This paper discusses the effects of local deformation, dent, and strain hardening properties on strain capacity in compression of a line pipe. Compression tests were conducted using two pipes with the nominal diameter of 400mm. These pipes had roundhouse type stress-strain curve, and correspond to L290 grade in Spec 5L of API (American Petroleum Institute) standards. One pipe was a plain pipe without dent, The other was a dented pipe. The depth of the dent was about 3% of the diameter. The test results explain that the strain capacity can be reduced by 25% due to the effect of dent. A series of finite element analyses were conducted to investigate the compression behaviors. The strain capacity in compression was defined as the longitudinal critical remote strain whose strain distribution was free from the effects of a dent. At first, that finite element analyses were verified that they could reproduce the results of compression tests. Next, the size of dent were changed on that finite element analyses model, some different case were analyzed in order to investigate the changes of the strain capacity in compression. The strain capacity, the longitudinal critical remote strain, decreased to about a half in case of 3%-depth dent, compared with a plain pipe. Seismic integrity of the pipeline with a dent is discussed in accordance with the seismic design guideline issued by Japan Gas Association. In case of the strong earthquake, “Ground Motion Level-1”, the dented gas pipeline is safe, even if the depth of the dent is 10% of the diameter. In case of the maximum earthquake, “Ground Motion Level-2”, the gas pipeline might buckle longitudinally in soft ground.

Newly-developed high quality high frequency electric resistance welded (HFW) linepipes have recently been applied to offshore pipelines by using the reel-lay method and onshore in extremely low temperature environments because of their excellent low temperature weld toughness and cost effectiveness. In order to clarify the applicability of these HFW linepipes to seismic regions, a series of full-scale tests such as the bending test with internal pressure and the uniaxial compression test were conducted according to the seismic design code of the Japan Gas Association (JGA). Based on these full-scale tests, the safety performance of high quality HFW linepipe when applied to seismic regions is discussed in comparison with the mechanical properties obtained in small-scale tests, such as the tensile and compression properties of the base material and weld seam, focusing especially on the compressive and tensile strain capacity of HFW linepipes from the viewpoints of full-scale performance and geometrical imperfections. The results of the bending test under internal pressure and the uniaxial compression test without internal pressure complied with the JGA seismic design code for permanent ground deformation induced by lateral spreading and surface faults. In addition, a full-pipe tension test was also conducted in order to investigate the tensile strain capacity of HFW linepipes for axial deformation.

Applicability of mandrel elbows to high pressure gas pipelines is discussed in this paper taking into account the seismic integrity to withstand liquefaction-induced permanent ground deformation. Bending test and FE analysis of X65, 45 deg. mandrel elbow with diameter of 24-in were conducted in order to evaluate the seismic integrity for lateral spreading due to liquefaction. Local buckling behaviors of the closing-mode test was simulated by FEA and calculation of existing seismic design code for high pressure pipelines can estimate maximum bending angle as limit state of the mandrel elbow conservatively. The results clarify that mandrel elbows can be applied to high pressure pipelines using conventional design method including the design code and FEA. In addition, buckling behaviors of the mandrel elbow were similar to those of high-frequency induction bends which have been used for high pressure pipelines in Japan.

Upheaval buckling of small diameter gas pipeline occurred due to strong seismic excitation during the 2007 Niigata-ken Chuetsu-Oki earthquake whose diameters were 4″ and smaller. This paper deals with investigation of the upheaval buckling of gas pipes conducted by Ministry of Economy, Trade and Industry of Japan to establish seismic design guidelines to mitigate upheaval buckling. Sand box and field tests were conducted using small diameter pipes to simulate the upheaval buckling behaviors and construct a simple finite element model. The results clarified that the tensile properties of pipe material and pipe-soil interaction were the most effective parameters to explain the buckling behaviors. Interaction curve of pipes can be found in the relationship between compression and bending moment in the combined loading tests. The deformation behaviors of the buried pipe tests followed the interaction curve and local buckling of buried pipes occurred in lower bending moment than that of pipes not buried.

This paper describes The Draft Seismic Design Guidelines to Mitigate Upheaval Buckling of Small Diameter Pipes which were reported by Ministry of Economy, Trade and Industry in 2011. Upheaval buckling of small diameter gas pipes occurred in a high-pressure gas pipeline and three middle-pressure city lines due to the strong ground motion during the 2007 Niigata Chuetsu Offshore earthquake which was a powerful earthquake with moment magnitude of 6.6. A three year research program had been conducted since 2008 to investigate the upheaval buckling behaviors and develop seismic design guidelines to ensure seismic integrity of small diameter high-pressure gas pipelines and middle-pressure main distribution lines.

It is aware that the expansion of gas utilization is an important issue to restrict CO 2 emission. The reduction of gas transportation cost is essential to increase gas supply to market. The high-pressure gas pipeline with high strength pipes has contributed for safe and economical transportation of natural gas and is expected more for the future demand of gas. The primary objective of high strength line pipe is to hold high pressure safely. The property in circumferential direction under hoop stress is the primary target of the line pipe. High strength and high toughness steel at low temperature has been developed for large diameter line pipes, which have been supplied to major gas pipelines. The increase of D/T of pipelines for transportation efficiency tends to decrease critical compressive strain. Since long distance pipelines come across various ground conditions, the pipeline might encounter some serious ground movement. It is pointed out that in this event the strain by the ground movement might be high enough to deform pipelines to leak or rupture. There are various forms of ground movement, but the Japanese guideline for earthquake resistance and liquefaction is considered as basic conditions for SBD and for FEA in this study. The relation between pipe deformation and property in axial direction is investigated to identify the effective parameter to design the steel property for gas pipelines. Metallurgical factors and microstructure can change the parameters not only on strength and toughness, but also on the critical strain of X80 line pipes. It is discussed that the effectiveness of those changes to improve the safe operation of high-pressure gas pipelines with X80 grade line pipe.

Guidelines for the seismic design of oil and gas pipelines have not been updated in a single reference document since 1984, when the American Society of Civil Engineers released their publication, Guidelines for the Seismic Design of Oil and Gas Pipeline Systems. Since 1984, substantial progress has been made in identifying and quantifying seismic hazards, understanding pipeline response under large, displacement-controlled strain conditions, and analytical methods for assessing pipeline response to permanent ground displacement. In 1998, the Pipeline Research Council International, Inc. (PRCI) initiated a project to update seismic design guidelines for pipelines with the goal of incorporating advances in current engineering practice since the early 1980s and to create a document that can be regularly updated to take advantage of new research findings. The PRCI project to develop the guidelines was undertaken by two investigators heavily involved in the 1984 American Society of Civil Engineers guidelines. Two teams of independent expert reviewers were used during the project to assure the recommended practices were technically consistent with the current state of knowledge of seismic hazard assessment, pipeline behavior, and analysis methods.