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发表于 2011-6-23 12:10:12
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1. Description of the submitted samples:
Two containers and some parts were received from Elo company, on both of containers there are two internal thread bushings and two external thread bushings, defects were found on internal thread bushing surface , crack was found in the external thread bushing.
Some tests as below were done to analyze the reasons which cause defect and crack.
The states of the samples are illustrated in the following form.
Sample state Sample number
￠18x3 Pipe ￠35 Bar
Perfect 1-1 2-1
Defect on surface 1-2 2-2
Crack 1-3 2-3
2. Hardness test:
Test method: GB/T4340.1-2009
Six parts of samples were cut and taken to do vickers hardness, which is “perfect”, “defect on surface”
and “Crack”, respectively. The results are illustrated in the following form.
Test Item Test location Sample number Result Require Conclusion
HV1.0 Section 1-1 174 184 172 HV≤200 Pass
1-2 190 164 160
1-3 188 194 162
2-1 275 258 269 Fail
2-2 269 262 248
2-3 291 281 288
3. Nonmetallic Inclusion content test:
Test method: GB/T 10561-2005
Result: The grade of the inclusion content is illustrated in the following form. The longest length of the inclusions in sample 2-3 is 2mm.
Sample number Result
Type A Type B Type C Type D Type DS
Fine Coarse Fine Coarse Fine Coarse Fine Coarse
1-1 1.0 - 2.0 - 0.5 - 1.0 - 1.5
1-2 0.5 - 2.5 - 0.5 - 1.5 - 0
1-3 0.5 - 3.0 - 0.5 - 1.0 - 0
2-1 3.0 - 0.5 - 3.0 - 1.0 - 2.0
2-2 2.0 - 0.5 - - 2.5 0.5 - 1.0
2-3 2.5 - 3.0 - Over 3.0 - 1.0 - 1.5
4. Metallographic analysis:
Teat method: GB/T13298-1991
Result: Equiaxed grain is observed on sample 1# and 2#, there are some carbide on grain side of 1-3 and 2-3 because of welding, there are more deformation martensite on sample 2-1,2-2,2-3 than 1-2,1-3,which make 2# is harder than 1#.The separated carbide on grain side will reduce the material’s corrosion resistant ability. The folder is found on the surface of sample 1-2.
Fig1 1-1 200×
Fig. 2 1-2 200×
Fig. 3 1-3 200×
Fig.4 2-1 200×
Fig. 5 2-2 200×
Fig.6 2-3 200×
Fig. 7 2-3 500×
Fig.8 the size of the defect on the surface of sample 1-2 100×
5. SEM analysis:
Test method: SEM
Result：There are some cavities on the fracture surface of 2-3(see Fig.9), there are some nonmetal material which make the sample of 1-3 have defects on surface(see Fig.10), the defect is folder equal to Fig.8.
Fig.9 2-3 1000X
Fig.10 1-3 200X
6. Chemical composition analysis:
Test method: OES
Element Sample C Si Mn P S Cr Ni Mo N Conclusion
Requirement - ≤0.030 ≤1.00 ≤2.00 ≤0.045 ≤0.030 16.0-18.0 10.0-14.0 2.0-3.0 ≤0.10
Result ,% 1-1 0.015 0.35 1.03 0.031 0.0042 16.81 12.54 2.05 0.052 Pass
1-2 0.020 0.34 1.09 0.041 0.0036 16.68 10.12 2.11 0.043 Pass
1-3 0.020 0.34 1.10 0.042 0.0036 16.65 10.13 2.10 0.043 Pass
2-1 0.043 0.56 0.84 0.036 0.011 16.77 10.08 2.10 0.049 C Fail
2-2 0.043 0.57 0.85 0.036 0.012 16.76 10.12 2.12 0.050 C Fail
2-3 0.044 0.58 0.92 0.035 0.012 16.57 10.12 2.07 0.046 C Fail
Conclusion: Through the tests on the samples of 1-1,1-2,1-3,2-1,2-2,2-3, we know the grade of the nonmetal inclusion content of samples of ￠35 bar are all beyond the requirement (The grade of nonmetal inclusion content is decided by buyer and seller. Generally, the sum of all grades should not exceed 5), so the parts made out of ￠35 bar are not suit for pressure vessel. Because of the separated carbide on grain side, the service life of 2-3 sample will shorter than others. As talk about ￠18×3 pipe, the grade of nonmetal inclusion content is almost up to the mustard, but the folder on surface will have negative influence on the mechanical property, so before put into use the parts surface should be check first, the parts with vice should not be put into use. Finally, the container’s weld pass should be check by RT or UT pro rata.
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