Consequently the tubes are MIAB welded (parameters as per trial
20 of Table 4) and radiography test is performed on the weld joint
after removal of the reinforcement. The result is shown in Fig. 8. It is
observed that the number of pores, has reduced to a greater extent
even as compared to the result shown in Fig. 7. This concentration
of pores is within the acceptable limits as per ASME section 5. Thus
the study demonstates that the butt surface of the tubes must be
free from impurities to get a better result for radiography test. These
small number of pores may arise due to the interaction of the gas
molecules in the weld region during the heating and cooling proces
of welding.
Hence, it is proposed that, by employing shielding gas during
MIAB welding, there is a possiblity to eliminate the pores.
However, in common with other forge welding techniques such
as flash and friction, MIAB weld quality cannot be assessed by the
non-destructive techniques of radiography. This is because it is possible
to have thin layers of oxide or flattened inclusion at the weld
line which are too small to detect but can give areas of low adhesion
and hence weakened welds.
Fig. 8. X-ray film indicating the presence of pores at the joint (without reinforcement).
4.3. Results of X-ray diffraction characterization
X-ray diffraction patterns are obtained using Rigaku X-ray
diffractometer with CuK radiation ( = 1.5406A˚ ) with 2 ranging
from 10◦ to 80◦. Indexing of planes is done and the peaks are compared
with the standard JCPDS (Joint Committee Powder Diffraction
Standards) values.
Figs. 9 and 10 show the X-ray diffraction patterns of the base
metal and weld region, respectively. The line broadening of the
diffraction peaks arises due to the particle size and strain present
inside material.
The X-ray diffraction spectra provide information on the crystal
phase in the base metal. The tallest peak contains chromium silicate
in a cubical phase. Similarly the other peaks constitute either
hexagonal phase silicon carbide or cubical phase chromium silicate.
There are a few irregularities with no defined peaks indicating the
existence of impurity phases. A good crystalline nature is observed
in the base metal.
Similarly, the X-ray diffraction spectra (Fig. 5.39) provide information
on crystal phase in the weld region. The tallest peak contains
in the presence of the reinforcement. From the test results it is
observed that there are several pores at the weld joint as shown in
Fig. 6.
Fig. 6. X-ray film indicating the presence of pores at the joint (with reinforcement).
Subsequently, the MIAB welded specimen 3 (parameters as per
trial 20 of Table 4) is subjected to radiography test. However, for
this test, the reinforcement is removed by grinding. Further, the
grinded weld area is cleaned before the radigraphy test. The result
from this test showed that considerable number of pores still exist
as shown in Fig. 7. However, there is a reduction in the number of
pores in the weld region. This indicates that the pores are highly
concentrated mainly on the reinforcement of the weld region and
not much concentarted in actual weld line along the thickness of
butt surfaces.
Secondly, the SA213A T11 tubes are grinded, then buffing is performed
and the butt surfaces are cleaned to remove the impurities.
Consequently the tubes are MIAB welded (parameters as per trial
20 of Table 4) and radiography test is performed on the weld joint
after removal of the reinforcement. The result is shown in Fig. 8. It is
observed that the number of pores, has reduced to a greater extent
even as compared to the result shown in Fig. 7. This concentration
of pores is within the acceptable limits as per ASME section 5. Thus
the study demonstates that the butt surface of the tubes must be
free from impurities to get a better result for radiography test. These
small number of pores may arise due to the interaction of the gas
molecules in the weld region during the heating and cooling proces
of welding.
Hence, it is proposed that, by employing shielding gas during
MIAB welding, there is a possiblity to eliminate the pores.
However, in common with other forge welding techniques such
as flash and friction, MIAB weld quality cannot be assessed by the
non-destructive techniques of radiography. This is because it is possible
to have thin layers of oxide or flattened inclusion at the weld
line which are too small to detect but can give areas of low adhesion
and hence weakened welds.
Fig. 8. X-ray film indicating the presence of pores at the joint (without reinforcement).
4.3. Results of X-ray diffraction characterization
X-ray diffraction patterns are obtained using Rigaku X-ray
diffractometer with CuK radiation ( = 1.5406A˚ ) with 2 ranging
from 10◦ to 80◦. Indexing of planes is done and the peaks are compared
with the standard JCPDS (Joint Committee Powder Diffraction
Standards) values.
Figs. 9 and 10 show the X-ray diffraction patterns of the base
metal and weld region, respectively. The line broadening of the
diffraction peaks arises due to the particle size and strain present
inside material.
The X-ray diffraction spectra provide information on the crystal
phase in the base metal. The tallest peak contains chromium silicate
in a cubical phase. Similarly the other peaks constitute either
hexagonal phase silicon carbide or cubical phase chromium silicate.
There are a few irregularities with no defined peaks indicating the
existence of impurity phases. A good crystalline nature is observed
in the base metal.
Similarly, the X-ray diffraction spectra (Fig. 5.39) provide information
on crystal phase in the weld region. The tallest peak contains
in the presence of the reinforcement. From the test results it is
observed that there are several pores at the weld joint as shown in
Fig. 6.
Fig. 6. X-ray film indicating the presence of pores at the joint (with reinforcement).
Subsequently, the MIAB welded specimen 3 (parameters as per
trial 20 of Table 4) is subjected to radiography test. However, for
this test, the reinforcement is removed by grinding. Further, the
grinded weld area is cleaned before the radigraphy test. The result
from this test showed that considerable number of pores still exist
as shown in Fig. 7. However, there is a reduction in the number of
pores in the weld region. This indicates that the pores are highly
concentrated mainly on the reinforcement of the weld region and
not much concentarted in actual weld line along the thickness of
butt surfaces.
Secondly, the SA213A T11 tubes are grinded, then buffing is performed
and the butt surfaces are cleaned to remove the impurities.
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