High-strength UOE steel pipe excellent in earthquake-proof performance and in low-temperature toughness of weld heat-affected zone

Abstract

A high-strength UOE steel pipe is provided which has excellent earthquake-proof performance and has a weld heat-affected zone having excellent low-temperature toughness. The pipe is suitable for use as a pipeline to be laid in, e.g., permafrost in cold latitudes or an earthquake-prone region. The UOE steel pipe has a steel composition which contains 0.03-0.07% carbon, 0.05-0.50% silicon, 1.6-2.2%manganese, up to 0.020% phosphorus, up to 0.003% sulfur, 0.20-0.60% copper, up to 0.10% chromium, 0.20-0.80% nickel, 0.005-0.030% niobium, 0.005-0.030% titanium, up to 0.0070% nitrogen, and 0.005-0.060% aluminum, with the remainder being iron and impurities, and has a hardenability index (Pcm) of 0.22% or less, and in which Cu+Cr+Ni is 0.4-1.5% and Nb+Mo+V is 0.05% or lower. The pipe has a yield strength in the axial direction of 480 MPa or higher and a yield ratio of 85% or lower. In the pipe, the weld heat-affected zone has a Charpy absorbed energy at -40 DEG C of 40 J or higher.

Description

technical field [0001] The present invention relates to a UOE steel pipe. Specifically, the present invention relates to a UOE steel pipe that is installed in permafrost in cold regions and earthquake-prone regions, is suitable for use as pipelines, and has excellent seismic performance and low-temperature toughness of welded heat-affected parts. High-strength UOE steel pipe. Background technique [0002] Due to the demand for cost reduction of pipelines, whose prices have risen in recent years, the strengthening of UOE steel pipes used for pipelines has also been promoted accordingly. Especially the rupture of long-distance pipelines used to transport natural gas and oil will cause major accidents. In order to apply the UOE steel pipe composed of high-strength steel to pipelines, it is most important to ensure safety against fracture. Conventional line pipes were designed based on stress-based design. Conventionally, it has been desired that UOE steel pipes used to form ...

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Problems solved by technology

Although some evaluation items for evaluating earthquake resistance have been known in the past, in fact, the specific performance requirements for earthquake resistance have not been established in foreign countries

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