AWS D – Download as PDF File .pdf), Text File .txt) or view presentation slides online. For years the pharmaceutical industry has relied heavily upon the American. Welding Society’s AWS D weld dis- coloration chart1 to gage the acceptability. A straw-coloured or yellow heat tint, up to and including AWS D Number 3 on the colour reference chart, would be considered acceptable in most situations.

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If another configuration is to be welded, the entire experiment must be repeated. Once that is determined, the next problem is to correlate the required pressure at the weld with the measured aws d18.2 at the delivery inlet.

This experimentation requires several trial pressures, with a weld coupon created for each test condition, aws d18.2 acceptable results are obtained; a time consuming and costly activity.

Dennis Cobb has spent more than 25 years both aws d18.2 and managing the design of semiconductor capital equipment. In addition, most standard gas pressure regulators are not nearly accurate enough to deliver the exacting performance required. This variable orifice is especially important because as the joint is welded shut, the effective purge gas exit area is reduced, so as the joint is sealed the SG-1 is aws d18.2 real-time adjustments to accurately maintain d182. required pressure.

Since the aws d18.2 pressure at the weld-site is dependent upon the purge gas delivery pressure, the distance from the entry measurement point and the weld, and the gas venting rate, a closed loop pressure controller awd required, such that a specific, low value pressure can be maintained.

Since the pressures are given as a range, aws d18.2 serve as a useful starting point for the empirical determination of the best pressure for the ideal weld profile.

However, in recent years, this focus on smooth, aws d18.2, particle-free internal weld requirement has migrated from the semiconductor industry to the biopharmaceutical industry, and on to the food equipment industry.


The internal pressure at the weld location, typically arrived at empirically, is influenced by the gas flow rate and the size of the exit orifice. This level of measurement and accuracy permits the EXEL SG-1 to repeatedly maintain aws d18.2 exact internal pressure required for a perfect weld.


Welding Journal, July Purging for Improved Aws d18.2 Profile. One way to establish the inlet pressure is to repeat the empirical testing with the aws d18.2 pressure as the controlled variable. The prepurge time is an empirically derived value dependent on many factors including tube size, gas flow rate, exit orifice size, number, sizes and locations of dead-legs or other components that can trap atmosphere, and thus take more time to purge.

The aws d18.2 gas is controlled both for pressure and flow, using a variable orifice iris controlled by aws d18.2 microprocessor in a closed loop system. In addition, measuring the pressure some distance from the weld location due to pressured drop will not provide an accurate method of determining the pressure at the weld zone.

Standard: AWS D18.2

The only aws d18.2 hurdle xws to obtain the corresponding inlet pressure for the known weld pressure, and fortunately, the EXEL SG-1 also ads the capability of measuring the inlet and weld pressures simultaneously.

However, this value will only be correct aws d18.2 the specific aws d18.2 tested. In the interest of exercising control over the weld profile, the ID purge is introduced with a aws d18.2 level of pressure, and in order to maintain consistency and repeatability that pressure must be consistent throughout the weld, and from weld to weld. Experimentation is required to establish the ideal pressure for a given tube size, wall thickness and material.

Since the pressures are aws d18.2 low, on the order of 0. Figure aws d18.2 – AWS D Aws d18.2 unit then utilizes this offset for all welds performed with this same configuration. SEMI Standard F78 includes a chart with minimum and maximum purge pressures and flow rates for various tube sizes and wall thicknesses. Most users are satisfied with the results obtained with pure argon as a purging x18.2 although a few organizations like to add a small percentage of hydrogen to produce a reducing environment.


Many methods have been devised to deliver the purge gas d81.2 the weld site, but few methods exist to control the internal gas pressure, thus the internal weld profile.

However, gauging aws d18.2 internal pressure such that the weld ID profile is acceptably flat is a aws d18.2 difficult task. It is conventional wisdom that the semiconductor industry was, and remains, the primary driver for the continuous improvement of orbital autogenous weld profiles and internal cleanliness for process gas delivery tubing.

In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm.

Purging for Improved Weld Profile | Arc Machines, Inc.

The initial purpose of internal tube purging with inert gas usually argon was aws d18.2 prevention of surface oxidation on the internal diameter of c18.2 tubing surrounding the weld Heat Affected Zone. He is a registered professional California Electrical Engineer. The combination of flow rate and prepurge time determines how much oxygen is still present, and thus, the amount of weld color aws d18.2 by oxidation.

However, given the dangers aws d18.2 with the use of hydrogen, it aws d18.2 hard to recommend it unless a critical need exists. The required weld pressure is input to the device, and it correctly offsets the pressure for the tubing awd as tested. Purging for suitable weld color is relatively simple.

Orbital Welding Internal Pressure Control.