Understanding the Role Welding Metallurgy Plays in Infrastructure Projects
Welding metallurgy is a critical component in infrastructure projects, but it’s often not completely understood among certain communities. With greater knowledge of welding processes and techniques, design-build teams may save money, reduce project ...
Welding metallurgy is a critical component in infrastructure projects, but it’s often not completely understood among certain communities. With greater knowledge of welding processes and techniques, design-build teams may save money, reduce project liability, and improve profitability.
Designers of welded structural components should have some measure of knowledge and experience involving the fabrication of building components. This would include operations such as the following:
-Cutting, forming, and shaping metals;
-Assembly of components;
-Preparation and execution of welded joints; and
-Weld acceptance criteria, which would include any mechanical, nondestructive, or other testing or examination protocols.
Fig 1: Ultrasonic testing of a weld to ensure joint quality.
In addition, critical areas that design-build teams should know about include the following:
-Weldability of metals,
-Variations in welding procedures,
-Thermal effects of welding, and
-The effects of restraint and stress concentration.
Outlined in this article are a few key concepts to consider that will ensure a more successful outcome.
The Role of the Welding Engineer
The welding engineer may be called upon to evaluate the proposed design details, the properties of the selected materials, and the suitability of welding processes and procedures. This may also include inspection recommendations to ensure the soundness of the welded joints to a quality level commensurate with the anticipated service.
Fig. 2: A welding engineer will get involved when problems arise with misalignment measurements.
While considering the above-listed details, the welding engineer will consider the weldability of the proposed material. The term weldability is not simply an arcane technical expression. It describes a significant material characteristic that must be thoughtfully considered. It further describes the relative ease with which a material may be welded. It should be noted that the chemical composition of the material looms large as a principal factor influencing weldability.
Welding engineers are good resources for design, material, and process selection. They can review joint design, analyze process and procedure selection, manage revisions, and oversee the project. Fabricators will often decide on processes, but a welding engineer will assist with the design and configuration.
At times, there can be a cavalier view about welding as well as the confident assurance that “If we weld this, it’s good” and “We don’t have to worry about it.” However, if that were always true, we wouldn’t have visual inspections and other special inspections, nondestructive examination (NDE) regimes, and mandated state along with federal infrastructure inspections on a periodic basis. What follows is an example of the importance of understanding weldability.
A Constructional Steel Case
Consider a constructional steel undergoing a welding operation. In the course of that operation, the local material is subjected to an extreme thermal event with consequent structural, dimensional, and compositional changes, which have a significant bearing on weldability. The resultant heating from the welding operation causes significant metallurgical modification in the immediate vicinity of the weld. Such changes influence the internal structure or microstructure of the material. Changes in the microstructure will influence the mechanical properties of the material.
Why is this important? Because changes in the mechanical properties will affect the behavior of the material to various conditions of loading.
Additionally, there is always the risk of consequential degradation of the mechanical properties in such heat-affected areas. In particular, the region immediately adjacent to the weld, which is known as the heat-affected-zone, is profoundly affected. This discreet area is often vulnerable to metallurgical changes that can be pernicious.
Therefore, appropriate countermeasures must be implemented to mitigate such potentially harmful effects. This would indicate that established welding metallurgical tools be employed as a matter of routine.
Selecting the Ideal Welding Partner
Seek out professionals who have experience and, most importantly, are conversant — not just in one particular narrow subject matter but more broadly across topics — in welding metallurgy.
Focusing on the Bigger Picture
There are welding engineers and engineering-technician types who can be extremely valuable, often having more exposure to the bigger picture than those doing design work. Unquestionably, such persons possessing technical expertise and relevant experience are very valuable. For example, Atlas Evaluation & Inspection Services (AEIS), South Plainfield, N.J., a provider of inspection, testing, certification, failure analysis, engineering, and material research services for infrastructure projects with an emphasis on welding metallurgy and NDE, must have individuals like that.
Good communication between the designer and fabrication shop is essential as well. There are often hundreds of shop drawings derived from many pages of a contract, but oftentimes, the design must be reconfigured. The design reconfiguration must be done properly to ensure a successful outcome and is often both time and labor intensive. Giving consideration to these things on the front end will permit streamlining of reconfiguration.
A recent crack discovered in the Hernando DeSoto Bridge in Memphis, Tenn. (Ref. 1), has put a new emphasis on testing and inspection. And reflecting on historical incidents, such as the Alaska oil pipeline that had 3955 “problem welds” (Ref. 2), insufficient welding and inspection can cost project owners. What’s more, project failures of this scope can have catastrophic effects on people and the environment, compromising public safety. Therefore, it behooves construction teams to partner with experienced and accredited welding metallurgy professionals throughout the lifespan of a project.
At the end of the day, engineers and design-build teams want the same result: safe, reliable projects built with a high level of quality and integrity. Understanding the welding metallurgy building blocks of a project will get project teams much closer to that positive end result.
Tennessee Department of Transportation. Interstate 40 Hernando DeSoto Bridge. tn.gov/tdot/projects/region-4/i-40-hernando-desoto-bridge.html
Cowan, Edward. 1976. Weld cracks found in Alaska pipeline; costly delay feared. nytimes.com/1976/05/22/archives/weld-cracks-found-in-alaska-pipeline-costly-delay-feared-cracked.html
This article was written by Richard Pimpinella and Nagesh Goel for the American Welding Society.