Creep Strength Evaluation of a Long-Term Used Boiler Weldment Part on 2.25Cr-1Mo Steel by Using Miniature Specimens

Standard size and miniature specimens of IN738 were taken from a service exposed turbine blade and vane for comparative stress relaxation testing at 800C, 850C and 900C. Base data taken from root section material were used to construct stress vs. creep rate parametric curves which could be used directly in design. Up to five decades in creep rates were obtained at each temperature from tests lasting less than one day. The data were also presented in the form of stress vs. predicted times to 0.5% creep which compared well with available long time creep data. Differences were noted in specimens taken from different locations in the airfoil regions which probably resulted from differences in grain size or orientation. Based on these measurements it was concluded that there was no significant effect of section size on creep strength as defined by this test, and that the alloy was quite insensitive to prior deformation and thermal exposures. A life management procedure, using a combination or creep strength evaluation based on the stress relaxation test and a separate fracture evaluation measurement, is outlined in which end of useful life is defined in terms of minimum acceptable performance levels.

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Stress Relaxation Testing of Service Exposed IN738 for Creep Strength Evaluation

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.1287345 ◽

2000 ◽

Vol 122 (3) ◽

pp. 451-456 ◽

Cited By ~ 4

Author(s):

David A. Woodford

Keyword(s):

Stress Relaxation ◽

Creep Strength ◽

Standard Size ◽

Strength Evaluation ◽

Management Procedure ◽

Section Size ◽

Long Time ◽

Evaluation Measurement ◽

Miniature Specimens ◽

Base Data

Standard size and miniature specimens of IN738 were taken from a service exposed turbine blade and vane for comparative stress relaxation testing at 800C, 850C, and 900C. Base data taken from root section material were used to construct stress versus creep rate parametric curves which could be used directly in design. Up to five decades in creep rates were obtained at each temperature from tests lasting less than one day. The data were also presented in the form of stress versus predicted times to 0.5 percent creep which compared well with available long time creep data. Differences were noted in specimens taken from different locations in the airfoil regions which probably resulted from differences in grain size or orientation. Based on these measurements it was concluded that there was no significant effect of section size on creep strength as defined by this test, and that the alloy was quite insensitive to prior deformation and thermal exposures. A life management procedure, using a combination of creep strength evaluation based on the stress relaxation test and a separate fracture evaluation measurement, is outlined in which end of useful life is defined in terms of minimum acceptable performance levels. [S0742-4795(00)01803-2]

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ATI 6-2-4-2

Alloy Digest ◽

10.31399/asm.ad.ti0169 ◽

2020 ◽

Vol 69 (8) ◽

Keyword(s):

Tensile Strength ◽

Titanium Alloy ◽

High Temperature ◽

Creep Strength ◽

High Strength ◽

Heat Treating ◽

Good Combination ◽

Long Term Stability ◽

Temperature Performance

Abstract ATI 6-2-4-2 is a near-alpha, high strength, titanium alloy that exhibits a good combination of tensile strength, creep strength, toughness, and long-term stability at temperatures up to 425 °C (800 °F). Silicon up to 0.1% frequently is added to improve the creep resistance of the alloy. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as creep. It also includes information on high temperature performance as well as forming, heat treating, machining, and joining. Filing Code: Ti-169. Producer or Source: ATI.

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