the general welding characteristics being sought. Solid wires featuring an AWS E70S- 6 classification, as well as metal cored wires such as AWS E70C-6 H4 products, are good options to reduce the opportunity for hydrogen-induced cracking. Metal cored wires with an AWS E80C-Ni1 H4 classification are also good for slightly higher strength properties. Solid wires tend to resist hydrogen pickup quite well as it is difficult for moisture to penetrate the solid steel structure. The copper coating on these wires also offers some protection against moisture. Metal cored wires tend to be nonhygroscopic and, therefore, provide good protection against moisture absorption and hydrogen pickup. While similar in terms of low hydrogen levels and moisture resistance, choosing between solid wires or metal cored wires becomes largely a matter of preference. Solid wires are well known and relatively widely accepted in the industry for high-strength applications; however, for some welding operations, the use of metal cored wires is preferred to gain faster travel speeds and higher deposition rates. Metal cored wires have a tendency to bridge root openings better and are 68 WELDING JOURNAL / APRIL 2015 also capable of minimizing pre- and postweld activities such as grinding due to the ability to weld through mill scale and the production of low spatter levels. Both solid and metal cored wires, due to their formulation, offer smooth welding characteristics, which is a benefit that can be slightly more challenging in flux cored wires offering low hydrogen levels. Maintaining good weldability in low-hydrogen flux cored wires can be a bit of a balancing act for filler metal manufacturers. These wires require the addition of fluoride, which acts like a scavenger to pull hydrogen from the weld pool. The fluoride can sometimes adversely affect the welding characteristics, making the arc flutter or be slightly more difficult to control. Fortunately, formulations have improved drastically over the years, with many smooth-operating flux cored wires being made available in the marketplace. Flux cored wires for low-hydrogen applications can range greatly in strength, with options from 70 ksi (AWS E71T-1MJ H4) up to 128 ksi (AWS E111T1-K3MJ H4) for cracksensitive quenched and tempered steels or for offshore structural fabrications that will be subject to temperature extremes. In addition to standard lowhydrogen flux cored and metal cored wires, there have also been advancements in filler metal manufacturing that can help reduce the opportunity for hydrogen-induced cracking. Seamless wires of both varieties are becoming a more popular option to mitigate cracking risks. These wires undergo a proprietary manufacturing process that eliminates the need to fold and draw the product as with standard tubular wires; they are filled with flux in a single, seamless tube via vibration. In addition to being low hydrogen (the products have an H4 designation), the lack of a seam offers increased resistance to moisture pickup, as does these wires’ copper coating. There is no place for the moisture to accumulate on the surface of the wire and, therefore, less opportunity for hydrogen to be introduced into the weld pool. As a result, these wires are very well suited for welding in challenging climates. Storage Considerations Proper filler metal storage is always important, and caring for lowhydrogen SMAW electrodes and GMAW and FCAW wires is no exception. Low-hydrogen filler metals typically ship from the manufacturer in a hermetically sealed package to protect against moisture pickup and damage. Welding operators should always take care to keep the filler metal packaging intact until ready for use, preferably in a dry storage area, and use clean gloves when handling the product. Low-hydrogen SMAW electrodes require additional care. These must be held in a holding oven at the temperatures recommended by the filler metal manufacturer after being opened. Some job codes may also dictate how long a package of low-hydrogen filler metals can be open and still be used. In the case of SMAW electrodes, the number of times the filler metals can be reconditioned may also be specified. Welding operators should always consult the specifications and codes for the given low-hydrogen filler metal to gain the best results — specifically to minimize cracking that could lead to costly downtime and rework. DERICK RAILLING is product manager, oil and gas, Hobart Brothers Co., Troy, Ohio, www.hobartbrothers.com. Fig. 2 — Using filler metals with low-hydrogen designations helps minimize one source of hydrogen in the welding process. In today’s marketplace, there are several options available for welding high-strength steels, each with their own characteristics that can also benefit the welding process. WJ
Welding Journal | April 2015
To see the actual publication please follow the link above