Consumable Insert Ring and Fillet Weld on Pipe Systems

I though I will felt fresh after take a holiday even only for a day, but the fact is the whole body is feel so numb, so sick, that's because I push my body too much when I looking for the rent house for me and my family, so the post of Piping & Fabrication delayed. But now Piping & Fabrication continue with Consumable Insert Ring and Fillet Weld on Pipe Systems.

Consumable Insert Rings. 

The chemical composition of a piping base metal is established primarily to provide it with certain mechanical, physical, or corrosion resisting properties. Weld ability characteristics, if considered at all, are of secondary concern. On the other hand, the chemical composition of most welding filler metals is determined with primary emphasis on producing a sound, high-quality weld. The steelmaking process employed in the manufacture of welding filler metals permits closer control of the composition range, which is usually considerably narrower than would be practical for the piping base metal where much larger tonnages of steel are involved. On some base metals, the welding together by fusion of only the base-metal compositions may lead to such welding difficulties as cracking or porosity. The addition of filler metal tends to improve weld quality. However, in inert gas tungsten-arc welding, the addition of welding filler metal from a separate wire, which the welder feeds with one hand while manipulating the tungsten arc torch with the other, is a cumbersome process and interferes with welding ease. The welder may leave areas with lack of penetration, which generally are considered unacceptable as can be seen, e.g., in the rules of the ASME Boiler and Pressure Vessel Code. Since some types of serious weld defects are detected only with difficulty during inspection (if they are detected at all), it is extremely important to provide the easiest welding conditions for the welder to produce quality welds.

FIGURE A2.26 Commercial consumable insert rings used in pipe welding (MIL-I-23413).Style D: for NPS 2 and larger. On Schedule 5 for NPS 5 and larger; style E: for NPS less than 2. On Schedule 5 for NPS less than 5.

One technique to produce high-quality welds is to employ consumable insert rings of proper composition and dimensions. Consumable insert rings which are available commercially are shown in Fig. A2.26. The three primary functions of consumable insert rings are to (1) provide the easiest welding conditions and thereby minimize the effects of undesirable welding variables caused by the ‘‘human’’ element, (2) give the most favorable weld contour to resist cracking resulting from weld-metal shrinkage and hot shortness, or brittleness, in hot metal, and (3) produce metallurgically the soundest possible weld-metal composition of desirable strength, ductility, and toughness properties.

The best welding conditions are obtained where the flat-land and extended U-bevel preparations are used. These joint preparations are particularly helpful where welding is done in the horizontal fixed pipe position (5G), since they ensure a flat or slightly convex root contour and provide by far the greatest resistance to weld cracking in those alloys particularly susceptible to microfissuring.

The weld-root contour conditions to be expected from different bevel preparations and consumable insert rings are illustrated in Fig. A2.27. Where sink is not acceptable, it is considered obligatory to use consumable insert rings with the special flat-land or extended U-bevel preparation. In horizontal-rolled (IG) and vertical-position (2G) welding, the insert ring should be placed concentrically into the beveled pipe. In horizontal fixed-position (5G) welding, the insert ring should be placed eccentric to the centerline of the pipe (as shown in Fig. A2.28). In this position, the insert ring compensates for the downward sag of the molten weld metal and aids in obtaining smooth, uniform root contour along the inner diameter and the joint.

Fillet Welds
Circumferential fillet-welded joints are generally used for joining pipe to socket joints in sizes NPS 2 (DN 50) and smaller. Figure A2.29 illustrates three typical fillet-welded joints. These types of welds are subjected to shearing and bending stresses, and adequate penetration of the pieces being joined is essential. This is particularly important with the socket joint, since the danger of washing down the end of the hub may obscure, by reason of fair appearance, the lack of a full and sound fillet weld. This condition is one which cannot be detected in the finished weld by the usual visual inspection. Additionally, a 1/16-in (1.5-mm) gap (before welding) must be maintained between the pipe end and the base of the fitting to allow for differential expansion of the mating elements.

There are service applications in which socket welds are not acceptable. Piping systems involving nuclear or radioactive service or corrosive service with solutions which promote stress corrosion cracking or concentration cell action generally require butt welds in all pipe sizes with complete weld penetration to the inside of the piping.