Before welding operations are started, the job should be inspected to determine whether or not the welding can be performed effectively at the work site. Satisfactory underwater welds are more difficult than welds laid down topside. The following factors make underwater welding difficult:
a. Diving apparel b. Where a steady platform cannot be provided from which to weld. (Working near the surface in rough water makes it difficult to provide a stable platform. When working from a stage, it is preferable to attach the stage to the object being welded rather than to the salvage ship, diving launch or float, since the rising and falling of the surface vessel in rough water changes the position of the stage relative to the object being welded.)
c. Adverse currents, d. Low temperature, e. Where the metal thickness is less than 0.20 inch.
f. Where the fit-up is poor. A 1/8-inch gap should be considered the maximum permissible for a quality wet weld using the self-consuming technique and 1/8-inch electrodes.
g. As the depth increases, due to the increase in hydrostatic pressure.
h. Where the visibility is extremely low and the diver has no groove to follow. 3-9 STRENGTH OF UNDERWATER FILLET WELDS
The strength of a completed weld joint may well become the most important factor in the success of an entire salvage operation. The loading on a member, such as a padeye, involves both static and dynamic forces. Dynamic loading may be a combination of tension, compression, shear and bending. Because there is always some doubt concerning the magnitude of loading, a safety factor of six is used in calculating the required length of a fillet weld, which in turn determines the strength of the weld.
The second factor is the overall length of the fillet weld. In many cases, this will be determined by the size of the patch or work in question. However, if in doubt, use the 1,000 pounds per linear inch as a safe guideline. For example, a padeye for a 10-ton load will require 20 linear inches of fillet weld, as shown below:
20, 000 pounds _ jnches of weld
1, 000 pounds per linear inch
Before going into actual welding procedures, a few word of definition are required. The primary application for wet welding is the fillet weld. Groove welds may also be worked. For best results when welding a groove weld, a backing strip should be used.
3-9.1 Parts of a Weld (Definitions). The following terms are used to describe the parts of a weld. The FACE is the exposed surface on the side from which the weld was made. The TOE is the junction between the face of the weld and the base metal. Figure 3-3a illustrates. The ROOT of a weld includes the points at which the bottom of the weld intersects the base metal surfaces, as seen in cross section. Figure 3-3b illustrates weld ROOTS. The LEGS of a fillet weld are shown in Figure 3-3c. When looking at a triangular cross section of a weld, the LEG is the portion of weld from the TOE to the ROOT.
3-9.2 Fillet Weld. A fillet weld is a triangular weld used to join two surfaces that are at approximately right angles to each other. i.e., lap, tee and corner joints are normally welded with a fillet weld. A fillet weld should have a leg length equal to the plate thickness up to 3/8-inch plate. For plate thicknesses 3/8-inch and greater, a minimum of 3/8-inch leg length is required on all wet welds.
As with surface welding, the use of larger wet welding electrodes will result in greater weld metal deposition. However, the larger electrodes tend to produce more porosity (gas voids) in the deposited weld metal. Also, a larger single pass weld will have a lower toughness and an equivalent size multipass weld; this is the result of the tempering effect that each pass of the multipass weld has on the preceding passes.
For most positional work, a 1/8-inch electrode is recommended. Therefore, the diver will need to make a number of passes, usually 3 to 5, to achieve a 3/8-inch leg length. The number of runs will be determined by position and technique. The important point is not the number of runs, but obtaining the 3/8-inch leg length. In cases where the metal to be welded is thin and in all overhead work, a 1/8-inch electrode is required. Using the smaller electrode means more passes, but as previously stated, it allows succeeding passes to temper the preceding ones. Multipass welds using smaller diameter electrodes will actually result in higher quality wet welds with better metallurgical properties.
3-9.3 Trial Weld. As in all welding, good root penetration and avoidance of defects are important. In some cases, a trial weld will be required on site. This should be done at the working depth and in the most difficult position required, usually overhead. The specimen weld should be brought to the surface and inspected before the actual welding dive commences. A visual inspection should be conducted for bead profile and lack of defects. The weld may also be Dye Penetrant Tested (PT) or Magnetic Particle Tested (MT). If neither of these testing methods are available, break the specimen with a sledgehammer to determine how easily it breaks. The weld interior should then be inspected for slag entrapment and/or lack of fusion into the root.
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