Advanced Welding Processes: Technologies and Process Control

4.2.1 Improved toughness
Filler materials for arc welding 45
Many structures, particularly in the offshore and cryogenic industries, are
expected to operate at temperatures well below 0 ∞C. Considerable
improvements in weld metal toughness of ferritic materials at temperatures
below –40 ∞C have been obtained by control of electrode formulation and
the addition of nickel. [37] The effect of this improvement on the notch
toughness of a series of ferritic MMA electrodes is shown in Fig. 4.1. [38]
4.2.2 Improved hydrogen control
Hydrogen-induced or hydrogen-assisted cold cracking (HICC or HACC) has
been a significant problem with low-alloy and higher-carbon steels, particularly
when thicker sections are welded. Control of the hydrogen content of the
weld metal may be used to avoid this problem and this control may in turn
be improved by electrode formulation, storage and packing. [39] Particular
attention has been given to limiting the re-absorption of moisture (the main
source of hydrogen) by the electrode coating, which is achieved by careful
selection of the coating constituents and special packaging. Basic hydrogencontrolled
electrodes that will give weld metal hydrogen contents of less
than 50 ml kg –1 with ambient conditions of 35 ∞C and 90% humidity for up
to ten hours after opening the packaging are now available. [40]
4.2.3 MMA electrodes for stainless steel
The operating performance of common austenitic stainless steel MMA
electrodes has been considerably improved by the introduction of rutile (TiO 2)
Crack opening displacement (mm)
1.4
1.2
1
0.8
0.6
0.4
0.2
C – Mn Electrode
2.5% Ni Electrode
0
–50 –40 –30 –20 –10 0 10 20
Test temperature (∞C)
4.1 Improvements in notch toughness for MMA consumables. [38]