Supercritical CO2 extraction equipment is an essential oil extraction equipment composed of various high-pressure containers and pumps. During the metal fabrication process, the fillet joint between the CO2 extraction vessels (high-pressure vessel)nozzle and the shell is difficult to weld due to structural limitations. Effective inspection is an important part of quality control.
Surface inspection
At present, the surface inspection methods of D-type joints of supercritical CO2 extraction machines mainly include penetrant inspection PT and magnetic particle inspection MT. For ferromagnetic materials, magnetic particle inspection MT is preferred.
During the surface inspection, in order to eliminate the interference of false defects, the weld should be polished before inspection to remove the oxide scale, paint, and rust on the edge of the weld until the metallic luster is exposed.
It should be noted that if it is “dissimilar steel” welding when the material composition is quite different (especially Cr and Mo elements), the magnetic field line shift is easy to form in the weld fusion area during magnetic particle inspection, and the magnetic trace is displayed as a line, which is easy to If misjudgment is caused, penetrant testing or even radiographic or ultrasonic testing should be used to confirm the defect.
Internal quality inspection
If the pipe diameter of the large-scale industrial-grade supercritical CO2 extraction equipment is large, the internal quality of the D-type joint can be detected by radiographic testing RT or ultrasonic testing UT.
However, for small-diameter nozzles, the detection of D-type joints has always been a difficulty, and ultrasonic testing is generally used for DN80 and above.
Radiographic inspection
Since the thickness of the transillumination varies greatly within the length and width of the weld, if the radiation source is transilluminated from the inside to the outside, the film cannot be close to the weld, and there is a certain gap between the weld and the weld, and the effect of the weld on the film will be deformed. , the case of magnification. Therefore, for the radiation detection of D-type joints, it is generally transmitted from the outside to the inside.
Ultrasonic testing
Ultrasonic testing of D-type connectors with DN ≥ 80 can be carried out with reference to NB/T47013.3, but due to structural limitations, double-sided and double-sided testing cannot be performed, and most of them can only perform single-sided and single-sided testing. If conditions permit, should be tested inside the cylinder.
Inspection of Internal Quality of 45° Angled Pipe Fillet Joints
The detection of 45° oblique pipe fillet joints has always been a difficult point. These factors include large changes in the curvature of the inspection surface, large changes in weld width, large changes in transillumination thickness, large changes in ray transillumination angle, limited local transillumination angle, and negative film The large deformation of the weld image makes transillumination extremely difficult, and the evaluation of the negative requires higher requirements for the reviewers.