Jae-Ki Kwon

Factors influencing fatigue crack propagation behavior of austenitic steels

In the present study, the fatigue crack propagation (FCP) behaviors of austenitic single phase steels, including STS304, Fe18Mn and Fe22Mn with different grain sizes ranging from 12 μm to 98 μm were investigated. The FCP tests were conducted in air at an R ratio of 0.1 using compact tension specimens and the crack paths and fracture surfaces were documented by using an SEM. The highest ΔKth value of 9.9MPa·m1/2 was observed for the Fe18Mn specimen, followed by 5.2MPa·m1/2 for the Fe22Mn specimen and 4.6MPa·m1/2 for the STS304 specimen, showing a substantial difference in the near-threshold FCP resistance for each microstructure. The crack path and fractographic analyses suggested that the near-threshold FCP behavior of these austenitic steels was largely influenced by the degree of slip planarity, as determined by stacking fault energy and grain size, rather than the tensile properties. In the Paris’ regime, the slip planarity still played an important role while the tensile properties began to affect the FCP. The FCP behavior of austenitic steels with different microstructural features are discussed based on detailed fractographic and micrographic observations.

Numerical Study for Development of Submerged Seawater Lift Pump

*Minreal Resources Research Division, KIGAM, Daejon, Korea**Naval Architecture, Ocean and IT Engineering, Kyungnam Univer sity, Changwon, KoreaKEY WORDS: Seawater lift pump 해수펌프, Mixed flow pump 사류펌프, Floating production storage and offloading 부유식원유생산설비, Total head 전양정ABSTRACT: Seawater lift pump systems are responsible for maintaining open canal levels to provide the suction flow of circulating water pumps at the set point. The objective of this paper is to design a 2- stage mixed flow pump (for seawater lifting), investigate the n ew impeller modeling method, and performance improvements of the impeller by using a commercial CFD code. The rotating speed of the impeller is 1,7 50 rpm with a flow rate of 2,700 m3/h. A finite volume method with a structur ed mesh and realized k-e turbulent model is used to guarantee a more accurate prediction of turbulent flow in the pump impeller. The performa nce variables such as the static head, brake horsepower, and ef ficiency of the mixed flow pump are compared based on changes in the impeller blade s hape.교신저자 우남섭: 대전광역시 유성구 과학로 124, 042-868-3134, nswoo@kigam.re.kr본 연구는 2011년 울산에서 개최된 해양플랜트설계연구회 춘계워크숍에 발표된 논문을 근간으로 하고 있음을 밝힙니다 .

Through-thickness SCC susceptibility of 2024-T351 and 7050-T7451 extrudates in 3.5% NaCl solution

The through-thickness stress corrosion cracking (SCC) behaviors of thick 2024-T351 and 7050-T7451 extrudates in 3.5% NaCl solution were studied at both anodic and cathodic applied potentials using a slow strain rate test method. The SCC susceptibilities of 2024-T351 extrudate tended to change in the throughthickness direction, with the lowest susceptibility for the surface specimen. 7050-T7451 specimens, on the other hand, did not show a notable change in the through-thickness SCC susceptibility. The fractographic analysis suggested that the grain boundary played an important role in determining the SCC susceptibility. The SCC process of each alloy was discussed based on the microscopic and fractographic examinations.

A Study on the Multiphase Flow Characteristics Inside Subsea Separation System

The implementation of subsea separation and liquid boosting is becoming a common development scheme for the exploration of deep water fields. Subsea separation system should be reliable to ensure successful operation in a wide range of 3-phase flow regime, without need for developments. A subsea separator can avoid or simplying costly surface platforms of floating vessels, as well as being an efficient tool to enhance hydrocarbon production. One solution of interest is the separation and re-injection of water at the seabed to avoid bringing the water up to the surface facility. In this study, multiphase flow characteristics inside subsea separation system are investigated for the design of subsea separation system.Copyright

Understanding of Offshore Drilling System and Trend Analysis

Offshore drilling refers to a mechanical process where a wellbore is drilled through a seabed. It is typically carried out in order to explore for and subsequently extract petroleum which lies in rock formations beneath the seabed. There are many different type of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs, combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units including semi-submersibles and drillships. These are capable of operating in water depths up to 3,000 m. In this paper, we introduce the drilling system, which is mounted on the offshore drilling facilities.

Drilling Riser System Design in Deepwater Environment

The development of deepwater oil and gas reserves constantly faces the challenge to reduce costs of all components and activities. A drilling riser is a conduit that provides a temporary extension of a subsea oil well to a surface drilling facility. With an increase in drilling operations in harsh environments, drilling riser requirements and limits have become more onerous due to uncertainties involved in response prediction and prolonged drilling programs. A high level of understanding is required of the response of the system to various conditions, and the design issues that govern the system. This paper presents an overview of the engineering challenges faced in designing drilling riser system for drill ship in water depths of 10,000 ft. Also, Static and dynamic analysis of drilling riser system have been carried out for the development of drilling riser joint.Copyright

FATIGUE BEHAVIOR OF API X-80 STEELS

API X-80 steel is extensively used as a piping material in oil and gas industries with good combination of strength, toughness and resistance to H2S damage. Drill riser, for example, is a conduit providing a temporary extension of a subsea oil well to surface drilling facility and is in large part made of welded X-80 steel pipe. The riser system is subject to fatigue loading from wave and tidal motion, vortex induced vibration (VIV) and operating loads at low temperatures in corrosive environments. The reliability of drill riser system is extremely important and therefore the effects of environmental factors, including temperature and seawater, on fatigue crack propagation (FCP) behavior of X-80 steels, both BM (base metal) and WM (weld metal), need to be well understood. In this study, S-N fatigue and FCP tests were conducted on X-80 steel, including BM and WM, in air at 25 and −50°C and an R ratio of 0.1. The FCP tests were also performed on X-80 steel BM in artificial sea water at both cathodically and anodically controlled voltages. The fatigue behavior of X-80 steel at various testing conditions are discussed based on detailed optical micrographic and SEM fractographic observations.Copyright