D-1.1 Section 6 of NSTM Chapter 074 specifies the required topside welding training, qualifications, and experience required of Navy personnel preparing for underwater welding qualification. Accordingly, the information presented herein is intended for those personnel who have a reasonable understanding and knowledge of welding using shielded metal arc welding electrodes.
D-1.2 The information contained herein applies to both underwater dry chamber (UWDC) welding and wet welding. The welder-diver will not notice a great deal of difference between topside welding and UWDC welding. Other than cramped conditions in the dry chamber and encumbrances resulting from the diving gear being worn, UWDC welding is basically the same as topside welding; the welder-diver will simply need to get used to a welding arc, which is slightly different from that of topside welding. Due to the ambient pressure at depth, the UWDC welding arc is a little constricted and results in slightly different puddle action.
D-1.3 Wet welding, on the other hand, is vastly different from topside welding. In addition to the influences of water current and bubbles, the welder-diver will find that “feel” plays a greater role in the welding process — the ability to feel differences in the way the end of the electrode is burning off.
D-2.1 Both UWDC and wet welding practice should be performed at a water depth of 15 feet or greater.
D-2.2 Practice should begin with bead-on-plate welds made in all four welding positions (flat, horizontal, vertical, and overhead); see 11-6.4 for welding position limitations. By depositing overlapping beads side-by-side, the welder-diver will become familiar with puddle characteristics at depth.
D-2.3 Once proficiency is obtained with the bead-on-plate welds, fillet weld specimens should be produced in each welding position. Fillet lodgments should be evaluated by visual inspection, break testing, and macro-section examination.
D-2.4 Finally, in order to obtain full underwater welding qualification as required by NSTM Chapter 074, Volume 1, practice groove butt weldments should be produced in each position. Recommended methods of testing, for purposes of practice welding, are visual inspection, radiographic inspection, bend testing, and macro-section examination.
D-2.5 Welding techniques for UWDC welding are basically the same as those for topside welding. Welding techniques for wet welding are addressed in section 8. Underwater welding troubleshooting criteria are covered in section 10.
D-3.1 D-3.1 Base metal should be ordinary strength steel of MIL-S-22698, or any scrap carbon steel readily available. Alloy steels, or carbon steels with high carbon equivalent (see section 4), should not be used due to the possibility of base metal cracking.
D-3.2 D-3.2 Recommended base metal thickness is 3/8 inch or greater for both UWDC welding and wet welding. After proficiency in wet welding is obtained using the thicker material, the trainee should begin practicing using 1/8-inch base metal.
D-4.1 Bead-On-Plate (BOP) Welding. BOP welds should be performed until the trainee is able to deposit side-by-side beads that meet the visual inspection requirements of section 6 of NSTM Chapter 074, Volume 1. This requires a bead overlap resulting in a smooth transition between beads without undercut. Valleys between beads should not exceed 1/32 inch in depth. For wet welding, the trainee may wish to deposit the first bead top-side; this should provide a guide which will allow the remaining beads to be deposited fairly straight.
D-4.1.1 It is suggested that the above BOP welding be performed using both DCEP and DCEN polarities during wet welding; this will better prepare the trainee for variations in wet welding behavior that can occur during underwater welding operations (see section 10).
D-4.1.2 Once wet welding proficiency is obtained at a water depth of 15 feet or greater, the trainee should perform similar welding at a water depth of 5 to 7 feet. Depending on the electrode being used, the trainee may find that the weld metal is influenced a little more by gravity at the shallower depth — especially in the overhead position.
D-4.2 Fillet Welding. As with BOP welding, fillet welding should be carried out in all four positions. The trainee will notice two primary differences when changing from BOP welding to fillet welding.
a. The puddle becomes more confined and easier to handle
b. More rod pressure is required
D-4.2.1 The increased rod pressure is required to enhance penetration during the initial (root) pass. Once the root pass has been deposited, the rod pressure will be reduced. The initial practice welding should be directed toward satisfactory deposition of the root pass, with a weld profile somewhere between slightly concave to slightly convex (see ANSI/AWS D3.6). Once an acceptable fillet weld profile is obtained, an evaluation should be made for weld quality and penetration using the fillet break test as described in D-5 below.
D-4.2.2 After developing the skill for satisfactory deposition of the root pass, additional passes should be deposited over the root pass to provide a fillet weld size (see section 3) of 3/8 inch or greater. The fillet weld contour should meet the visual acceptance standards of section 6 of NSTM Chapter 074, Volume 1. Bead overlap should be as outlined above for the BOP welding. Once an acceptable multiple-pass fillet weld profile is obtained, an evaluation should be made for weld quality and penetration using the fillet break test described in D-5 below.
D-4.3 Groove Butt Welding. Groove butt welding practice and testing will quickly show the competence level of the trainee, since weldment evaluation is more detailed and more likely to reveal weld discontinuities which would have been missed during BOP and fillet welding testing. To put it another way, groove butt weldment evaluation is less forgiving of welding mistakes.
D-4.3.1 For wet welding practice, the weld should be made against a backing bar as shown in Figure D-1.
D-4.3.2 For UWDC welding, the practice welding can be made against a backing bar as shown above, or the plates can be butted together without the backing bar — in which case the weld joint would be completed, after which the backside would be ground or gouged to sound metal and rewelded to obtain a sound weld root.
D-4.3.3 When wet welding using the above joint design, it is best to leave a root opening (1/4 to 3/8 inch when using a 1/8-inch electrode) large enough to deposit a two-pass root. This allows the trainee to concentrate on tying in each side of the root separately. When depositing the root passes, the technique is basically the same as that used for making the root pass of a fillet weld.
D-4.3.4 Since root pass deposition requires the greatest skill, it is wise to limit initial evaluations to the root passes. This evaluation should consist of visual inspection and macro-section examination. Once satisfactory root pass deposition techniques have been confirmed, fully welded joints can be produced and evaluated.
D-4.3.5 Visual inspection of the completed weldments should meet the standards described above for the BOP and fillet weldments. Radiographic inspection is recommended to verify that invoked acceptance criteria are met while providing a method of weeding out those weldments which may contain gross weld defects to the extent that destructive testing is not warranted.
D-4.3.6 Once weld quality has been confirmed by nondestructive testing, destructive testing by bend testing and macro-section examination should be performed as specified in D-5.
D-4.4 Welding Variables. The primary welding variables of interest for purposes of this appendix are:
a. Amperage
b. Voltage
c. Travel speed
D-4.4.1 Recommended ranges for amperage and voltage, and occasionally travel speed, will be provided by the electrode manufacturer. Section 5 addresses approved electrode manufacturers as well as amperage and voltage meters. During initial practice welding, amperage is the variable that is of the greatest importance. Once the amperage is adjusted to obtain acceptable bead appearance, the arc voltage should be close to the optimum required (acceptable weld beads require proper arc length; arc length controls arc voltage). It should be remembered that both amperage and voltage will vary as the welding progresses, since the arc length does not stay constant. The longer arc gives increased arc voltage (more resistance) and thus reduces the amperage, and vice versa.
D-4.4.2 D-4.4.2 As the welder-diver refines his technique, closer attention can be paid to arc voltage and travel speed. Observation of arc voltage will show arc length variations which can show problem areas that may not be obvious to the welder-diver while welding is progressing. The range of travel speeds that produce acceptable results should be recorded to allow additional input in developing optimum welding techniques. Travel speed is the speed at which a weld bead is deposited in inches per minute; it is calculated as follows:
Travel speed = (Length of bead in inches / time in seconds) x 60
D-5.1 For purposes of this document, two methods of destructive testing should be considered; both methods are described below. Additional information and acceptance criteria for these destructive testing methods are specified in section 6 of NSTM Chapter 074, Volume 1 and the referenced specifications invoked therein.
D-5.1.1 Fillet Break Testing. This testing method is used to evaluate internal weld quality and penetration. The weld is broken open by bending or hammering in a direction to cause the weld to fracture in tension as shown in Figure D-2. This test can easily be performed in the field by using, for example, a vise and a sledge hammer.
D-5.1.1.1 In evaluating penetration, adequate penetration shows weld metal extending at least to the edge of the web member of the above “T” specimen. Slag entrapment in the root can interfere with penetration. The slag can be seen in the fillet weld break, or where the slag has fallen out, there will be a shiny area with ripples similar to the surface of a weld. Note that fillet breaks will be easier to break if the tack welds are ground off.
WARNING |
D-5.1.2 Macro-Section Examination. This examination can be used for both the BOP welding and the fillet welding. A cross section of the weldment is removed by sawing, exposing the weld and adjacent base metal. The cross-section is then ground or sanded to produce a flat, smooth finish of 60 grit or finer. An etching solution of 90 percent denatured alcohol/10 percent nitric acid can then be wiped onto the surface (using a cotton swab, for example) to bring out weld and heat-affected zone details. The etching solution should be washed off, using denatured alcohol, as soon as the microstructural details become visible; this should occur in less than 1 minute.
D-5.1.2.1 The 60-grit finish will show minimal details of weld quality. A finer finish (i.e. 400 grit) gives a more detailed picture of weld quality and the heat effects of welding. The finer finish also requires less time for etching.
D-5.1.2.2 Macro-section examination provides an accurate picture of weld penetration and allows evaluation for small weld defects that might not be otherwise detected.
D-6.1 In planning for the practice welding detailed above, the welder-diver trainee should be prepared to spend a significant number of man-hours “burning rods”; no one reaches any degree of underwater welding competence without a lot of arc time, and this is especially true of wet welding. Once proficiency is reached using base metal approximately 3/8 inch thick, the trainee will find that welding on thin materials (e.g., 1/8 inch and less) will require some significant changes in welding techniques. All in all, and especially for wet welding, a good deal of time will be required to develop the competency required for successful underwater welding qualification.
D-6.2 However, it should be understood that passing qualification testing, under ideal welding conditions, does not necessarily guarantee that the welder-diver will be able to perform underwater welding of equivalent quality during an actual production welding underwater repair. As described in section 8, water current, fit-up problems, and many other factors can influence weld quality. It is only after numerous production underwater welding jobs, where on-site problems are encountered and overcome, that the welder-diver truly becomes proficient in the work.