Arc cladding, also known as welding arc cladding, is the process of applying an alloy layer to a component to impart a desired property, such as hardness or corrosion resistance. The process is conducted with different arc welding processes, including gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), plasma transferred arc welding (PTAW), and shielded metal arc welding (SMAW), allowing components to be enhanced for demanding environments without having to replace the entire part. The process uses a welding arc to fuse a filler metal as the cladding material to a base metal, creating a metallurgically bonded layer that is typically between 2 and about 20 mm thick.
Our decades of expertise in arc cladding has allowed us to work on projects for a range of industries and applications:
- Effect of Flux Cored Arc Welding Conditions on Microstructure and Abrasive Wear Resistance of Two Iron-Based Hardfacing Alloys
This 1986 core research project was created to produce guidelines for fabricators to follow when using hardfacing consumables to deliver improved wear resistance to components. These surfaces create cost savings by reducing maintenance and replacement costs as well as avoiding unexpected down-times as a result of breakdowns. The key to the guidelines was to be able ensure maximum wear resistance whilst maintaining cost-effectiveness through adequate deposition rates. The study investigated two iron-based self-shielded flux-cored arc welding abrasion resistant consumables; a low alloy steel of composition 0.5%C, 6.0%Cr, 1.2%Mo, O.3%Ti and 1.0%Mn, and a high chromium austenitic iron containing about 5.0%C, 1.0%Mn, 22.5%Cr and 5.5%Nb. Weld pads were fabricated from these consumables, with varying current, voltage and electrode stickout, and samples were taken for laboratory wear testing, metallography and chemical analysis. Correlations between the wear test data, welding conditions and deposit microstructure were then created.
- Cladding Disbonding Explored
Our work with arc cladding also included research into the resistance of cladding to in-service, hydrogen-induced disbonding. This project began after the Japanese JGC Corporation placed an order for the fabrication of a number of heavy wall pressure vessels from 2 1/ 4Cr-1Mo steel for hydrogen service at high temperatured and pressures. The fabricator, Rotterdamsche Droogdok Maatschappij BV (RDM), proposed to apply an internal single layer austenitic stainless steel cladding to the vessels, deposited by submerged-arc or electroslag welding and designed to have type 347 composition instead of the conventional two layer 309L/347 cladding. Our experts applied a standard hydrogen charging procedure to the samples that were either subjected to a single post-weld heat treatment (30hr at 690◦C) or to a second, lower temperature heat treatment (5hr at 600◦C). An ultrasonic (C-scan) examination then determined the extent of any disbonding after an incubation period at room temperature. The results found that the two-stage heat treatment reduced disbonding susceptibility, leading to a lower peak hardness in the cladding/base metal interface region where disbonding occurs.
- Welding CRA Clad Materials: Three Layer Butt Weld Trials
In 2012, our experts undertook an investigation into the feasibility of using a buffer layer approach for welding of corrosion resistant alloy (CRA) clad/lined pipes, as an alternative to the current approach of using CRA weld metal. This core research project was a progression of previous work that described the disadvantages associated with the current industrial practice of using CRA weld metal for circumferential welds in clad/lined pipes. The main issue for the use of nickel alloy consumables, was that the resulting weld metal might under-match the strength of parent materials at high operating temperatures (above 140°C) for high-strength-grade pipes (X65 and above). A buffer layer approach promised the potential to overcome this issue by enabling the use a carbon steel filler metal to overmatch the pipe properties, as well as lowering consumable costs, particularly for thick-walled pipes.
- Mechanically Lined Pipes (MLP) Project Launched
Our knowledge of arc cladding was also used in a comparative nature on a joint industry project that assessed the use of mechanically lined pipes (MLPs). Clad and mechanically lined pipes are used to transport corrosive production fluids in the oil and gas industry. With clad pipes the corrosion reistant alloy (CRA) is metallurgically bonded to the pipe’s backing steel, whereas with MLPs, a CRA sleeve is inserted into the backing steel and a weld overlay is used to seal the ends. This project reviewed current and emerging practices as well as existing specifications to capture the current state-of-the-art for the manufacture and safe use of MLP. This review allowed us to identify gaps in existing guidance so that future research can be focussed to address them.