Tube and pipe welding are especially challenging. Today, filler metal manufacturers are formulating new products to address the emerging demands of the industry — from the need to lessen cracking risks to options for faster welding, and more.
Changes in the fabrication industry inevitably bring new challenges, especially to the welding process. New materials, emerging applications and the drive to complete more work with fewer skilled welding operators all impact the manner in which companies approach their operations. Maintaining a high level of productivity and quality, while also finding technology solutions that are cost-effective, is important to remain competitive.
While they represent only a small portion of the total cost of the welding process, filler metals play an integral role in achieving such goals. Today, filler metal manufacturers continue to develop new products that can address the emerging demands of the industry — from the need to lessen cracking risks to options for faster welding and more. These solutions address applications requiring the use of both thick and thinner materials, and help ensure the completed welds have the appropriate mechanical and chemical properties.
Filler metals for cleaner environments
Safety is key in any welding operation — and it’s becoming even more important as companies seek to maintain regulatory compliance, and to attract and retain skilled welding operators with a cleaner environment.
Currently, the Occupational Safety and Health Administration (OSHA) provides environmental regulations at the federal level for weld fume, setting the permissible exposure limit (PEL) of 5 milligrams per cubic meter of air as a ceiling limit for manganese. State requirements for manganese vary. There are also recommendations from the American Conference of Governmental Industrial Hygienists (ACGIH) for manganese levels, which are much stricter. The ACGIH recommends a threshold limit value (TLV) for respirable manganese of 0.02 milligrams per cubic meter of air as an 8-hour time-weighted average.
To help companies ensure compliance and improve the welding environment for employees, filler metal manufacturers have made low manganese flux-cored and metal-cored wires available in the marketplace. These wires generate manganese levels up to 70% lower than standard filler metals and some are also available with low diffusible hydrogen levels to minimize cracking risks that could jeopardize quality.
Modifying the welding process through the use of a new filler metal is on course with the first step in OSHA’s Hierarchy of Controls (Elimination/Substitution) — a four-step process for reducing workplace hazards. Some companies choose to combine a low manganese filler metal with other weld fume management solutions such as fume extraction systems or personal protective equipment (PPE) like a half-mask or powered air purifying respirator (PAPR). These solutions are recommended in collaboration with air sampling conducted by a certified industrial hygienist.
On the left is a weld made with a low hydrogen, metal-cored wire. On the right is a weld completed with a cellulosic (non-low-hydrogen) SMAW electrode. Both welds were completed following the same procedures and submerged in mineral oil to show the presence of hydrogen diffusing from the welds.
Products to reduce cracking risks
In recent years, some industries have transitioned to the use of higher strength materials (typically greater than 70 ksi) to reduce the weight of the final product, and also to gain the necessary properties for service in climates with extreme temperatures. Pipeline construction, offshore fabrication and heavy equipment manufacturing are some examples. Inherent to higher strength materials, however, is a greater tendency toward hydrogen-assisted cracking.
As a result, filler metal manufacturers have seen a trend toward the use of low-hydrogen filler metals to combat that risk. Some material manufacturers actually require the use of these filler metals for applications using their steels as added protection against cracking, and to help fulfill quality and warranty requirements.
As a general rule, low-hydrogen filler metals contain less than 8 ml of diffusible hydrogen per 100 gm of weldment, as indicated by the American Welding Society (AWS) designator of H8. More commonly, companies turn to products with as low as 4 ml of hydrogen per 100 gm of weldment (H4) for added protection against hydrogen-assisted cracking.
Low-hydrogen filler metals come in a variety of options, including solid, flux-cored and metal-cored wires. Formulations for flux-cored wires, in particular, have undergone advancement in recent years that have significantly improved their weldability while still offering low hydrogen properties. Companies are increasingly turning away from low-hydrogen stick electrodes due to the frequent changeover and stub loss, which can hinder productivity.
Seamless low-hydrogen flux-cored and metal-cored wires are also now available. The absence of a seam on the surface of the wire eliminates the opportunity for drawing lubricant (which contains hydrocarbons) to become trapped and thereby reduces the chance of hydrogen entering the weld pool and causing cracking. These wires also resist moisture pickup when exposed to challenging climates.
Yesterday’s answers won’t solve today’s issues. As materials and processes evolve to address new challenges, staying at the forefront of new welding technologies, including filler metals, is imperative.
The benefits of metal-cored wires
Metal-cored wires have become increasingly popular as a means to improve welding quality and productivity. While not new, they are now more prevalent in industries such as automotive manufacturing, where materials like galvanized steel are being used to reduce vehicle weight to help increase gas mileage. While these steels are valued for their high strength and corrosion resistance at thinner gauges, they pose challenges such as burn-through and subsurface porosity when welded. That challenge is in part due to the protective layer of zinc oxide on the surface and in other part due to the thinness of the steel.
Newer metal-cored wires, classified as AWS E70C-GS, weld efficiently on galvanized steel when paired with a power source providing pulsed welding. This combination offers faster travel speeds than welding with solid wire. E70C-GS metal-cored wires also generate a softer arc, which reduces the risk of burn-through, and improve the penetration profile of the weld joint. This classification of filler metal can also effectively weld through the zinc coating on the surface of the galvanized material to minimize porosity issues.
Metal-cored wires, in general, can provide positive results on a variety of manufacturing and fabrication applications, where faster travel speeds and higher deposition rates are desired.
Options for impact toughness
The need for new energy sources has generated changes that affect the type of filler metals required to complete sound welds. In particular, the service conditions offshore platforms and pipelines encounter are becoming increasingly harsh since they are built in more remote areas with lower temperatures. For example, drilling platforms are now often located in deeper and colder ocean waters.
As a result, there is an increasing need for filler metals that can provide
greater impact toughness properties — the ability to plastically deform and absorb energy before fracturing under rapidly applied stress.
Filler metal manufacturers have responded with the development of wires that
can withstand impacts ranging from 50 to 100 joules (37 to 74 ft-lb) or more at temperatures as low as -60 degrees Celsius (-76 degrees Fahrenheit), or lower in some cases. An added benefit of these filler metals is that they also help reduce cracking risks associated with the loss of toughness that steels experience at sub-zero temperatures.
Typically, these filler metals contain one percent nickel or less. Too much nickel can cause a reaction with the hydrogen sulfite found in oil and gas, which can result in corrosion of the weld and base material.
Additional thoughts
As companies seek ways to improve quality, productivity and cost savings — in an effort to become more competitive and profitable — they require a flexible approach to the changes in the industry. As materials or processes evolve to address new challenges, staying at the forefront of new welding technologies, including filler metals, is imperative. Fabrication needs are likely to continue changing in the coming years and being prepared for potential transitions can help make it easier to address new welding demands.
