Experimental methods of hydrogen testing to prevent Hydrogen Assisted Cracking (HAC) during the Submerged Arc Welding (SAW) process

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Experimental methods of hydrogen testing to prevent Hydrogen Assisted Cracking (HAC) during the Submerged Arc Welding (SAW) process

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Abstract

One of the main problems associated with the welding of ferritic steels is that of hydrogen assisted
cracking (HAC), popularly known as cold cracking or delayed cracking. As the name suggests, it is
caused by hydrogen present in the weld metal. One of the methods to mitigate this type of cracking is to
control and minimize the amount of diffusible hydrogen content in the welds. This in turn calls for
standard test methods to measure diffusible hydrogen present in weldments made with different welding
consumables, processes etc. The methods employed to measure hydrogen vary from simple manometer to
sophisticated mass spectrometers and sensors. The present volume of this paper highlights identification, causes and factors responsible for hydrogen cracking. Each factor influencing the risk of hydrogen cracking is described in detail with clear figures and mathematical formulation. Different methods of measurement of diffusible hydrogen and methods of hydrogen testing are also covered. The paper explains the welding procedure of hydrogen testing using SAW (submerged arc welding) process. T

Abstract of the study
Introduction
Idetification: Visual appreance of hydrogen cracking
Definitation of Metallography
Factors that cause hydrogen cracking
Main factors that influence the risk of cracking
Methods of hydrogen testing
Conclusion
Reference

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[...] The main source of hydrogen is the moisture present in the flux coating of the welding electrodes in the case of shielded metal arc Hydrogen cracking can happen during various manufacturing operations or operational use, anywhere where the metal comes in contact with atomic or molecular hydrogen. Processes which can lead to this include cathodic protection, phosphating, pickling, and electroplating. A special case is arc welding, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special lowhydrogen electrodes are used for welding highstrength steels). [...]

[...] In stead of 24 hours, it is only 6 hours with gas chromatography and is almost instantaneous if the arc hydrogen sensors are used. Instead of diffusible hydrogen content which requires separate specimen preparation and long time completion of measurement, hydrogen in the welding arc would be used as a parameter to assess the susceptibility of the weld to cracking and with the help\of intelligent welding systems, welding parameters would be suitably altered to prevent cracking REFERENCES: [1]Jewett, R.P. (1973), “Hydrogen Environment Embrittlement [...]

[...] weave width /dwell MEASUREMENT HYDROGEN: OF DIFFUSIBLE Preparation of weld specimen: One of the methods used to mitigate this type of cracking is to control and minimize the amount of diffusible hydrogen content in the welds. This in turn calls for standard test methods to measure diffusible hydrogen present in weldments made with different welding consumables, processes etc. Measurement of Hd essentially consists of: Preparation of the weld specimen, Determination of hydrogen, Methods recommended for preparation of the specimen vary marginally in different standards that give detailed procedures for diffusible hydrogen measurements. [...]

[...] Transgranular cracking is more often found in C-Mn steel structures OF weld metal hydrogen parent material composition parent material thickness stresses acting on the weld during welding or imposed (shortly) after welding heat input HYDROGEN 5.1 :WELD METAL CONTENT: Fig. Crack along the coarse grain structure in the HAZ In fillet welding, cracks in the HAZ are usually associated with the weld root and parallel to the weld. In butt welds, the HAZ cracks are normally oriented parallel to the weld bead. [...]

[...] Hydrogen generated by the welding process, or by contamination of the weld area. A hard brittle structure, which is susceptible to cracking. Residual tensile stresses acting on the welded joint (restraint) In C-Mn steels, because there is a greater risk of forming a brittle microstructure in the HAZ, most of the hydrogen cracks are to be found in the parent metal. With the correct choice of electrodes, the weld metal will have a lower carbon content than the parent metal and, hence, a lower carbon equivalent (CE). [...]

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