Nobuyuki Hisamune

Metallurgical Design of Newly Developed Material for Seamless Pipes of X80–X100 Grades

With the increasing development of oil and gas fields in deepwater or ultra-deepwater with deep well depth, the development of high strength seamless pipe has become necessary. This paper describes a metallurgical design of seamless pipe with high strength reaching X80–X100 grade (minimum yield strength, 552 MPa–689 MPa) manufactured by steel containing very low carbon and with a microstructure of uniform bainite. The effect of microstructure of quenched and tempered (QT) steel on strength and toughness is investigated in laboratory. Uniform bainitic structure without coarse martensite-austenite constituent (M-A) is obtained by lowering bainite transformation temperature during quenching process by controlling the alloying elements. Moreover the structure is very effective in obtaining good toughness for tempered steel even with the high strength X100 grade. Sufficiently low hardness and good toughness in heat affected zone (HAZ) are confirmed by welding tests. The trial production of developed steel is conducted by applying inline QT process in medium-size seamless mill according to an alloying design obtained in laboratory tests. The seamless pipes of the trial production achieve grades X80 to X100 by changing tempering temperature. Some data of mechanical properties of the produced pipes is introduced.Copyright

Development of Welding Procedures for X90-Grade Seamless Pipes for Riser Applications

Ultra-high strength seamless pipes of X90 and X100 grades have been developed for deepwater or ultra-deepwater applications. Girth welding procedure specifications (WPSs) should be developed for the ultra-high strength pipes. However, there is little information for double jointing welding procedure by using submerged arc welding process for high strength line pipes.This paper describes mechanical test results of submerged arc welding (SAW) and gas shielded flux cored arc welding (GSFCAW) trials with various welding consumables procured from commercial markets. Welds were then made with typical welding parameters for riser productions using high strength X90 seamless pipes.The submerged arc weld metal strength could increase by increasing alloy elements in weld metal. The weld metal with CE (IIW) value of 0.74 mass% achieved fully overmatching for the X90 pipe. The weld metal yield strength (0.2% offset) was 694 MPa, and the ultimate tensile strength was 833 MPa. It was also confirmed that the reduction of boron in weld metal can improve low temperature toughness of high strength weld metal. Furthermore, it was confirmed that the HAZ has excellent mechanical properties and toughness for riser applications.In this study GSFCAW procedures were also developed. GSFCAW can be used for joining pipe and connector material for riser production welding. The weld metal with a CE (IIW) value of 0.54 mass% could meet the required strength level for X90-grade pipe as specified in ISO 3183. Cross weld tensile testing showed that fractures were achieved in the base metal. Good Charpy impact properties in weld metal and HAZ were also confirmed.© 2012 ASME

Development of High Strength Heavy Wall Seamless Pipes of X80–X100 Grade for Ultra-Deep Water Application

This paper describes the development of high strength heavy wall seamless pipes of X80 to X100 grade for ultra-deep water application. Steel pipes with higher strength generally tend to have low fracture toughness either in pipe body or in weld joint and low weldability. Therefore, improvement of fracture toughness and weldability are particularly important with respect to development of higher strength seamless pipes. Metallurgical research in laboratory test was carried out and the effect of microstructure of quenched and tempered steel on strength and toughness was particularly investigated. As a result uniform lower bainite phase containing no or minimized coarse martensite-austenite (M-A) constituent at a quenched condition is suitable microstructure to perform high strength and high fracture toughness after tempering. The steel having such microstructure showed excellent performance even in the high strength grade of X100. Lowering a transformation temperature from austenite phase to bainite phase during quenching process is effective to obtain suitable microstructure by adding and controlling alloy elements such as Mn, Cr, Mo. In order to suppress an increase in carbon equivalent as Pcm value by addition of alloy element, lowering content of carbon is necessary. As a consequence of the low Pcm value mitigation of hardening in coarse grain heat affected zone (HAZ) and good toughness were confirmed by welding tests. A trial production of the developed steel based on a new metallurgical design mentioned above was conducted by applying inline heat treatment process in medium-size seamless mill. In conjunction with tremendously rapid cooling system of inline heat treatment facility the seamless pipes of the trial production achieve grades X80 of 40 mm wall thickness and X80 to X100 grades of 20 mm WT by changing tempering temperature. A good combination of high strength and good fracture toughness was confirmed.Copyright

Development of High-Strength Heavy-Wall Sour-Service Seamless Line Pipe for Deep Water by Applying Inline Heat Treatment

High strength heavy wall sour service seamless line pipe suitable for deep water applications has been developed by Sumitomo Metal Industries, Ltd.,. This paper describes the concept of developing these pipes applying inline heat treatment technology, equipped in a newly constructed, medium-size seamless mill. Increasing hardenability through inline heat treatment achieved higher strength (X70) for heavy wall pipe (40mm) even though carbon equivalent was lower than in a conventional Q&T process. Good toughness was obtained by the control of microalloying elements such as titanium or sulfur. The produced pipe passed the hydrogen-induced cracking (HIC) test conducted according to NACE TM 0284 solution A. Controlling the microstructure and suppressing maximum hardness, utilizing the uniform quenching facility during inline heat treatment, contributed to the test result. Satisfactory data on weldability for practical use were also obtained.Copyright