>>     I don't know if it's applicable here, but I have heard that
   stainless
    >> is
    >>     welded, the back side of the weld needs to be in an O2 purged
    >>     environment.  I wonder if/how that's done when the inside of
   the pipe
    >> is
    >>     being welded to a flange..
    >>
    >>>     Matt-
    >>
    >>     That is true for tube butt joints such as headers. You need a
    >>     separate supply of nitrogen gas behind the weld. Not so for a
    >>     flange welded on the end of a tube as the slag, if any, can be
    >>     mechanically removed.
    >>
    >>     Paul Lamar ...No rotor no motor
    >>
    >> Paul,
    >> Let's hope that Matt mistyped O2 for N2! Oxygen wouldn't be used in
    >> almost any weld process other than flame cutting.
    >> Bill Jepson
    >>
    >> Thanks Bill. I missed that.
    >>
    >> Paul Lamar ...No rotor no motor.
    >>
    >
    > Matt and Bill both agree; I think that darned English language is
   getting
    > in
    > the way. "Purge" means "to eliminate." In the old Soviet Union, for
    > example,
    > when an official was "purged" from the party, it meant he was
   sent on a
    > permanent vacation somewhere else.
    >
    > So an O2 purged environment is just one where oxygen is not
   present and
    > has
    > been replaced with another gas. Nitrogen was Bill's suggested
   replacement
    > gas; argon, available to TIG welders everywhere, would also work
   well.
    >
    > Barry Gardner
    > Wheaton, IL
    >
    > Darn! One of them there big words. You are right of course.
    >
    > --
    > Paul Lamar ...No rotor no motor.



   If all you are welding are 300-class stainless steels you can use
   nitrogen
   as a purge gas. But nitrogen is soluble in the molten puddle of many
   alloys
   and causes them to be brittle. Argon is the best all around
   shielding and
   purge gas and does not cause brittleness. Inconel alloys if not cleaned
   properly WILL crack. The thin oxide layer found on Inconel and stainless
   steel alloys must be removed from the weld zone. The reason for this
   is that
   the oxide layer melts at about 1000 degrees F higher than the base
   metal. If
   it is not removed it can become a stratified layer within the weld
   metal and
   a failure point. The oxide layer found on steel (rust) melts at
   about the
   same temperature as the base metal so it is less of a problem. Other
   sources
   of contamination are dirt, oil, pencil marks, even fingerprints can
   cause
   cracks in welds. The oils from a fingerprint can cause cracks in
   some types
   of Inconel. And by the way watch the heat input with high heat input
   comes a
   large heat affected zone. Examine the weld joints that have failed
   and you
   will see that the failure is in the HAZ [heat affected zone] and not
   the weld itself.

   Russ Keith


Great information Russ!

I have to appologize for using the phrase "O2 purged environment."  I
certainly meant "conduct the weld in an environment which contains no
oxygen (the backside included).."  Sorry for the confusion.

And Paul, I read what you said about slag removal from a flange weld..


Regards,

Matt-


The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.