The New API RP 2A, 22nd Edition Tubular Joint Design Practice

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSince the early 1990s, API sponsored a series of research projects to develop advanced formulation for design of nonoverlapping tubular T, Double T (DT-X), and K offshore platform joints (API RP2A Upgrade Plan, 1990). The University of Illinois at Urbana-Champaign, sponsored by API, developed nonlinear finite element models and verified them against available test results. These models were then used to simulate a wide variety of geometries and static loading conditions, establishing a broader database than available test results. Advanced closed form parametric formulations were developed and verified against these analytical results to reduce scatter and generate more reliable formulation than provided in the API RP 2A WSD 14 th through 21 st Editions. One significant feature of the new static design formulations is better representation of the chord load and geometry effects and the boundary conditions that are not possible with physical testing (Pecknold 2000, 01, 02, 05).The Task Group also evaluated and upgraded the tubular joint fatigue design procedures. The welded joint X and X' fatigue design curves in the RP 2A Editions 11 thru 21 have been replaced by a basic SN curve with a slope m=3 that changes to 5 at ten million cycles. Fatigue life correction factors for seawater, thickness, and use of weld profile control, grinding, and peening have also been introduced. In addition, the comprehensive Efthymiou 1988 equations replaced the Alpha Kellogg Stress Concentration Equations. The Simplified Fatigue Design Procedure has been maintained, with the allowable peak hot spot stresses rechecked for the new SN curve. SN curves and fatigue design requirements for cast nodes and grouted joints have also been introduced.

Comparative Study of Tubular Joint Design Formulas According to API RP 2A WSD 21st Edition and 22nd Edition

“…The development of API RP 2A WSD static strength check design calculation will be discussed below. In summary, the modification from API RP 2A WSD 21th Edition to API RP 2A WSD 22nd Edition involved a relaxation of the 2/3 limit on tensile strength, additional guidance on detailing practice, removal of the punching shear approach [7], new Q u and Q f formulations, and a change in the form of (8) the brace load interaction equation but the joint load capacity and interaction equations based design philosophy and the basic formulation has been maintained [5].…”

“…This variable accounts for the existence of a nominal string load and has been completely rewritten to better represent the effect of tendon tension on different joint types and loads [5]. Chord stress effects are difficult to simulate in physical tests so that the finite element model used for 22nd edition formulation allowed for a better representation of the chordal stress effects [7]. The With λ equal to 0.030 for axial, in-plane, and out-of-plane bending stres at brace.…”

Fixed Offshore Platform Design

“…As a result, simpler, easier-to-test joint geometries, such as the nonoverlapping T and K joints were first to be tested and formulated. The University of Illinois method is in the process of being adopted by the API as their RP2A 22 nd Edition, under development [Karsan, et al 2005]. This enabled accurate formulation of the chord stress effects and more complex joint geometries, such as the overlapping and stiffened tubular joints and stress concentration factors for fatigue design [Eftymiu, 1988].…”

“…For further details see Karsan (2005) and Pecknold (2000Pecknold ( , 2001Pecknold ( , 2003. 374 Chapter 6 Load Transfer Across Chords…”