WELD-THRU DECK PROCEDURE
Does your job specify studs to be welded thru-decking? Do you see the abbreviation “WTD” after your stud description? If so, the procedure needed to successfully weld thru-deck studs is below.
In order to achieve success when welding studs thru-decking you must first make sure that your surface area is free of paint, excessive rust, mill scale, dirt, moisture, as well as any other foreign contaminants that may affect the welding procedure. This includes galvanized beams.
When installing the decking material, it is important that the deck be held as tight as possible to the beam. Any separation between the beam and flange will cause an inconsistent gap arch length and also allow the molten metal to escape the weld area. This will then be a cause for inconsistent welds. Prior to welding, the decking surface should be prepped as well. The surface should be swept to remove all dirt, sand, or any other foreign materials that have accumulated during construction. The deck must also be dry. If the deck is wet due to rain or humidity, it may be necessary to heat or blow dry each stud location in order to remove moisture from between the deck and beam flange.
Grounding is another very important step in the weld-thru deck procedure. The welding ground or (C-CLAMP) should be attached to a spot on the beam flange that has been prepped by grinding the beam down to its bare metal. Poor or inadequate ground connections will result in loss of weld current and therefore, affect the weld quality.
When it comes to your power source, consult either the manufacturer or manual for the recommended fusing, primary wire size and primary wire length for the power source to be used. Inadequate primary power or incorrect wire size or length can contribute to a reduction in weld current when some rectifier type power sources are used. Inadequate power or fusing can also hamper the starting and output current for a gas powered generator.
It is essential to have the correct weld current for this application, normally between 1,500 and 1,900 amps. When excessive cable lengths are used the result will be a reduction in weld currents. This can contribute to weld inconsistency or even weld failure. Always use 4/0 cables in the welding circuit. The amount of cable totally depends upon the power source being used. It may be necessary in some cases to parallel cable when long runs are needed.
Whenever flashing is used as a closure on steel beams, special care should be taken to make sure the deck is flush against the beam as opposed to lapping. In most cases, the flashing is made of hot dipped galvanized sheet without controls on the amount of zinc. Most deck manufacturers limit the deck coating to 1-¼ oz/sq ft. The welding of studs should be avoided at lapped points due to the lack of proper nesting, resulting in gaps between the sheets. If it is necessary to weld in a lapped area, it is recommended that a portion of the top sheet be removed, especially in the case of hot dipped galvanized decking.
Weld settings cannot be given because no two jobs are the same. Actual settings will depend upon job site conditions such as: deck thickness, decking material type, the amount of galvanizing and ambient temperature. Listed below are approximate settings, minimum and maximum. Most jobs will fall within these settings. Light gauge, lightly galvanized or painted black iron deck of single thickness should fall close to the minimum setting. Double thickness and heavily galvanized deck will be close to the maximum setting.
Weld Time: 0.8 to 1.6 sec (48-96 cycles)
Weld Current: 1,500-1,900 amps DC Lift 1/8”
Plunge: ¼ “- 1/2”
Gun lift should be measured with a stud and ferrule in place and the gun compressed to weld. The controlled plunge jet (brass screw) should be removed from the stud gun.
Arc Gun Accessories for Welding ¾’’ diameter Weld Thru-Deck Studs:
Extension Legs B-0109-18 18”
Foot Piece B-0021
Foot Extension Assembly
*Weld current should be checked by using a time current monitor. It should be monitored periodically due to cable heating which can be caused by a reduction in weld current.
All pre-weld and weld testing should be done in accordance with American Welding Society Structural Welding Code D1.1. (In the case of severe cold weather conditions, testing should be completed before the stud is cold, but yet not while it is hot, preferable when the stud is warm to the touch. Reference: Weld Test Procedure Report.
After the completion of the weld a visual inspection should be done. The visual inspection should identify a full 360 degree weld fillet, but not necessarily the same fillet height around the circumference of the stud. Any undercutting at the weld interface will be cause for rejection. If the fillet is something less than 360 degrees the stud should be tested by hammer blow or bending with a pipe to 15 degrees. The bending method is preferred. If a failure does not occur, the weld should be considered successful and left in the bent condition. If the weld fails, the studs should be replaced.