Butt welds

In this paper, 2D simulations of the ultrasonic testing of different types of (transversely isotropic) austenitic V-butt welds are presented they have been obtained with an EFIT-code developed by Marklein [5]. 

The austenitic and, hence, anisotropic V-butt weld is embedded in isotropic steel it has a width of 10 mm at its baseline and a height of 30 mm. If a notch is present, it has a width of 1 mm and a height of 15 mm it is located at the right-hand side of the V-butt weld. The simulated transducer is a commercial 45°-shear wave probe (MWB45-2E). The parameters varied during the simulations are ... 

Simulations of that kind result in a wide variety of A-scans and wavefront snapshots. The first screening of this material reveals, that the simulations in which the transducer is coupling partly to the V-butt weld and partly to the steel exhibit quite a number of pulses in the A-scans because the coupling at the interface of the weld results — due to the anisotropic behavior of the weld — in a complicated splitting of the transmitted wavefront. The different parts of the splitted wavefront are reflected and diffracted by the backwall, the interface, and — if present — by the notch and, therefore, many small signals are received by the transducer, which can only be separated and interpreted with great difficultie.s. 

Only the simulations in which the transducer is coupling either to the V-butt weld or to the surrounding steel can be analyzed in a simple and intuitive way, which means that the different pulses in the A-scan signals can be related uniquely to the reflection or diffraction of the wavefront at the weld, the backwall, and/or the notch. 

Second corner reflection The first corner reflection appears as usual when the transducer is coupled to the probe at a certain distance from the V-butt weld. The second corner reflection appears if the transducer is positioned well above the V-hutt weld. If the weld is made of isotropic material the wavefront will miss (pass) the notch without causing any reflection or diffraction (see Fig. 3(a)) for this particular transducer position. In the anisotropic case, the direction of the phase velocity vector will differ from the 45° direction in the isotropic case. Moreover, the direction of the group velocity vector will no longer be the same as the direction of the phase velocity vector (see Fig. 3(b), 3(c)). This can be explained by comparing the corresponding slowness and group velocity diagrams. 

Figure 7 V-butt weld with perpendicular grain orientation and an inclination of the interface of 15° left without, right with backwall breaking notch...

Valve bodies are also standardized to mate with common piping connections flanged, butt-weld end, socket-weld end, and screwed end. Dimensional information for some of these joints and class pressure-temperature ratings are included in Sec. 10, Process Plant Piping. Control valves have their own standardized face-to-face dimensions that are governed by ISA Standards S75.03, 04, 12, 14, 15, 16, 20, and 22. Butterfly valves are also governed by API 609 and Manufacturers Standardization Society (MSS) SP-67 and 68. 

Plain-end pipe used for socket-weld joints (Fig. 10-126) is available in all sizes, but fittings and valves with socket-weld ends are limited to sizes 3 in and smaller, for which the extra cost of the socket is outweighed by much easier alignment and less skill needed in welding. The joint is not so resistant to bending stress as the butt-welded joint but is otherwise equal, except that for some fluids the crevice between the pipe and the socket may promote corrosion. ANSI B16.il—1973,... 

V-clamp joints (Fig. 10-140) are attached to the pipe by butt-weld or expanded joints. Theoretically, there is only one relative position of the parts in which the conical surfaces of the clamp are completely in contac t with the conical surfaces of the stub ends. In actual practice, there is considerable flexing of the stub ends and the clamp also complete contact is not required. This permits use of elastomeric gaskets... 

Components without Specific Ratings Components such as pipe and butt-welding fittings are gener y furnished in nominal... 

Furnace butt weld, continuous Straight As required by listed specifications 0.60... 

Butt-welded joint, reducer, or weld-neck flange Double-welded slip-on flange Fillet welded joint or pocket-weld flange... 

Designers are cautioned that cast butt-welded fittings may have considerably heavier walls than that of the pipe with which they are used. Large errors may be introduced unless the effect of these greater thicknesses is considered. 

Subsection B This subsection contains rules pertaining to the methods of fabrication of pressure vessels. Part UW is applicable to welded vessels. Service restric tions are defined. Lethal service is for lethal substances, which are defined as poisonous gases or liquids of such a nature that a very small amount of the gas or the vapor of the liquid mixed or unmixed with air is dangerous to life when inhaled. It is stated that it is the user s responsibility to advise the designer or manufacturer if the service is lethal. All vessels in lethal service shall have all butt-welded joints fully radiographed, and when practical, joints shall be butt-welded. All vessels fabricated of carbon or low-aUoy steel shall be postweld-heat-treated. 

Attack at welds due to bacteria is possible, but it is not nearly so common as is often supposed. Because of residual stresses, microstruc-tural irregularities, compositional variation, and surface irregularities, welds show a predisposition to corrode preferentially by most corrosion mechanisms. Attack is common along incompletely closed weld seams such as at butt welds in light-gauge stainless steel tubing (Fig. 6.9A and B). Attack at carbon steel welds may occur. Figure 6.10 shows a severely corroded carbon steel pipe from a service water sys-... 

Figure 15.18 Examples of crack patterns due to stress-corrosion cracking and corrosion fatigue in butt welds. (Reprinted with permission from Helmut Thielsch, Defects and Failures in Pressure Vessels and Piping, New York, Van Nostrand Reinhold, 1965.)...

Electric are attd resistance welding transformers as for spot, seam and butt welding. 

Two pieces of work-hardened 5000 series aluminium alloy plate were butt welded together by arc welding. After the weld had cooled to room temperature, a series of hardness measurements was made on the surface of the fabrication. Sketch the variation in hardness as the position of the hardness indenter passes across the weld from one plate to the other. Account for the form of the hardness profile, and indicate its practical consequences. 

Change in section at weld bead. Gives stress concentration. In the case of butt welds this can be removed by grinding back the weld until flush with the parent plates. Grinding marks must be parallel to loading direction otherwise they can initiate fatigue cracks. 

All circumferential and longitudinal butt welds of pressure containing casings shall be 100% radiographed, if possible. All other welds shall be magnetic-particle or liquid-penetrant examined. 

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