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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Purging for Improved Weld Profile. Experimentation is required to establish the ideal pressure aws d18.2 a given tube size, wall thickness and material.

Many methods have been aws d18.2 to deliver the purge gas to the weld site, but few methods exist to control the internal gas pressure, thus the internal weld profile. The internal pressure at sws weld location, typically arrived at empirically, is influenced by the gas flow rate and the size of the exit orifice.

However, given the dangers associated with the use of hydrogen, it is hard to recommend it unless aws d18.2 critical need exists. Since the pressures are quite low, on the order of 0. Figure 1 – AWS D However, in recent years, this focus on smooth, clean, aws d18.2 internal weld requirement has migrated from the semiconductor industry to the aws d18.2 industry, and on to the food equipment industry.

Welding Journal, July Dennis Cobb has spent more than 25 years both designing and managing the design of semiconductor capital equipment. If another aws d18.2 is to be welded, aws d18.2 entire experiment must be repeated.

Purging for suitable weld color is relatively simple. In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm. The combination of flow rate and prepurge aws d18.2 determines how much oxygen is still present, and thus, the amount of weld color caused by oxidation. The input gas is controlled both for pressure and aws d18.2, using a variable orifice iris controlled by a microprocessor in a closed loop system.


The initial purpose of internal tube purging with inert gas usually argon was the prevention of surface oxidation on aws d18.2 internal diameter of the tubing surrounding the weld Heat Affected Zone. Orbital Welding Internal Pressure Control. He is a registered professional California Electrical Engineer.

This experimentation requires several trial aws d18.2, with a weld coupon created for each test condition, aws d18.2 acceptable results are obtained; a time consuming and costly activity. SEMI Standard F78 includes a chart with minimum and aws d18.2 purge pressures and aws d18.2 rates for various tube sizes and wall thicknesses.

In addition, most standard gas pressure regulators are not nearly accurate enough to deliver the exacting performance required. Since the pressures are given as a range, they serve as a useful starting point for the empirical determination of the best pressure for the ideal weld profile.


In the interest of exercising control over the weld profile, the ID purge is aws d18.2 with a certain level of pressure, and in order to maintain consistency and repeatability that pressure must be consistent throughout the weld, and from weld to weld. This level of measurement and accuracy permits the EXEL SG-1 to repeatedly maintain the exact internal pressure required for a perfect weld. Once that is determined, the aws d18.2 problem is to correlate the required pressure at the weld with the measured pressure at the aws d18.2 inlet.

The unit then utilizes this offset aws d18.2 all welds performed with this same configuration. The required weld pressure is input to the device, aws d18.2 it correctly offsets the pressure for the tubing configuration as tested. One way to establish the inlet pressure is to repeat the empirical testing with the inlet pressure as the controlled variable.

Purging for Improved Weld Profile

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

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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 aws d18.2 weld zone.

It is aws d18.2 wisdom that the semiconductor industry was, and remains, the primary driver for the continuous improvement of orbital autogenous weld awz and internal cleanliness for process gas delivery tubing. This variable orifice is especially important because as the joint is welded shut, the effective xws gas exit area is reduced, so as the joint is sealed the SG-1 is making real-time adjustments to accurately maintain the required pressure.

The only remaining hurdle is to obtain the corresponding inlet pressure for the known weld pressure, and fortunately, the EXEL SG-1 also provides the capability of measuring the inlet and weld pressures simultaneously. However, this value will only be correct for the specific assembly tested.

Most users are satisfied with the results obtained with pure argon as a purging aws d18.2 although a few organizations like to aws d18.2 a small percentage of aws d18.2 to produce a r18.2 environment.

However, gauging the internal pressure such that the weld ID profile is aws d18.2 flat is a more difficult task. The prepurge time is an empirically derived aws d18.2 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.

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