Preventing Hydrogen-Induced Cold Cracking in Welding Operations

Hydrogen-induced cold cracking (HICC) poses a significant risk in welding processes, potentially leading to structural failures long after the welding is completed. This phenomenon requires three conditions: the presence of hydrogen, a hard and brittle microstructure, and tensile stresses. If any one of these factors is eliminated, HICC can be effectively prevented. Proactive measures are not only more cost-effective than remediation but also essential in ensuring safety and reliability in welds.

Understanding Hydrogen Sources in Welding

Hydrogen can infiltrate the weld metal from various sources, including the welding process itself, environmental factors, and contaminants. The welding techniques chosen can greatly influence hydrogen levels. For instance, processes like GTAW (Gas Tungsten Arc Welding), SAW (Submerged Arc Welding), and GMAW (Gas Metal Arc Welding) are capable of producing welds with minimal hydrogen content.

When these methods are impractical, SMAW (Shielded Metal Arc Welding) with low-hydrogen electrodes such as E7018-H4 or E7018-H8 can be employed. However, proper storage of these electrodes is crucial. They should be kept in hermetically sealed packages and transferred to heated storage immediately upon opening. Any electrodes that have been outside of a controlled environment for more than four hours must be discarded or reconditioned by qualified personnel to maintain their effectiveness.

Effective Techniques for HICC Prevention

A significant source of hydrogen contamination comes from hydrocarbons like grease, oil, paint, and rust. The intense heat generated during welding can decompose these compounds, releasing hydrogen into the weld. Therefore, thorough cleaning of the weld joint and surrounding area is paramount. Surfaces affected by plasma or oxyfuel cutting may have oxidized layers that trap moisture, necessitating grinding to expose clean metal.

Preheating the workpiece is another effective approach. By slowing the cooling rate, hydrogen has more time to diffuse out of the weldment, resulting in a softer microstructure. Typical preheat temperatures range from 100 to 200 degrees C, depending on material thickness and carbon content. Thicker materials often require higher preheat temperatures to ensure adequate cooling rates. Additionally, employing higher heat inputs during welding and insulating welds post-process can facilitate hydrogen diffusion.

Post-weld heat treatment is particularly beneficial for critical applications, such as piping and pressure vessels. This technique alleviates residual stresses and enhances hydrogen diffusion, thereby reducing the risk of cracking.

Reducing stress in weldments necessitates careful planning. While welders may not always control stresses directly, they can adopt strategies like minimizing weld gaps, avoiding overly constrained joints, and distributing welding tasks evenly. Maintaining low interpass temperatures also contributes to minimizing residual stress.

Inspection of welds is crucial, especially since HICC may not manifest until long after welding. As a result, most welding codes recommend inspections occur at least 48 hours post-welding. Areas that warrant close examination include weld toes, high restraint regions, and locations with stress concentrations.

HICC can lead to significant financial losses and reputational damage, as well as serious safety risks. A systematic approach to preventing HICC starts with identifying materials and applications prone to this risk, particularly high-strength materials and thicker sections. Following established, qualified welding procedures and educating welders and supervisors about HICC dangers are essential components of an effective prevention strategy.

Utilizing appropriate equipment, including proper electrode storage ovens, preheating devices, and inspection tools, is far less costly than addressing the consequences of a single HICC failure. By fostering a culture of attention to detail and education within the workplace, organizations can lay the groundwork for producing crack-free welds.

Jeff Molyneaux, the Executive Director and CEO of the Materials Joining Innovation Centre (MaJIC), emphasizes the importance of these practices. His organization, located at 140 Government Rd. E., Kirkland Lake, Ontario, stands as a resource for promoting best practices in welding and materials joining. For more information, MaJIC can be reached at 705-498-1567 or through their website at www.majic-ca.org.