Development and Properties of Ultra-High Strength UOE Linepipe

Abstract

High-pressure operation through high strength linepipe reduces long distance transportation cost of natural gas. In order to maximize the cost reduction, X120 UOE pipe has been developed. Low C-Mo-B steel with fine-grained lower bainite (LB) microstructure realizes high strength, excellent low temperature toughness and good weldability. The technology was verified in small-scale commercial production or “mini-rolls”. Suitability for use as linepipe was demonstrated through an extensive development program that covers burst test, fracture toughness evaluation, girth welding technology, etc. A demonstration line was successfully constructed using the pipes manufactured in the “mini-rolls”.

On strength of microalloyed steels: An interpretive review

“…Yield strengths in excess of 850 MPa (X120) in 12-18mm plate and strip have been achieved in MA steels processed using TMCP (3,4 Figure 13. The data of Figure 13 were generated with ULCB plate steels with rich chemistries intended for heavy gauge applications (29).…”

“…It is obvious from Figure 1, that the accelerated cooling after rolling was largely responsible for the very high strengths attainable, practically independent of composition. With suitable cooling practices, yield strengths in excess of 690 MPa (X100) can be achieved in low carbon steels containing less than 2 Wt% Mn and with C. E. and Pcm values near 0.5 and 0.2, respectively (3,4). One central question is what is the role of the MAE in obtaining these strength levels?…”

Latest developments in mechanical properties and metallurgical features of high strength line pipe steels

“…They are characterized by the low sulphur content and reduced amount of detrimental second phases such as oxides, inclusions and pearlite. Figure 1 shows the continuous evolution of HSS line pipe steel grades in terms of strength and toughness over the last decades, as well as a short description of the main alloying elements and processing applied [4][5][6].…”

“…Thus, each individual element coupled with the cooling rate will determine the type and volume fraction of phases that will form in a given steel processed under given conditions [4,25]. Figure 3 presents an overview of chemical compositions for 'conventional' and 'developed (marked with an asterisk *) API line pipe steel (from X70 to X120) [3,5,7,9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The same figure also shows the parameters that characterize good weldability, known as carbon equivalent (CE) and critical metal parameter for weld cracking (Pcm).…”

“…The latter are often quantified on the basis of Charpy V-notch (CVN) tests and Battelle drop weight tear tests (B-DWTT). Figure 6 shows the average results of the abovementioned mechanical properties for different steel grades reported in the literature [5,7,9,[11][12][13][14][15][16][17][18][19][20]26]. The tensile test specimens were extracted in the longitudinal direction.…”