• T

    T: Abbreviation for temperature; t: abbreviation for time. 


    A joint between two members located approximately at right angles to each other in the form of a T. 

  • T-WELD

    A weld in which one plate is welded vertically to another, as in the case of the edge of a transverse bulk-head being welded against the shell plating or deck. This is a weld which in all cases requires exceptional care, and can only be used where it is possible to work from both sides of the vertical plate. A T-weld is also used for welding a rod in a vertical position to a flat surface, such as the rung of a ladder, or a plate welded vertically to a pipe stanchion, as in the case of water closet stalls. 


    A weld made to hold the parts of a weldment in proper alignment until the final welds are made.

    A tack weld is a short weld made at intermittent points to hold abutting edges together. The length of the weld, spacing between welds, and design of the tack weld should always be specified. Specifications usually include the length of each tack weld and the measurement from center to center of the tack welds. The particular design of the tack weld is often not specified. 


    A nonstandard term for TACK WELDER. 


    Welding at several points on the welding line to hold the workpieces together and prevent the pieces from shifting during the actual welding operation. See TACK WELD. 


    The American Society for Mechanical Engineers (ASME) maintains a Boiler and Pressure Vessel (B&PV) Code which contains material standards and specifications that cover tanks made from carbon and alloy steels. The ASME codes govern design, construction, maintenance, and inspection of power boilers, heating boilers, nuclear power plant components, pressure piping systems, and pressure vessels operating at 103 kPa (15 psi) and higher.

    The American Petroleum Institute (API) has prepared material specifications for welding steel tanks, vessels, and tubular products used in the petroleum industry.

    Persons involved in tank welding should become familiar with the ASME B&PV Code and API Standard 1104. Refer to American Welding Society, Welding Handbook, Volume 1, 8th Edition, American Welding Society, Miami, Florida. 1989.

    Tank Repair- There are many types of tanks and piping systems which have contained hazardous substances. All are potentially dangerous. Information on safe practices for tank repair is found in ANSVAWS F4.1, Recommended Safe Practices for Preparation for Welding and Cutting of Containers and Piping.

    Metal storage tanks commonly located at the top of buildings to supply water for private fire protection are welded subject to rules and regulations of the American Water Works Association (AWWA) and the National Board of Fire Underwriters. These rules are set forth in ANSVAWWA DlOO (AWS D5.2), AWWA Standard for Welded Steel Tanks for Water Storage. 


    Tanks which contained flammable oil, gasoline, vapors or gas must be handled with caution when making repairs by welding. These tanks may contain sufficient air and residual fumes to cause an explosion when mixed with the gas used with a cutting or welding torch. The document, AWS F4.1, Recommended Safe Practices for the Preparation for Welding and Cutting Containers and Piping That Have Held Hazardous Substances, should be consulted.

    Before welding or cutting a tank with an arc or torch it is essential to clean the tank thoroughly and remove all possibility of a flammable mixture remaining in the tank. 


    (Chemical symbol: Ta). A ductile, gray metallic element. It is known for its resistance to a wide variety of acids, alcohols, chlorides, sulfates, and other chemicals. Tantalum is used as an alloy in metals, and is also used in electrical capacitors and high-temperature furnace components. Atomic number, 73; atomic weight, 181; melting point, 2910°C (5270°F).

    Although tantalum has an extremely high melting point, and readily combines with all but the inert gases, this reactive metal will produce strong, ductile welds when welded by the gas tungsten arc welding (GTAW) process. Welding is preferably done in a vacuum chamber. The thermal conductivity of tantalum is somewhat lower than that of steel; the thermal coefficient of expansion is about the same as steel. 


    Removing a tap which has been broken off below the surface of the workpiece can be done using the following procedure:

    If the hole provides clearance, a coated electrode can be used to build up the tap until it is above the surface. This is best accomplished by dipping it in and out of the puddle. The coating on the electrode helps to prevent damage to the threaded walls of the hole.

    Once the tap has been built up above the surface, the end can be filed into a square, gripped by a wrench, and the tap backed out. 


    The time interval after upslope during which the current is constant. 


    The time interval when current increases or decreases continuously from the welding current to final taper current. 

  • TAPS

    Connections to a transformer winding that are used to vary the transformer turn ratio, thereby controlling welding voltage and current. 


    (Chemical symbol: Te). A silver-gray, metallic element of the sulphur group. It is a poor conductor of heat and electricity. Tellurium forms well-defined compounds, known as tellurides, with other elements. It is used as an alloy in steel, lead, and ceramics, and is used in thermoelectric devices. It is used to some extent in the covering of welding cables to make them more resistant to abrasion. Atomic weight, 147.6; melting point, 461°C (862°F); specific gravity, 6.25. 


    The degree of hardness produced in an alloy by heat treatment and controlled cooling. 


    The microstructure of a casting of any type of malleable iron is derived by controlled annealing of white iron of suitable composition. During the annealing cycle, carbon that exists in combined form, either as massive carbides or as a micro constituent in pearlite, is converted to a form of free graphite known as temper carbon.


    Temper colors on bare, clean, bright steel provide a useful visual method of estimating time and temperature of exposure of heat-affected areas in weldments, judging from surface appearance. When a weld is made by localized heating, temper colors ranging from shades of black, through blue, red, brown and tan will run in bands parallel to the long axis of the weld after the weld has cooled. These variations in color are the effect of various thicknesses of oxide films that form on the surface of iron and steel when heated in air. Sand blasting or pickling can be used to prepare a surface on which temper colors from welding can be observed. Temper colors can give a rough indication of the maximum temperature imposed on the base metal at varying distances from the weld. For example, if two different welds are compared for temper colors, and the brown-purple transition is found closer to the edge of the weld in the first plate, it can be concluded that the weld in the first plate was heated more rapidly and cooled faster than the weld in the second plate. The colors formed on iron and carbon steel by progressively higher temperatures are listed in Table T-2. 

  • TEMPER TIME, Resistance Welding

    The time following quench time during which a current is passed through the weld for heat treating. See Figure I-1. 


    The level of intensity of thermal energy that exists in a substance.

    Temperature changes in welding are important variables. Heat is a fundamental factor in most of the welding processes and in thermal cutting. Cooling rates also have significant consequences that must be considered. Heat is a fundamental factor in most welding processes and in thermal cutting. See METALLURGY. 


    The two temperature scales commonly used in metal work are Fahrenheit (F) and Celsius (C).

    On the Fahrenheit scale, the freezing point of water is 32°F and boiling point of water is 212"F.On the Celsius scale, 0°C is the point at which water freezes and 100°C is the boiling point. Thus, 100 divisions on the C scale equal 180 divisions on the F scale. This makes 1"C equivalent to 9/5 or 180/100 of 1oF

    To convert from °C to °F: °F = 9/5 °C + 32.

    To convert from °F to °C: °C = 5/9 (°F -32). 

  • TEMPERATURES, Arc Welding

    It has been estimated that the temperature of the metal arc is approximately 3300°C (6000°F). The temperature of the carbon arc varies considerably and is dependent on the arc length and the graphite content of the electrode. Its range is from 3790 to 5290°C (6850 to 9550°F).The atomic hydrogen flame has a theoretical temperature of 4000°C (7250°F). The heat absorption due to the formation of atomic hydrogen, however, reduces this temperature to about 2950°C (5340°F).

    The temperature of the gas tungsten arc has been estimated to be 5500°C (10 000°F). The temperature produced by a plasma arc cutting torch is estimated to be 16 600°C (30 000°F). 


    A number of fuel gases are used in welding and cutting operations, including acetylene, propane, methylacetylene-propadiene, propylene, natural gas and hydrogen. Table T-1 shows characteristics of the common fuel gases. See also FURNACE, Temperature. 


    A process for increasing the degree of hardness or resiliency of a metal; the reheating of iron base alloys after hardening at a temperature below the critical range, followed by a specified rate of cooling. 


    A pattern or prototype of a part from which identical copies can be made. Templates also provide a permanent record of the size and shape of a part.

    The most common template used in metalworking is the flat template made on heavy sheet metal. By laying the template on new stock and scribing around it, additional parts can be made at any time. Templates are frequently used for outlining parts in flame cutting operations. See PIPE WELDING, Accessories. 


    A weld made to attach a piece or pieces to a weldment for temporary use in handling, shipping, or working on the weldment.