This is just my opinion.
It's hard to impossible to maintain preheat temp on big bore pipe with one welder, unless you're putting the flame to it while the welder is welding. By the time he has the bead in the pipe has turned cold, and that little bead is wanting to crack.
Today it seems like everybody wants a hot filler soon after the HP, just to have some meat in the joint to avoid cracks. With pipe grades constantly creeping up. After the HF the joint is pretty secure.
There is a awful lot of stress on a heavy wall big bore joint with only a bead in it. Especially with sidebooms moving the pipe, internal clamps crawling along and slamming up, skids settling in the ground, big up and down hills involved, overbends/sags.
Then you add in outside temp changes, you can hear the pipe growing or shrinking, it cracks on the skids. They want enough weld to make the joint secure until the firing line shows up.
If you've ever been on the front end when one broke out, it's a big, big noise and can injure or kill anyone working around the pipe.
On tie ins you can have considerable stress at the joint from making the fit. People get killed from the pipe coming out of the clamps. You want as much weld in the joint as fast as possible.
Plus it's just waaaaay too slow in a production setting, that's why they run 4 bead hands/4 HP/4HF on bigger pipe. One bead hand would have 3-5 tractors just sitting and all the front end labor dead in the water for hours each day.
JT
edit, not to be all long winded, but it's in everybody's best interest to go from a loose joint in the clamps, to a secured but unfinished joint as fast as possible.
And it's in the pipes best interest to get the preheat up and the front end welding done as fast as possible while maintaining that heat.
Everybody has time limits between B & HP and HP & HF, and requirements for how much weld has to be on the pipe before you go off and leave it to cool.
This is straight X42, 16", .250 wall. Other than double joints we start each day with a bell hole and as I said we're lucky to get 160' a day most of the time it's 80'. The company standards state bead is to be done by two welders. After that it can be finished by one as long as each pass is completed around the pipe. I'm looking to convince the company to let us use one welder for the entire weld. We are using 5/32 on the bead which gives a substantial bead. We are also diametrically opposed on the bead. Standards state pipe is not to be moved until bead is complete, we don't move it until weld is complete.
Do you think I should just let the dog lay or make a proposal to use one welder under these circumstances? If propose, any thoughts on what to propose. What would sell this? I suspect they may just say no because the job was bid for two on 16" so it would not be fair to the others who also bid.
I get it. That's a lot of payroll for 80'/day. Hopefully whoever bid the work understood how much ditch to expect in a day, if not that'd hurt.
Uphill battle for sure trying to sell one welder on 16". I'm no help whatsoever on that point. That's been in 1104 since right after the pilgrims landed on the rock.
Good luck.
JT
I think Superflux's answer is as close to truth as anything. I work in a fab shop where the conditions of pipelining are non existent and yet I see this very spec in the oil and gas stuff we do, with no relief.
Though JTMcC's response is one of the best I've seen in a long time and probably the root of the logic behind it, the tradition thing (or perhaps engineering ignorance) has to play in when a shop controlled environment lacking much of what was pointed out (sidebooms, internal clamps, and cellulosics, etc.) will still have the requirement imposed.
Having said this, so many of the specifications I see are cut and paste jobs of the engineers themselves are often quite ignorant. Getting relief is like pulling teeth. Nobody wants to stick their neck out when they are ignorant of the original intent. Works the same way with code bodies.
Roger that js55, on the cut and paste engineering, sometimes ignorance, sometimes laziness or a little of both. It IS easier for them that way, even if it doesn't apply to the particular situation. And like has been mentioned it sometimes doesn't.
J
It gets frustrating when you're bidding work and you see rediculous verbiage in the job specs...one that comes to mind is a large undergroung CHW/HW pipe project that I bid, got and ran 6-7 years ago.
We had already tested, insulated and burried a couple hundred welds when the QC/Mech. Eng. read the specs and frantically said to me,"We have to dig up all the pipe, strip the insulation and PWHT all of the welds."
I'd hoped no one read that paragragh and actually thought it applied to our project. It was a requirement in that spec from another project that should have been removed, like a dozen others.
The hairy part is; will they expect a deduct since everybody bid on the job using those specs. If you deal with a competent person, you would win this battle because they have done dozens of these projects with great similarity on the same base (Ft. Bragg) No other project required PWHT, the system is designed with ex. loops, bolster pads, anchors, guides, pipe/insulation movement inside of the HDPE outer cover. Neither the grade of material nor the thickness would require PWHT.
He was a worry wart that wouldn't let it go so we went to the ACOE (Army Corp. of Engineers) with the delimma and he (ACOE) laughed and said it was not needed and should have been removed from the specs before sent out for bids.
These specs were notorious for cut/paste and lack of proper cleaning but we did so many we knew what was needed and would submit RFI's when needed. Still, it's frustrating and sometimes a gamble.
Was this discussed in the meeting, with all principals, prior to start of project?
The GC and Mech. Contractor were present but we subcontracted from them so we weren't part of that process. We had done several projects with the same group, GC/MC and pretty much knew the deal but it's still a little risky when new people are involved.
JTMcC.........In the estimating world it's called "Short of the runway" .........NEVER want to be the one "caught " in that CLUSTER FAQ.........
You have a nice juicy bead until the monkey with the grinder removes 70% of it. the issue with just a bead is cracking. Even X42 can crack if it is handled improperly. In the days of wood ships and iron men you did not grind the bead. Hot pass hands knew how to burn out the wagon tracks without removing all that reinforcement. If all the grinder monkeys are doing is hitting the stops and starts you should not have a issue with cracking. But all the bead grinders I have met lately seem to think their job is to remove everything the bead hand just put in. And there is a lot of weight to be held up with most of the bead removed.
Not to say a good grind will not make a better weld, it will. But that grinding adds a risk you would not have if the bead was not ground.
Why not just do the bead and hot pass then when you get finished, have the two welders fall back and do the strip and cap?
Well put JT. Very informative in understanding what is involved.
Have a Great Day, Brent
