Working with special steel grades

Tallinn Machinebuilding Factory (TMT) has gained several years' worth of experience in the design and manufacture of various vessels, as well as heat-exchange equipment with the use of superaustenitic chrome-nickel steels. The widespread use of such steels in the chemical, oil and gas, cellulose, and medical industries is accounted for their increased corrosion resistance in strong aggressive environments, as well as the resistance to pitting, crevice and intergranular corrosion. Depending on specific operating conditions and customer requirements, the TMT factory offers heat exchange equipment made of the 1.4563; AISI 904L; Sanicro 28; Uranus 28, Alloy 28, Incoloy 800 steels, with chromium content in some of them of up to 27% and nickel content of up to 35%.
TMT has developed and certified welding procedures for working with the said steels, and also operates high-performance welding equipment for the MIG, MAG and TIG welding processes (semi-automatic and argon-arc welding). The welding units are equipped with microprocessors allowing the application of special welding software designed for welding of the said steels. Welding regimes are set automatically depending on the thickness and spatial position of the parts to be joined.
The heat-exchange equipment made of duplex and super duplex steels is used in conditions demanding increased mechanical strength, resistance to aggressive environments and sea water. The TMT factory has mastered the production of multi-purpose heat exchangers and vessels, pipelines and pump parts made of the Duplex 2205 steel, as well as the Super Duplex 2507 steel, which are widely used for equipment designed for the chemical and petrochemical industries. An important reason for the widespread use of the duplex steels is their relatively low cost in comparison with superaustenitic steels due to lower content of scarce nickel.
The TMT factory offers heat exchange equipment made of the Hastelloy C-276 steel alloy, which has exceptional properties of resistance to stress corrosion in chloride-containing solutions and is also resistant to sulfide cracking. These properties are especially valuable for equipment used in oil fields, as well as at chemical plants that use very aggressive chemical processes at elevated temperatures of up to 500 °C.
In collaboration with specialized research institutions and laboratories, the TMT factory is ready to participate in determining the type of material used in designed equipment to ensure its reliable and durable operation.
TMT uses titanium, which has excellent corrosion resistance and good mechanical properties, for the manufacture of chemical industry equipment designed for operation in aggressive environments, such as perchloric, nitric and sulfuric acids, and at high temperatures. In addition, the use of titanium in the manufacture of equipment increases its structural reliability, reduces its weight and extends its lifetime.
Technological aspects of titanium processing and welding are determined by its high melting point, as well as the negative impact of atmospheric air on its structure. At temperatures above 400 °C, hot zones require additional protection, along with the basic insulation of the weld pool itself. When the temperature rises to 900 °C and above, grain growth occurs and large pores are formed, which further affects the strength characteristics of welded assemblies. Due to these factors, titanium welding shall be performed in protective gaseous media, and preliminary, meticulous edge preparation is required.
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