Creep Life Assessment Method for Welded Joint of Grade 91 Steel Considering Material Properties of Individual Piping

This paper details a case study on the effect of weld peak geometry on the expected creep life of a piping system operating in a refining environment. Inspection of the 1-1/4 Cr piping system revealed significant peaked geometry at the longitudinal weld locations. A Finite Element Analysis (FEA) assessment of the remaining life was made using the Omega method of creep life assessment. The sensitivity of the results to modeled pipe geometry and assumed material properties was assessed. The variability of life prediction that was obtained indicated a necessity to perform further more detailed assessment of the pipe geometry and material properties by the removal of samples at the weld locations. The improvement obtained in the assessment accuracy and final life predictions from the sample analysis is presented in the paper and practical implications on the operation of the piping system are detailed. Suggestions and cautions for the practical assessment of similar peaked pipe problems are also discussed.

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Estimation of Creep Strength of Grade 91 Steel Welded Joint in Time Region Over 100,000 Hours

ASME 2018 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries ◽

10.1115/etam2018-6720 ◽

2018 ◽

Cited By ~ 1

Author(s):

Masatsugu Yaguchi ◽

Sosuke Nakahashi ◽

Koji Tamura

Keyword(s):

Creep Strength ◽

Welded Joints ◽

Welded Joint ◽

Base Metals ◽

Creep Life ◽

Initial State ◽

Creep Tests ◽

Grade 91 ◽

Grade 91 Steel

A creep strength of welded joint of ASME Grade 91 steel in a region exceeding 100,000 hours was examined in this work. Creep tests were conducted on the steel used at USC plants for long-term, and remaining creep life of the material for operating condition was calculated on a fitting curve using Larson-Miller parameter. Total creep life of the material, which means a creep life at initial state, was presumed to be a summation of the service time at the plants and the remaining creep life. The estimation was conducted for welded joints used at five plants for long-term, and all results lay within 99% confidential band by the creep life evaluation curve of the material proposed by Japanese committee in 2015, while a significant heat-heat variation of creep strength was found even in the region exceeding 100,000 hours. Creep tests on base metals related to each welded joint were also conducted, and the estimation results of the total creep life of the base metals were compared to those of the welded joints. It was suggested that the heat-heat variation of the welded joints eminently depends on the creep life property of the corresponding base metal.

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A creep life assessment method for boiler pipes using small punch creep test

International Journal of Pressure Vessels and Piping ◽

10.1016/j.ijpvp.2009.04.005 ◽

2009 ◽

Vol 86 (9) ◽

pp. 637-642 ◽

Cited By ~ 38

Author(s):

Toru Izaki ◽

Toshimi Kobayashi ◽

Junichi Kusumoto ◽

Akihiro Kanaya

Keyword(s):

Creep Test ◽

Assessment Method ◽

Life Assessment ◽

Creep Life ◽

Small Punch ◽

Creep Life Assessment ◽

Small Punch Creep Test

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Effective Portion of Sample Taken From USC Boiler Pipes to Consider Heat-to-Heat Variation of Creep

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2018-84173 ◽

2018 ◽

Cited By ~ 1

Author(s):

Masatsugu Yaguchi ◽

Masato Tomobe ◽

Shin-ichi Komazaki ◽

Akihiro Kumada

Keyword(s):

Base Metal ◽

Outer Surface ◽

Welded Joint ◽

Creep Property ◽

Assessment Method ◽

Life Assessment ◽

Thickness Direction ◽

Base Metals ◽

Creep Life ◽

Creep Properties

One of authors proposed a creep life assessment method for USC boiler pipes that can consider heat-to-heat variations of the creep property of each welded joint, where the creep property of the welded joint is estimated from that of each base metal. In the method, it is assumed that the creep property of each base metal in actual pipes is approximately constant in the thickness direction of the pipes, and test results with small samples cut from base metals at the outer surface of pipes are useful for representing the creep properties of the pipes. In this work, the assumption was examined for five pipes of Grade 91 steel, which had been used for longer than 100,000 h at USC power stations. The microstructure, chemical composition, hardness, void density and remaining creep life were investigated in detail in the thickness direction of the pipes. No difference was observed for these items, except in an area less than about 0.2 mm from the outer surface of the pipes, which means that the assumption in the assessment method is valid except in this area. Therefore, it is suggested that an effective portion of the sample taken from USC boiler pipes to consider heat-to-heat variations of the creep properties of base metals is the material excluding the area less than about 1.0 mm from the outer surface of the pipes.

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