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SEMI F78-0304 © SEMI 2003, 2004 3 5.1.23 encroac hment — non-standard term for ID convexity. 5.1.24 examiner — a pers on who performs examination of a part icular object, or evaluates an operation, for com pliance to a g…

SEMI F78-0304 © SEMI 2003, 2004 2

A450 (Section 25) — General Requirements for

Carbon, Ferritic Alloy, and Austenitic Steel Tubes

A632 — Specification for Seamless and Welded

Austenitic Stainless Steel Tubing (Small Diameter) for

General Service

4.4 AWS Standards

AWS A3.0 — Standard Welding Terms and Definitions

AWS B2.1 — Specification and Qualification of

Welding Procedures and Welders for Piping and

Tubing

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Definitions

5.1.1 angular misalignment — the condition that exists

when the tubing angle is unintentionally changed at the

weld.

5.1.2 autogenous weld (2) — a fusion weld made

without filler metal.

5.1.3 automatic arc welding downslope — the time

during which the welding current is reduced

continuously from the final level until the arc is

extinguished.

5.1.4 axial misalignment — the offset caused by tubing

being in line but not centered at the weld.

5.1.5 backing gas — an inert gas (or gas mixture) on

the interior of the weld joint used to prevent or reduce

formation of oxides and other detrimental surface

substances during welding, and to provide pressure for

weld profile.

5.1.6 bead (2) — non-standard term for weld bead.

5.1.7 bead overlap — in a pulsed weld the amount of

coverage of a weld pulse of the previous weld pulse,

usually measured in percentage of the diameter of the

pulse.

3 American Welding Society, 550 NW LeJeune Road, P.O. Box

351040, Miami, Florida 33135, USA. Telephone: 800.443.9353,

Website: www.aws.org

4 The terminology has been derived from the following sources:

(1) Webster’s New World College Dictionary Fourth Edition

(2) ANSI/AWS A3.0 Standard Welding Terms and

Definitions

(3) ASME BPE Bioprocessing Equipment Standard

5.1.8 bead variation — the amount of change of ID

bead width from one area to another.

5.1.9 bead width — the width of the weld bead on the

ID, normally measured in units of T, where T is the

nominal tube wall thickness.

5.1.10 center line shrinkage — a profile-reducing

defect or discontinuity normally formed by shrinkage

during solidification.

5.1.11 color — the darkness of the oxidation of the

weld or adjacent surfaces. Non-standard term for

discoloration.

5.1.12 color line — acceptance criteria of the

maximum amount of discoloration allowed on the weld

or adjacent surfaces.

5.1.13 concavity (3) — a condition in which the

surface of a weld is depressed relative to the surface of

the tube or pipe. Concavity is measured as a maximum

distance from the outside or inside diameter surface of a

weld along a line perpendicular to a line joining the

weld toes.

5.1.14 convexity (3) — a condition in which the surface

of a weld is extended relative to the surface of the tube

or pipe. Convexity is measured as a maximum distance

from the outside or inside diameter surface of a weld

along a line perpendicular to a line joining the weld

toes.

5.1.15 coupon — weld sample which is opened for

inspection to insure that the weld meets specifications.

5.1.16 coupon-in — first coupon prior to production

welding of butt weld joint.

5.1.17 coupon-out — last coupon after production

welding of butt weld joint ends.

5.1.18 discoloration (3) — any change in surface color

from that of the base metal. Usually associated with

oxidation occuring on the weld and heat affected zone

on the outside and inside diameter of the weld joint as a

result of heating the metal during welding. Colors may

range from pale bluish-gray to deep blue, and from pale

straw color to a black crusty coating.

5.1.19 downslope — See automatic arc welding

downslope.

5.1.20 dross (2) — non-standard term for slag.

5.1.21 electrode (2) — non-standard term for tungsten

electrode.

5.1.22 enclosed weld head — weld head in which the

weld joint is held and welded within a closed chamber

containing a shielding purge gas.

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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