Tack welds

It is important to ensure that tack welds are either made using the same procedure as is used for the main welds, or that the procedures for them are safe. They must be of adequate length, i.e. at least 50 mm, or four times the length of the thicker part, whichever is less. 

1 Gledhill P K and Goult E L The production of universal beams and columns in high yield structural steels . ISI Publication 104, 1967, 182-7, 243. 

2 Smith N and Bagnall B I The influence of sulphur on HAZ cracking of G-Mn steel welds . Brit Weld J15 (2) 1968 63-9. 

3 Hewitt J and Murray J D The effect of sulphur on the production and fabrication of C-Mn steel forgings . Ibid, (4), 151-8. 

This Book will make a Traveller of thee, 

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Fixed rher and pyramidal cap of welded construction with cop tack welded to troy. 

Proper condensate removal is important. An inverted split cup inside the shell, with the upper capped end above the nozzle and the lower open end -in. above the bottom tubesheet, should be used to cover the oudet nozzle. This can be made by splitting a pipe that is one size larger than the condensate oudet down the centerline. In this case, a 2-in. split is adequate. This cup must be fully seal welded (not tack welded) to force condensate down to the -in. clearance above the bottom tubesheet. A common error is to allow 6 in. or more above the tubesheet for the centerline of the condensate oudet. In this case, 6 in. of tube is 10% of the surface. If the cup is not used, add 10% more tubes to correct for the dead liquid space near the bottom. This is in addidon to the 10% safety factor. 

The component parts are heated. The blade shape is laid out on the hub disc and tack welded, which ensures that the blade cannot be misaligned. The hub disc with the tack welded blades are placed on the automatic impeller welding machine and heated for welding. After the blades are completely welded to the hub disc, the cover disc is welded on by the same means. The completely welded impeller is then ready for annealing and finish machining. 

Tack welds shall be made with the filler metal specified by the WPS and made by a qualified welder or welding operator. Tack welds shall be removed or fused within the root pass weld. Permanent tack welds shall be examined visually for defects and, if found to be defective, shall be removed. All bridge tacks shall be removed prior to welding the root pass or subsequent deposit. 

Renewable wear rings shall be held in place by a press fit with locking pins or threaded dowels (axial or radial) or by flanged and screwed methods. Other methods, inclnd-ing tack welding, require the purchaser s approval. The diameter of a hole in a wear ring for a radial pin or threaded dowel shaU not be more than one third the width of the wear ring. 

Wetted parts subject to welding, including fabrication and tack welding (for example, removable wear rings), shall be stress relieved, if required, so that both the welds and the heat-affected zones meet the yield strength and hardness requirements of this paragraph. 

Flat Bottoms Flat bottom vertical cylindrical tanks present particular problems. The bottom must be so constructed and supported as to be completely rigid and well ventilated from the sides and underneath. This may usually be provided by I beams. The bottom shall be tack welded to the I beam so that the bottom will not flex and crack the lining when it is installed. (Reference 8, p 74). The maximum free span between I beams can be calculated on the basis that the maximum deflection under full load conditions shall not exceed the free span divided by 1000. However, in the case of vessels containing only gas at atmospheric pressure and no internal spheres, then the deflection can be as great as the distance divided by 500. It is good design to leave sufficient space between I beams to allow for maintenance perhaps enough space for a man to crawl between them. 

Caps are sometimes tack-welded into place for longterm durability, or they may be fastened with double lock-nuts or hold-down bars installed parallel to the liquid flow. 

Sununu [173] and Genetti and Priebe [174] used Kenics static mixers for heating of viscous oils (Figs. 11.26 and 11.28, curves e and f). These mixers consist of 360° segments of twisted tapes every second element is inverted and the segments are tack-welded together. The... 

Vehicle repair techniques, overseen by the insurance industry, are also being developed for bonding sheet steel panels. Epoxides and polyurethanes are used, and the benefits of using adhesives include the need for access only to the outside surface of the repair area as well as overall cost and time savings. Crash and impact tests have confirmed the suitability of such repairs as well as highlighting, as with new build operations, the need for judicious use of tack welds or rivets. 

The box was assembled using stabilizing struts and tack welding from the inside (Figure 6). 

It will be noted that the adhesive force dropped off as the temperature of the detachment operation was increased. This is explained on the basis that, when the surface, which had been heated to 400°C, was placed in a colder medium, tack welding of the particles takes place, and the adhesion increases. An increase in the detachment temperature eliminated to a considerable degree the tack welding process, so that the adhesion was reduced. It was established experimentally that, when a specimen that had been coated with dust in an air medium (temperature 20°C and humidity 50-60%) was placed in a medium at low temperature (below 0°C), the adhesive force increased very sharply owing to freeze adhesion of the particles to the surface as a result of moisture condensation between the contact surfaces. If the dust deposition operation itself was performed at low temperature, however, the adhesive force was not increased. 

Assembly of vessel with only tack welding prior to final welding, root run of welding... 

Bottom-head removal can be expedited by installing a track-mounted air gun for unbolting the bottom head. The track is attached to the circumference of the coke drum cone as shown in Figure 2-10, and the gun is slid along the track. This feature, combined with tack-welding the nut to the bottom flange, permits one person to unbolt the bottom head easily. 

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