A steel for grade r6 offshore mooring chain with high strength and high toughness and its chain use in anchoring and mooring floating bodies with cathodic protection

US20210285069A1Pending Publication Date: 2021-09-16JIANGYIN XINGCHENG SPECIAL STEEL WORKS CO LTD
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Patent Information

Authority / Receiving Office
US · United States
Current Assignee / Owner
Publication Date
2021-09-16

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Abstract

The present application relates to a steel for grade R6 offshore mooring chain for use in anchoring and mooring floating bodies with cathodic protection: the chemical composition are C 0.18˜0.24%, N 0.006˜0.024, P 0.005˜0.025, S≤0.005, Si 0.15˜0.35, Mn 0.20˜0.40, Cr 1.40˜2.60, Ni 0.80˜3.20, Mo 0.35˜0.75, Cu≤0.50, Al≤0.02, Ti≤0.005, V 0.04˜0.12, Nb 0.02˜0.05, Ca 0.0005˜0.004, O≤0.0015, H≤0.00015, the balance is Fe: the total content of alloy ΣM=(Si+Mn+Cr+Ni+Mo+Cu), 3.4<ΣM≤6.8; the total content of microalloy ΣMM=(Ti+Al+Nb+V), 0.065≤ΣMM≤0.194. The corrosion potential is adjusted to prevent hydrogen embrittlement caused by cathodic overprotection on the basic premise of maintaining the strength, toughness and low corrosion rate of the steel. Where V is only used for strengthening, and the content of N in VCN is increased, especially for the increase of the temperature for chain quenching to make M3C, M2C and VCN fully dissolved in solid solution and fully precipitated in tempering, which improves the precipitation strengthening effect.
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Description

TECHNICAL FIELD

[0001] The present application relates to alloy steel and ferrous metallurgical products for offshore engineering, in particular a grade R6 steel and chain for offshore mooring in the steel series for offshore mooring chain and the evaluation of its offshore environmental performance degradation resistance.BACKGROUND ART

[0002] A mooring system is acquired for positioning and mooring with floating bodies in the process of the marine exploration, deep-sea oil and gas extinction, national defense construction and so on. The main component of the mooring system is offshore mooring chain by the steel. According to the standard in DNVGL (Det Norske Veritas-Gemtanischer Lloyd) named Offshore Standards, DNVGL-OS-E302 Offshore mooring chain. Edition July 2018, the offshore mooring chain can be classified into six grades called R3, R3S, R4, R4S, R5, and R6 according to its strength grading. The tensile strength of the chains at all grades after overall quenching-tempering shall b...

Examples

Embodiment Construction

0]The present invention is further described in detail with reference to carrying out example.

[0071]Carrying out example (invention example) 1-4 and contrast example 3 are about the process wherein continuous casting bloom with tire size of 390×510 mm are rolled into the round bars with a diameter of 120 mm, while contrast example 1, 2 and 4 are about the process that 420 kg test ingots are forged into round bars with a diameter of 95 mm, and then the round bars are processed in sequence by blanking, heating, bending, flash welding, forming chain and heat treatment (quenching+tempering) to obtain the finished chain. The performance data is the average value of the results of three groups of specimens. Numerical treatment of the third place after the decimal point: ≤discard and ≥6 into 1.

[0072]See Table 2 for the chemical composition of carrying out example 1 to 4 and contrast examples 1 to 4. See Table 3 for process parameters and performance of the chain, and see Table 4 for the si...