Non-integral risers are made up of independent strings. These risers are typically based on either a single string of drillpipe (for which minimal access to the annulus is required), or one or more strings of production tubing, clamped together at various points along their length as they are run, similar to a downhole dual completion string. In either case, the workover control functions are supplied via an umbilical which is secured to the riser at various points, as it is run.
Integral risers consist of “prefabricated” joints/assemblies in which the multiple pipe strings are terminated at either end in dual-bore connections, thus simplifying the handling and make-up operations. In cases where high tensile and/or bending loads on the riser are anticipated, an integral riser may also include an outer structural housing to provide additional strength. In this case the hydraulic and/or electrical control lines may also be incorporated into the prefabricated joints, however this approach obviously introduces a significant number of additional connections (and therefore potential failure points) into the workover control system circuits.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards
Riser which is made up of independent production and annulus strings or bores. NOTE This type of riser is normally run with joints slightly staggered to allow conventional tubing or drill pipe-handling tools to be used for make-up of joints. Clamping the tubular members as they are assembled provides ease of handling and some structural stiffening. A non-integral C/WO riser can be grouped into two types: a drill pipe riser and a tubing riser.
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards