Seam welds

Weldments subjected to corrosive attack over a period of time may crack adjacent to the weld seams if the residual stresses are not removed. Gas—tungsten arc welding and gas—metal arc welding ate recommended for joining magnesium, the former for thinner materials and the latter for thicker materials. Maintaining a protective atmosphere is a critical issue in welding these alloys. 

Two sections of steel condenser tubing experienced considerable metal loss from internal surfaces. An old section contained a perforation the newer section had not failed. A stratified oxide and deposit layer overlaid all internal surfaces (Fig. 5.14). Corrosion was severe along a longitudinal weld seam in the older section (Fig. 5.15). Differential oxygen concentration cells operated beneath the heavy accumulation of corrosion products and deposits. The older tube perforated along a weld seam. 

Figure 5.15 Rough internal surface contour of the tube shown in Fig. 5.14. Note the preferential attack on the weld seam. (Magnification 7.5x.)...

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 6.9 Irregular deposit and corrosion-product mounds containing concentrations of sulfate-reducing bacteria on the internal surface of a 316 stainless steel transfer line carrying a starch-clay mixture used to coat paper material. Attack only occurred along incompletely closed weld seams, with many perforations. Note the heat tint, partially obscured by the deposit mounds, along the circumferential weld.

Figure 6.9S Longitudinal cross section showing a pit tunneling into an incompletely closed weld seam.

Seams. As defects, seams are distinct from weld seams and may be found in nonwelded (seamless) tubes. They are caused by crevices that have been closed by some rolling process but remain unfused. 

Weld-seam defects. Failure to fuse the metal fully along the weld line in welded tubes may result in a linear open seam or crevice. 

Weld-seam defect. This appears as a linear groove or crevice running along the seam formed in a welded component. 

Figure 14.1 illustrates one of many similar pinhole perforations found in this and other tubes within the exchanger. Figure 14.2 shows the typical appearance of the internal surface immediately after removing the tube from the exchanger. Laboratory acid cleaning of the internal surface revealed a defective weld seam (Fig. 14.3). 

Figure 14.3 Close-up of the internal surface following acid cleaning. Note the perforation in the tube wall along the weld seam.

Chemical removal of deposits and corrosion products revealed the appearance of the groove (Fig. 14.5). The crevice formed by the incompletely fused weld seam fostered the establishment of differential concentration cells (see Chap. 2). This resulted in localized corrosion and eventual perforation through the greatly thinned tube wall at the bottom of the crevice. The tubercle, which is composed of corrosion products, is a simple result of the corrosion process occurring locally within the crevice. 

Figure 14.4 Tubercle capping a pit located in a weld-seam defect.

Started to rise from the reaction, causing the vessel bottom head to fail at the weld seam. The force from the escaping gases propelled the tank into the ceiling and overhead structural steel. A small fire erupted which was quickly brought under control by the automatic sprinkler system. Even though the chemists had reviewed the chemistry and did not anticipate any problems, use testing could have identified this problem in the laboratory rather than the plant. 

The tank fails at the welding seam between the curved roof and the cylindrical plate wall with break area, A. 

Hugged e tenor cunsittu tiun of I l-gauyc cftUi rolitui steel with ctinimtionsly welded seams. 

The material of constmction of the vessels D and C was not suited for use under low temperature conditions. Vessels A and B were, however, suitable. The location of initial brittle fracture in vessel C was the weld seam near the manhole. Vessel D probably failed as a result of impact from a fragment from vessel C. 

The major portion of drill string is composed of drill pipe. The drill pipe is manufactured by the seamless process. According to API Specification 5A (Thirty-fifth Edition, March 1981), seamless pipe is defined as a wrought steel tabular product made without a welded seam. It is manufactured by hot working steel or, if necessary, by subsequently cold finishing the hot worked tabular product to produce the desired shape, dimensions and properties. 

Part 2 Steel containers up to 450 liters water capacity with welded seams... 

Titanium stabilised fillers should not be used in argon-arc welding as titanium will be vaporised and its effectiveness as a stabiliser lost. Carburising the weld seam by pick-up from surface contamination, electrode coatings or the arc atmosphere leads to increased tendency to intercrystalline corrosion. 

After some deliberation, sheet flooring was chosen rather than tile. Commercial grade vinyl was used in a color which harmonized with the laboratory furniture. The flooring was installed before any furniture arrived. While this called for more material, labor cost was much less. A sealer was applied to all seams. Although it stood up quite well, flooring with welded seams, not mentioned by either engineer or contractor, would no doubt have been more desirable. 

Cylindrical sections are usually made up from plate sections rolled to the required curvature. The sections (strakes) are made as large as is practicable to reduce the number of welds required. The longitudinal welded seams are offset to avoid a conjunction of welds at the comers of the plates. 

Center of the U.S. Bureau of Mines. The radon chamber in Denver Research Center is designed to provide adjustable humidities and a well controlled, monitored radon and CN concentration. It has a length of 213 cm, a diameter of 152 cm, and a volume of about 3.89 m. The walls are made of 0.5-cm rolled steel with welded seams. Figure 1 shows the general scheme of the test chamber excluding the transducers and data aquisition system. 

A flammable liquid is to be stored in a large storage vessel. Two vessels are available. One vessel is called a weak seam roof tank, with the weakest part of the vessel being the welded seam between the roof and the vertical wall of the tank. The other vessel is a domed roof tank, with the weakest part being the seam along the bottom of the tank. Which tank is the best choice for storing this material ... 

A 2-ft-diameter float was fabricated using stainless steel and welded seam construction. Pipefitters were given the job of checking the welds for leaks. They were instructed to use 5 psi of air pressure and a soap solution to identify the leaks. 

There are also some technological factors that influence the quality of the polymer. The design of the reactors, the flow of the molten polymer and the way of heating the systems are decisive for quality and performance [28], Valves, tube turns, in- and out-take flanges, mixing elements and welding seams are often... 

Weld seams should be continuously smooth, and free from porosities and blow holes, projections and burrs. These should be smoothened out by grinding. See figure 4.2 below. 

Figure 4.2 Grinding of weld seams in a duct before shot blasting and coating of adhesive.

Improper grinding of weld seams at corners and sharp edges. 

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