Petrobras has been using a 6-5/8 in. drillpipe based riser system for intervention work offshore Brazil for several years. The primary advantage of the drillpipe based system relates to the rotary shoulder connections (RSC). RSC’s make-up and break-out quickly, are rugged and are superior at resisting galling and other handling damage compared to OCTG connections that are often used for riser applications.

Petrobras has been prevented from expanding their use of the intervention risers in sour gas areas because there were no fully Sulfide Stress Cracking (SSC) resistant tubulars with RSC’s. The intervention riser configuration consists of upset to grade tubes friction welded to tool joints that are typically constructed from forgings. Sour service drillpipe has been available for some time. This pipe is built with SSC resistant upset tubes and tool joints. The friction welds joining the upset tubes and tool joints were not resistant to SSC. This is acceptable for drilling since the weld is not the high stress area of the assembly and the drilling environment can be controlled through the drilling fluid properties and additives. Petrobras’ critical sour riser applications could entail direct and prolonged exposure to H2S gas. Consequently, a fully SSC resistant system including the friction weld was required.

This paper presents the successful development and qualification of SSC resistant friction welds for intervention riser systems. It describes the engineering and manufacturing philosophy employed, laboratory testing procedures and results and Petrobras’ applications for the new risers. Since NACE MR-0175 does not address friction welds the engineering team developed unique and innovative criteria and testing procedures for the new weld technology. A new patent pending four point bending test procedure and fixture were develop that employed unpolished samples that closely represent the finished product surface finish (NACE testing typically uses polished specimens).

You can access this article if you purchase or spend a download.