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NEW FAB Te ch notes
TECHNOLOGY
J OURNAL 技術專文
weld area that has been re-melted
during the overlap is more susceptible
to corrosion than the portions of the
weld that are only melted one time.
Conclusion
The number of times that 316L or
304L stainless steel material is melted
and allowed to re-solidify at ambient
temperature has a direct affect on the
corrosion resistance of the material. If
it were possible to clean and repassiv-
ate the areas after welding, the corro-
sion resistance of the joint would be
improved. This repassivation is
common in the bio-pharmaceutical
industry, but is not practical in the
semiconductor industry. As the proce-
dure for repassivation requires the
chemicals for passivation, usually a
strong acid to remove free Fe ions
from the surface of the material, to be
distributed via an aqueous solution
this is not practical for use in UHP gas
service systems.
Of course, if a gas system will not
be exposed to corrosive gases it may
be allowable to make multiple pass
welds without regard to the reduced
corrosion affect. This would need to
be carefully monitored closely to
assure that corrosive gas piping was
welded using a single pass process.
This would be very time consuming
and not very cost effective as multiple
pass welds are most commonly only
employed when joining piping used in
gas systems that are ½©and smaller,
usually special gas piping.
There are also instances where double
pass welding must be employed. When
hand welding, it is more effective to
employ a joint that has beveled edges
and a gap between the two members.
These members are then joined by
filling the gap between them with a
filler metal of the same or similar
chemical composition to the parent
material. In most cases these types of
052
NFPED
joints are more effectively joined by 1T and 2T welds were tested under PRACTICE FOR GAS TUNGSTEN
Single-Pass Weld welding them twice. The first pass the same conditions and there was no ARC (GTA) WELDING OF FLUID
joining the two members and the indication that the 2T welds were any DISTRIBUTION SYSTEMS IN SEMI-
second pass filling the space left due more susceptible to corrosion than the CONDUCTOR MANUFACTURING
III to beveling the pipe. As this type of 1T welds, but when welds were pro- APPLICATIONS in 2007 the param-
welding is most commonly done on duced over 2T in width there was a eters for an acceptable weld ID bead
large systems, >150mm in diameter, substantial increase in corrosion. Also, were changed from 1~1.5T to 1~2.5T,
and larger systems are normally used it was determined that it takes up to thus allowing ID bead widths up to
Art Start to deliver inert gases such as Argon, 3X longer to develop a program for 1T 2.5T. With all of this in mind it would
Nitrogen, or CDA (Clean Dry Air) they welds than for 2T welds due to the be suggested that much consideration
End Last Level
are not exposed to corrosive sub- precision required to weld consistent go into the decision to use multiple
stances. 1T welds. pass welds to join piping systems ≤
Finally, it has been determined In almost all cases throughout the 150mm in diameter. The susceptibility
II
I End Downslope that it is more cost effective to pro- U.S., companies have moved away of these multiple pass welds to corro-
duce weld beads that are 2T, T being from multi-pass welds for UHP gas sion is very apparent, not to mention
the wall thickness of the parent mate- delivery systems, opting instead for a the added value of the single pass 2T
rial, in width than it is to make 1T weld that is 2T in width and single welds on small diameter tube systems,
Orbital tube welding is done as a fusion GTA weld on a square welds with no loss of corrosion resis- pass. In fact, in the revision to the ≤1/2© in diameter.
end preparation, usually in a single pass. Weld current is
reduced around the weld circumference in a series of steps or tance. An experiment was done where SEMI Standard SEMI F78-0304,
levels. A timed current downslope completes the weld.
ob Bearden graduated from Central rently holds certifications as SNT Level
B Missouri State University with a II for VT (visual testing) and LT (leak
Bachelor§s Degree in Electrical Engineer- testing) HMSLD.
ing in 1987. Upon completion of studies Bob is currently working for Resplen-
Bob entered the field of QA/QC for instal- dence Technology Limited at TSMC
lation of process piping for Semiconduc- Fab14P4 as lead 3rd Party QA/QC for the
tor Manufacturing Facilities. In the con- installation of gas, chemical and slurry
vening 20+ years, Bob has continued in systems.
the QA/QC field and has expanded to
Reference
Project Management, Construction Man-
agement and QA/QC services for bio- 1. S.H. Lin, "Corrosion protection of high
pharmaceutical production plants, qualifi- copper aluminum alloys and stainless
cation of biohazard containment units and steels by surface modification," Ph.D.
most recently testing of nuclear dry cask thesis University of Southern California,
storage units for spent nuclear fuel. Bob 1995.
2. Barbara K. Henon, ¨Tube Welding -
was instrumental in developing ASME
Orbital Welding of 316L Stainless Steel
BPE, the standard used for installation of
Tubing,© Arc Machines, Inc., Originally
bio-pharmaceutical piping systems. Bob presented at the Twelfth Annual World
was also instrumental in developing the Tube Congress, October 7-10, 1996, spon-
first certification HMSLD (Helium mass sored by the Tube and Pipe Association,
spectrometer leak detection) and cur- International (TPA)
053
JANUARY 2011