Diversifying Chemical Compositions of Casing and Tubing Steel According to the Final Applications

by Kwang Seop Ro, Adel Al-Butairi

Publisher - Saudi Iron and Steel Company (Hadeed)

Category - General Novel

There are many different ways to prepare the future. Diversifying the kinds of steels according to the customers’ needs is one of the best policies for the steel makers. In case of oil and gas field, many different grades and types of casing and tubing steels are currently used. Among those, API 5CT-J55 steel is one of the most popular grade in the application. However, even in J55 steel, characteristics and the requirements are varying with the final applications. The common requirement for J55 steel is low tensile to yield ratio. Medium carbon content about 0.24% is usually suitable to show low yield ratio. However, medium range of carbon is not proper to get good low temperature toughness that is especially required for casing application. Medium C-Mn steel is proper for tubing application but it is very frequently showing surface defect due to crack formation in the slabs caused from continuous casting. Therefore, the tight control of processing parameters of continuous casting is very important. On the contrary, lower carbon leads to higher yield ratio. The solution will be lower carbon content added with micro-alloying elements through optimum controlled rolling and controlled cooling conditions in hot-rolling mill. Up-graded tube needs good hardenability especially for minimizing strength drop due to coarsening of austenite grains from heat treatment. Micro-alloying addition was the key point to control strength change during heat treatment. In this paper, the details for casing and tubing steels have been explained with the optimum chemical composition and processing parameters especially for J55 grade according to the different applications.

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