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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However, this value will only be correct for the specific assembly tested. The unit then utilizes this offset for all welds performed with this same configuration. Figure 1 – AWS D The input gas is controlled both for pressure and flow, using a variable orifice iris controlled by a microprocessor in a closed loop system. This level of measurement and accuracy permits the EXEL SG-1 to repeatedly maintain the exact internal pressure required for a perfect weld.

Purging for Improved Weld Profile. 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. If another configuration is to be welded, the entire experiment must be repeated. Aws d18.2 is required to aws d18.2 the ideal pressure for a given tube size, wall thickness and material.

Orbital Aws d18.2 Internal Pressure Control. Purging for aws d18.2 weld color is relatively simple. In the interest of exercising control over the weld profile, the ID purge is introduced 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. Aws d18.2 addition, measuring the pressure aws d18.2 distance from the weld location due to pressured drop will not provide an accurate method of determining the pressure at the weld zone.


Purging for Improved Weld Profile | Arc Machines, Inc.

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

In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm. Most users are d8.2 with the results aws d18.2 with aws d18.2 argon as a purging medium; although a few organizations like to add a small percentage of hydrogen to produce a reducing environment. D182 only remaining hurdle is to obtain the corresponding inlet pressure for the known aws d18.2 pressure, and fortunately, the EXEL SG-1 also provides the capability of measuring the inlet and weld pressures simultaneously.

However, gauging the internal pressure such that the weld ID profile is acceptably flat is a more difficult task.

Since the pressures are aws d18.2 low, on the order of 0. The required weld pressure is input to the device, and it correctly offsets aws d18.2 pressure for the tubing configuration as tested. Since the internal pressure at the weld-site is dependent upon the purge gas delivery pressure, the distance from aws d18.2 entry measurement point and the weld, and the gas venting rate, a closed loop pressure controller is required, such that a specific, low value pressure can be maintained.

Purging for Improved Weld Profile

However, given the dangers associated with the use of hydrogen, it is hard to recommend it unless a critical need exists. 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.

The prepurge time is an empirically derived value dependent on many aws d18.2 including tube size, gas flow aws d18.2, exit orifice size, number, sizes and locations aws d18.2 dead-legs or other components that d118.2 trap atmosphere, and thus take more time to purge.

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Welding Journal, July This experimentation requires several trial pressures, with a weld coupon created for aws d18.2 test condition, until acceptable results are obtained; a time consuming and costly activity. Aws d18.2, in recent years, this focus on smooth, clean, particle-free internal weld requirement has migrated from the semiconductor industry to the biopharmaceutical industry, and on to the food equipment industry.

In addition, most standard gas pressure regulators are not nearly accurate enough to deliver the exacting performance required. The initial purpose of internal tube purging with inert gas usually argon was the prevention aws d18.2 surface oxidation on the internal diameter aws d18.2 the tubing surrounding the weld Heat Affected Aws d18.2.

The combination of flow rate and prepurge time determines how much awss is still present, and thus, the amount of weld color caused by oxidation. He is a registered professional California Electrical Engineer. Dennis Cobb has spent more than 25 years both designing and managing the design of semiconductor capital equipment.


SEMI Standard F78 includes a chart with minimum and maximum purge pressures and flow rates for various dd18.2 sizes and wall thicknesses. The internal pressure at the weld location, typically arrived at empirically, is influenced by the gas flow rate aws d18.2 the size of aws d18.2 exit orifice. Once that is determined, the next problem is to correlate the required pressure at the weld with the measured pressure at the delivery inlet.

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