Table 2 — Descriptive Statistics. Analysis of the Welding Data Recorded in the PQR as argon or helium, a reactive gas such as carbon dioxide, or a combination of gases that may have minor additions of oxygen or hydrogen. The gas or gas mix to be used is influenced by the welding process, the base metals being joined, and, possibly, the welding position. AWS first published A5.32, Specification for Welding Shielding Gases, in 1997. Shielding gases meeting the requirements of A5.32 are pure enough for all welding applications except for the gases used for laser beam welding. In addition to listing the shielding gas, the WPS needs to list the appropriate flow rates. The flow rate is a function of the shielding gas and the diameter of the gas nozzle used. Different shielding gases have different densities, which necessitates using the proper flow meter and flow rate to provide adequate shielding of the molten weld pool. The shielding gas is usually an essential variable. The WPS will have to be requalified if the manufacturer decides to change to a different shielding gas or mixture of shielding gases. Trailing gases and purge gases are also listed when they are required. The need to use a purge gas and the type of purge gas required is not left to the discretion of the welder. While on the subject of purge gases, it is my recommendation that a method of determining when the purge is satisfactory should be included in the WPS. Different base metals can tolerate different levels of contamination. Reactive base metals are intolerant of moisture, oxygen, or nitrogen when compared to austenitic stainless steel. Success or failure when welding reactive and refractory base metals can depend on the completeness of the purging operation. Specific instructions for detailed information about purging can be provided to the welder through use of another annex. The WPS can simply list that purging is required and reference the appropriate annex for more detailed information. Welding Parameters The WPS has to provide the information the welder needs to set the welding parameters. The information the welder needs includes the type of welding machine suitable for the welding process to be used, current type, polarity, arc voltage, amperage (wire feed speed), electrode extension (if applicable), tungsten type and end preparation (if applicable), travel speed, etc. The parameters listed in the WPS are those that are appropriate for the welding process being used. The WPS is based on the information gathered while welding the successful PQR. If the PQR was properly documented, it will list the welding parameters the welder used while welding the test coupon. The parameters listed in the PQR serve as the starting point for the WPS. The welding parameters used to weld the test coupon are “good” because the test weldments passed all the required tests. The welding parameters used when the test weldments were welded are likely to vary somewhat from bead to bead. An example of the welding parameters recorded in the PQR are listed in Table 1. Recording the welding parameters in a MicroSoft Excel™ spreadsheet makes it easy to determine the minimum, maximum, and ranges for each parameter used to weld the test coupon. The descriptive statistical tool provided by MicroSoft Excel™ can be used to analyze the data. The presentation is shown in Table 2. Some welding standards such as AWS D1.1, D1.5, B2.1, etc. allow the ranges listed on the WPS to be “opened up” by certain amounts, usually expressed as percentages of the values recorded on the PQR. In such a case, I would typically use the median value shown in Table 2 as my data point. It is acceptable to use the parameter ranges listed by the manufacturer if the welding standard used does not impose limits on those ranges, i.e., voltage, wire feed speed (WFS), amperages, etc. The ranges listed by the WPS should be reasonable. The average welder should be able to deposit an acceptable weld using the high and low values of the ranges listed in the WPS. There are three important welding parameters to note when welding with either FCAW or GMAW. They are important because they are “constants” that the welder sets. The parameters are arc voltage, wire feed speed, and electrode extension (EE). In general, once the wire feed speed is dialed into the wire feeder, it does not change whether the welder is actually welding or holding the gun in the air. Amperage will vary as the welder increases or decreases the electrode extension. Welders can use the electrode extension to their advantage to increase the amperage by shortening the EE slightly or decrease the amperage by 32 Inspection Trends / January 2011 Data Analysis Procedure Qualification GF-F6P1-A 19-Oct-2010 Volts Amps WFS Seconds Travel HI PH/IPT Mean 26.7 221.2 332.8 238.8 8.1 44507.9 200.1 Median 27.0 230.0 350.0 231.5 8.3 43276.2 214.0 Standard Deviation 0.4 16.8 23.0 46.6 1.3 5006.5 67.3 Range 1.0 40.0 51.0 133.0 4.8 19954.3 205.0 Minimum 26.0 199.0 299.0 181.0 5.8 35125.3 84.0 Maximum 27.0 239.0 350.0 314.0 10.6 55079.7 289.0
Inspection Trends - January 2011 - Winter
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