By Sue McCraven
When acetylene and oxygen from pressurized cylinders meet a spark, a 6,000 F welding torch is created with a flame hot enough to melt through steel. Known as “hot work,” welders and pipefitters use regulated torches to cut or fuse pieces of metal. And as high temperatures, an ignition source, potential fumes and job site conditions are linked with the trade, a welding professional requires constant training, skill and safety awareness.
Technology is transforming the welding industry from an art to a technical and scientific trade with improved work conditions, thanks to health and safety regulations. This article is a refresher on safety and welding terms, but cannot cover all OSHA and American Welding Societyi (AWS) regulations and guidelines. According to AWS, the next edition of the Structural Welding Code – Reinforcing Steel D1.4, will be issued in late 2016 or early 2017, so specific code changes won’t be known for the next year while the draft is developed.
Precast welding requires constant awareness
With more than 40 AWS Safety & Health Fact Sheets for welders, including everything from burn protection, combustible dust, glove selection, confined spaces, and electrical hazards, plant welders need to regularly review the trade safety rules and regulations.
Welding performed at precast concrete plants includes fabricating metal forms or positioning reinforcement bars and welded wire assemblies. Tack welding of reinforcing bars is not recommended, because it can create “notches” in the bar that decrease the steel’s yield strength and compromises the concrete durability.ii All welded splices for reinforced concrete must conform to AWS D1.4:2005, Structural Welding Code – Reinforcing Steel.
Yet more often, a precast plant welder may be called to fabricate, modify or repair a variety of equipment – forklifts, trucks, hitches, pipes, mixers and, most critically, lifting device welding – a skill requiring certification. Workplace risks grow as welders employ different methods as materials and site conditions vary. For this reason, a welder must be well trained and qualified to work on many materials with a range of tools.
To see a more comprehensive list of all AWS Safety & Health Fact Sheets, visit aws.org/technical/facts.
Welding safety: new OSHA standard
OSHA is preparing to release a new set of HazCom requirements, warnings and safety data sheets for workplaces as part of its new GHS Hazardiii Communication Standard. The AWS committee advised the new rule would affect precast concrete plants specifically by proposing to reduce the permissible exposure limit (PEL) to crystalline silica. Crystalline silica dust is a basic component in soil, sand, granite or other minerals. When breathed in, it can cause severe health problems. “This should be the most significant single regulatory-change impact to hit this industry in some time,” said AWS committee members. For more details and deadlines, visitosha.gov/dsg/hazcom/HCSFactsheet.html
Unlocking the jargon
In addition to a myriad of potential hazards and their corresponding safety rules, the welding profession uses numerous acronyms, some of which can cause confusion. AWS members say the biggest acronym confusion is MIG and TIG as opposed to GMAW and GTAW. Here are the five most common acronyms used:
• SMAW – Shielded Metal Arc Welding is also known as MMW, Manual Metal Arc Welding, and is one of the most prevalent and versatile types of welding. SMAW is commonly known as “stick welding” and requires more time to accomplish, because the consumable electrode rod (usually steel filler material) requires frequent replacement. The welding rod is coated with flux, and after completing the weld, the slag (residue from the flux) must be removed.
• MIG – Metal Inert Gas welding combines two pieces of metal using a consumable wire connected to an electrode current. MIG’s faster welding speed is due to a continuous wire feed passing through the welding gun at the same time as the inert gas. The inert gas protects the electrode from contaminants. MIG is also known as GMAW, and its electric arc can generate very high temperatures – from 6,000 F to 43,000 F.
• TIG – Tungsten Inert Gas welding uses nonconsumable tungsten along with an inert gas and is typically used to weld thinner pieces of material together. While TIG welding requires more skill and time to set up, it produces a precise, high-quality weld and generates fewer fumes and sparks. The tungsten electrode provides the electricity, creating a weld where one part melts into the other. TIG can also use a separate filler material. TIG is also known as GTAW, a process most often used on stainless steel and light metals, and can produce temperatures of up to 35,000 F.
• FCAW – Flux Cored Arc Welding uses the flux of the welding wire in the center of the electrode instead of on the outside. This more rapid, expensive welding process uses feed spools and cable rather than stick-welding’s solid rods.
• SAW – Submerged Arc Welding uses a continuous wire feed and covers the arc beneath a layer of flux so that no fumes or airborne contaminants are produced. SAW is known for its high productivity – rapid wire deposit rate – and improved working conditions. Because SAW uses a high-quality arc and rapid welding, it is commonly used on large industrial products, such as pressure vessels.
Spot vs. tack welds
As with numerous acronyms, there is also confusion about the difference between “tack” and “spot” welding.
Tack welding is an important first step where the welder deposits separate short beads to properly position, align and secure pieces together using filler material prior to final welding. Tack welds save time and effort in assembly, because if a misalignment or defect is noted, tack welds are easily removed to correct the problem.
Spot welding is the final step, using both pressure and heat – with no filler material – to permanently fuse two pieces together. Spot welding is used mainly on foils or thin materials that have a thickness of a ¼ in. or less. The simplest way to remember the difference between tack and spot welds is tack welds are a preliminary step for positioning and securing pieces for welding, whereas spot welding is the final and permanent join.
Welders earn respect
Skilled welders are responsible for properly assembling, repairing and modifying our industrial equipment and the infrastructure and buildings where we work and live. The welder’s dedication to precision and safety merits the respect of those who work under less arduous conditions.
For this reason, proper ventilation and protective gear – helmets, gloves, cotton clothing and quality eye protection – are critically important. It is exposure to potential toxic, carcinogenic fumes and chemicals, from either the welding gases themselves or from cleaners, paints and sealants used on welding surfaces that pose the greatest threat to welders.
Sue McCraven, NPCA technical consultant and Precast Inc. technical editor, is a civil and environmental engineer.
i The American Welding Society develops and publishes standards that apply to welding and related disciplines.
ii See “Hot Topic: Welding Reinforcement” by Claude Goguen, March-April 2011 Precast Inc. magazine
iii Globally Harmonized System of Classification and Labeling of Chemicals (GHS)