11.6 - Stud welding: Testing
The testing and recording of welded shear stud tests should be undertaken in accordance with BS EN ISO 14555:2014 and BCSA Code of Practice for Metal Decking and Stud Welding.
Pre-start test
At the start of every welding shift a Welding Procedure Qualification Record Test (WPQR) must be undertaken. The settings used during this test should fall within the parameters set out in the SMD Welding Procedures Specification (WPS).
Refer to SMD WPS Technical Guidance sheet 551 for more information.
Refer to SMD WPS Technical Guidance sheet 552 for more information.
The WPQR test involves welding 10 no. test studs. These studs shall be bent to an angle of 30 degrees from their original axis by placing a bending bar over the stud and manually bending the stud in the direction of the span of the beam towards the nearest column. Should failure occur, the equipment should be reset and settings adjusted, replacement studs welded and tests repeated to ensure acceptable quality. A record of the WPQR location and settings should be marked on a QA record drawing in line with the requirements of BS EN 14555:2014.
Note: The settings for the WPQR will differ for each site due to numerous factors including; atmospheric conditions, weather, parent steel grade, cable distance, ambient temperature etc.
Surveillance testing
As welding progresses, the ferrules shall be broken away from the base of the stud to enable visual inspection. The broken ferrules are typically left on the deck to be absorbed into the concrete and treated as inert aggregate. All shear studs shall then be ring tested by tapping the head of the shear stud with a hammer, studs that do not give a resonating ring sound should be bend tested.
Bend testing must be carried out as described in the Pre-Start (WPQR), but to an inclination of 15 degrees (1 in 4). The bend test shall be carried out to the greater of 5% or at least 2 no. studs per beam. Should a shear stud fail in any location, three studs on either side should also be tested.
Any failing studs will need to be replaced. Tested and failed studs shall be noted and marked up on a QA record drawing.
When testing shear studs reference should be made to the manufacturer’s instructions, BS EN 1994-1-1, BS5950: Part 3: Section 3.1, BCSA Code of Practice for Metal Decking and Stud Welding, National Structural Steelwork Specification and BS EN ISO 14555:2014.
Refer Nelson Stud Welding – Application Information: Removal of Broken Ferrules - WTD (31/01/2006). Stud welding at low temperatures – D.J. Laurie Kennedy
11.6.1 Removal of broken ferrules
To comply with the American Welding Society (AWS) Construction Welding Code, Steel, D1.1, the ceramic ferrules used for stud welding process must be broken and removed from the welded studs in order to conduct the required visual inspection. A WS D 1.1 Section 7.4 Workmanship paragraph 7.4.6 Arc Shield Removal reads as follows: "After welding, arc shields shall be broken free from studs to be embedded in concrete, and, where practical, from all other studs". The visual inspection involves being sure that there is a full 360 degree weld flash.
The question is frequently asked: "When studs are welded through metal deck to steel beams, is it necessary to remove the broken ferrules from the deck prior to pouring the concrete slab?"
The ceramic ferrules used for stud welding are made from a fireclay mixture that is compressed with organic binders. The ferrules are then fired at temperatures approaching 2300 degrees F. As such, they are totally inert and have no ingredients that would react with or be detrimental to the poured concrete. After firing, the ferrules are similar to standard duty refractory bricks and have a density of 140-150 pounds per cu.ft. The compressive strength of the fired ferrules is approximately 10,000 psi.
The ferrule material meets the requirements of the ASTM C-330 specification for the aggregate material. This specification is the most frequently used specification regarding the aggregates that are to be used for making concrete.
During the studs welding process, the interior cavity of the ferrule undergoes a second "firing". The inside of the ferrule is exposed to the weld arc and comes in contact with molten steel. A layer of the inner surface of the ferrule actually melts, becoming vitrified. The exposed surface becomes like glass or the glaze that is on the exterior of pottery or ceramics. The cavity portion of ferrules that have been used for welding is even harder than unused ferrules.
The broken ferrules on the deck should not be collected into clumps or piles. If they are left scattered and loose on the decking they should become adequately wetted and mixed with the concrete as it is poured. They will simply be added to the aggregate in the concrete mix as the concrete. The broken ferrules will not interfere with the placement or strength of the concrete.
Based on the facts that broken ferrules represent only a small quantity of material, they have good compressive strength, and they will not absorb much water, it is the opinion of Nelson Stud Welding that broken ferrules left on the decking will have no adverse effect on the strength or performance of the concrete.
Unless the contract contains a statement that requires the removal and disposal of the broken ferrules from the deck, it is our opinion that broken ferrules are not detrimental to the strength of the concrete and that it is not essential that they be removed from the metal deck before the concrete is poured.
The above text and guidance is extracted from Nelson Stud Welding Inc (Ohio) technical statement dated 31/01/2006
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