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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Figure 1 – AWS D The required weld pressure is input to the device, and it correctly offsets the pressure for the tubing configuration as tested. SEMI Standard F78 includes a chart with aws d18.2 and maximum purge pressures and flow rates for various tube sizes and wall thicknesses.

Once that is aws d18.2, aas next problem is to correlate the required pressure at the weld aws d18.2 the measured pressure at the delivery inlet. However, given the dangers associated with the use of hydrogen, it is hard to recommend it unless a critical need exists.

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

Standard: AWS D18.2

Orbital Welding Internal Pressure Awz. Most users are s18.2 with the results obtained with pure argon as a purging medium; although a aws d18.2 organizations like to add a small percentage of hydrogen to produce a reducing environment. Since the pressures are quite low, on the order of aws d18.2. The combination of aws d18.2 rate and prepurge time determines how much oxygen is still present, and thus, the amount of weld color caused by oxidation.

Purging for Improved Weld Profile

In addition, aws d18.2 standard gas pressure regulators are not nearly accurate enough to deliver the exacting performance required. This experimentation requires several aws d18.2 pressures, with a weld coupon created for each test condition, until acceptable results are obtained; a time consuming and costly activity.


The unit then utilizes this offset for all welds performed aws d18.2 this same configuration. Purging for suitable weld color is relatively simple.

The initial purpose of internal tube purging with inert gas usually argon was the prevention of surface oxidation on the aws d18.2 diameter of the tubing surrounding the weld Heat Affected Zone. This level of measurement and accuracy permits the EXEL SG-1 to repeatedly maintain the exact internal pressure required for a perfect weld.


aws d18.2 However, this value will only be correct for the specific assembly tested. 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.

aws d18.2 He is a registered professional California Electrical Engineer. In order for all color to be eliminated, oxygen levels must depending on the material fall below approximately 20 ppm. It is conventional wisdom that the semiconductor industry was, and remains, the primary driver for the continuous improvement of orbital autogenous weld aws d18.2 and internal cleanliness for process gas delivery tubing.

In the interest of exercising control over the weld profile, the ID purge is introduced with a certain level of pressure, and in order aws d18.2 maintain d182 and repeatability that pressure must be consistent throughout the weld, and from weld to weld.

aws d18.2 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 aws d18.2 to purge.

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 making real-time adjustments to accurately maintain the required pressure.

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E18.2, in recent years, this focus on smooth, clean, particle-free internal weld requirement aws d18.2 migrated from the semiconductor industry to the biopharmaceutical industry, and on to the food aws d18.2 industry.

In addition, measuring the pressure some distance from the weld location d18.22 to pressured drop will not provide an accurate method of determining the pressure at the aws d18.2 zone. 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. Aws d18.2 input gas is controlled both for pressure and flow, using a variable aws d18.2 iris controlled by a microprocessor in a closed loop system.

Purging for Improved Weld Profile.

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

Welding Journal, July Experimentation is required to establish the ideal pressure for a given tube size, wall thickness and aws d18.2. Dennis Cobb has spent more than 25 years both designing and managing the design of semiconductor capital aws d18.2. 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. If another configuration is to be welded, the entire experiment must be repeated.