Ultra High Purity Stainless Steel Pipework System Used Orbital Welding Technology

Ultra High Purity Stainless Steel Pipework System Used Orbital Welding Technology


All cutting, facing and welding operations are carried out in the Mobile Class 100 Clean Room/Workshop.

McAlpine Process Systems is a specialized division which was set up 18 months ago, in response to the requirements of the semi-conductor processing, pharmaceutical and food related industries. This division has successfully completed the design, fabrication and installation of £1.1 million of ultra high purity stainless steel pipework at the Fujitsu Microelectronics plant, and is now currently working on Phase II of a major research development for the T.S.L. Group at Wallsend.

Ultra high purity can only be obtained when the piping systems used to deliver the gases to the clean room are extremely clean and free of leaks. To achieve this, all tubing, fittings, valves and regulators are electropolished on the interior surface to a 15 micro-inch (RMS) finish achieve a smooth, high lustre surface that will eliminate particulate contamination. All joints are welded, using the Arc automatic orbital gas tungsten welding equipment. These compact portable microprocessor-controlled power units have a -/+ 1% accuracy of the power supply which makes it possible to obtain consistently repeatable high quality welds when other parameters such as Tungsten length, joint preparation, temperature and metallurgical properties remain reasonably constant.

Training of the operators is initially carried out by Arc themselves on the correct way to operate these machines, but full training of personnel in the cutting, facing, welding, cleaning and bagging methods is carried out on site in our own Class 100 clean room facilities.


Completion of 31 gas lines conveying Nitrogen (N2) Oxygen (O2), and Methane (CF4) to a Major Research Development for The T.S.L. Group, Wallsend, Newcastle upon Tyne.

On completion of construction each system is tested and validated to determine whether it conforms to the specification. A helium leak test is used to check the integrity of the system and then tests for contaminants such as particles, oxygen and moisture are carried out. The challenge presented to McAlpine Process Systems was to achieve a Class 1 UHP piping system and satisfy ourselves, Fujitsu and BOC that these systems would pass all the required analytical tests. A number of key factors contributing to this goal were, the use of our own Class 100 fabrication workshop, the supply of cryogenic liquid argon for purging, detailed isometric drawings and a highly motivated workforce. The result was a non-contaminated gas piping system that passed all the required tests.


By Barbara K. Henon, Ph.D., Arc Machines, Inc.