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SEMI F3-94 © SEMI 1990, 2003 3 NOTICE: These standards do not purport to address safety issues, if any, associat ed with their use. It is the responsibility of the user of these stand ards to establish appropriate safety…
SEMI F3-94 © SEMI 1990, 2003 2
7.1.5 Surfaces for welding should be clean and should
be free from oxidation, discoloration, oil, scale, chips,
or other material that is detrimental to welding.
7.1.6 All components should be maintained in a clean
condition until welded into the system.
7.2 Welding Requirements
7.2.1 Welding equipment used to make welds should
be operated in accordance with the manufacturer’s
operating and safety instructions.
7.3 Welding Procedures
7.3.1 Prior to the welding of a particular size, wall
thickness, alloy, and heat of material, sample welds
should be made, dissected, and analyzed.
7.3.2 These welds should be checked for poor
penetration, joint contamination, joint soundness,
surface oxidation, discoloration, pitting, cracking,
defects of fit-up, or defects of workmanship.
7.3.3 Once a sample weld is found to be acceptable, the
sample weld should be the on-site work sample against
which other welds of the same size, wall thickness,
alloy, and heat of material are judged. All essential and
supplementary essential variables should be
documented in the procedure qualification record.
7.3.4 Any significant deviation(s) from the on-site
work sample (7.3.3) will cause the weld(s) to be
rejected. Rejected welds should be removed and
replaced.
7.3.5 Sample test welds should be made periodically.
These tests should be compared to the on-site work
sample (7.3.3). Deviation from the on-site work sample
should be cause for rejection. The sample test welds
should be made at/when:
1. The beginning of each shift.
2. The end of each shift.
3. Any change in welding procedure, materials, tubing
size, equipment, or equipment adjustments are
made.
4. Any time that a concern or deviation to the weld
quality has occurred.
7.3.6 Sample test welds should be kept on file and may
be reviewed at any time during the construction.
7.3.7 Where a weld is found defective, the preceding
two welds should be tested as indicated in Paragraph
7.3.2. If either of these welds shows signs of poor
penetration, joint contamination, lack of joint
soundness, surface oxidation, discoloration, pitting,
cracking, defects of fit-up, or defects of workmanship,
then all welds made since the last welding procedure
was established should be removed and replaced.
7.4 Weld Set-up
7.4.1 Check parameters and verify that they are in
accordance with the qualified welding procedure.
7.5 Purging
7.5.1 During welding, all tubes, fittings, valves, sub-
assemblies, and all other components should be
continuously purged.
7.5.2 Automatic orbital head welding equipment
should supply a constant gas-backing shield to the weld
head during welding.
7.5.3 During all welding, a sufficient amount of
purge/shield gas should be maintained until the weld
head is removed from the newly welded parts.
7.5.4 Both purge/shield gas supply lines should contain
flow indicators to ensure proper purging.
7.6 Weld Identification
7.6.1 A daily log should be maintained on all welds,
and as-built drawings recording all data should be
maintained in the welding area.
7.6.2 All welds should be identified with a code
number and cross-referenced with the drawings for
future evaluation.
7.7 Additional Requirements
7.7.1 Maintain sufficient distance between weld joints
and valve seats to avoid damage to valve seats or valve
stem tips.
SEMI F3-94 © SEMI 1990, 2003 3
NOTICE: These standards do not purport to address
safety issues, if any, associated with their use. It is the
responsibility of the user of these standards to establish
appropriate safety and health practices and determine
the applicability of regulatory limitations prior to use.
SEMI makes no warranties or representations as to the
suitability of the standards set forth herein for any
particular application. The determination of the
suitability of the standard is solely the responsibility of
the user. Users are cautioned to refer to manufacturer’s
instructions, product labels, product data sheets, and
other relevant literature respecting any materials
mentioned herein. These standards are subject to
change without notice.
The user’s attention is called to the possibility that
compliance with this standard may require use of
copyrighted material or of an invention covered by
patent rights. By publication of this standard, SEMI
takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any
item mentioned in this standard. Users of this standard
are expressly advised that determination of any such
patent rights or copyrights, and the risk of infringement
of such rights, are entirely their own responsibility.
SEMI F3-94 © SEMI 1990, 2003 4
APPENDIX 1
SAMPLE WELDING
SPECIFICATION
NOTE: This related information is not an official part of this
SEMI guide and is not intended to modify or supercede the
official guide. It has been derived from industry
specifications. Publication was authorized by full letter ballot
procedures. Determination of the suitability of the material is
solely the responsibility of the user.
A1-1 General
A1-1.1 The entire piping system will be kept under a
continuous purge until all welding is complete.
A1-1.2 All tools and fixtures used for the assembly and
welding shall be maintained clean and shall not be
removed for use outside of the Class 100 preparation
area.
A1-2 Tubing Preparation Requirements
A1-2.1 Use only tools and handling techniques that
will not mar, disturb the shape of, or in any way reduce
the quality of the materials used in this system.
A1-2.2 Tubing must be under inert gas purge during
the cutting and end-facing/truing operation.
A1-2.3 Tube ends shall be covered while the purge is
removed using a technique that will minimize the
amount of infiltration or contamination. Covers shall be
of non-particulating material.
A1-2.4 Cut ends shall be de-burred and faced to be
square to an appropriate tolerance, per orbital welding
equipment manufacturer’s recommendation. The tubing
shall not be scratched during de-burring. Abrasive
wheels shall not be used. A lathe, milling, or portable
end prep tool that clamps to the exterior of the tube is
permitted.
A1-2.5 Make all necessary preparations for installing
tubing and tube sub-assemblies so that exposure of the
interior surface to atmosphere is minimized.
A1-2.6 Tubing and tube sub-assemblies shall be
mechanically fitted into place, dimensionally verified,
clearances verified, welding parameters set, and all pre-
weld procedures completed in readiness to begin the
welding process prior to removing protective covers.
A1-3 Welding Process Requirements
A1-3.1 Welding shall be by the gas tungsten arc
welding (GTAW) process with backing shielding and
inside tubing purge. All stainless steel tubes shall be
joined using an automatic orbital butt-welding machine.
A1-3.2 During welding, all gas lines must be
continuously purged.
A1-3.2.1 Stainless steel tubing purge lines shall be
used. Flow measurement and control shall be with a
clean rotameter.
A1-3.2.2 Weld shield purge gas shall be filtered with a
0.01 µ m filter connected to the inlet bulkhead fitting of
the welder.
A1-3.3 Every weld shall be tagged, logged, and
inspected.
A1-3.3.1 A daily log shall be maintained on all welds
and an as-built isometric drawing recording all data
shall be maintained in the welding area.
A1-3.3.2 All welds shall be identified with a code
number and cross-referenced with the isometric
drawings for future evaluation.
A1-3.4 As much welding as is feasible will be
performed in the preparation area in the form of sub-
assemblies.
A1-3.5 Alignment of tubing of nominal size 2" in
diameter and larger for orbital welding shall be by an
external clamping jig where space permits.
A1-3.6 Valves shall be located so as to allow space to
operate the valve after installation at the job site.
A1-4 Welding Procedure Requirements
A1-4.1 All materials, testing of welders, and welding
procedures shall comply with the requirements of SEMI
F3.
A1-4.2 Set up the fabrication in a suitable preparation
area or at the job site.
A1-4.3 Make all necessary preparations for installing
tube and tube sub-assemblies such that exposure of the
interior surface to atmosphere is minimized. Insure that
there is purge flow prior to welding.
A1-4.4 On tubes larger than a nominal size of 1/2" ,
place a reducing cap on the discharge end of the tube
with a 12-mm (0.5" ) or smaller outlet.
A1-4.5 Insert the tube ends into the orbital tube weld
holder for butt-welding.
A1-4.6 Perform only one weld joint at a time.
A1-4.7 The completed sections of the piping system
should never be without positive purge pressure and
flow to all system extremities. System extremities
should not be capped in such a way as to permit purge
flow to stop. This purge must be maintained at all
times, including overnight and during weekends and
breaks.