Design Considerations in Attaching Pressure Vessel Internals


Process equipment which employs a corrosion resistant alloy (CRA) layer cladded to steel is common in refineries and petrochemical plants. There are two regularly employed methodds for welding attachments and internals to clad process vessels. One is to remove the CRA cladding and make the attachment to the base metal (steel). The other eliminates the step of removing the cladding, simplifyng the attachment process. With the lack of data to support direct attachment, 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. So which method is better? Recently, a technical study, including significant testing, has been undertaken to verify the bond between clad material and the base steel is robust enough to withstand the heaviest attachments in the harshest conditions. The theory behind the technical study will be presented along with results of this study.