API Load Rating of Marine Riser Couplings: Application of RP 2R Guidelines and Supplemental Methods

ABSTRACT This paper provides an example of the use of the American Petroleum Institute's Recommended Practice 2R in determining the load rating of a riser coupling, and includes additional supplemental guidelines and information. The supplemental information is based on results from analyses and full-scale testing of a dog-type marine riser coupling. An example of determining the capacity of a non-axisymmetric section is provided, followed by recommendations for shear and bearing design limits. The API RP 2R fatigue life factor (FLF) is discussed with comments on its use. The paper concludes with additional recommendations for the axisymmetric tension and pressure tests. INTRODUCTION Before publication of the American Petroleum Institute Recommended Practice for Design, Rating, and Testing of Marine Drilling Riser Couplings1 (API RP 2R), there was no generally accepted-method for specifying the load rating of a riser coupling. Each manufacturer, contractor, and operator used different terminology and design critp.ria. Therefore, each riser system and coupling was analyzed and evaluated independently. As a result, it was difficult to compare and group riser coupling load carrying capacities for different connectors. API RP 2R was developed as a standard method for establishing load ratings. It has been published for two years, has been generally well accepted by the industry, and is now scheduled to change from a recommended practice to a design specification. This paper illustrates how API RP 2R guidelines wp.re used in the design, rating, and testing of a dog-type marine riser coupling. API RP 2R provided good general guidance, although not all details of connector design, analysis, and testing were addressed. Supplemental information and guidelines are presented here that prove useful in developing marine riser connectors. SUMMARY OF API RP 2R API RP 2R has established guidelines for riser coupling design in five general areas:Design Parameters.API RP 2R defines the important parameters that need to be considered in designing marine riser couplings, including external load conditions and the effects of internal preload. Additionally, standard nomenclature and connector types are defined.Analytical Guidelines. Finite element analysis is recommended as the appropriate analytical technique to determine stress distribution in a riser coupling. Recommendations for modeling and evaluating results are provided. The von Mises criterion, also known as the octahedral shear stress theory, is suggested as the correct failure theory to use in comparing calculated stress with API-defined allowable stress.Fatigue Life Factor. Fatigue resistance is addressed in API RP 2R by the Fatigue Life Factor (FLF). A standard method for determining FLF is specified. This method results in a comparative numerical value that indicates the resistance of a coupling to fatigue failure. However, as stated in API RP 2R, the FLF only provides a basis for comparison and does not provide an absolute measure of the fatigue resistance of a coupling. Currently, API RP 2R does not recommend a minimum FLF.Riser Coupling Rating. The load rating procedure establishes a design loan which represents the safe load-carrying capability of the riser coupling. This design load is an axisymmetric tension representative of combined bending and tension.