1. Field of the Invention
This invention relates to the art of welding dissimilar tubes end to end and more specifically to a welding ring designed to effect that desired union.
2. Description of the Prior Art
The present practice of end joining tubes or pipes composed of dissimilar grades or compositions and having unequal inside diameters is both time consuming and expensive.
When it is necessary to weld a higher grade tube having a thinner wall end to end to a lower grade tube having a thicker wall, various involved fabricating steps must be carefully followed in order to prepare the ends of the two tubes for the reception of a welding ring.
It should be noted that if high temperature and/or high pressure service requirements are contemplated for the welded tubes, it may be unsafe to machine the lower grade tube to any great extent. To do so, is to court possible tube failure.
The involved prior practice requires the following steps: first, the higher grade tube must be internally upset. To accomplish this, a tube end is heated to a sufficiently softened state. The hot tube end is then placed in a die of the desired contour whereupon axial pressure is applied to the tube. After the tube has assumed the proper shape, it is allowed to cool. Finally, the tube is heat treated to remove any residual stresses.
The second step entails boring the internal upset end of the higher grade tube to conform its inner periphery to that of the lower grade tube. The upset is machined to an appropriate taper to effect a properly aligned seating surface for a symmetrical welding ring to be inserted between the two tubes. A similar taper is provided on the lower grade tube end. In addition, a weld groove is machined along the end faces of both tubes to provide a circumferential notch for subsequently deposited weld beads.
The third step involves inserting the symmetrical welding ring between the two tapered end surfaces whereupon weld beads are then deposited about the joint in the usual manner.