TPT January 2010

H eat and S urface T reatments

New tube materials in development For energy-conducting tubes (oilfield, conduits and boiler tubes), the trend is moving towards higher-tensile alloys as preferred materials. Pipeline producers must operate their pipelines under increasingly harsh environmental conditions and at higher pressure, in high-tensile steel grades such as X80, X100 and higher. In addition, the trend in the large tube sector is moving towards thicker walls and increased resistance to low temperatures. New hot strip grades for oil and gas pipelines measuring units and measures the strength in kilopond per square inch. The approximate value for the minimum limit of elasticity in Megapascal (MPa) results from the multiplication of the X-value with a factor of seven. Micro-alloyed tube steel grades contain exact amounts of niobium, vanadium and titanium, which are used to precisely determine the strength of the material. The viscosity of the materials is also controlled via the alloy concept. For example, high viscosity can

ThyssenKrupp Steel’s latest developments in tube steel grades involve higher tensile materials for standard grades and HIC steel grades

be avoided by producing steel grades with a high purity level and an even texture. HIC grade steel must be desulphurated, so it contains less than 0.0015% sulphur. In addition, calcium is injected into the liquefied material during production. Composite materials with customised characteristics Tribond ® , a new product from ThyssenKrupp Steel, is described as a customised composite material off the coil. The hot- rolled material combines various, in part oppositional, material characteristics in one three-layer steel strip. The basic idea revolved around the development of a material that combines high resistance to wear and tear with good plasticity. In the meantime, there are further developments that combine a comparatively low-cost, quality, hot rolled steel strip with a thin corrosion-resistant stainless steel surface. Further research concerns MultiBond ® products that expand the original three- layer TriBond design to five or more layers. Hot roll bonding of various steel grades in itself is not new. However, to date it has not been used with coil material, but rather for heavy plates in the production of corresponding slabs. The procedure creates a homogenous metalline bond at the atomic level between the individual layers in a single step. The high adhesive power of this bond can be evidenced using shear tests, among other things. As a coil material, TriBond can be processed economically, and it can be etched, cold-rolled and processed like conventional steel strips. During production, the preliminary strips and the appropriately prepared slabs are first cleaned of any forging scales, placed on top of each other and connected with circular welds. The welds stabilise the steel package and prevent the intrusion of furnace atmosphere between the individual layers

Germany’s largest steel producer, ThyssenKrupp Steel AG, is a manufacturer of feedstock for tube production. Since the middle of the 1980s the company has been supplying hot strips for tubes welded with longitudinal and spiral seams. In doing so, the supplier specialised in input stock for tubes with diameters of more than 20" (508mm) and in sour-gas resistant qualities. ThyssenKrupp Steel delivers around 500,000 tons per year to tube manufacturers around the globe. The company is also aware of the increasing demands of the input stock. Customers mainly demand higher strengths in order to be able to transport larger oil or gas volumes at higher pressure, among other things. While a few years ago, an operating pressure of 80 bar was standard for gas pipelines, today pipes are run at a pressure of up to 100 bar. To keep pace with this trend, the development of higher-tensile tube steel grades with a classification of X80 for the standard grades and X70 for sour- gas resistant materials is underway. The ‘X’ classification is based on the American

prevent the creation of kilometre-long tears caused by small defects exposed to the pressure in a pipeline. High-tensile, sour-gas-resistant tube steel grades Just under a quarter of the pipe casings supplied by ThyssenKrupp Steel are comprised of the so-called HIC (hydrogen induced cracking) grades. It is planned to expand the strength range of these sour- gas resistant tube steel grades and offer HIC steel grades with strengths of up to X70. If the transported oil or gas contains hydrogen sulphide, hydrogen-induced cracks can appear in the pipeline tubes. Such sour-gas wells exist in the Gulf region, as well as in Canada and Mexico. During hydrogen induced cracking, the hydrogen sulphide connects to the water or water vapour in the oil or gas to form sulphuric acid, which attacks the tube walls. During the corrosion process, hydrogen is produced, which diffuses into the steel and can lead to cracking. This can only

During the hot roll bonding process, a homogenous metalline bond at the atomic level is formed

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J anuary 2010

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