Evaluation of Corrosion Fatigue Strength and Corrosion Degradation of TMCP Steel

WPFS ᖝム ✈ⱥ⽼㿜 ▗ ✈ⱥ㻄⇤ᖝᵌ 㵑ᖈ

愛滊笛^*· 愶壟笾^**

Evaluation of Corrosion Fatigue Strength and Corrosion Degradation of TMCP Steel

Jinhyung Park, and DongHo Bae

Key Words : Corrosion degradation(⿖㔳㡊䢪), Corrosion fatigue strength(⿖㔳䞒⪲ṫ☚), Corrosion susceptibility(⿖㔳⹒Ṧ㎇), Corrosion fatigue design(⿖㔳䞒⪲㍺

Ἒ)

Abstract

In order to develop a method of corrosion fatigue design and estimate reliability of TMCP steel using as the material of heavy industries and plants, its corrosion susceptibilities, corrosion fatigue strength, and determination of fatigue design criterion considering corrosion degradation were investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. The corrosion fatigue strength in 25ଇ, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with the frequency decrease in the same environment. It is expected that the developed corrosion fatigue design method for TMCP steel is useful. However, it is necessary to verify its reliability for actual application.

1. 昢 嵦

䟊㟧ῂ㫆ⶒ, 㭧䢪䞯䝢⩢䔎, 䢪⩻ ⹥ 㤦㧦

⩻ ⹲㩚䝢⩢䔎 ❇㦮 ㍺゚㢖 ῂ㫆ⶒ㦖 㡂㩚 䧞 Ṗ䢏䞲 䢮ἓ㫆Ị 䞮㠦㍲ ㌂㣿♮₆ ➢ⶎ 㠦, 㧊✺㦮 ㍺Ἒ, 㩲㧧 ⹥ ⽊㑮ὖⰂ㠦 㧞㠊

㍲ 㨂⬢㦮 ㍶䌳, 䠞㣿㦧⩻㦮 ἆ㩫, 㑮ⳛ㡞䁷

❇㦚 㥚䞲 ◆㧊䎆Ṗ ▪㤇ٻ 㣪ῂ♮ἶٻ 㧞┺ډٻ

⁎Ⰲἶڇٻ 䞲䘎㦒⪲⓪ٻ ṫ☚⯒ٻ 䢫⽊䞮ἶٻ ⌊ῂ

㎇ὒٻ 㞞㩚㎇㦚ٻ 䢫⽊䞮₆ٻ 㥚䟊㍲⓪ٻ 㧊✺㦮ٻ

⿖㔳㌗䢿ὒٻ⹿㔳⹿⻫㠦ٻ╖䞲ٻ㩗㩫䞲ٻὖⰂṖٻ 䟟䟊㪎㟒ٻ䞾☚ٻ㧎㔳♮ἶٻ㧞┺ډٻ⁎⧮㍲ٻⰤ㦖ٻ 㡆ῂ㧦✺㠦ٻ 㦮䟊ٻ 㭒㣪ٻ ㌆㠛㍺゚ٻ 㨂⬢✺㠦ٻ

╖䞲ٻ ⿖㔳ٻ 㡊䢪☚㢖ٻ ⿖㔳㦚ٻ ἶ⩺䞲ٻ ṫ☚䘟 Ṗ㠦ٻὖ䞲ٻ㡆ῂṖٻ㰚䟟♮ἶٻ㧞㦚ٻ㈦Ⱒٻ㞚┞

⧒ٻ 㾲⁒㠦⓪ٻ ㌆㠛㍺゚㦮ٻ 㞞㩚㎇ὒٻ 㔶⬆㎇ٻ 㥶㰖⯒ٻ 㥚䞲ٻ ㍺゚䐋䞿ὖⰂ㔲㓺䎲ٻ ῂ㿫㹾㤦 㠦㍲ٻ⿖㔳㌗䢿㦚ٻ㧦☯㩗㦒⪲ٻ㔺㔲Ṛ㠦ٻ⳾┞

* ㌒㎇㭧Ὃ㠛

** ㎇‶ὖ╖䞯ᾦ ₆ἚὋ䞯⿖

E-mail : [email protected]

TEL : (031)290-7443 FAX : (031)290-5849

䎆Ⱇ(monitoring)䞮⓪ٻ ₆㑶Ṳ⹲☚ٻ 㰚䟟♮ἶٻ 㧞┺ډٻ㧊⯒ٻ䐋䞮㡂ٻ㔺㩲䢮ἓὒٻ㡃䞯㩗ٻ㫆Ịٻ 䞮㠦㍲ٻ㌂㣿♮ἶٻ㧞⓪ٻ㌆㠛㍺゚㢖ٻῂ㫆ⶒ㦮ٻ 㔺㩲ٻ⿖㔳㌗䢿㠦ٻ╖䞲ٻ㩫⽊䣣✳ὒٻ㧪㫊㑮ⳛ 㦮ٻ㿪㩫ڇٻ⽊㑮ٻ⹥ٻᾦ䢮㔲₆㦮ٻἆ㩫ڇٻ⿖㔳㤦 㧎ٻ䟊㍳ٻ⹥ٻ⹿㔳⻫㦮ٻ䣾ὒ䕦㩫ٻ❇㧊ٻṖ⓻䞶ٻ ộ㦒⪲ٻ₆╖♮ἶٻ㧞┺^ڃڌڈڏڄډٻ

⁎⧮㍲ڇٻ 㧊⩂䞲ٻ ㌆㠛㍺゚㢖ٻ ῂ㫆ⶒ✺㦮ٻ 㔺㔲Ṛٻ䐋䞿ὖⰂ㼊Ἒ⯒ٻῂ㿫䞮ἶ㧦ٻ䞮⓪ٻ㧒

⩾㦮ٻ㡆ῂ⪲㍲,ٻ⽎ٻ㡆ῂ㠦㍲⓪ٻ㨂⬢㦮ٻ⿖㔳ٻ 㡊䢪☚㢖ٻ ⿖㔳䞒⪲ṫ☚⯒ٻ 㔺䠮㩗㦒⪲ٻ 䘟Ṗ 䞮ἶڇٻ 䣣✳♲ٻ ◆㧊䎆⯒ٻ 㧊㣿䞮㡂ٻ ⿖㔳䢮ἓ 㦚ٻ ἶ⩺䞲ٻ 㨂⬢㦮ٻ ⿖㔳㡊䢪ٻ ⹥ٻ ⿖㔳䞒⪲ṫ

☚⯒ٻ 㡞䁷䞾㦒⪲㖾ڇٻ ㍺゚㢖ٻ ῂ㫆ⶒ㦮ٻ 㞞㩚 ὖⰂ㼊Ἒ⯒ٻ ῂ㿫䞮⓪ٻ ₆㽞㧦⬢⪲ٻ 㧊㣿䞮ἶ 㧦ٻ䞮㡖┺ډٻ

2. TMCP 儛汞 洊匶筚穟洇 抆柣瞿 昷磏儆

2.1 柢竞碾

㣿㩧㎇ὒٻ⌊㰚㎇㧊ٻ㤆㑮䞮ἶڇٻ㫆㍶ٻ⹥ٻ䟊 㟧ῂ㫆ⶒڇٻ䕢㧊䝚⧒㧎(pipe line)ٻ❇㠦ٻ㩗㣿♮

ἶٻ 㧞⓪ٻ TMCP ṫ㠦ٻ ╖䞲ٻ ⿖㔳㡊䢪☚⯒ٻ ASTM G5⁽⁵⁾㠦ٻ㦮Ệ䞮㡂ٻ䘟Ṗ䞮㡖┺ډٻTMCP ṫ㦮ٻ䢪䞯㎇⿚ὒٻ₆Ἒ㎇㰞㦖ٻTable 1 ὒٻṯ

┺ډٻ㩚₆䢪䞯㩗ٻ⿖㔳㡊䢪☚ٻ䘟Ṗ⯒ٻ㥚䞲ٻ㔲 䠮䘎㦖ٻ 10ശ10ശ10mm³ 㦮ٻ 㩫㥷Ⳋ㼊⪲ٻ 㩲㧧 䞮㡖ἶڇٻ 㠦䙃㔲(epoxy)㑮㰖⪲ٻ Ⱎ㤊䕛 (mounting)䞲ٻ 䤚ڇٻ 䚲Ⳋὒٻ Ⱎ㤊䕛ٻ Ṛ⁏ٻ ㌂㧊 㦮ٻ䔞ٻ⿖㔳(crevice corrosion)㦚ٻ⹿㰖䞮₆ٻ㥚 䟊ٻ䗮㧎䕛(painting)䞮ἶٻ24 㔲Ṛٻ㌗㡾㠦㍲ٻỊ 㫆㔲䆆┺ډٻ㔲䠮䘎ٻ䚲Ⳋ㦖ٻ⳾⚦ٻ600-grit SiC paper ⪲ٻ㔋㔳㡆Ⱎڃwet polishing)䞮㡖┺ډٻ ٻ

2.2 柪竞 沫獞

㩚₆䢪䞯㩗 ⿖㔳㡊䢪☚ 䘟Ṗ 㔲䠮㧻䂮⓪ Potentiostat(Perkin Elmer Co., Model 273A)⯒

㌂㣿䞮㡖┺. ☯㩚㥚⿚⁏㔺䠮(potentiodynamic

Table 1 Chemical composition and mechanical properties of TMCP steel

polarization)㦚 㥚䞲 㔲䠮䘎㦖 open-circuit potential 㦚 㥶㰖䞲 䤚 㔺䠮㦚 㔲㧧䞮㡖ἶ, -250mV ⿖䎆 10mV/m(0.166mV/sec)⪲ scan 䞮 㡖┺. 㩚⁏㦖 ⽊㫆 㩚⁏(counter electrode)㦒

⪲ 䌚㏢⽟㩚⁏ 2 ṲṖ ㌂㣿♮㠞ἶ, ₆㭖㩚⁏

(reference electrode)㦒⪲⓪ Ṧ䢣㩚⁏(SCE)㧊

㌂㣿♮㠞┺. ⁎Ⰲἶ, ⽎ 㔺䠮㠦㍲⓪ TMCP ṫ㦮 㔺㩲㣿☚⯒ ἶ⩺䞮㡂 0૫10ଇ⻪㥚㦮 㩖㡾ὒ 60૫90ଇ ⻪㥚㦮 ㌗㡾 㧊㌗(㧊䞮 ἶ 㡾)㠦㍲ ⿖㔳㡊䢪㠦 ╖䞲 㡾☚㦮 㡗䟻㦚 Ỗ 䏶䞮㡖┺ډٻ

(a) ٻ

(b) ٻ

Fig. 1 Corrosion cell for low and high temperature

C Mn Si P S Cu Ni

0.1 1.49 0.25 0.014 0.001 0.024 0.25

Yield Strength (MPa)

Young’s Modulus (GPa)

Elongation (%)

519 228 34.2

Fig. 1(a)㦮 㩖㡾 ⿚⁏㔺䠮㦚 㥚䞲 ⿖㔳㫆 (corrosion cell)⓪ 㞚䋂Ⰺ(acryl)ὒ ⽊㡾㨂⯒

㌂㣿䞮㡂 㩖㡾 ⿚㥚₆Ṗ 㧻₆Ṛ 㥶㰖♶ 㑮 㧞☚⪳ 㩲㧧䞮㡖ἶ, 㞷䢪㰞㏢㢖 㞢䆲(alchol) 㦚 㧊㣿䞮㡂 㣿㞷㦮 㡾☚⯒ ⌄㿪㠞┺. 㔲䠮

₆Ṛ ☯㞞 㩖㡾㫆Ị㧊 Ἒ㏣ 㥶㰖♮☚⪳ 䞮

₆ 㥚䟊㍲ 㩖㡾㣿 㡾☚㫆㩞₆(thermo controller)㢖 ㏪⩞⏎㧊✲ ⺎ぢ(solenoid valve)

⯒ ㌂㣿䞮㡖┺. ⁎Ⰲἶ, Fig. 1(b)㦮 ἶ㡾㣿

⿖㔳㫆☚ 㧻₆Ṛ 㡾☚Ṗ 㥶㰖♮㠊㟒 䞮₆

➢ⶎ㠦 㡾☚㫆㩞₆㢖 㡊㩚╖(thermo couple)

⹥ ㍳㡗䧞䎆(heater)⯒ ㌂㣿䞮㡖┺.

2.3 柪竞 浶兺

⿖㔳㣿㞷㦖 㡒䢪ⶒ㠦 㦮䞲 㨂⬢㦮 ⿖㔳㡊 䢪☚⯒ ゚ᾦ࡞䘟Ṗ䞮₆ 㥚䟊 㯳⮮㑮㢖 3.5wt.% NaCl 㑮㣿㞷㦚 ㌂㣿䞮㡖┺. 㔺䠮㡾

☚⓪ 㯳⮮㑮㢖 NaCl 㑮㣿㞷 Ὃ䧞, 5, 10, 25, 60, 90 ଇ⪲ ㍺㩫䞮㡖㦒⋮, NaCl 㑮㣿㞷㠦㍲

⓪ 0ଇ⯒ 㿪Ṗ䞮㡖┺.

2.4 柪竞冶刂 愕 処然

Fig. 2 ⓪ 㯳⮮㑮㢖 NaCl 㑮㣿㞷㦮 㡾☚⼖

䢪㠦 ➆⯎ ⿚⁏ἷ㍶(polarization curve)㦒⪲⿖

䎆 Tafel 㣎㌓⻫㦒⪲ ῂ䞲 ⿖㔳㏣☚(corrosion rate)⯒ 㩫⨟Ṩ㦒⪲ ☚㔲䞲 ἆὒ㧊┺. NaCl 㑮 㣿㞷ὒ 㯳⮮㑮 ⳾⚦ 㡾☚⼖䢪㠦 ╖䞲 ⿖㔳

㏣☚⓪ Ệ㦮 ㍶䡫㩗㦒⪲ 㯳Ṗ䞮⓪ ἓ䟻㦚

⋮䌖⌊ἶ 㧞┺. NaCl 㑮㣿㞷㦮 ἓ㤆 ⿖㔳㏣

☚⓪ 0ଇ㠦㍲ 1.094mpy, 90ଇ㠦㍲ 961.4mpy 㧊Ⳇ, 㯳⮮㑮㦮 ἓ㤆⓪ 5ଇ㠦㍲ 0.133mpy, 90ଇ㠦㍲ 65.3mpy ⪲ 䁷㩫♮㠞┺. ⽎ 㔺䠮㠦

㍲⓪ ⿖㔳㣿㞷㭧㦮 㣿㫊㌆㏢⯒ ἶ⩺䞮㰖 㞠 㞮㰖Ⱒ, 㡾☚Ṗ ㌗㔏䞮Ⳋ 㣿㞷㦮 㩦㎇

(viscosity) Ṧ㏢㢖 ⿖㔳䢲㎇ 㧊㡾(ion)㦮 䢲㎇

☚(activity) 㯳Ṗ⪲ 㨂⬢䚲Ⳋ㦮 ㌆䢪Ⱏ(oxide film)㧊 ⿞㞞㩫䟊㰦㦒⪲ 㧎䟊㍲ ⿖㔳㧊 㽟㰚

♲ ộ㦒⪲ ㌳ṗ♲┺. 䔏䧞 3.5wt.% NaCl 㑮 㣿㞷㦮 ἓ㤆㠦⓪ ⿖㔳䢲㎇ 㤦㏢㧎 㡒䢪㧊㡾 (Cl^ڈ)㧊 㻾Ṗ♮㠞₆ ➢ⶎ㠦, 㯳⮮㑮㠦 ゚䟊

㧊⩂䞲 䡚㌗㧊 ▪㤇 ⹒Ṧ䞮Ợ ⋮䌖⋲ ộ㦒

⪲ ㌳ṗ♲┺^(6,7).

Fig. 2 Relationship between Rcorr and T

3. TMCPࣜ儛汞ࣜ抆柣穂嵢儛壊ࣜ磏儆

3.1 柢竞碾

TMCP ṫ㦮 ⿖㔳䞒⪲ṫ☚ 䘟Ṗ⯒ 㥚䞲 㔲 䠮䘎㦖 ASTM E606-92⁽⁸⁾㠦 㦮Ệ Fig. 3 ὒ ṯ 㧊 㩲㧧䞮㡖┺. 㔲䘎㦮 㰗ἓ㦖 6mm, 䁷㩫₎

㧊⓪ 30mm ⪲ 䞮㡖㦒Ⳇ, ⁎Ⱃ(grip)ὒ 㡆ἆ

⿖⿚㦖 M14 ⋮㌂⪲ 㩲㧧䞮㡖┺. 㔲䘎㦖 ⳾

⚦ 1000-grit SiC paper ⪲ 㡆Ⱎ䞮㡖㦒Ⳇ, 㔲䠮 䘎 䚲Ⳋ㦖 㽞㦢䕢 ㎎㻯₆⪲ ㎎㻯䞮㡖┺.

Fig. 2 Configuration of specimen for corrosion fatigue test 3.2 柪竞 沫獞

⿖㔳䞒⪲⓪ 㨂⬢䞒⪲㔲䠮₆(MTS, 10ton)㢖

⽎ 㡆ῂ㧦✺㧊 ㍺Ἒ࡞㩲㧧䞲 㑮䘟㔳 䞒⪲㔲 䠮₆⯒ ㌂㣿䞮㡖┺. ⿖㔳㫆(corrosion cell)⓪

ͪͥ͢͟͡

ͣͧͥͥͧͦͦ͟͢͟ ͧͤͪͤ͟

ͩͪͥ͢͟

ͪͧͥ͢͟

ͤͤͨͧ͟͢͟͢͡͡

ͪͩͨ͟͡

ͤͤ͟͢

ͧͦͤ͟

Ϊ͑ͮ͑ͥ͟͢͢͢͡Ζ^{ͨͩͤ͟͡͡Ω} Ϊ͑ͮ͑ͦͣͩ͢͟Ζ^{ͨͤͩ͟͡͡Ω}

͢͟Ͷ͢͞͡

͢͟Ͷ͜͡͡

͢͟Ͷ͜͢͡

͢͟Ͷͣ͜͡

͢͟Ͷͤ͜͡

͢͟Ͷͥ͜͡

͡ ͢͡ ͣ͡ ͤ͡ ͥ͡ ͦ͡ ͧ͡ ͨ͡ ͩ͡ ͪ͡ ͢͡͡

Whpshudwxuh#+佾,

Fruurvlrq#udwh#+ps|,

ͿΒʹΝ 溣幞朞

㔲䠮䘎 㣎 ┺⯎ ⁞㏣㦮 Ṟ⹪┟ ⿖㔳 (galvanic corrosion)㦚 ⹿㰖䞮ἶ, 㧻₆Ṛ 㔺䠮

☯㞞 ⌊ῂ㎇ὒ 㭒㠊㰚 䢮ἓ(㡾☚, 㞫⩻)㧊 㥶㰖♮☚⪳ Fig. 4 㢖 ṯ㧊 㩲㧧䞮㡖┺.

Fig. 3 Corrosion cell for Corrosion fatigue test 㣎⼓㦖 㞚䋂Ⰺ(acryl)㑮㰖⯒ 㧊㣿䞮㡂 Ṟ⹪

┟ ⿖㔳㦚 ⹿㰖䞮⓪ 䞲䘎, 㔺䠮㧊 㰚䟟♮⓪

☯㞞 ⿖㔳㫆 ⌊㦮 ㌗䢿㦚 ὖ㺆䞶 㑮 㧞☚⪳

䞮㡖┺. 㔲䘎ὒ 㣿㞷㧊 㩧㽟♮⓪ Ⳋ㦖 䎢䝚

⪶ 䆪䕛(teflon coating)㦚 䞮㡖ἶ, 㔺Ⰲ䆮 (silicon)㦒⪲ 㑮⹖(sealing)㦚 㥶㰖䞮㡖㦒Ⳇ, 㞚䋂Ⰺ㑮㰖㢖 ╕⓪ ⿖⿚㦖 㡺Ⱇ(O-ring)㦚

㌓㧛䞮㡂 ⑚㑮⯒ ⹿㰖䞮㡖┺. ⁎Ⰲἶ, 㔺䠮 㧊 㰚䟟♮⓪ ☯㞞 ⿖㔳㫆 ⌊ ⿖㔳㣿㞷㦮 䢪 䞯㩗 䘟䡫㦚 㥶㰖䞮₆ 㥚䟊 㑲䢮㧻䂮⯒ 㧊 㣿䞮㡂 ⿖㔳㣿㞷㧊 50ml/min ⪲ Ἒ㏣ 㑲䢮♮

☚⪳ 䞮㡖┺.

3.3 柢竞 浶兺

⿖㔳䢮ἓ㠦㍲ 䞒⪲ṫ☚⯒ 䘟Ṗ䞮₆ 㩚 Ὃ

₆ 㭧㠦㍲㦮 䞒⪲ṫ☚䘟Ṗ⯒ 㥚䟊 Pmax= 0.8Py (Py; yielding load), 䞮㭧⹮⽋ ㏣☚

(frequency), 30Hz ⪲ 䞮㡂 䞒⪲㔺䠮㦚 㑮䟟䞮 㡖┺. ⿖㔳䞒⪲㔺䠮㦚 㥚䞲 䞮㭧㫆Ị㦖 Ὃ

₆㭧ὒ Ⱎ㺂Ṗ㰖⪲ P = 0.8P ⯒ 㾲㽞 㔺䠮

䞮㭧㦒⪲ ㍺㩫䞮㡂 䞮㭧Ṧ㏢⻫(10% down)㦒

⪲ 㨂⬢㦮 ⿖㔳䞒⪲ṫ☚⯒ 䘟Ṗ䞮㡖┺ډٻ 㧊ٻ

➢ڇٻ䞮㭧゚(R= Pmin /Pmax)⓪ٻ0.1 ⪲ٻ䞮ἶڇٻ೼

P=㧒㩫㫆Ị 䞮㠦㍲ 䞒⪲㔲䠮㦚 㑮䟟䞮㡖┺.

⿖㔳㣿㞷ὒ 㔲䘎䚲Ⳋὒ㦮 ⿖㔳㧧㣿 ⹥ ⿖㔳 䣾ὒ(corrosion effect)⯒ 㽟㰚㔲䋺ἶ 䞮㭧⹮⽋

㏣☚(frequency)㦮 㡗䟻㦚 ゚ᾦ䘟Ṗ䞮₆ 㥚䟊

㍲ 䞮㭧⹮⽋㏣☚⯒ 1Hz 㢖 3Hz ⪲ 䞮㡂 㔺 䠮㦚 㑮䟟䞮㡖┺. ⁎Ⰲἶ, NaCl 㑮㣿㞷㦮 㡾

☚⓪ ㌗㡾(25ଇ)㦒⪲ 㥶㰖 㔲䆆㦒Ⳇ, 㣿㞷㦮

⏣☚⓪ 㧎Ὃ䟊㑮㠦 ㌗╏䞮⓪ 3.5wt.%⪲ ㍺ 㩫䞮㡖┺. 㧊㌗㦮 㫆Ị✺㦚 Table 2 㠦 㩫Ⰲ 䞮㡖┺.

Table 2 Fatigue test conditions Condition Contents

in 3.5wt.%

NaCl solution

in air

Load ratio

(R= Pmin /Pmax) 0.1 0.1 Load range

(೼P ) Con’t Con’t Maximum load

(P_max) (N) 11,748 13,950 Loading

condition

Load frequency 1, 3Hz 30Hz

3.4 柢竞冶刂 愕 処然

Fig. 5 ⓪ Table 3 㦮 㫆Ị㠦㍲ TMCP ṫ㦮

⿖㔳䞒⪲ṫ☚⯒ ೼ౚ- Nf 㦮 ὖἚ⪲ ⋮䌖⌎

ἆὒ㧊┺.

Ὃ₆ 㭧㠦㍲⓪ 㨂⬢㦮 䞒⪲ṫ☚Ṗ 䟃⽋ṫ

☚㦮 80%㠦 䟊╏䞮⓪ 䞮㭧㠦㍲ 䞒⪲䞲☚

(fatigue limit, 10⁷ cycles)⯒ ⋮䌖⌊⓪ ゚ᾦ㩗

⏨㦖 䞒⪲䔏㎇㦚 Ṗ㰖ἶ 㧞㦢㧊 䢫㧎♮㠞┺.

⁎⩂⋮, 25ଇ, 3.5wt.% NaCl 㑮㣿㞷㦮 ⿖㔳䢮 ἓ 䞮㠦㍲⓪ ⿖㔳䞒⪲ṫ☚Ṗ Ὃ₆ 㭧㠦 ゚ 䟊 㩚㼊㩗㦒⪲ ㌗╏䧞 㩖䞮♮⓪ ἓ䟻㦚 ⋮ 䌖⌊㠞┺.

⁎Ⰲἶ, ☯㧒䞲 ⿖㔳䢮ἓ㠦㍲ 䞮㭧⹮⽋

㏣☚㦮 㡗䟻㦚 ゚ᾦ࡞䘟Ṗ䞲 ἆὒ, 䞮㭧⹮⽋

㏣☚Ṗ ⓼㠊㰖Ⳋ ἶ 㦧⩻⻪㥚㠦㍲⓪ 1Hz 㢖 3Hz 㦮 ⿖㔳䞒⪲ṫ☚Ṗ 䋆 㹾㧊⯒ ⽊㧊㰖 㞠㦒⋮, 㩖 㦧⩻⻪㥚㠦㍲⓪ ㌗╏䧞 Ṧ㏢䞮

⓪ ἓ䟻㦚 ⋮䌖⌊㠞┺. 㧊⩂䞲 ἆὒ⓪ 䞮㭧

⹮⽋㏣☚Ṗ ⓦⰊ㑮⪳ ⿖㔳䢲㎇ 㧎㧦㦮 䂾䒂 㔲Ṛ㧊 ₎㠊㰖ἶ, 㧊㠦 ➆⯎ 㩚₆䢪䞯㩗 ⿖ 㔳㧧㣿㦮 㡗䟻㧊 䋂Ợ 㧧㣿䞲 ➢ⶎ㧎 ộ㦒

⪲ Ṛ㭒♮Ⳇ, 㧊ộ㦖 㧒⹮㩗㧎 ἂ䟊㢖☚ 㧒 䂮♲┺⁽⁹⁾.

Fig. 5 㠦㍲ 3.5wt.% NaCl 㑮㣿㞷㦮 ⿖㔳䢮 ἓ 䞮㠦㍲⓪ ㌗╏䧞 ⌄㦖 㑮㭖㦮 㦧⩻⻪㥚 㠦㍲☚ 㧻㔲Ṛ 㔲䠮㧊 㰚䟟♮Ⳋ, 䞒⪲䞲☚

(10⁷ cycle 㠦 䟊╏䞮⓪ 㦧⩻) ⌊㠦㍲☚ 㔲䘎 㧊 䕢┾♶ Ṗ⓻㎇㧊 㧞㦢㦚 㞢 㑮 㧞┺. ➆

⧒㍲, 㡊㞛䞲 ⿖㔳䢮ἓ㠦㍲ 㤊㩚♮⓪ ㌆㠛

㍺゚㦮 䢮ἓṫ☚䞯㩗 ㍺Ἒ⯒ 㥚䟊㍲⓪ 䞚㣪 䞲 䞮㭧⹮⽋㏣☚㠦㍲ 㧻 㑮ⳛ 㡗㡃₢㰖㦮 S-N ㍶☚⯒ 㧧㎇䞮ἶ ⿖㔳䞒⪲⯒ ἶ⩺䞲 䞒

⪲㍺Ἒ ₆㭖㦚 ㍺㩫䟊㟒Ⱒ 䞲┺. ⁎⩝Ợ ♮ Ⳋ, 㧻㔲Ṛ㦮 㔺䠮㦒⪲ 㧎䞲 ἓ㩲㩗, 㔲Ṛ㩗

⿖╊㧊 ⿞Ṗ䞒 䟊㰚┺.

⁎⧮㍲, ⽎ 㡆ῂ㠦㍲⓪ 㧊㢖 ṯ㦖 ⶎ㩲⯒

Ṳ㍶䞮⓪ ⹿⻫㦒⪲㍲ Ὃ₆㭧㦮 䞒⪲ṫ☚(ౚ

a)⪲⿖䎆 ⿖㔳䞒⪲ṫ☚(ౚac)⯒ 㿪㩫䞮⓪ ⹿

⻫㦚 㩗㣿䞮ἶ㧦 䞮㡖┺. 㯟, ౚa 㢖 ౚac ⹥ Nf ㌂㧊㠦⓪ ┺㦢ὒ ṯ㦖 ὖἚ㔳㦒⪲ ⋮䌖

⌊㠊㰚┺⁽⁹⁾.

ౚac=ౚa/{1+BപNfڃۋچیڄ} (1)

Bപ={(ౚwc/ౚw) ڈٻ1}/(Nf)^ڃۋچیڄ (2)

㡂₆㍲, ౚwc/ౚw ⓪ ⿖㔳䞒⪲ ⹥ Ὃ₆ 㭧 䞒⪲䞲☚ ゚⯒ ⋮䌖⌊Ⳇ,ౚwc/ౚw, (p+q)⓪ Fig. 6 㦒⪲⿖䎆 ἆ㩫♲┺. 㧊㌗㦮 㔳(2)㢖 Fig. 6 㦒⪲⿖䎆, Fig. 5 㦮 ἆὒ㠦 ╖䞲 ౚa㢖 ౚac ⹥ Nf㦮 ὖἚ㔳(1)㦖 Fig. 7 ὒ ṯ㧊 ⋮ 䌖⌊㠊㰚┺.

⽎ 㡆ῂ㠦㍲⓪ 㔳(2)㦮 Nf =6ശ10⁵ cycles

⪲ 䞮㡂 B'⯒ Ἒ㌆䞮㡖┺. 㧊㌗㦮 ἆὒ⓪ 㧻

₆Ṛ㦮 㔺䠮㧊 㣪ῂ♮⓪ ἓ㤆㦮 ⿖㔳䞒⪲ṫ

☚⯒ ἓ㩲㩗㦒⪲ 㿪㩫䞶 㑮 㧞㦚 ộ㦒⪲ 䕦

┾♮⋮, 㿪㩫䂮㠦 ╖䞲 㔶⬆㎇ Ỗ㩫㠦 ╖䟊

㍲⓪ 㼊Ἒ㩗㦒⪲ Ἒ㏣ 㡆ῂ♶ 䞚㣪Ṗ 㧞┺

ἶ ㌳ṗ䞲┺.

70 90 110 130 150 170 190 210 230 250

1.E+04 1.E+05 1.E+06 1.E+07

Nf (cycles)

ǻıa (Mpa)

in air (30 Hz)

in NaCl solution (3Hz, smooth specimen) in NaCl solution (1Hz, notch specimen) in NaCl solution (1Hz, smooth specimen)

Fig. 4 ೼ౚ-Nf curve of corrosion fatigue test

0.0 0.5 1.0

0.0 0.5 1.0

ı_wc/ ı_w

p, q , p+q

Fig. 5 Relationship between (ౚwc /ౚw) and (p+q)⁽⁹⁾

Fig. 6 Prediction of corrosion fatigue design criterion

4. 冶 嵦

㌆㠛㍺゚㢖 ῂ㫆ⶒ✺㦮 㔺㔲Ṛ 䐋䞿ὖⰂ㼊 Ἒ⯒ ῂ㿫䞮ἶ㧦 䞮⓪ 㧒⩾㦮 㡆ῂ⪲㍲,⽎

㡆ῂ㠦㍲⓪ 㨂⬢㦮 ⿖㔳㡊䢪☚㢖 ⿖㔳䞒⪲

ṫ☚⯒ 㔺䠮㩗㦒⪲ 䘟Ṗ䞮ἶ, 䣣✳♲ ◆㧊 䎆⯒ 㧊㣿䞮㡂 ⿖㔳䢮ἓ㦚 ἶ⩺䞲 㨂⬢㦮

⿖㔳㡊䢪 ⹥ ⿖㔳䞒⪲ṫ☚⯒ 㡞䁷䞮⓪ ₆⻫

㦚 㡆ῂ䞮㡖┺. 㠑㠊㰚 ἆ⪶㦖 ┺㦢ὒ ṯ┺.

1) TMCP ṫ㦮 3.5wt.% NaCl 㑮㣿㞷㠦 ╖ 䞲 ⿖㔳㡊䢪☚⓪ 㡾☚Ṗ ㌗㔏䞮Ⳋ ㍶䡫㩗㦒

⪲ 㯳Ṗ䞮㡖┺. ⁎Ⰲἶ, ☯㧒䞲 ⿖㔳㣿㞷㠦

㍲ 㧚㦮 㡾☚㠦 ╖䞲 ⿖㔳㏣☚⯒ 㡞䁷䞶 㑮 㧞⓪ ⿖㔳㏣☚㢖 㡾☚㦮 ㌗ὖὖἚ⯒ 㩲㔲䞮 㡖┺.

2) TMCP ṫ㦖 Ὃ₆ 㭧㠦㍲⓪ ⏨㦖 䞒⪲

ṫ☚⯒ Ṗ㰖⋮, 25ଇ, 3.5wt.% NaCl 㑮㣿㞷 ⿚ 㥚₆㠦㍲ ⿖㔳䞒⪲ṫ☚⓪ ⰺ㤆 Ṧ㏢䞮⓪ ἓ 䟻㦚 ⽊㡖㦒Ⳇ, 䔏䧞, 䞮㭧⹮⽋㏣☚Ṗ ⓦⰂ Ⳋ, ⿖㔳䞒⪲ṫ☚☚ ▪㤇 Ṧ㏢䞮㡖┺.

3) Ὃ₆ 㭧 䞒⪲ṫ☚⪲⿖䎆 ⿖㔳䞒⪲ṫ

☚⯒ 㡞䁷䞮⓪ ₆⻫㦚 㩲㔲䞮㡖┺. ⁎⩂⋮, 㔺㩲 ㌆㠛㍺゚㦮 䢮ἓ㦚 ἶ⩺䞲 䞒⪲㍺Ἒ㠦 㩗㣿䞮₆ 㥚䟊㍲⓪ ⽎ ₆⻫㠦 ╖䞲 㔶⬆㎇

Ỗ㩫㠦 ╖䞲 㼊Ἒ㩗㧎 㡆ῂṖ 䞚㣪䞮┺.

篊 匶

⽎ٻ㡆ῂ⓪ٻ䞲ῃὒ䞯㨂┾ٻ㌆䞮ٻ㎇‶ὖ╖䞯 ᾦٻ ㌆㠛㍺゚㞞㩚㎇䘟Ṗٻ 㡆ῂ㎒䎆㦮ٻ 㡆ῂ゚ٻ 㰖㤦㦒⪲ٻ 㧊⬾㠊㰚ٻ ộ㦒⪲㍲ڇٻ 㧊㠦ٻ ὖἚ㧦ٻ 㡂⩂⿚℮ٻṦ㌂ٻ✲Ⱃ┞┺ډٻ

ٻ ٻ ٻ ٻ ٻ ٻ ٻ ٻ ٻ ٻ

焾処怾竒

(1) ASTM, 1984, "Corrosion Monitoring in Industrial Plants Using Nondestructive Testing and Electrochemical Methods", ASTM STP 908.

(2) AIME, 1985, "High Temperature Corrosion in Energy Systems", The metallurgical society of AIME.

(3) 螔膩絣篥谷赬, 1984, “絣篥粱褂肵࿾讣荼 艃罚࿸豻苯絛菵”, 螔膩絣篥谷赬.

(4) Sung D. Kwon, Seok S. Yoon, Sung J. Song, Dong H. Bae,2000,"The Evaluation of Corrosion Strength of 12Cr Steel using Backward Radiated Ultrasound", KSNT/

SC0005, pp. 49૫55.

(5) ASTM, 1987, "Standard Reference Test For Making Potentio-static and Potentio-dynamic Anodic Polarization Measurement", ASTM G5, pp.73૫76.

(6) Herbert H. Uhlig, R Winston Revie, 1984,

"Corrosion and Corrosion control", pp.95૫96.

(7) 㧊䞯⪂, 1990, “⁞㏣ٛ⿖㔳 Ὃ䞯”, pp.54૫ 55.

(8) ASTM, 1993, "Standard Practice for Strain- Controlled Fatigue Testing", ASTM, pp.632૫ 646.

(9) 螔膩絣篥谷赬, 1985, “臔萳࿸讣籸”, 螔膩 簴蔋艧, pp.171-177.