Ammonia plant intervention notice
-Ammonia plant intervention procedure

Actual arc time was probably around 30mins. Whole job took 5hrs including paperwork, setting up and packing up.

Electricians can now connect, laggers to insulate the pipes, job done.

Coldman,
Is that a guided radar level indicator or just a float switch?

Len

Len,
The existing switch on the left is a float switch. The new unit I installed in the new column is a level sensor. Not entirely sure how it works but i believe it is conductivity between the sensor element (which looks like a 1/2" × 80" teflon rod) and the pipe column. As liquid rises up the length of the element the sensed conductivity increases which is scaled to a 4-20mA signal which is then input to a plc or scada for display or control.
Vic.

With a poor conductor like ammonia, I would guess it's a capacitive sensor (probably fully self-contained with two conductors, rather than measuring between a single conductor and the outer pipe) that uses an RLC ocillator circuit to convert frequency to a 4-20 signal. I've seen many fluid-level sensors designed this way.

Regardless of the details, nice work, Coldman, and good-on-ya for sneaking a picture.

Steve S

Steve,
So now, of course, I had to check this out.

I can confirm the manufacturer's guff does use the word capacitance.

Interesting foot note. The say to use conductive thread paste when installing and specifically not to use teflon tape. The sensor is a 2-wire but grounds through the pipe system apparently (I thought it was to do with sensing resistance, but no).
Now we don't like using pipe paste on ammonia joints unless it is Loctite high pressure pipe sealant. In the old days we used to use litharge and glycerine. These days we use teflon tape so we leave the first few threads clean to provide the ground and seal further up the taper. Easily checked with a multimeter.