increasing the EE by a small amount. Some FCAW electrodes require a short EE of ½ to ¾ in. and other electrodes require 1½ to 3 in. to operate properly. It is also important to recognize the need to control EE when welding with GMAW. Short circuiting transfer requires a shorter EE than either the globular or the spray transfer modes. The type of tungsten electrode required when welding with the GTAW process should be included in the WPS. The end preparation should be noted as well. The base metal to be welded and the type of current (direct or alternating current) used can influence the choice of electrode. The current type used largely dictates the end preparation. If direct current electrode negative is used, the tungsten is typically tapered to a blunted point. If alternating current or direct current electrode positive is used, the end of the tungsten has a balled end. Welding with pulsing characteristics presents a host of new concerns. Each manufacturer has developed specific waveforms utilizing various values for the frequency, upslope, downslope, duration, peak, and background currents, and in some cases even the characteristics of the power supply varies from constant current to constant potential while the “arc is on.” To state it as simply as possible, it is nearly impossible to qualify a pulse welding procedure for GMAW using a welding machine and program developed by one manufacturer with a machine manufactured by a different company. ASME requires the “power” to be recorded as a “work around” of the complexities introduced by the pulsing mode of welding. It is a move in the right direction, but simply matching the “power” of one pulsing machine to another is not going to produce the same results. The only way to compare the output of one machine model to another is to use an oscilloscope. The bottom line is that if you intend to write a WPS for pulsing, use the same model of welding machine for Inspection Trends / Winter 2011 33 Annex B-2 Welding symbols shall be interpreted in accordance with AWS A2.4-2007, Symbols for Welding, Brazing, and Nondestructive Testing. The following shall be considered default values when interpreting welding symbols. 1. Intermittent Fillet Welds: The following requirements apply to intermittent fillet welds; a. Intermittent fillet welds shall begin and terminate at the ends of the joint. The end welds shall be no less than two-times the specified segment length. b. Length: The length specified by the welding symbol shall be the minimum acceptable length of each weld segment. The minimum segment length shall be 1½ in. c. Size: The weld size specified by the welding symbol shall be the minimum acceptable weld size of each weld segment. d. Spacing: The maximum unwelded length between adjacent weld segments shall be no greater than the specified pitch minus the length of the weld segment. The sketches that follow are Standard Details. Other joint details may be utilized provided a welding symbol or sketch provides all the applicable information. Typical Branch Connection consisting of a coupling or half-coupling welded to the run pipe. The diameter of the coupling shall not exceed the smaller of NPS 2 or ¼ the diameter of the run pipe. As a minimum the coupling shall have a rating of Class 2000. Fig. 3 — Annex B-2 is an example of one page from an annex showing the joint details.
Inspection Trends - January 2011 - Winter
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