The Study On CTOD Temper Of Welded Joint In Offshore Platform

Since 1940s, crisp subversive accidents of big jointing structure have happened successively in the world. Toughness problem of jointing structure have been attached importance to by many countries. At the present time, offshore structure tend to be good-sized and the strength of steel on the offshore structure becames higher and higher while oil been empoldered in deep water. Toughness problem of the steel and welded joints on offshore structure must be one pop research in the correlative domain in the world.Firstly, CTOD method test to the toughness of the steel and welded joints on offshore structure has been introduced in the paper. Secondly, the CTOD toughness has been tested to someone offshore platform in low temperature(-10℃). The test results indicate that:one aspect, the CTOD of the welded joints in different welding procedure are different obviously; the other aspect, the discrete degree of the CTOD in different thickness and different extent are also different. Based on the characteristic showed by the test results, the following two aspects has been analysed emphasizedly in the paper:one, factors affected to the toughness of welded joints; the other, the dispersion of the CTOD for welded joints. This paper will give some test warranties for toughness research to welded joints of ultra-high strength steel, and can supervise practice production farther in one aspect; the other aspect, new viewpoints and thoughts have been gaven about the technique assessed CTOD toughness to welded joints of ultra-high strength steel.Factors affected to the toughness of welded joints has been analysed in two different aspects. One, welded material and welded procedure; the other, macrofractography and microstructure. The results indicate that:one, the variety of welding linear energy has a visible influence to CTOD both of fusion line and weld center, but the rule affected to is different, this rule gives a test gist for advancing toughness of welded joints in manufacture; another, the macrofractography both of fusion line and weld center show cleavage brittle fracture, and both of fusion line and weld center has different degree gas pore and oxide slag; last, the microstructure both of fusion line and weld center show well ductility tempered sorbite or acicular ferrite. Based on the microstructure characters of welded joints, together according to the statistical rule of test results, new viewpoints have been gaven about allowable value of CTOD to ultra-high strength steel.For high discrete characteristic of CTOD to welded joints of ultra-high strength steel, the method compared simply by limited sample values with allowable value has some localization, while CTOD toughness of ultra-high strength steel has been assessed. It must be more scientific when probability and statistic analytic method has been imported. Below this idea, probability and statistics method based on normal school for assess to CTOD toughness has been established. At the same time, based on different discrete degree, new advices have been gaven to the sampling number both of fusion line and weld center.