semi合集-English.pdf - 第4251页
SEMI F78-0304 © SEMI 2003, 2004 4 5.1.54 tungsten — non-standard term for tungsten electrode. 5.1.55 tungsten electrode (2) — a component of the electrical circuit that terminates at the arc, molten conductive slag, or b…
SEMI F78-0304 © SEMI 2003, 2004 3
5.1.23 encroachment — non-standard term for ID
convexity.
5.1.24 examiner — a person who performs
examination of a particular object, or evaluates an
operation, for compliance to a given standard. The
examiner performs quality control for the manufacturer,
fabricator, or erector.
5.1.25 fluid (1) — liquid or gas.
5.1.26 gas (1) — the fluid form of a substance in which
it can expand indefinitely and completely fill its
container; form that is neither liquid or solid.
5.1.27 gas tungsten arc welding (GTAW) (3) — an arc
welding process that uses an arc between a tungsten
electrode (nonconsumable) and the weld pool. The
process is used with a shielding gas.
5.1.28 halo — non-standard term for discoloration
resulting from welding procedure.
5.1.29 haze — non-standard term for discoloration
resulting from welding procedure.
5.1.30 heat-affected zone (HAZ) (2) — the portion of
the base metal whose mechanical properties or
microstructure have been altered by the heat of
welding.
5.1.31 heat tint/color — non-standard term for
discoloration resulting from welding procedure.
5.1.32 inclusion (2) — entrapped foreign solid
material, such as slag, flux, tungsten, or oxide.
5.1.33 inert gas — a gas that normally does not
combine chemically with materials. A protective
atmosphere.
5.1.34 inspector — a person who verifies that all
required examinations and testing have been completed,
and who inspects the assembly to the extent necessary
to be satisfied that it conforms to all applicable
examination requirements. The inspector performs
quality assurance for the owner. The inspector is
designated by the owner and shall be the owner, an
employee of the owner, an employee of an engineering
or scientific organization, or of a recognized insurance
or inspection company acting as the owner’s agent.
5.1.35 lathe welding — automatic or machine welding
of tubes or pipes in which the electrode is stationary
and the weld joint rotates. Lathe welding as defined
here is a fusion process without the addition of filler.
5.1.36 liquid (1) — having its molecules moving freely
with respect to each other so as to flow readily, unlike a
solid, but because of cohesive forces not expanding
infinitely like a gas.
5.1.37 liquid cylinder — often referred to as a dewar,
an insulated and pressure controlled metal cylinder used
to store fluids in their liquid form.
5.1.38 meandering (3) — of or pertaining to a weld
bead that deviates from side to side across the weld
joint rather than tracking the joint precisely.
5.1.39 orbital welding (3) — automatic or machine
welding of tubes or pipes in-place with the electrode
rotating (or orbiting) around the work. Orbital welding,
as it applies to this standard, is a fusion process without
the addition of filler.
5.1.40 oxidation (3) — the formation of an oxide layer
on a metal surface. When excessive oxidation occurs as
a result of welding, it is visible as discoloration.
5.1.41 oxide island — non-standard term for slag.
5.1.42 pressure cylinder — a metal cylinder used to
store gases under pressure.
5.1.43 profile defect — any defect or discontinuity that
reduces the wall thickness below that of the parent
metal.
5.1.44 pulsed gas tungsten arc welding — a gas
tungsten arc welding process variation in which the
current is varied in regular intervals.
5.1.45 purge — the application of an inert gas (or gas
mixture) to the OD or ID surface of the weld joint to
displace non-inert atmospheric gases. A block purge is
a non-flowing purge with positive pressure.
5.1.46 purge gas — an inert gas (or gas mixture) used
to displace the ambient atmosphere from the inside (ID)
of the weld joint.
5.1.47 root — non-standard term for root surface.
5.1.48 root surface (2) — the exposed surface of a
weld opposite the side from which the welding was
done.
5.1.49 rotation delay — time delay between when the
arc is initiated and the rotor begins to turn.
5.1.50 shield gas — inert gas (or gas mixture) that
protects the electrode and molten puddle from
atmosphere and provides the required arc
characteristics.
5.1.51 slag (2) — a non-metallic product resulting
from the mutual dissolution of non-metallic impurities
in some welding processes.
5.1.52 tack weld (2) — a weld made to hold the parts
of a weldment in proper alignment until the final welds
are made.
5.1.53 tail-out (2) — non-standard term for automatic
arc welding downslope.
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5.1.54 tungsten — non-standard term for tungsten
electrode.
5.1.55 tungsten electrode (2) — a component of the
electrical circuit that terminates at the arc, molten
conductive slag, or base metal. A non-filler electrode
made principally of tungsten and used in arc welding.
5.1.56 undercut (2) — a groove adjacent to the base
metal at the edge of the weld left unfilled by weld
metal.
5.1.57 underfill (2) — a groove weld condition in
which the weld face or root surface is below the
adjacent surface of the base metal.
5.1.58 weld bead (2) — a weld resulting from a weld
pass.
5.1.59 weld level — a segment or portion of a weld
schedule in which one or more weld parameters can be
changed independently; part of a weld sequence.
5.1.60 weld sequence — a series of steps executed by
the welding power supply to make a particular orbital
weld.
5.1.61 welder — a person who does welding
(sometimes used to refer to a welding machine or
power supply).
5.1.62 welding equipment — power supply, weld
heads, torches, and associated cables and accessories
used for welding.
5.1.63 welding operator — a person who welds with
an orbital or machine welding system.
6 Summary of Practice
6.1 The welding procedure is shown in the flow chart
in Figure 1.
7 General Requirements
7.1 All welding performed under this practice shall
conform to the applicable requirements of the ASME
Boiler and Pressure Vessel Code, Section IX, ANSI
B16.25, B31.3 Chapter V, and AWS B2.1, to the extent
that they are included herein.
7.2 All welds shall be based upon Welding Procedure
Specifications (WPS) and be documented with
associated Procedure Qualification Records (PQR) in
accordance with ASME Boiler and Pressure Vessel
Code, Section IX, or with AWS B2.1.
7.3 Qualification of the welding procedures to be used,
and of the performance of welders and welding
operators, shall conform to the requirements of the
ASME Boiler and Pressure Vessel Code, Section IX,
Articles II and III, or AWS B2.1.
7.4 All welding shall be performed only by certified
welders and welding operators. Certification procedures
shall include, at the minimum, producing three
acceptable welds in a row of typical GTA weld joints of
the smallest and largest diameters of each alloy to be
welded. Welding parameters shall be set by the welder
or welding operator. Certification shall expire after six
months of inactivity.
7.5 The weld assembly shall be kept under a
continuous purge until all welding is complete.
7.6 Welders shall use clean room-compatible gloves
any time that the tubing or component to be welded is
removed from protective covering.
8 Apparatus
8.1 Welding equipment shall be of the GTAW,
constant current, DCEN (direct current electrode
negative) and electronically controlled type with rapid
dynamic response capable of 5 Hz (CPS) or greater
pulsed welding.
8.2 All welding fixtures and weld heads shall be clean
and free of any particulate and excessive discoloration.
Weld heads shall rotate freely and smoothly at all
speeds. All clamping and holding fixtures shall fit
tightly around applicable fittings/tubing, allowing no
movement after clamping in excess of 0.003 inch
(0.008 cm). The welding fixturing shall allow viewing
of the weld joint to insure proper fit-up.
8.3 Electrodes shall be precision ground to the factory
specification for head and weld type. Electrode gap
shall be set using tooling or procedures that provide
accurate and repeatable gaps to be set to within 0.002
in. (0.005 cm). The use of 2% Ce-doped or 2% La-
doped tungsten electrodes is recommended.
8.4 Purge gas apparatus shall be stainless steel tubing
and components with face seal fittings, when possible.
PFA plastic tubing is acceptable as the final run to
allow flexibility for hook-up. Lengths shall be restricted
to less than ten feet. All components that come into
contact with the weldment shall be stainless steel. Only
heavy wall PFA or stainless tubing shall be used on the
ID purge. Only stainless tubing shall be used on HP
systems.
8.5 Purge gas flow shall be measured and controlled.
8.6 Facing equipment shall be of the dry end
machining style. The equipment shall be capable of
tolerances of 0.003 inches from a plane perpendicular
to the centerline of the tube, the OD and /or ID burr of
less than 0.005 inches. The equipment shall be capable
of controlling the cut curl so as that it does not enter the
tubing or cause scratching of the ID surface. The
equipment shall not use oils or lubricants in a way that
SEMI F78-0304 © SEMI 2003, 2004 5
may contaminate the tubing being faced. The cutting or
facing shall not be of a abrasive type.
8.7 Severing or parting equipment shall be of the
machining type that will separate the tubing without
contaminating the ID of the tubing. Wheel type cutters
designed to cut stainless steel and CRAs are allowed
with purge. Dry saws of orbital type or cutoff are
allowed only when followed by cleaning to 12.5. All
cut ends shall meet the tolerances for facing equipment
or be followed by end preparation with a facing tool.
9 Materials
9.1 All materials to be welded shall be manufactured to
ASTM specifications and so certified by the
manufacturer. Certification shall conform to ASTM
A450, Section 25.
9.2 All seamless austenitic stainless steel tubing shall
be in conformance with SEMI F20 or customer
specification.
9.3 A backing (ID) gas is required during welding, and
while tacking (if tacking is used).
9.4 Weld parameters are affected by the choice of
shield gas. Argon, due to its effectiveness and material
compatibility, is the most commonly selected shielding
and purging gas. Argon and helium are inert and
therefore have no effect on the weld metal. These gases
do have very different ionization potentials, thermal
conductivity, and reactivity.
9.5 Argon/hydrogen mix is a reducing gas that avoids
the formation of oxides. It also reduces the amperage
required for a given ID weld bead width while reducing
the OD bead width. Argon/hydrogen mixes adversely
affect high ferrite materials (above 80% ferrite). Use of
argon/hydrogen mixes will shorten tungsten electrode
life. The weld parameters will be affected by hydrogen
to argon percentages. Hydrogen mixes above 5 vol%
are not recommended for safety reasons.
9.6 Nitrogen will cause instability of the arc in mixes
above 3 vol% in the shield (OD) purge gas. It is a
acceptable backing (ID) gas for austenitic stainless and
many CRAs. Nitrogen when exposed to welding
temperatures will cause nitride formation in some high
ferrite materials (above 80% ferrite). Use of nitrogen
mixes in the shielding (OD) gas will shorten the
tungsten electrode life.
9.7 The ID purge gas will be certified to 99.9997%, or
less than 3 ppm total contaminants (moisture, oxygen,
and other contaminants).
10 Safety Precautions
10.1 This practice does not purport to address all of the
safety issues associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine
the applicability of regulatory limitations prior to use.
10.2 Welding equipment used to make welds shall be
operated in accordance with the manufacturer’s
operating and safety instructions.
10.3 All welding performed under this practice shall
conform to the applicable requirements of ANSI/ASC
Z49.1.
10.4 Welding gas mixtures containing more than
5 vol% H
2
are not recommended due to the potential for
fire hazard.
10.5 Do not reweld stainless steel that has been used
for corrosive gas delivery.
10.6 See Appendix 1 for information on stainless steel
and welding fume.
11 Test Specimens: Couponing
11.1 Prior to the welding of a particular size, wall
thickness, and alloy, a primary standard sample weld
shall be made, sectioned, and analyzed at the job site.
The primary standard sample weld shall become the on-
site work sample against which other welds of the same
size, wall thickness, and alloy are judged. This on-site
work sample may be used indefinitely or reproduced
each day at the discretion of the examiner.
11.2 The primary standard sample weld shall be
checked for compliance with SEMI F81, “Specification
for Visual Inspection and Acceptance of Gas Tungsten
Arc (GTA) Welds in Fluid Distribution Systems in
Semiconductor Manufacturing Applications.” Coupons
shall be cross-sectioned and inspected visually. Weld
coupon criteria are the same criteria for all system
welds.
11.3 Once a sample weld is found to be acceptable, all
essential and supplementary essential variables shall be
documented in the procedure qualification record.
11.4 Any significant deviation(s) from the on-site
work sample will cause the weld(s) to be rejected.
Rejected welds shall be removed and replaced.
11.5 Sample test welds shall be made periodically.
These sample test welds shall be compared to the on-
site work sample and checked for compliance with
SEMI F81. Deviation from the on-site work sample or
SEMI F81 shall be cause for rejection. If the weld
inside diameter is inspectable using a sight tube or other
device, sample test welds may be production welds.