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SEMI F3-94 © SEMI 1990, 2003 5 A1-4.8 Sub-assemblies, after completion, shall be purged and co vered for subsequent installat ion in the field. A1-4.9 A bac king shield (purge t hrough the weld hea d) is required during …

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.

SEMI F3-94 © SEMI 1990, 2003 5

A1-4.8 Sub-assemblies, after completion, shall be

purged and covered for subsequent installation in the

field.

A1-4.9 A backing shield (purge through the weld head)

is required during welding.

A1-4.10 Where a weld is found defective, the

preceding two welds should be tested as described in

Paragraph 7.3.2 of SEMI F3. 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.

A1-4.11 On-site work sample welds shall be made

before each series of welding operations. On-site

sample welds shall also be made at the start of each

workday and any time any welding parameter is

changed.

A1-4.12 Sample test welds shall be made periodically.

These tests shall be compared to the on-site work

sample. Deviation from the on-site work sample shall

be cause for rejection. The sample test welds shall 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 a concern or deviation to the weld quality

has occurred.

A1-4.13 If the system becomes contaminated due to a

fabrication technique, the contaminated sections shall

be re-cleaned.

A1-4.14 Welding at the job site shall be enclosed in a

clean work area.

A1-4.15 When the welding is performed in a clean

envelope, the envelope shall have openings for the tube

to extend in two directions, a clean polyester film

window, and openings for the hands. HEPA-filtered air

shall be supplied to the envelope under pressure to

ensure a clean working environment.

A1-4.16 The envelope shall be installed prior to

removal of the tube caps. Full purge through the tube to

be welded shall be completed before removing the

clean envelope to attach the weld head.

A1-4.17 Final positioning of the weld head and weld

process shall be performed within the clean envelope.

APPENDIX 2

HEXAVALENT CHROMIUM

ALERT

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 the cited document.

Publication was authorized by full letter ballot procedures.

Determination of the suitability of the material is solely the

responsibility of the user.

A2-1 General

A2-1.1 Hexavalent chromium, which is given off when

stainless steel is welded, causes lung cancer in humans.

For information about hexavalent chromium, refer to

HESIS Hazard Alert, June 1992, Hazard Evaluation

System & Information Service, California Occupational

Health Program, 2151 Berkeley Way, Annex 11, Third

Floor, Berkeley, CA 94704.

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.

International), 3081 Zanker Road, San Jose, CA 95134. Reproductio

of the contents in whole or in part is forbidden without express writte

consent of SEMI.