African Fusion August 2018

Hybrid electro slag cladding

This paper from the IIW 2018 International Conference of July 2018 held in Bali, Indonesia, details a hybrid electro slag strip cladding (H-ESC) process that better controls dilution lev- els to achieve clean undiluted single layer surface chemistry for all commonly used nickel and stainless steel alloys. H-ESC: A high-speed innovation in electro slag strip cladding Vincent van der Mee, Zhuyao Zhang and Pallav Chattopadhyay

T he application of strip cladding using the electro slag welding (ESW) process to cover large surface areas of vessels for the oil and gas industries has been com- mon over the last few decades. There has been continuous development by welding consumable suppliers to improve this method further, through introduction of high speed ESW flux and specially designed over-alloyed welding strips to achieve required weld metal chemistry in a single layer for some specific alloys. The conventional method, however, had limitations in achieving the desired chemistry in a single layer, among which, the Ni-625 alloy with maximum 5% Fe dilution limit is most notable. A newvariant of electro slag cladding called hybrid electro slag cladding or H-ESC has successfully been introduced into the market by Lincoln Electric, wherein a 3 rd dimension has been added to the conventional ESWstrip cladding technique, in the form of the addition of multiple hot metal cored wires into the molten electro slag weld pool. The addition of mul- tiple hot coredwires in a particular proportion into themolten weld pool by a uniquely designed digital weld control system helps in controlling the dilution level, thereby achieving clean undiluted cladding chemistry coupledwith at least 50%higher welding speed and nearly double the weld deposition rate as compared to conventional ESW cladding techniques. In this newhigh-speed single layer cladding technique that uses neutral flux, it is possible to achieve an Fe content of less than5%forNi-625clad layersandgreater than40%Ni inasingle Ni-825 clad layer. Similarly, this new technique offers unique solutions in case of high speed single layer austenitic stainless steel cladding, wherein only one standard stainless steel strip type is usedalongwithneutral flux to easily achieve thedesired AWS clean weld metal chemistry for SS 308L, SS 316L, SS 347 andSS317L layersbyusing suitablydesignedmetal coredwires.

Table 1: Comparisons of deposition rates for different weld cladding processes. Such solutions help fabricators immensely in minimising working capital and for receiving faster deliveries of weld con- sumables, in addition to reaching desired 3.0mmof undiluted weld metal chemistry while using a high-speed, single layer clad layer of only 3.5 mm thick. On the industrial applications’ side, Walter Tosto SpA – Italy supported Lincoln Electric as a partner in successfully implementing this new technique for the first time in theworld by applying single layer high speed SS 347 cladding using 60×0.5 mm and 90×0.5 mm wide consumable strips on Cr-Mo vessels. Introduction In the oil and gas industries for vessels dealing with highly corrosive service fluids, applying a protective layer is manda- tory. This protective layer is called cladding. There are various methods of applying clad materials to protect the substrate. Weld overlay is the most commonly used method as it offers high reliability to plant owners as well as high degree of flex- ibility for fabricators (Figure1). The process of cladding is very sensitive and can take up to months under precise controlled quality procedures. The weld overlay process, therefore, has been through an evolu- tion over the past decades to make the process more reliable andmore productive. It has been, for example, a long pending wish fromcritical process equipment (CPE) fabricators around the world to reach Ni-625 chemistry in single layer of cladding with a maximum Fe content of 5% without having to use an alloyed flux. Cladding Cladding is applied across the whole spectrum of industries, from nuclear, oil and gas and petrochemical to the steelmak- ing industry. Cladding is required on the process side of high pressure CPE to provide corrosion resistance against severely

Figure 1: An internal view of a typical vessel that requires protective weld cladding.

10

August 2018

AFRICAN FUSION