Low hydrogen electrodes

Low hydrogen electrodes are normally required to produce the necessary strength and toughness, although sound welds can be made with rutile electrodes, especially in thin section. 

Scrap materials often can be put to good use. When using scrap, however, it is best to weld with a low-hydrogen E7016-18 type of electrode, since the analysis of the steel is unlikely to be known, and some high-carbon steels may be encountered. Low-hydrogen electrodes minimize cracking tendencies. Structural scrap frequently comes from dismantled structures such as elevated railroads, which used rivet-quality steel that takes little or no account of the carbon content. 

Note E6010-11 and E7010-11 are cellulosic electrodes. All others are low-hydrogen electrodes and are better suited to welding higher-strength steels. 

Low-carbon unalloyed steels andlor low-alloyed steels. For thin-sec-tion, unalloyed materials, these materials can normally be readily welded. However, when welding thicker-section material with a flux process (MMA), there is a risk of HAZ cracking and low-hydrogen electrodes need to be used. The more highly alloyed materials also require preheat or a low-hydrogen welding process to avoid HAZ cracking. 

Ni Steels, CrMo, and CrMoV creep-resisting steel. Thin-section material may be welded without preheat, using a gas-shielded process (TIG and MIG) for thicker-section material, and when using a flux process, preheat with low-hydrogen electrodes (MMA) is needed to avoid HAZ and weld metal cracking. Postweld heat treatment is used to improve HAZ toughness. 

Low hydrogen electrodes should be used when welding high carbon steels to reduce chance of hydrogen cracking. 

If the wall thickness is less than 0.250 in (6.4 mm), there may be a need to take special precautions to minimize the risk of bum-through. These precautions include minimizing the penetration of the arc into the pipe wall by using small-diameter, low-hydrogen electrodes and a procedure that hmits heat input. 

For in-service welding applications, low-hydrogen electrodes in smaller quantities (e.g., 10-lb (4.5-kg) cans) (Figure 4.14) should be specified. This is particularly true for smaller jobs (e.g., small-diameter lines) where it would be difficult to use an entire 50-lb (22.7-kg) can. Howcvct, there may also be a price premium for this type of packaging. 

Low-hydrogen electrodes with the H4R supplemental designator (e.g., E7018-H4R), packaged in small quantities hermetically sealed cans are ideally suited for in-service welding. 

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