In a 1998 study, costs for corrosion in USA were estimated to be about 276 billion US-$. One way to reduce this gigantic amount of money is to use modern stainless steels and nickel alloys with excellent resistance to various forms of corrosion in corrosive environments like seawater, brines, oil and sour gas wells.
Process equipment which employs a corrosion resistant alloy (CRA) layer cladded to steel is common in refineries, petrochemical plants and other plants processing highly corrosive media. There are two regularly employed methods for welding attachments and internals to clad process vessels. One is to remove the CRA cladding for welding the attachment to the steel base metal assuming dissimilar welds and restoring CRA by weld overlay. The other eliminates the step of removing the cladding, simplifying the attachment process by direct welding of the internals onto the clad layer. With the lack of data to prove the integrity of direct welding attachment onto the clad layer, designers frequently demand the cladding be removed or allow only a conservatively low stress limit for what can be attached directly to the clad surface. It is well understood that eliminating the step of removing clad increases the simplicity, improves the lead-time, and reduces the cost of making these attachments for trays or other internals, but there are concerns about clad disbonding risks. With the aim to provide data around the integrity of direct welding attachments for better risk assessments, a technical study was undertaken. In this study, it will be shown that the bond between clad material and the base steel is robust enough to withstand the heaviest attachments and harshest conditions. The theory behind the technical study will be presented along with the results of this study
The use of High-Velocity Thermal Spray (HVTS) technology has been well adopted for sour conditions; particularly where low, or locally low, pH conditions result in corrosion and shell thinning. High alloy systems resistant to low pH or acidic conditions are effective at providing a metallurgical barrier, protecting the underlying substrate from material loss. Moreover, HVTS processes have also been employed for mitigating environmentally induced cracking (EIC) in sour service. This paper discusses the suitability and performance of modified HVTS alloys for service where high pH general corrosion or caustic cracking (CSCC) may occur. Extensive testing has been undertaken in both ambient and high pressure and temperature autoclave conditions to better understand material performance in caustic environments. While Nickel Alloy 200 and Monel 400 may be deemed appropriate based on traditional material selections, thermal spray process considerations in the material deposition and the impact of ancillary elements in the process stream, such as halides, render these alloys unsuitable. More complex Nickel alloy cladding systems are evaluated in this study with suitable material recommendations for remediation without the deleterious heat impact of welding or to protect surfaces where heat affected zones have been created and post weld heat treatment is problematic.
Esab is always committed to technological innovations to support its customers in improving productivity and quality in their production units. This high focus has recently brought to the market an innovative cladding solution.
It is about the Integrated Cold Electrode for SAW process, launched in 2012 for joining application only. However, taking the benefits of its high flexibility and of the continuous development around it, it is now also possible to use it for cladding applications. It delivers the required weld deposit chemistry in a single layer solution by combining different wire grades with very low dilution.
Esab also has a long experience in LNG application, where a dedicated flux is well known all over the world. It has been designed some years ago to reduce crack susceptibility when NiCrMo wires are used to weld 9%Ni plates.