Abstract: A method of repairing a turbine rotor wheel having a damaged dovetail includes removing the damaged dovetail from the turbine wheel, leaving a turbine wheel body and welding a ring about the turbine wheel body in place of the removed damaged dovetail. During the welding process, including during preheating, welding or stress relieving, the temperature of the wheel body and ring is differentially controlled to introduce residual stresses in the ring. After welding a dovetail is formed in the ring for receiving turbine bucket dovetails. As a result, the ring has residual compressive stresses in a cold condition of the turbine whereby reduced net stresses in the ring in the location of the new dovetail during hot turbine operating conditions are reduced.

Abstract: A steam turbine rotor is constructed from a first forging of a first alloy, and a second forging of a second alloy different than the first alloy. For example, one of the alloys is suitable for use in a high temperature environment and the other in a low temperature environment. The forging ends are contoured so as to provide central portions, which may be disc-shaped, and the contoured portions may be in the shape of truncated cones. A first weld, such as a root weld formed by inertia, friction, or electroslag welding, joins the central portions, and the contoured portions are joined by a second weld different than the first weld, such as a submerged arc weld. This allows the rotor forgings to be joined in relatively inexpensive horizontal facilities, and reduces the demands on the welding technology required to obtain a sound root weld.

Abstract: A steam turbine rotor is constructed from a first forging of a first alloy, and a second forging of a second alloy different than the first alloy. For example, one of the alloys is suitable for use in a high temperature environment and the other in a low temperature environment. The forging ends are contoured so as to provide central portions, which may be disc-shaped, and the contoured portions may be in the shape of truncated cones. A first weld, such as a root weld formed by inertia, friction, or electroslag welding, joins the central portions, and the contoured portions are joined by a second weld different than the first weld, such as a submerged arc weld. This allows the rotor forgings to be joined in relatively inexpensive horizontal facilities, and reduces the demands on the welding technology required to obtain a sound root weld.

Abstract: A method of repairing a turbine rotor wheel having a damaged dovetail includes removing the damaged dovetail from the turbine wheel, leaving a turbine wheel body and welding a ring about the turbine wheel body in place of the removed damaged dovetail. During the welding process, including during preheating, welding or stress relieving, the temperature of the wheel body and ring is differentially controlled to introduce residual stresses in the ring. After welding a dovetail is formed in the ring for receiving turbine bucket dovetails. As a result, the ring has residual compressive stresses in a cold condition of the turbine whereby reduced net stresses in the ring in the location of the new dovetail during hot turbine operating conditions are reduced.

Abstract: A method for weld repairing an article formed of a low-alloy steel, such as a steam turbine component. The method generally includes the step of depositing a first weld repair (14) on a surface of the article, during which a hard heat-affected zone (HAZ) (18) having a fine grain size is formed in the article beneath the surface on which the weld repair (14) is deposited. The first weld repair (14) and at least a portion of the HAZ (18) adjacent the first weld repair (14) are then locally heat treated at a temperature above a critical temperature A.sub.1 of the alloy from which the article is formed. As a result of this localized heat treatment, the original grain structures of the first weld repair (14) and the HAZ (18) are entirely replaced with a fine-grain structure with acceptable hardness. Thereafter, at least one additional weld repair layer (16) is deposited on the first weld repair (14).

Abstract: A method for repairing the rim of a steam turbine rotor, and a weld material for repairing such rotors. The method generally includes the steps of removing a damaged rim and its associated dovetail region, so as to form a surface at the perimeter of the rim portion. A weld repair region is then formed on the surface, which is machined to reconstruct the rim portion and the dovetail region exclusively with the weld repair region. Thereafter, an appropriately configured blade is secured to the rim portion with the dovetail region. The method is particularly intended for the repair of a steel alloy rotor, such as a NiCrMoV, NiMoV and CrMoV alloy, while the weld repair is formed with a nickel-base superalloy whose mechanical and thermal properties are compatible with the repair method and the steel alloy over a broad temperature range.

Abstract: The welding method for repairing a turbine rotor dovetail includes removal of buckets from damaged dovetails, removing a damaged dovetail from a turbine wheel, leaving a rotor wheel body having a rim. A plurality of ring sections are disposed about the wheel body rim, leaving axially opening annular grooves along opposite sides of the wheel. Welding apparatus including an electrode, welding wire and gas-carrying tube are inserted into the groove through an axial face of the wheel. One or more cover plates are disposed to overlie the groove at the location of its opening through the axial face of the wheel to at least partially seal the groove at its opening and maintain welding gas in the groove, enveloping the electrode and weld wire.

Abstract: A turbine rotor comprising a radially-inward portion of a steel alloy and a radially-outward rim portion circumscribing the radially-inward portion, the rim portion being formed by a weldment that includes a nickel-base superalloy region joining the rim portion to the inward portion of the turbine rotor, the nickel-base superalloy having a room temperature ultimate tensile strength of at least about 690 MPa.

Abstract: A method for weld repairing an article formed of a low-alloy steel, such as a steam turbine component. The method generally includes the step of depositing a first weld repair (14) on a surface of the article, during which a hard heat-affected zone (HAZ) (18) having a fine grain size is formed in the article beneath the surface on which the weld repair (14) is deposited. The first weld repair (14) and at least a portion of the HAZ (18) adjacent the first weld repair (14) are then locally heat treated at a temperature above a critical temperature A.sub.1 of the alloy from which the article is formed. As a result of this localized heat treatment, the original grain structures of the first weld repair (14) and the HAZ (18) are entirely replaced with a fine-grain structure with acceptable hardness. Thereafter, at least one additional weld repair layer (16) is deposited on the first weld repair (14).