Can you explain “profile work pls.
‘
*From:* owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] *On Behalf Of
*vbra676539@aol.com
*Sent:* 17 April 2009 08:39
*To:* personal_submersibles@psubs.org
*Subject:* Re: [PSUBS-MAILIST] Re: Pressure vessel welding
One side note here is that ABS and the ASME code frowns on profile
work on pressure vessel welds. The issue as I understand it was all
about maintaining thickness on full penetration welds. Professor Lance
and Brother Frank will know more about that than I do, or they're in
more trouble than I think.
Vance
-----Original Message-----
From: Sean T. Stevenson <cast55@telus.net>
To: personal_submersibles@psubs.org
Sent: Thu, 16 Apr 2009 4:27 pm
Subject: Re: [PSUBS-MAILIST] Re: Pressure vessel welding
Backgouging, or backgrinding, is necessary to ensure that the weld is
full-penetration. The root pass is the one most susceptible to
inclusions, voids or incomplete fusion as a result of insufficient
shielding, poor temperature control (rapid cooling), contamination
(inclusions from dirt or moisture, etc.) or pool flow into the gap you
are bridging and rapid cooling of the bead without actual fusion to
the parent material. Ideally, a full-penetration weld between two
cylinders would be a double-V butt joint, in order to assure complete
fusion with a minimum amount of rod fill. In your example, a 1/2" wall
would entail a 0.20" - 0.25 chamfer" on both sides, such that you
either have a perfect V or a small parallel land in the center of the
wall. In either case, the root pass fills the gap and joins! the two
cylinders at the wall centerplane (center-cylinder?), and then you
begin to lay passes on one side. Given that the root pass could have
poor fusion due to the cooling / bead flow problem, you grind it away
from the side you haven't welded yet, to the extent that you are 100%
assured of having ground back into material which is high quality,
strong weld that is fully fused to both sides of the assembly -
essentially removing the weld toes of the root pass on both sides and
exposing the fusion interface to assure its quality. Then, you start
laying passes into the ground-out root to guarantee 100% fusion.
Granted, the double V is a lot of work to prepare, and if you can't or
won't do that, you can effect a full-penetration weld on a strict
square-ended butt joint, but you have to ensure that if you lay a root
pass on one side, your electrode can reach fully down into it from the
opposite side to achieve 100% fusion - here, you have conflicting
goals, because the larger the gap between the two cylinders, the
easier access you have for the electrode (essentially achieving the
effect that the V preparation is intended for), but in increasing this
gap you make it much more difficult to lay a quality root pass to
begin with, necessitating deeper grinding when you backgouge it to
ensure that you expose perfect weld before covering it. You may end up
having to grind out this pass entirely, exposing your first covering
passes from the other side, and then covering those. I would recommend
considering the weld-preparation, as it may very well save you the
same amount of effort in back! gouging and recovering.
As for your covering passes, you should be able to maintain high
quality 100% fusion welds as you proceed, but if you notice a mistake,
or are at all suspect about the extent of fusion of any given bead (or
any other quality issue), just backgouge it until you have it back to
a perfect weld, and proceed from there.
Once you have a high-strength, high-quality weld, you can further
improve its fatigue life by profile grinding (where you remove
geometric discontinuities / stress concentrations at the exposed weld
surface) and stress-relieving with heat.
-Sean