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

During the construction of a 56km long 16 in. carbon steel sour gas pipeline, repetitive surface
preparation failures were detected during visual inspection of pipeline girth weld internal surface prior to
coating application. Such failures represented 67% of the total pipeline girth welds and were manifested
by excessive sharp-edges at the root pass. To identify the failure causes, an investigation was
performed through reviewing the pipeline, fabrication and coating application specifications and
procedures, quality control records and performing an extensive visual inspection through an advanced
video robotic crawler on all pipeline girth welds made. Upon investigation analysis, the failures were
caused by sharp-edges in the root pass which were attributed to improper practices during
manufacturing, field fabrication and pre-coating quality control. The failure analysis indicated that the
mechanized Gas Metal Arc Welding process, with the parameters used, was not suitable for internal
girth weld coating application. In addition, a more stringent requirement should be applied to the
acceptable pipe-end diameter tolerance and pre-coating quality control to ensure absence of similar
premature surface preparation failures. The pre-coating quality control can be improved through
utilization of robotic laser contour mapping crawler for precise detection and sizing of unsatisfactory
surface weldment defects, including sharp edges.