Steffen Zimmermann

Corrosion Assessment Method Validation for High-Grade Line Pipe

The present paper deals with the pressure containment and deformation capacity of corroded high-grade steel line pipe. Firstly, some well established models are investigated concerning their predictive accuracy if applied to high-grade line pipe steel. In particular, it will be shown that all models under consideration tend to overestimate the remaining strength in the case of high-grade steel pipes. Afterwards, FE-analyses are performed in order to study the local evolution of plastic flow in the area of the corrosion defect; at the same time, the burst pressure is predicted applying von Mises plasticity and a simple failure criterion. Although different defect geometries are associated with well pronounced differences in the evolution of the plastic flow around the corrosion defect no significant effect on the burst pressure is found. Finally, the main results of a hydrostatic burst test performed on a pristine X100 line pipe joint are presented. It appears that the material under consideration seems to have anisotropic plastic material properties which may have effect on burst pressure.Copyright

Investigation of the Stress-Strain Behaviour of Large-Diameter X100 Linepipe in View of Strain-Based Design Requirements

The use of high strength steels is considered as the best economical option to transport large gas volumes under high pressure from remote areas to the market. Exploration of new energy resources located in areas of complex ground and ambient climate imposes strict requirements on pipeline material and design. One of the major research issues in such areas is differential ground movement, which may be associated with large longitudinal straining in addition to plastic circumferential elongation. Hence, common design principles need thorough re-consideration, notably with respect to strain hardening properties of both base metal and girth welds. The present paper addresses several characteristics of axial and circumferential stress-strain behaviour as it is encountered in high-grade UOE line pipe. Two delivery states are taken into account, namely the “as expanded” as well as the “as coated” state. In a first experimental step, the effect of thermal cycle of the anti-corrosion coating process on stress-strain behaviour is simulated subjecting pipe material to temperatures in the range of 180° up to 250° C. In a second experimental step, stress-strain behaviour in both axial and transverse direction is mapped along the pipe production process in order to assess when and to what extent plastic strain capacity is lost during cold forming. The experimental work is complemented by instrumented ring expansion tests and instrumented burst tests. In a third future step, stress-strain information measured in both directions will be analyzed using a theoretical model based on Hill’s plasticity in order to clarify in which way circumferential stress-strain behaviour may impose constraints on strain capacity of axial direction. Within the scope of this paper, first and foremost, underlying principles are outlined and discussed and indications with respect to modelling implications given. Based upon these three sequential investigatory steps, it will be possible to draw conclusions with respect to stress-strain behaviour of parent material and the pipe forming process and to show that unfavourable effects triggered by coating do not show within the structure while they might do in material tests.Copyright

Anisotropy: Benefits for UOE Line Pipe

Plastic anisotropic material behavior of UOE line pipe is investigated in view of its structural response. Common load cases are considered and their resultant strain capacity concerning Strain Based Design demands are discussed. Hill’s yield function is used to analyze steel line pipe under internal pressure and bending moment. Here, a three-dimensional anisotropic plastic strain evolution is considered. It was shown, that underlying anisotropic material behavior can be beneficial for the structural response of line pipe, although it depends on the load case and the directional anisotropy. That is in some way contrary to the demands in specifications, where isotropic material behavior is desired.Copyright

Numerical Modeling of Plastic Deformations in UOE Line Pipe

In this contribution a model to investigate the structural response of pipelines in view of strain based design is developed. The approach is based on analytical modeling and verified with finite element solutions. The model is derived at first for isotropic structural behavior. Several load cases, namely pressure containment and combined loads are then evaluated with specific strain based requirements and their corresponding stress states. As a result the influence of Y/T ratio and hardening exponent on the structural behavior can be confirmed numerically. Finally, the model is extended to anisotropic structural behavior. With this extension pressure-strain diagrams from numerical and experimental hydro tests show an enhanced correlation to each other.Copyright

Mechanical Properties and Component Behaviour of X80 Helical Seam Welded Large Diameter Pipes

The paper discusses the development and processing of hot rolled X80 coil material and its conversion into thick-walled helical seam welded pipes. Microstructure, texture and mechanical properties of strips and pipes produced are characterized and compared. High strength characteristics and good deformability as a result of the fine homogenous mainly bainitic microstructure have been determined. Stress strain characteristics and the response to cold deformation during pipe forming have been investigated. Correlations between strip and pipe properties are described and have been used as a data basis for FEM simulations of the pipe forming process. The real pipe behavior has been investigated by means of burst tests performed on 48″ and 42″ pipe sections with 18.9mm wall thickness. The results achieved have been compared with results for other pipe grades, dimensions and types of pipe. An outlook will be given on future material and process development steps and use of X80 HSAW-pipes produced.Copyright

Enhancement of Collapse Resistance of UOE Pipe Based on Systematic Exploitation of Thermal Cycle of Coating Process

The present paper discusses recent results of an ongoing study on the effect of thermal treatment on collapse strength of cold formed pipes, for instance those following the UOE production route. It has been recognized that thermal treatment as encountered during thermal cycle of pipe coating processes may compensate the reduction of compressive yield strength owing to cold plastic deformation induced during forming. This effect has been systematically analyzed. Enhancement of collapse resistance exploiting the thermal cycle of coating process was studied based on experimental evidence, Finite Element simulations as well as theoretical analysis. It is herein shown that appropriate thermal treatment manifests itself positively with respect to compressive yield strength, leading to significantly improved collapse pressures. As a result fabrication factors of one and even higher may be applicable.Copyright