Managing Dissimilar Metal Welding in Hydrogen Rich and Low Temperature Petrochemical Applications

Abstract

Dissimilar metal welds (DSMW) have been used for extensive time in hydrogen rich and low temperature petrochemical applications. Frequently they are used when there is a temperature or corrosivity stream transition aiming to optimize initial project costs. Experience shows a mix of successful and failure applications. Industry standards have slowly adding guidance to prevent failures. The wide variety to DSMWs materials combinations and service conditions poses a significant challenge for standardization. Maximizing the lives of dissimilar metal weldments requires early involvement starting with the design and continuing with the fabrication, operation, and inspection phases. Although common goal is to avoid them, in practice there are situations when is no practical to elude them when constructing new units. In this paper in additional to a literature review section, several real examples of ferritic-ferritic, austenitic-austenitic, and ferritic-austenitic dissimilar welds are described along with the steps involved as described above to prevent failures. Butt welds and weld overlays are covered, as well as some failures. Cases covered include dissimilar metals welds in steam methane reformers, hydroprocessing and olefin units at high and low temperatures. Examples of metallurgical characterization and fitness for service assessments are included. Also, a summary of industry code guidance for designing, fabrication and inspection are included. The paper finally includes a summary of recent research activities in this field.