Table 5 Creep rupture test(625C)results of T92/HR3C dissimilar steels welded joints 625℃ Rupture No.(, MPa) Time(h) 180 3 T92 base material 1234567 160 T92 base material 150 T92 base material HAZ of T92 Weld seam 110 4182 Weld seam 1000 LMP=T(25+g(tr)×10 Fig. 6 Plot of stresses with LMP for welded joints. Table 6 LMP values and rupture times under stresses of 30, 35 and40 MPa at625°C Service stress (MPa) LMP value(x10-) Rupture time(h) 27.15 168060 19198 87631 fers from 19.5 to 36 according to a variety of references Fig 5 Double logarithmic plot of load stress versus rupture time involved.33,34 However, thanks to sufficient practical ap- plication experiences of T92 in the past decade, the value of C has been modified according to lots of firsthand and the value of n is generally ranging from 1. 2 to 1.65 data. Hence, a value of 25 is now commonly adopted for C to predict the service lives of T92 for better accordance tIv, in thi (2) rupture data for the T92/HR3C dissimilar steels welded In this case, we take n= 1.5. and the permitted joints can be plotted in terms of lgo versus Larson-Miller stress [ a] of T92/HR3C dissimil elded joint parameters(LMP)in Fig. 6, where the LMP is expressed can be determined from Eq (3),w value 41.26 Eq(5) MPa also exceeds the steam stress of USC conditions LMP=T(25+Igt). 6819=q 1541.26MPa. (3) Also, the Igo versus LMP curve displayed in Fig. 6 is then polynomial fitted for the convenience of service life pre In terms of service life prediction for high-temperature diction for the welded joints under different stresse components in boilers, the Larson-Miller equation, seen for USC boilers, service steam stresses commonly in Eq(4), is always applied to estimate the allowable from 30 to 40 MPa, whose LMP values can then be easily stresses under specific steam conditions read from Fig. 6. Table 6 lists the lmP values and thei P=T(C +Igt) corresponding rupture times under stresses of 30, 35 and (4) 40 MPa, respectively. It is obvious that rupture times un- where T is the absolute temperature in K, and t, is the der 30 and 35 MPa at 625 oC both exceed the recom- pture time in hours. Actually, C is a constant depend- mended service life of 10 h, even if the rupture time of ing on different materials. Owing to the fact that T92 40 MPa is long enough in practical applications (nearly base material is the weakest part of T92/HR3C dissimi- 10 years). Actually, the rupture time under 40 MPa at lar steels welded joint, the value of C can be determined 625C is still longer than that counterpart values of from T92 matrix material. As for T92, the value of C dif- P91/P22 dissimilar ferritic steels welded joint(less tha @2010 Blackwell Publishing Ltd Fatigue Fract Engng Mater Struct 34, 83-9688 Y. GONG et al. Table 5 Creep rupture test (625 ◦C) results of T92/HR3C dissimilar steels welded joints Sample Load stress Rupture Rupture No. (σ, MPa) Time (h) position 1 180 378 T92 base material 2 160 865 T92 base material 3 150 930 T92 base material 4 140 1640 T92 base material 5 130 2787 HAZ of T92 6 120 3164 Weld seam 7 110 4182 Weld seam Fig. 5 Double logarithmic plot of load stress versus rupture time for the welded joints. and the value of n is generally ranging from 1.2 to 1.65.22 [σ] = σ625 ◦C 105 n . (2) In this case, we take n = 1.5, and therefore the permitted stress [σ] of T92/HR3C dissimilar steels welded joints can be determined from Eq. (3), whose result value 41.26 MPa also exceeds the steam stress of USC conditions. [σ] = 61.89 1.5 = 41.26 MPa. (3) In terms of service life prediction for high-temperature components in boilers, the Larson–Miller equation, seen in Eq. (4), is always applied to estimate the allowable stresses under specific steam conditions:32 P = T(C + lg tr ), (4) where T is the absolute temperature in K, and tr is the rupture time in hours. Actually, C is a constant depend￾ing on different materials. Owing to the fact that T92 base material is the weakest part of T92/HR3C dissimi￾lar steels welded joint, the value of C can be determined from T92 matrix material. As for T92, the value of C dif￾Fig. 6 Plot of stresses with LMP for welded joints. Table 6 LMP values and rupture times under stresses of 30, 35 and 40 MPa at 625 ◦C Service stress (MPa) LMP value (×10−3) Rupture time (h) 30 27.15 168060 35 27.01 119198 40 26.89 87631 fers from 19.5 to 36 according to a variety of references involved.33,34 However, thanks to sufficient practical ap￾plication experiences of T92 in the past decade, the value of C has been modified according to lots of firsthand data. Hence, a value of 25 is now commonly adopted for C to predict the service lives of T92 for better accordance with the actual conditions. Consequently, in this case, the rupture data for the T92/HR3C dissimilar steels welded joints can be plotted in terms of lgσ versus Larson–Miller parameters (LMP) in Fig. 6, where the LMP is expressed as given in Eq. (5). LMP = T(25 + lg tr ). (5) Also, the lgσ versus LMP curve displayed in Fig. 6 is then polynomial fitted for the convenience of service life pre￾diction for the welded joints under different stresses. As for USC boilers, service steam stresses commonly range from 30 to 40 MPa, whose LMP values can then be easily read from Fig. 6. Table 6 lists the LMP values and their corresponding rupture times under stresses of 30, 35 and 40 MPa, respectively. It is obvious that rupture times un￾der 30 and 35 MPa at 625 ◦C both exceed the recom￾mended service life of 105 h, even if the rupture time of 40 MPa is long enough in practical applications (nearly 10 years). Actually, the rupture time under 40 MPa at 625 ◦C is still longer than that counterpart values of P91/P22 dissimilar ferritic steels welded joint (less than c 2010 Blackwell Publishing Ltd. Fatigue Fract Engng Mater Struct 34, 83–96