Need some help on this one;
If I was welding an x65 subsea pipeline steel (600DN x 30mm) what welding
technique would one use? (along with approx. time to weld each joint, NDT
test and what kind of acceptance criteria could be used.)
also, what NDT technique could be best used? assuming we are using a
lay-barge. If using a lay-barge, how many welding stations would be optimal?
Many thanks in advance.
On the lay barges I worked on in the Gulf of Mexico, it went something like
Fitup, and root pass with 6010++, grind out some of the pass.
Pipe is moved along to second station:
Hot pass and cover passes with 7018.
x-ray, and if x-ray passes, wrapping the weld, and banding on a styrofoam
billett every so often to soften the bending while it was going to the
Depending on the pipe diameter, the barge was either winched ahead, or
Caterpillar like hydraulic treads gripped the pipe and rolled it. Time per
station depends on diameter of pipe, efficiency of welders, sea conditions,
amount of grinding, cut outs and repairs, efficiency of all related teams.
At times, all stops while anchors are moved. It can only be recorded as
XXXX feet of pipe layed today, and that will vary from day to day.
And, contrary to what some other posters have said here, ALL welding is done
topside before it hits the water.
Negative to that, even with bigger pipe. Pipe has to be flexible to avoid
overbends before it hits the bottom. Thus, the addition of styrofoam
billets to add bouyancy. There is some bouyancy there from the air inside,
but not a lot compared to the weight of the steel. I was on a 90 mile
stretch of pipe done by Bannister (the Alaska Pipeline people). It was 54"
OD concrete coated pipe. I was amazed at how much that big stuff flexed.
Realize there is a difference between flexing where it will return to its
original shape, and bending, where it will not.
Barges ride really steady in the water. I would 10x rather be stationed on
a barge than a vessel. Most of a barge rides underwater, and is not
affected a lot by the waves. It does not pitch and yaw nearly as much as a
vessel. A barge is a LOT easier to work on, sleep on, and eat your dinner
without having to chase it, or hold it in your lap so it don't go heading
The anchoring systems of lay and jet barges start out at about 40,000#, that
is four 10,000# Danforth anchors. It goes up from there, either by more
anchors or larger anchors. Comaratively, the pipe is just a very small very
weak appendage of the barge that is so small and weak and flexible, it can't
be left to hang there on its own weight. Were a barge to break loose from
its anchoring system, it would very quickly break off the pipe stem, or drag
it like a car would drag a chain. The gross weight of a barge to the weight
of a pipe string is no contest.
I worked about eight years as a diver, welder, and crane operator in the
Gulf of Mexico on oil pipelines and oil rigs. Like you said, it never
ceased to amaze me. Some of the spectacular successes, and some of the
spectacular failures. Well kicks. Blowouts. Hurricanes. Fires.
It was high adventure that I will take to my grave. One day I'll be sitting
in my Depends in my wheelchair, mumbling, with a smile on my face. And
people looking at me will wonder, "What in the world is that old fart
Cheers Steve, many thanks.
Just a few more queries based on your remarks;
* what welding method did you use/ or you suggest? I assume the 6010++, 7018
are filler metal type (?) sorry for the ignorance, but I am just learning
* have u got an approximate time based on your comments below on time it
would take to do a weld + inspection?
thanks again, jet
That's an Ernie question. From what I know, the 70 corresponds to the
tensile strength, and the number after the dash refers to the metallurgy in
it. A good welding manual would probably have it, or a call to your local
supplier. Maybe even look at the Lincoln website.
Steve, out of curiousity, what did you do when it failed x-ray? Obviously
you re-did the joint -- but how much did you redo? Did you have to grind it
all down and start from scratch? All around the pipe, or only in the flawed
I, personally, did not do the xrays, but spent a lot of time with inspectors
watching them do it, and asking questions.
The flaw in the pipe dictated what kind of action would be taken. If it was
just one bubble of porosity, or a small slag inclusion, the welder was given
one chance to grind it out and weld a pass over that grind. This was
limited to only one flaw per joint. More than one, it was a cutout. If the
flaw did not pass the second time, it was a cutout.
Incomplete penetration, or lack of fusion was always a cutout.
Different jobs had different requirements because of what was going to be
pumped through the pipeline, and what the operating pressure was going to
be. One size did not fit all.
One try to correct, eh? I guess it's a good thing I'm not planning on making
a living by welding!
When you say "cutout," does that mean cutting the pipe on either side of the
weld and starting from scratch (back to station 1)? What did they use to cut
the pipe -- a manual OA cut, or something more automated?
For that matter, why only one try to correct -- was there a concern with the
added heat affecting the metal around the joint, or ?? After making several
passes (6010 plus a couple of passes with 7018 if I understood correctly),
what's one or two more?
Once again, I'm just curious -- thanks for indulging my curiousity!
Cutouts were done a specific distance from the bad weld. They were done
with a mechanical collar and OA torch. It was run by a little hand crank
that cut and beveled the pipe. Further dressing was needed before welding.
The piece that was cutout was only 3-4" long.
Not sure. You would have to ask the inspector on that one.
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