Introduction
Welding is a vital topic for structural engineers, but they rarely have the opportunity to study it. Several welding-related myths continue to circulate, typically by well-intentioned but ignorant professionals. These fallacies persist in the absence of proper structural engineering training to refute such assertions. Because many structural frames require field welding during assembling operations, structural engineers must be familiar with the welding process. This article aims to list all the important points essential for Structural Engineers.
Source: Havit Steel Structure
Properties of Metals
Every metal has certain physical qualities that can be adjusted or altered during welding. Knowing what these properties are and how they might change will help us change our process when we run into challenges.
– Ductility
The ability of a metal to be permanently bent, twisted, or otherwise manipulated without breaking or shattering is referred to as ductility. Ductile metals include mild steel, copper, aluminum, and zinc.
– Hardness
Hardness refers to a material’s ability to resist a permanent change in shape when subjected to an external force. Some metal’s hardness can be reduced by heat, while others can be increased by cold.
– Conductivity
The ability of a metal to transfer or conduct electricity and heat is referred to as electrical and thermal conductivity. When welding, mass is important because one piece of metal in the welding area can move heat quicker than another.
– Brittleness
Brittleness refers to a material’s propensity to fail or fracture when subjected to a minor shock, stress, or impact. Brittleness and hardness are inextricably linked, as when metal’s hardness rises, so does its brittleness.
Weldment Design
The connecting of two separate metal parts into one weldment assembly is called a weldment. In other terms, a weldment is the result of multiple pieces of metal being welded together. The type of weldment assembly produced is determined by the weldment design.
Source: Weldment Design, LLC
Welded Design Consideration
Some of the general principles involved in welding are:
- It is advisable to choose a material that is easy to weld. Low carbon steel is generally easier to weld than high carbon steel as higher carbon concentration causes the welded joint to harden, making it more vulnerable to cracking.
- It is recommended to use the fewest number of welds possible. In welded assemblies, distortion is a major issue as it makes it difficult to keep finished assemblies in the correct shape, size, and tolerances.
- The designer should specify standard sizes for plates, bars, and rolling sections.
- The welded junction should be placed in a location with minimal loads and deflection. It should also be placed so that the welder and welding machine have unrestricted access to it.
Types of Welding
There are several methods of creating weldments like arc welding, electroslag welding, gas metal arc welding, tungsten inert gas welding, plasma arc welding, and sheet metal arc welding.
- An electric arc fuses a base or parent metal with the additional metal in arc welding with a direct current or an alternating current.
- Electrosag welding is generally utilized for big horizontal weldments that need the joining of two massive plates.
- Metal inert gas welding, also known as gas metal arc welding, is a method of welding that uses a gas to protect the welded area.
- Tungsten inert gas welding, also known as gas tungsten arc welding, uses tungsten electrodes as part of the arc to provide the heat required to weld the metal.
- In shield metal arc welding, the heat generated melts the coated electrode and the metal being welded together, resulting in an alloy of the welded metals.
- In plasma arc welding, electrodes and ionized gases form a highly hot plasma jet directed at the weld area to melt the metal.
Advantages & disadvantages
Some of the advantages of welded joints are:
- Welded joints are more cost-effective since they need less work and material.
- The welded joint has a higher efficiency than the riveted joint.
- Unlike riveting, there is no noise made during the welding process.
- In comparison to riveted joints, the fabrication pace is faster.
Some of the disadvantages of welded joints are:
- Welded joints are more brittle than connected members; hence their fatigue strength is lower.
- Internal air pockets, slag inclusion, and partial penetration are among the most challenging defects to identify.
- Welding involves both skilled work and electricity.
- Because welded connections do not allow for expansion and contraction, racks are a viable option.
Welding symbols
Standard symbols can be used in a drawing to give you more control over the aesthetic and mechanical attributes of the finished fabrication.
Some of the types of welding symbols are:
- The tail – The tail is attached at the end of the reference line opposite the arrow with a greater-than or less-than sign.
- An arrow line – The arrow is the first element of a welding sign to examine. It is a required component of any welding symbol and must point to the welded junction.
- A reference line – A reference line is a horizontally drawn straight line related to the arrow on a drawing. The arrow can be connected to the reference line at either end.
Source: Arc Helmets
- Fillet welds – The fillet weld sign is a right triangle with the perpendicular leg on the left, placed on the reference line.
Edge Preparation
Any of the following processes should be used to prepare the welded edges to meet the joint design requirements:
- Carbon steel: Methods such as gas cutting, machining, or grinding must be utilized. Oxides must be removed after gas cutting by chipping or grinding.
- Low alloy steels: Gas cutting, machining, or grinding processes must contain up to 5% chromium. On the cut surface after gas cutting, machining or grinding is required.
- Nickel alloys, high alloy steels, and stainless steels: Methods such as plasma cutting, machining, or grinding must be used.
Levels of Inspection
Inspectors should carry out the following tasks:
- Before welding – It involves reviewing drawings and codes, understanding weldment requirements, etc.
- During welding – It involves quality assurance, welding examinations, etc.
- After welding – It involves NDE review, documentation audit, etc.
Acceptance Criteria
Some of the typical requirements of weld products include-
- The product must be finished precisely to the dimensions specified in the design.
- The product must have the necessary functionality and durability.
- The weld’s look must meet the acceptable standard.
- Full penetration welds that fuse and unite the whole interface between the base materials or weld joints containing partial penetration welds should be employed to provide the required stiffness.
Conclusion
Professional engineers who wish to take the structural engineering certification exam should be aware of the different welding methods, welding joint measurements, and welding angle criteria. Furthermore, all the above information is essential for structural engineers to develop an economic and well-designed metal for the industry.
References
- Piping Engineering, “Edge Preparation and Alignment for Welding of Pipes”
- NBBI, “Welding Symbols: A Useful System or Undecipherable Hieroglyphics?”
- Sam Fabrications, “Welding Symbols”
- School of PE, “AN INTRODUCTION TO WELDING FROM A STRUCTURAL ENGINEERING PERSPECTIVE”
- SE University, “Welding Myths that Structural Engineers Need to Know About”
- Tulsa Welding School, “What Are the Mechanical Properties of Metals?”
- Longevity, “PROPERTIES OF METALS AFFECTED BY WELDING AND HEAT”
- Welding Handbook, “Guide To The Types Of Metals (Updated Nov 2021)”
- Wise Geek, “What is a Weldment?”
- Engineers Arena, “Design Considerations of Welded Assemblies | Machine Design”
- Mecholic, “Advantages And Disadvantages Of Welding Joints”
- Civilblog, “WHAT ARE THE ADVANTAGES AND DISADVANTAGES OF WELDING JOINTS?”
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