Integral failure criteria in numerical low-temperature strength calculations of marine facilities

Abstract

Object and purpose of research. This paper studies welded structures of marine facilities operating at the temperature of -40 °С and lower. To justify necessary strength margins, new international and Russian standards for strength and reliability of Arctic oil & gas facilities require ultimate structural strength calculations taking into account possible deteriorationin plasticity and fracture resistance of materials and welds. However, these requirements still cannot be implemented because, as yet, there is still no answer to the fundamental question: how to formulate failure criteria when structure comes to its limit state? Along with it, current regulations of Classification societies about fracture resistance of welds for these structures usually cannot be fulfilled due to a number of technological and economic reasons, and the formalist approach to this matter implicates prohibition for these structures to operate at low temperatures. The purpose of this study is to develop criteria of brittle and ductile strength at low temperatures, so as to solve key questions about limit strength of welded structures, based on a new procedure of direct FEM-based static strength calculation of welded structures taking into account realistically achievable fracture resistance and plasticity levels of the material used in welds. Materials and methods. Strength calculation method envisages FEM-based procedures in combination with verification methods for strength of steel structures as per integral criteria of brittle failure and limit plastic straining.Main results. Integral brittle and ductile failure criteria developed in this study are intended for limit structural strength assessments. It has been shown that these new integral criteria for limit strength considerably increase accuracy of calculations and ensure proper selection of materials, manufacturing technologies and optimal design of marine structures operating at low temperatures. Conclusion. Newly developed brittle and ductile failure criteria for structures were used to develop a new approach to limit strength calculations of marine facilities, including oil & gas production rigs, based on direct calculations. This approach is an important element of system ensuring trouble-free work, operational safety and development technology for structures of Arctic ships and marine platforms. This study provides for proper selection of materials, manufacturing technologies and optimal design of marine facilities operating at low temperatures.

Keywords

• limit structural strength
• strength criteria
• strength of Arctic marine facilities
• low-temperature strength
• cold resistance of structures