Satoshi Igi

Evaluation of mechanical behavior of new type bellows with two-directional convolutions

Abstract Bellows are widely used as the element of expansion joint in various piping systems. Piping systems for industrial plants often suffer excessive deformations or displacements caused by heat expansion, vibration, nonuniform subsidence of ground, etc. Bellows have the function to absorb regular or irregular expansion and contraction in such piping systems. Conventional bellows, however, have difficulties such as the instability of deformations under cyclic loadings, and the inability to absorb torsional deformations. In order to solve these problems, a new type of bellows, so-called “double convolution bellows”, were proposed. This new type of bellows has convolutions in two directions: the first convolutions in the longitudinal direction are the same as the conventional bellows; and the second convolutions are added in the lateral direction. This paper presents a study on the mechanical behaviors of the new type bellows and conventional bellows to examine the deformation behaviors under repeated axial loading, internal pressurizing and torsional loadings, and the results show an improvement in thickness distribution, instability and torsional flexibility.

Mechanical Properties of Newly Developed API X80 Grade HFW Linepipe for Long-Term Exposure at Elevated Temperature

API X80 grade UOE double submerged arc-welded pipe has been applied to steam injection oil sand recovery systems to increase the volume of steam to be injected and decrease the installation cost. The pipes for the systems are subjected to high temperature for a long period, such as 350 °C for 20 years. Therefore, it is important to ensure the reliability of the pipes during and after long-term operation. In this study, based on the recent development of high-frequency electric-resistance-welded (HFW) linepipe with a high-quality weld seam, the durability of newly developed API X80 grade HFW linepipe for long-term high-temperature operation was investigated. The change in the microstructure of the pipe body and weld seam was small after exposure to 400 °C and lower temperatures. The tensile strength of the base metal and weld seam after heat treatment with temperatures as high as 400 °C can be determined using the Larson-Miller parameter, which depends on the temperature and holding time of the heat treatment. The newly developed API X80 grade HFW linepipe was considered to have sufficient tensile strength during and after long-term operation at 350 °C for 20 years, similar to API X80 grade UOE pipe. No significant change in the Charpy absorbed energy during long-term heating was observed. Creep tests indicated that the time to rupture at 400 °C or lower exceeded 106 hours, and the creep effect was considered almost negligible at temperatures less than 400 °C. The rupture stress at approximately 350 °C was estimated to be far higher than the typical hoop stress of approximately 200 MPa on the steam distribution system. High-temperature fatigue properties were also measured to ensure reliability under varying stress conditions.Copyright

Deformation Capacity of Weld Seam of the High Quality HFW Linepipe

Newly-developed high quality high frequency electric resistance welded (HFW) linepipes have recently been used in pipelines in reel-lay applications and low temperature service environments because of their excellent low temperature weld toughness and cost effectiveness. In order to clarify the applicability of these HFW linepipes to the seismic environment, a series of full-scale tests such as bending test with internal pressure and uniaxial compression test were conducted according to the seismic design code in Japan gas association (JGA).Based on the above-mentioned full-scale tests, the safety performance of high quality HFW linepipe to apply to the seismic region is discussed in comparison with the mechanical properties in the small-scale tests such as the tensile and compression property of the base material and weld seam, especially focused on the strain capacity of HFW linepipe from the view points of full-scale performance and geometrical imperfection.Test results of the bending test with internal pressure and the uniaxial compression were complied with the JGA seismic design code for the permanent ground deformation induced by lateral spreading and surface faults.Copyright

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip.The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.© 2014 ASME

Full Gas Burst Test for HFW Linepipe at Low Temperature

A full gas burst test at low temperature below −40°C was performed using a high frequency welded (HFW) linepipe with high-quality weld seam, “MightySeam®,” [1–4] in order to verify the applicability of the Drop Weight Tear Test (DWTT). Residual stress exists in the pipe body of HFW linepipe because the manufacturing method includes a sizing process. Therefore, it is necessary to clarify the difference between the arrestability in the DWTT without residual stress in the specimen and that in the full gas burst test with residual stress in the pipe body.The full gas burst test is performed using a test pipe specimen in which a notch is introduced into the base material by an explosive cutter. In addition, a test pipe specimen with a notch introduced into the weld seam was used in this study because the developed HFW linepipe, “MightySeam®,” has excellent low-temperature toughness as a result of control of the morphology and distribution of oxides generated in the welding process by temperature and deformation distribution control. The Charpy transition temperature of “Mighty Seam®” was much lower than −45 °C.Ductile cracks were initiated from the initial explosive notch, and these cracks were arrested after ductile crack propagation of about 1 m in base material on both sides. The fracture behavior was similar in appearance in the DWTT without residual stress and the full gas burst test with residual stress.Copyright

Full Scale Reeling Simulation Test of X65 HFW Linepipe

Reel-lay method is widely recognized cost effective installation process for offshore pipelines. In the process of reel-lay, cyclic plastic strain is expected at pipelines due to reeling, unreeling, aligning and straightening. In order to maintain integrity of pipelines subjected to large bending deformation it is necessary to understand the bending deformability and change in mechanical properties of pipelines.Advanced HFW (High Frequency electric resistance Welded) linepipe “MightySeam®” has superior low temperature toughness at seam weld and base material and has some advantages in application to offshore pipelines from a viewpoint of change in toughness due to pre-straining, coatings and long time exposure.In this paper full scale reeling simulation tests of X65 HFW linepipe were conducted in order to study bending deformability and the change in mechanical properties. The tests were performed by bending pipe alternately to reeling former and straitening former with different radii. Girth welding were applied to test pipes in order to investigate effect of strain concentration around girth weld by strength mismatch or weld reinforcement. Small scale reeling simulation tests with/without aging were also conducted and the results were compared to those of full scale reeling simulation tests.In full scale reeling simulation test, some strain concentration arose around girth weld by strength mismatch and local contact of weld reinforcement to former. Some ovalizations were advanced during tests, however local buckling could not be recognized throughout pipes even if strain concentration occur around girth welds. Tensile properties were changed proportional to last introduced plastic strain as a result of Bauschinger effect and work hardening at strain history. Low temperature toughness of base material and seam weld did not change significantly by pre-straining or aging.Copyright

Effect of Hammer Peening Processing on Fatigue Property of Welded Joints After Overload

One general method for improving the fatigue strength of welded joints is introduction of compressive residual stress by peening. However, there is concern that the fatigue strength of the welded joint may decrease if excessive preloading is applied after peening.It has been found that fatigue strength decreased after applying compressive preloading to a welded joint due to cancellation of the compressive stress at the weld toe.In the present research, the influence of excessive preloading on the fatigue strength of welded joints with compressive residual stress at the weld toe was clarified by experiments using hammer peening with an improved pin.When hammer peening was applied to welded joints, increasing the radius of the weld toe reduced the decrease of compressive residual stress due to excessive preloading. As a result, the decrease of the fatigue strength of the welded joint was also reduced.Copyright

Assessment of Fatigue Crack Growth in Imperfect Lap Joint: Part 2 — Crack Propagation Analysis Using “SCANP”

The deck plates of single-deck-type floating roofs for large oil storage tanks are joined by single-welded Full-fillet lap joints. In areas with frequent strong winds, fatigue cracks sometimes occur in the welds of the deck plate. The aim of the present study is to investigate the effect of the gap imperfection of the lap joints on the fatigue life. In the case that tensile load acted on Full-fillet lap joints, the stress at the crack face becomes larger by gap imperfection of the lap joint. The authors have developed a software system called “SCANP (Surface Crack Analysis Program)”, a software system to evaluate the stress intensity factor, K, and to simulate fatigue crack propagation for surface cracks for arbitrarily distributed surface stresses. The fatigue life of a lap joint was predicted by the “SCANP” using the calculated stresses at the root crack face and the toe crack face. The number of loading cycles to penetration for arbitrary bending load amplitudes and tensile load amplitudes are obtained.Copyright

Assessment of Fatigue Crack Growth in Imperfect Lap Joint: Part 1 — Analysis of Stress Distribution on Virtual Crack Plane

The deck plates of a single-deck-type floating roof for large oil storage tanks are joined by single-welded full-fillet lap joints. In areas with frequent strong winds, fatigue cracks sometimes occur in the welds of the deck plates. The aim of the present study is to investigate the effect of the gap imperfection of the lap joint on the fatigue life. Generally, weld imperfections significantly reduce the fatigue crack propagation life of the welded joints. A stress analysis using the finite element method was performed to provide the basic data for the fatigue crack growth analysis.Copyright