Izumi Takeuchi

Fracture Propagation and Arrest in High-Pressure Gas Transmission Pipeline by Ultra High Strength Line Pipes

The fracture arrest of high pressure gas pipelines is one of the keen subjects for application of high strength line pipes. To examine the arrestability of high strength line pipes against crack propagation, several full scale fracture propagation tests have been conducted. The fracture propagation tests of X100 or X120 under high pressure revealed that the existing models of arrest energy prediction failed to predict the arrest energies. By careful investigations of the test results, it is found that the failure in prediction is mainly due to the uncertainty of crack velocity curve prediction. On the other hand, accuracy of predicted gas decompression curve is relatively high even in the case of high pressure condition. Experimentally, the arrest energies have been determined by full-scale fracture propagation tests with increasing toughness arrangement. Different from actual pipeline, extremely low toughness pipe has been employed in crack initiation pipe with intention of getting steady state propagation. However, arrestability of pipe might be underestimated in the increasing toughness arrangement test as the initial crack velocity increases. Together with recalibrated crack velocity curve, Sumitomo model (HLP method with Sumitomo’s crack velocity curve) predicts that even toughness arrangement, which is the case of real pipelines, could arrest the propagating shear fracture in high pressure gas pipelines by X100.Copyright

Property of X80 Grade SAW Pipes for Resistance to Ground Movement

It is aware that the expansion of gas utilization is an important issue to restrict CO2 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.Copyright

Evaluation of Compressive Strain Limit of X80 Saw Pipes With Girth Welding by FE Analysis

The expansion of supply capacity of natural gas to market is expected from the concern of environmental conservation by less CO2 emission. Transportation cost has been focused for natural gas to be competitive in the market. High-pressure gas pipelines have constructed by large diameter and high strength line pipes to improve transportation efficiency of gas transmission pipelines. High strength line pipes have been developed to cope with high-pressure operation. Strength in circumferential direction on line pipe is the prime target to hold high pressure safely. In terms of pipe size, pipe diameter has been increased to lead larger D/t. Both of higher strength and larger D/t result in less favorable to deformability of pipeline. To apply strain based design to pipeline, the evaluation of strain capacity, which is related to deformability of line pipe, is required supposing the pipeline encounters large scale ground movement such as earthquake or landslide. It is not simple to find the criteria to prevent leak or rupture of pipeline in such events, as not only pipe property but also interaction between pipe and soil are needed to consider. Gas transmission pipelines are constructed by joint girth welding. The strain capacity of pipeline with girth weld has to be investigated for strain based design. Full scale bending test of joint welded pipe was conducted and FEA model to assess strain capacity of pipeline with girth weld is developed.Copyright

Development of High Strength Line Pipe for Sour Service and Full Ring Evaluation in Sour Environment

To establish mass production technology of high strength line pipe up to API-X70 grade for sour service, the HIC (Hydrogen Induced Cracking) phenomena in line pipe has been carefully examined. The micro-segregation zone originated at final solidification front, which has MnS inclusion and hard phase, was identified as the location of the initiation site of HIC. The proper procedures of Ca treatment to eliminate elongated MnS and TMCP application to reduce maximum hardness have proved to increase the HIC resistance in such segregation zone. In addition to the standard HIC test, full ring test under applied stress was conducted to assure the performance of high strength line pipe in sour service. The clean steel in mass production, which has enough HIC resistance, was attained for high strength line pipe up to API-X70.© 2004 ASME

Pipe Bending Test With Girth Welding on X80 Grade SAW Pipes

This study was planned as a part of a test program to confirm the effect of girth welds on the strain capacity of pipes. In this study, full-scale pipe bending tests are performed by using X80 SAW pipe. This paper covers pipe manufacturing procedure, developed welding procedure to obtain even match weld metal and properties of welded joints. And this work demonstrated that the X80 pipes welded under the developed procedure fractured in base metal remote from girth welded portion by full scale pipe bending test conducted under the internal pressure of 72% SMYS of X80.Copyright