Welding practices

In categorizing the various weld types, it is possible to separate these types by the time periods in which they were used. C-E qualified each particular combination of weld wire and flux lot at least one time before using a specific heat of weld material. After receiving welding wire and flux material from the suppliers, a weld test plate was prepared which used the specific combination of a heat of wire and lot of flux. This test plate was analyzed chemically and mechanically to assure compliance with all required 

Irradiation Embrittlement of Reactor Pressure Vessels (RPVs) 

Depending on the amount of weld material in a given heat, many different RPV and surveillance welds could have been made with each unique combination. Similarly, different flux lots could also have been qualified with the same heat of weld wire. Once a welding procedure was qualified, this procedure was typically used for many welds over a time period that could span several years. 

B W used similar ASA welding techniques to those just described for C-E. In the years during which B W fabricated RPVs, few changes were made in the welding procedures. In fact, B W used a relatively small number of different weld wire/flux lot combinations. All of the RPV welds produced by B W were made with Linde 80 flux type. Due to the smaller number of different weld wire/flux lots used by B W, many RPVs were made with the same specific weld number. There are many commonalities between the Linde 80 flux type welds in the B W-fabricated RPVs. One unfortunate feature of these welds is the low Charpy upper-shelf energy. The Linde 80 welds made by B W are considered as one class of welds, since there are characteristics common to all these welds. 

Note that many of the Westinghouse plants have RPVs fabricated by B W, which share the common characteristic of having low upper-shelf energy welds. Low upper-shelf energy also may be a concern for some of the BWR RPVs fabricated by B W. 

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Transition Joints. Use of explosion-clad transition joints avoids the limitations involved in joining two incompatible materials by bolting or riveting. Many transition joints can be cut from a single large-area flat-plate clad and deflvered to limit the temperature at the bond interface so as to avoid undesirable diffusion. Conventional welding practices may be used for both similar metal welds. 

Employ sound welding practice. Porosity should be minimized, and full penetration is required. Continuous welds are preferred to many short runs. 

Lasers can be used to weld practically invisible joints in plastic sheeting, in which heat transfer is greatly assisted by the presence of infrared absorbers. ... 

Fig. HI.2. Plastic welding practice, (a) Some typical welds. (b) Technique for feeding rod into weld. With the rod bent back into a 45° angle, it is easy to heat and the rod is forced into the seam. The torch should be fanned between the rod and the parts being welded, with somewhat greater concentration on the latter, (c) An edge seal accomplished on a hot plate.

Fig. IV.1. Welding practice for vacuum apparatus. Nole that the general approach is to weld on the inside and avoid dead spaces which may present leaks that are extremely hard to locate.

Limited data show that both welding practice and location of defects can dictate the hydrogen embrittlement snsceptibility of a weld. A study on microalloyed steel API 5L Grade X60 examined weld joints that were fabricated using either one or two weld passes." Fractnre mechanics specimens were extracted from the base metal, fusion zone, and heat-affected zone and tested in 7-MPa hydrogen gas. Results showed that Kj values measured in the weld fnsion zones were similar to valnes in the base metal, i.e., Rju was approximately 100 MPaVm in each region. In contrast, the heat-affected zones were more susceptible to hydrogen embrittlement, and Rju was difficult to measure. The heat-affected zone in the two-pass weld was most susceptible. 

The most frequent application of gamma radiography is checking the welds in pipelines. This is done most conveniently by putting the source inside the centre of the pipe and attaching the film to the outside of the weld. For checking long pipelines, sophisticated, self-propelled crawlers which travel in the pipe are used. These devices can be positioned exactly at the desired position from the outside. At a command the exposure is made. Then the crawler is instructed to move on to the next weld. Practically all new gas- or oil-pipeline systems are checked with this type of equipment. 

Figure 5.28(b) illustrates the ability to fully recover hardness when welding in the T4 temper followed by an artificial age, whereas when welding in the T6 temper (Fig. 5.28a), small hardness minima still are evident in the HAZ. Note the similarity in hardness drop for the T6 temper between Fig. 5.27 and 5.28(a), except for the hardness isotherm in Fig. 5.27 attributable to the tool shoulder. This one difference may be due to location of the hardness trace, sheet thickness, and/or weld parameters. However, with potentially different welding practices, that is, different heat inputs between these two research studies, it is interesting that the hardness curves are nearly identical. 

Baker R G, Watkinson F and Newman R P The metallurgical implications of welding practice as related to low alloy steels . Proc 2nd Commonwealth Welding Conf, Inst of Welding, 1966, 125-131. Graville B A, Baker R G and Watkinson F Effect of temperature and strain rate on hydrogen embrittlement of steel . Brit Weld /14 (6) 1967 337-342. 

RPV shell plate material specifications have evolved since the beginning of the commercial nuclear power industry in the mid-1950s. Due to safety concerns for nuclear RPVs, cautious steel-making was paramount, as well as careful RPV fabrication and welding practices. Nevertheless, the need for familiarity in steel-making and fabrication processes initially led to the selection and use of old steels typical of prior (non-nuclear) pressure vessel service. Table 1.1 lists the principal steel plate materials used in construction of nuclear RPV components. All of the plate materials used... 

Talk to your supervisor if you have questions regarding safe welding practices. 

Figure 2.39 continued) This structure is based on welding practice and does not favour the adhesive. By reversing the closing panel, the load in the joint becomes compressive and the left-hand box is 3-4 times stronger than that on the right. 

ASTM G 58, Practice for the Prepeuation of Stress Corrosion Test Specimens for Weldments, describes use of aU of the before-mentioned smooth test specimen configurations. It also includes some configurations unique to welding practices, and references citing use of specimens and procedures unique to SCC testing of weldments. 

Following are some of the codes and standards that serve as guides to safe welding practices ... 

Weldment design Fabrication technique Welding practice Welding sequence Moisture contamination Organic or inorganic chemical species Oxide film and scale Weld slag and spatter Incomplete weld penetration or fusion Porosity... 

The corrosion problems commonly associated with welding of anstenitic stainless steels are related to precipitation effects and chemical segregation. These problems can be eliminated or minimized through control of base metal metallurgy, control of the welding practice, and selection of the proper filler metal. 

Improving welding practices and establishing welding codes. 

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