Wet-Spot Welding Method
Revolutionary Welding System Removes the Need for Skilled Welders
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We have developed solutions to the long-standing problems associated with underwater wet welding and in particular the skills required to produce high quality welds. The new system, which has been named Hammerhead™ answers the problems to obtaining high quality wet welds in nil visibility, without the need for experienced, trained and/or qualified welder-divers.
The electrode used is a specially formulated Cr-Ni-Mo (stainless steel) electrode and is available in 3.2 mm (1/8") diameter. Although this electrode has been specifically designed for use with the Hammerhead wet-spot welding system (spot-welding), it may also be used for conventional wet welding of stainless steels and/or high strength carbon steels, as it is highly resistant to hydrogen cracking and offers high strength and high toughness electrode properties. For mechanical properties and chemical analysis see the brochure.
This type of welding process may also be used in air, for general construction, using the software installed into Mahe 420 amp welding inverter.
The Hammerhead™ wet-spot welding process results in a quick and reliable joining method by means of a spot/plug weld, using a standard DC welding power source.
See Hammerhead in action on these video clips:
Video 1: (dry-spot demo) shows Drew Maslin of Northern Divers (non-welder) using the system in air. The weld is then broken to show the fusion faces.
Video 2: (wet-spot demo) shows David Keats of Speciality Welds using this system to weld plate J2.1. The report for this weld (S402472) can be read here (pdf file).
Video 3: Shows the welding of a 3 pass fillet weld underwater using Barracuda Gold electrodes. (These welds were made to aid comparison between standard fillet welds and wet-spot welds.)
Video 4: Shows the tensile testing of weld sample D1.2. The report for this weld (S401924) can be read here (pdf file).
In removing the skills necessary to carry out underwater wet welding you must change the fundamental approach to how welding is carried out. The benefits include; no need for specific joint configurations and all the preparation that goes with them.
No need even for a conventional fillet or butt joint for that matter. No need for cleaning the joint area or for chipping off slag before laying down additional passes, in fact there’s no need for additional passes, as the process is a one-shot process i.e. one electrode produces one complete spot/plug weld.
By removing the actual welding skills from the operation, there’s no need for the diver-welder to control parameters like travel speed, electrode angles, arc length, etc, as associated with conventional welding skills. There’s even no need to have good visibility as the diver doesn’t need to see or control an arc in the conventional sense. Even when visibility is poor high quality welds are produced time after time.
How is all this achieved?
By using our new control system (as seen) connected to the welding machine, this controls the welding operation. The process will penetrate the two materials required to be joined and then through the control unit the currents necessary to pierce and then fill the hole results in a spot/plug weld being formed, which has sufficiently penetrated both sets of material to form a sound joint, similar in principle to a rivet. The benefits include, no need for specific joint configurations and all the preparation that goes with them.
The size and frequency of welds can be determined by the formula as shown.
Typically the shear strength is generally assumed to be 4/5 the ultimate tensile strength for most steels. The electrode has a tensile strength of 650N/mm2 and therefore will offer a shear strength of approx. 520 N/mm2. Therefore a 10.0mm diameter weld nugget will produce a max load capability of 40840 N per spot (40.84kN).
The control system which sits above water controls three things:
- Peak current
- Low current
The operator sets these in accordance with a set of guidelines calculated for thickness of material.
The 1st current value allows the electrode to pierce the material directly, creating a hole through which the materials can be joined together. During this operation the diver or indeed robot need only apply sufficient pressure to push the electrode through the materials to be joined. Absolutely no welding skills are required. After the first weld cycle is completed and the depth of penetration is achieved a 2nd current is automatically initiated which then allows the electrode to fill up this hole, thereby creating a spot/plug weld, which has penetrated both sections of material; thus creating a nugget/spot weld. The system can join materials up to a combined thickness of 32mm (1 1/4in) thick.
Although the process is not completely automatic, as after all the process is still ‘manual metal arc’, however, the skills necessary for a diver to produce a weld have been removed, as have many of the traditional preparations and environmental factors, which normally have such an influence on welding underwater. If this wasn’t enough the final weld quality is also improved, with the majority of the weld being confined within the through thickness of the material, factors such as erosion, corrosion are less of a concern. The heat-affected zone (HAZ) is smaller and the overall weld hardness is lower and the potential for weld defects are minimised.