Page 55 - Vol.01

NEW FAB Te ch notes
TECHNOLOGY
J OURNAL 技術專文

weld area that has been re-melted joints are more effectively joined by 1T and 2T welds were tested under PRACTICE FOR GAS TUNGSTEN
during the overlap is more susceptible Single-Pass Weld welding them twice. The first pass the same conditions and there was no ARC (GTA) WELDING OF FLUID
to corrosion than the portions of the joining the two members and the indication that the 2T welds were any DISTRIBUTION SYSTEMS IN SEMI-
weld that are only melted one time. 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,
Conclusion and larger systems are normally used it was determined that it takes up to thus allowing ID bead widths up to

The number of times that 316L or 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
304L stainless steel material is melted End Last Level
and allowed to re-solidify at ambient 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 ≤
temperature has a direct affect on the
Finally, it has been determined In almost all cases throughout the 150mm in diameter. The susceptibility
corrosion resistance of the material. If II
it were possible to clean and repassiv- I End Downslope that it is more cost effective to pro- U.S., companies have moved away of these multiple pass welds to corro-
ate the areas after welding, the 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
sion resistance of the joint would be
rial, in width than it is to make 1T weld that is 2T in width and single welds on small diameter tube systems,
improved. This repassivation is
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.
common in the bio-pharmaceutical end preparation, usually in a single pass. Weld current is
industry, but is not practical in the 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.
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 ob Bearden graduated from Central rently holds certifications as SNT Level
be carefully monitored closely to B Missouri State University with a II for VT (visual testing) and LT (leak
assure that corrosive gas piping was Bachelor§s Degree in Electrical Engineer- testing) HMSLD.
welded using a single pass process. ing in 1987. Upon completion of studies Bob is currently working for Resplen-
This would be very time consuming Bob entered the field of QA/QC for instal- dence Technology Limited at TSMC
and not very cost effective as multiple lation of process piping for Semiconduc- Fab14P4 as lead 3rd Party QA/QC for the
pass welds are most commonly only tor Manufacturing Facilities. In the con- installation of gas, chemical and slurry
vening 20+ years, Bob has continued in systems.
employed when joining piping used in
the QA/QC field and has expanded to

gas systems that are ½©and smaller, Reference
Project Management, Construction Man-
usually special gas piping.
agement and QA/QC services for bio- 1. S.H. Lin, "Corrosion protection of high
There are also instances where double
pharmaceutical production plants, qualifi- copper aluminum alloys and stainless
pass welding must be employed. When cation of biohazard containment units and steels by surface modification," Ph.D.
hand welding, it is more effective to most recently testing of nuclear dry cask thesis University of Southern California,
employ a joint that has beveled edges storage units for spent nuclear fuel. Bob 1995.
2. Barbara K. Henon, ¨Tube Welding -
and a gap between the two members. was instrumental in developing ASME
Orbital Welding of 316L Stainless Steel
These members are then joined by BPE, the standard used for installation of
Tubing,© Arc Machines, Inc., Originally
filling the gap between them with a bio-pharmaceutical piping systems. Bob presented at the Twelfth Annual World
filler metal of the same or similar was also instrumental in developing the Tube Congress, October 7-10, 1996, spon-
chemical composition to the parent first certification HMSLD (Helium mass sored by the Tube and Pipe Association,
spectrometer leak detection) and cur- International (TPA)
material. In most cases these types of

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NFPED JANUARY 2011