As covered in our previous blog post, welding is a fundamental process used to join separate pieces of material into a single, unified piece. This process involves heating the materials to a temperature where they melt or soften, enabling the metals to flow together and form a bond. In structural welding, a filler material is often added from an electrode to reinforce the weld joint and enhance its strength.
Different welding positions are employed based on the orientation of the weld joint and the most efficient method for performing the weld. Here are the main welding positions commonly used in structural welding:
Flat Welding Position:
In the flat welding position, the face of the weld is approximately horizontal, and welding is typically performed from above the joint. This position offers several advantages, including ease of access, cost-effectiveness, and excellent penetration into the base material. Flat welding is commonly used for horizontal joints where accessibility and penetration are critical. This is the most commonly used welding position.
Horizontal Welding Position:
In the horizontal welding position, the axis of the weld is horizontal relative to the ground. For groove welds, the face of the groove is typically vertical, while fillet welds are applied at a 45-degree angle. Horizontal welding is often used for joints that are oriented horizontally, such as connections between beams or plates.
Vertical Welding Position:
In the vertical welding position, the axis of the weld is vertical, perpendicular to the ground. This position requires careful control to ensure proper fusion and penetration of the weld metal. Vertical welding is commonly used for joints that are oriented vertically, such as connections between columns or vertical members.
Overhead Welding Position:
In the overhead welding position, welding is performed from underneath the joint, with the weld metal deposited on the upper surface. Overhead welding presents unique challenges due to gravity, including issues with weld penetration and control of the molten metal. It is often used for welding joints located above ground level or in positions where access from above is limited. This type of welding is commonly used in fieldwork where two assemblies or miscellaneous components require a rigid joint as per design specifications, and the operation cannot be avoided.
Methods of Welding
SMAW (Shielded Metal Arc Welding):
SMAW, also known as manual or hand welding, involves creating an electric arc between a coated metal electrode and the steel components to be welded. The intense heat generated by the arc melts the base metal and the electrode, forming a pool of molten metal. As the arc progresses along the weld joint, the molten metal cools and solidifies, creating a strong bond. The electrode coating serves dual purposes: it forms a protective gas shield around the weld pool and acts as a flux to purify the base metal and remove impurities.
GMAW (Gas Metal Arc Welding)/MIG (Metal Inert Gas Welding):
GMAW, also known as MIG welding, is a fast and economical welding process. It involves feeding a wire electrode from a spool through a welding gun, where it melts and forms a molten mixture with the base metal. An inert gas, such as argon or helium, is fed through a separate conduit in the welding apparatus to create a protective shield around the weld pool, preventing atmospheric contamination. GMAW is widely used in various applications due to its versatility and efficiency.
Fig 2. Methods of welding
Flux Core Welding:
Flux core welding is similar to MIG welding but utilizes a flux-core electrode instead of a solid wire electrode.The flux core contains materials that release gases to shield the weld pool from atmospheric contamination. This method is particularly useful in exposed conditions where traditional shielding gases may be affected by wind or other environmental factors. Flux core welding offers excellent penetration and deposition rates, making it suitable for a wide range of welding applications.
SAW (Submerged Arc Welding):
SAW involves feeding a continuously fed filler metal electrode, along with a layer of granular flux, into the weld zone.The granular flux creates a protective barrier around the weld pool, preventing atmospheric contamination and promoting deep weld penetration. After welding, a layer of slag is produced on the weld surface, which can be easily removed by chipping. SAW is typically used in flat or horizontal positions and is known for its ability to produce high-quality welds with deep penetration and minimal spatter.
Some of the commonly used weld types are fillet welds and groove welds. Visit our previous blog posts to get detailed information.
General Weld Information:
In welding, weld sizes typically increase in increments of 1/16 inch, with a minimum size requirement of 3/16 inch. The strength of the weld is determined by its effective throat, which is the shortest distance from the root to the face of the weld as depicted diagrammatically.
Non Destructive Testing of Welds:
Non-destructive testing methods are crucial for ensuring the quality of welds without compromising their integrity.
Visual inspection, the most common method, involves scrutinizing the joints prior to the commencement of welding to check fit-up, preparation bevels, gaps, alignment and other variables. This is often the only method that is used unless specified otherwise.
Dye penetrant testing is used to detect surface cracks and porosity by applying a red colored dye that seeps into surface discontinuities. This is applied by using a pressure spray can. The dye penetrates any crack or crevice open to the surface.
Magnetic particle testing utilizes iron filings and electric currents to identify defects in magnetic materials by attracting the particles to areas with irregularities. A magnetizing current is introduced with a yoke or contact prods into the weldment to be inspected. This induces a magnetic field in the work, which will be distorted by any cracks, seams, inclusions, etc. located on or near the surface.
Radiographic testing employs X-rays to detect internal flaws within welds, although it tends to be more expensive. In order to be detected by radiography, the crack must be oriented roughly parallel to the impinging radiation beam.
Ultrasonic testing utilizes sound waves to detect internal defects quickly and economically, making it a preferred method for many applications. This inspection process is comparable to radar. (Refer Part 8 of the structural steel manual by AISC).
Symbols of Non-Destructive Examination
A non-destructive examination symbol can include several parts (see figure below). However, only three parts are essential: the horizontal reference line, the arrow, and the examination method(s). Additional details can be added to provide more specific non-destructive examination information if needed.
Sometimes, examination details are communicated through notes, drawings, or references to specifications, standards, or codes. In such cases, these details do not need to be included directly in the symbol.
The tail of the symbol is typically used to include extra information, such as specifications or references required for the examination process.
When used, each part of the symbol has a specific place, as shown in the figure. While there are rules about where each element should be located, this does not mean every element must appear in every symbol. (Refer Chapter 17 ‘Symbols for Nondestructive Examination’, of the ‘Standard Symbols for Welding, Brazing, and Nondestructive Examination manual’ by AWS)
Fig 4. Standard Location of the Elements in the Symbol for Nondestructive Examination
In conclusion, the integration of steel components into robust and dependable structures relies on the meticulous application of bolting and welding techniques. By understanding the anatomy of bolts, the types of bolted connections, and the various methods of welding, engineers can ensure the structural integrity and longevity of steel structures.
Additionally, the careful selection of bolt types, washers, and hole types, along with the appropriate methods of tightening bolts, further enhances the reliability of bolted connections. Welding, with its versatile methods and positions, offers a complementary approach to bolted connections, allowing for the seamless joining of steel elements.
Furthermore, weld symbols provide essential information for welding operations, ensuring precision and accuracy. Finally, non-destructive testing methods play a crucial role in verifying the quality of welds, ensuring that structural integrity is maintained without compromising safety. Overall, a comprehensive understanding of bolting, welding, and non-destructive testing is essential for engineers and fabricators involved in the construction and maintenance of steel structures.
