Preparation is the key to stopping crack propagation. Attempts to stop a crack by filling in with weld metal most often result in failure as the crack is very likely to open up again through the weld. Therefore, small patches, preferably circular ones, are recommended. These patches can be readily attached to the hull of a ship by fillet welding because the groove of the fillet provides a guide for depositing the electrode.
The following procedures are recommended:
a. Locate the ends of the crack by appropriate non-destructive testing techniques; Ultrasonic Testing (UT) or Magnetic Particle (MT).
b. Drill small holes at the extreme ends of the crack to prevent further crack development. Alternatively, the holes may be burned.
c. An area of approximately 2 inches should be scraped or wire brushed shiny clean around the crack where the patch is to be fixed. Prepare the patch, to extend beyond the crack 6 inches in all directions. Contour the patch as necessary to fit the work.
3-13.1 Using a Rectangular Patch. The following procedure is recommended for repairing cracks in underwater structures using a rectangular patch. Figure 3-8 illustrates this procedure.
a. Round the corners of the rectangular patch using a 3-inch radius.
b. Place the patch over the crack and attach by fillet welding. To allow for venting, do not weld the uppermost 3-inch section of the patch during the root pass.
c. Turn the patch on a 45° angle, if necessary, to reduce the need for overhead welding.
3-13.2 Using a Circular Patch. The following procedure is recommended for repairing cracks in underwater structures using a circular patch. Figure 3-9 illustrates this procedure.
Figure 3-8. Repair Method for Cracks in Underwater Structures Using a Rectangular Patch.
a. Tack the patch on at the 12 o'clock position, tap it down and tack it on at the 6 o'clock position. Then tack at the 3 and 9 o'clock positions.
b. Clean the slag from the tacks and grind all tack ends to a feather edge.
c. Begin welding downhill at the 12 o'clock position. Weld clockwise to and including the tack at the 6 o'clock position.
d. Return to the 12 o'clock position and move approximately 3 inches away from the previous weld. Then weld downhill counter clockwise to the 6 o'clock position.
e. To finish, weld the remaining 3 inches at the top. Clean the entire weld bead and fill in any incomplete tie-ins. Additional passes are required to obtain the mandatory 3/8-inch leg length. Always completely de-slag previous beads before welding.
Was this article helpful?