The electric arc welding process uses an electric arc to generate heat to melt the parent material and the filler material (electrode) to form a molten weld pool in the joint. The electric arc welding method is preferred over other methods due to its affordability.
The most commonly used fastening methods for joining steel members of a steel structure are welding, riveting, and bolting. While riveting and bolting use rivets and bolts to join the workpieces, welding relies on melting the workpieces to fuse it together.
In this article, we discuss the procedure of laying, fabricating, welding, assembling, and erection of steel structure by electric arc welding method.
1. Laying Out Steel Members
- A figure of the steel structure to be fabricated shall be drawn on a level platform to full scale.
- This may be done in full or in parts, as shown in drawings or per the site condition.
- Steel tape shall be used for measurements of the steel members.
2. Fabrication of Steel Members
- In all steelworks, shop drawings shall give complete details for the fabrication of the steel component, including the location, type, length, size, and details of welds. Also, the component shall be prepared prior to the actual fabrication.
- The steel members shall be marked or painted with the identification marks as given in the shop drawings.
- The work of fabrication shall be carried out with great accuracy so that these can be assembled without being unduly packed, forced into position, or strained.
- When built up, the members shall be true and free from twist, kinks, buckles, or open joints.
- The templates shall then be marked on the steel members, and places of welding shall be indicated on them.
- The ends of the steel members shall be marked for cutting as per the required dimensions.
- The steel section shall be straight or be straightened or flattened by pressure and shall be free from twists.
- No two pieces shall be welded or joined to make up for the required length of the member.
3. Electric Arc Welding
- All the welding of steel members shall be carried out by the electric arc process.
- At the places where electricity is not available, gas welding method shall be used using an oxyacetylene flame.
- The welding shall be carried out only by fully trained and experienced welders.
- The welding process shall be done as shown in the shop drawings, which should indicate all the details of the joints to be welded, shop and site welds, type of welds, and types of electrodes to be used.
- As far as possible, effort shall be made to limit the post-erection welding to avoid the improper or faulty welding that is likely to occur due to heights and difficult positions on scaffolding, etc., apart from the aspect of the economy.
- The maximum diameter of electrodes for welding any work shall be as per IS: 814 and appendix “B” of IS: 823.
- Joint surfaces that are to be put together shall be free from loose mill scale, rust, paint, grease, or other foreign matter, which may adversely affect the quality of weld and workmanship.
- When welding is carried out in open air, steps shall be taken to protect the places of welding against wind or rain.
- The weld shall correspond to design shapes and dimensions.
- The weld shall not have any defects such as cracks, incomplete penetration, fusion undercuts, rough surfaces, burns, blowhole, and porosity, etc. beyond permissible limits.
- The test and inspection shall be carried out during the welding operation, and approval of finished elements are as shown in Table 1 below-
Table 1: Inspections and Tests for Welding
|Sl.No||Inspection of test||Coverage||Procedure||Evaluation and remedy of defects|
|1||Inspection of weld seam appearance||All welds||Naked eye or lens||All faulty welds shall be rectified.|
|2||Checking of sizes||At least one for each weld seam||Ordinary measuring instruments (Rule template)||Should faulty weld be found, all welds shall be checked and all defects shall be rectified.|
4. Assembling of Steel Members
- Before welding is commenced, the members to be welded shall first be brought together and firmly clamped or tack welded to be held in position.
- The temporary connection has to be strong enough to hold the parts accurately in place without any disturbance.
- Tack welds located in places where final welds will be made later shall conform to final weld in quality and shall be cleaned off before final weld is made.
5. Erection of welded steel Members
- At the time of erecting a welded structure, adequate means shall be employed for the temporary fastening of the members together and bracing the framework until the joints are welded.
- Temporary fastening consists of erection bolts, tack welding, or other positive devices imparting sufficient strength and stiffness to resist all temporary loads and lateral forces, including wind.
- All the different members which shall be fillet welded shall be brought in close contact.
- The gaps due to faulty workmanship or incorrect fit, if any, shall not exceed 1.5 mm. If the gap exceeds 1.5 mm or more, the size of fillet weld shall be increased at such position by an amount equal to the width of the gap.
FAQs on Electric Arc Welding
The electric arc welding process uses an electric arc to generate heat to melt the parent material and the filler material (electrode) to form a molten weld pool in the joint.
The weld shall not have any defects such as cracks, incomplete penetration, and fusion undercuts, rough surfaces, burns, blowhole, and porosity, etc. beyond permissible.