近年の鋼管体設計手法・ソフトの開発動向

Abstract

The conventional tubular design is based on the API recommendation where collapse tests are conducted under fluid confining pressure. However, the tubular string collapsing process is significantly different when an external load is applied through a solid formation. Laboratory tests showed that tubular strings started yielding significantly earlier if the load was applied through a formation rather than through a confining liquid. However, during additional loading after tubular string yielding, the deformation of the tubular string installed in a formation remained small since most of the external load was supported by the surrounding formation. These laboratory data and field applications of tubulars to deeper fields enlighten field engineers to change the design methods of tubular strings. Since these new design methods are more complex than conventional one, softwares to design tubulars have been also evolved. Analytical or numerical solutions have been developed to calculate the stress state and deformation before yielding and after yielding for gravel packed or cemented tubular strings under directional in-situ stresses. The API tubular string failure criteria have been also modified so that they could be applied to more general stress state around a tubular string. Using the tubular string stress state and the generalized API pipe failure equations, a guideline is given for field design of tubular strings under geotectonic load based on the experimental observations. A software to simplify the tubular string design is also presented.