(Courtesy of the Oxweld Acetylene Co.)
Fig. 71.—Welded Cracks between Staybolts.
(106) In the repair of boilers many a feasible job has been given up as impossible by the unthinking welder. Cracks have been found in fire-box sheets around the staybolts which, as soon as they are touched with the flame, seem to run and keep running. They really discourage those who are not familiar with this class of work. Many such welds have been executed and are apparently all right until tested, when they give way and make the job worse than it was previously. The trouble is in these instances that the welder has made no provision for contraction and while the job might appear to be successful, yet the internal strains exerted will not show themselves at the test. Many boiler shops have found that the flat patch is not to be relied upon and when a crack is found between two stay-bolt holes, such as shown in [Fig. 72], a round hole is cut as shown by the dotted line. A circular plate is then cut slightly larger than this hole and after being brought to a red heat, it is bellied by the use of a hammer or a set of dies, so that it assumes the shape of a saucer and is called by many a “dished” patch. Some idea may be had of such a patch from [Fig. 73].
Fig. 72.—A Crack between the Staybolts in a Boiler should be Cut Out as Shown by the Dotted Line, to Prepare it for a “Dished” Patch.
Fig. 73.—A “Dished” Patch.
(107) The patch is placed in the sheet with the concave side toward the operator and should be securely welded in place, adding as little metal for reinforcement as possible, but seeing to it that a perfect fusion is made between the patch and the sheet all the way through. As soon as the weld is complete the torch is played upon the high part of the patch, which is protruding, and as the weld cools off, sharp quick blows can be applied to the center of the patch, which should be kept in a heated condition until it is nearly flat. This will take care of any contraction that might set up and is a very good way of handling patches which do not exceed six or eight inches in diameter.
Fig. 74.—A “Corrugated” Patch.