Acoustic Emission Detection and Evaluation of Hydrogenation Reactors

Abstract: Aiming at the safe operation of hydrogenation reactors, a key equipment in the petrochemical industry, acoustic emission testing is carried out at the same time as pressure resistance tests are carried out during manufacturing and in-service maintenance to improve the safety and reliability of hydrogenation reactors. This paper gives the test results of 5 hydrogenation reactors. Through the continuous improvement and perfection of the detection technology, supplemented by other detection methods and evaluation, the safety status of hydrogenation reactors can be well evaluated.
Keywords: Acoustic emission (AE); non-destructive testing; evaluation Ultrasonic level meter Ultrasonic level meter Ultrasonic cleaning machine Ultrasonic thickness gauge Washing machine 0 Introduction Acoustic emission technology is a dynamic non-destructive testing method that has emerged since the 1950s and is becoming increasingly mature. It was widely used in the factory inspection of hydrogenation reactors and key nuclear power equipment in foreign countries in the early 1980s. China began to study and apply acoustic emission in the 1970s. Through decades of efforts, it has made great progress in both the depth and breadth of application. At present, it has been widely used in structural integrity detection and evaluation in the fields of material testing, petrochemical pressure vessel inspection, aerospace, energy, construction, transportation, etc. With the rapid development of computer technology and signal processing technology, the emergence of fully digital acoustic emission instruments and their integration with international standards, users of China's petrochemical industry have increased acoustic emission testing for hydrogenation reactors, whether they are newly manufactured or in-service, in order to improve the safety and reliability of hydrogenation reactors. In addition, other non-destructive testing methods and assessments can be used to evaluate the safety status of hydrogenation reactors in production and in use. The five hydrogenation reactors described in this article are three newly manufactured factory inspections and two in-service inspections. 1 Overview of hydrogenation reactors The basic parameters of hydrogenation reactors are shown in Table 1. Table 1 Basic parameters of hydrogenation reactor No. Container name Container No. Specification Material Design pressure MPa Design temperature ℃ Remarks 1 Hydrogenation refining reactor R3001 Ф4200×201.5×22462 2 1/4Cr-1Mo-1/4V 15.55 445 New, forged welding 2 Hydrocracking reactor R3002 Ф4560×198.5×25872 2 1/4Cr-1Mo-1/4V 15.34 445 New, forged welding 3 Hydrogenation reactor R4001 Ф3800×140.5×20062 2 1/4Cr-1Mo-1/4V 11.34 437 New, forged welding 4 Hydrogenation refining reactor R2101C Ф800×58×8950 0Cr18Ni10Ti 13.65 400 In use, plate welding 5 Hydrogenation refining reactor R001A Ф500×42×7127 1Cr18Ni9Ti 15.12 380 In use, plate welding 1-3# hydrogenation reactors are subjected to acoustic emission testing during factory pressure test, 4# and 5# are subjected to acoustic emission testing during pressure test when surface cracks were found on the outer surface during the comprehensive inspection of shutdown, and they are qualified after welding repair. 2 Acoustic emission testing and evaluation 2.1 Acoustic emission testing conditions Instrument: American PAC DISP32 acoustic emission system, frequency range 100~400KHz; sensor fixing method: magnetic fixer or bandage; coupling agent: vacuum grease; testing standards: GB/T18182-2000 "Methods for acoustic emission testing and result evaluation of metal pressure vessels", JB/T7667-95 "Methods for acoustic emission testing and evaluation of in-service pressure vessels". The instrument parameter settings are shown in Table 2. Table 2 Instrument parameter settings No. Container No. Monitoring and positioning method Sound velocity (m/s) Threshold (dB) Number of sensors Maximum distance between sensors (m) Maximum test pressure (MPa) 

 














 

1 R3001 overall monitoring, cylindrical positioning 5500 45 20 5 22.41
2 R3002 overall monitoring, cylindrical positioning 5500 45 20 6 22.13
3 R4001 overall monitoring, cylindrical positioning 5000 45 20 5.5 16.32
4 R2101C overall monitoring, cylindrical positioning 5500 45 8 2.5 12.5
5 R001A overall monitoring, cylindrical positioning 5500 45 8 2.5 13.3
2.2 Arrangement of sensors and calibration of acoustic emission instrument
The arrangement of sensors is shown in Fig. 1a and Fig. 1b.

Figure 1a R3001 sensor layout Figure 1b R001A sensor layout
Acoustic emission instrument calibration
Use the AST function of the acoustic emission instrument itself to determine whether the acoustic emission system is calibrated normally and the response amplitude of each channel sensor meets the standard requirements, or use a 0.5mm lead core break as a simulation source, give a simulation signal at the corresponding position, observe the characteristic parameters and positioning accuracy of each signal, and adjust those that do not meet the standard requirements.
2.3 Positioning method and loading procedure
The overall monitoring cylindrical positioning method is adopted. The new reactor uses clean water as the test pressure medium. The reactor in use cannot be emptied due to the presence of catalysts, and nitrogen or argon is used for pressure testing. According to the provisions of the "Container Regulations" and referring to JB/T7667-95 "Acoustic Emission Detection and Evaluation Methods for In-service Pressure Vessels", the pressure is maintained in three steps, namely 80% test pressure for 15 minutes, test pressure for 30 minutes, and reduced to 80% test pressure for 15 minutes. The loading curve is shown in Figure 3.
Ultrasonic level meter Ultrasonic level meter Ultrasonic cleaning machine Ultrasonic thickness gauge Washing machine 2.4 Acoustic emission test results and analysis 2.4.1 Acoustic emission test results of new hydrogenation reactor During the pressure test of the newly manufactured hydrogenation reactor, the acoustic emission test showed that there were more acoustic emission signals in the low-pressure stage, fewer signals in the high-pressure stage, and fewer signals in each pressure-maintaining stage. Typical acoustic emission signal positioning diagrams are shown in Figures 3 and 4. As can be seen from Figures 3 and 4, there are many signals in the boost stage. By observing the characteristic parameters of the positioning signals of each sound source, it is found that most of them are noise signals, which are related to the mechanical noise caused by multiple factors in the low-pressure stage and are difficult to shield. They are only used as references during analysis. There are fewer signals in the pressure-maintaining stage, and the characteristic parameter values ​​such as amplitude, count, and energy are relatively low. According to the comprehensive rating of strength and activity of the JB/T7667 standard, they are all Class I and Class II sound sources, and do not need to be re-tested using conventional non-destructive testing methods or other methods. 

 

Figure 3. Location of acoustic emission sources during the pressure increase stage of R3001 from 0 to 15.55 MPa

Figure 4 Location of acoustic emission source for R3001 15.55 MPa pressure maintenance for 10 min Figure
2.4.2 Results of acoustic emission detection of in-service hydrogenation reactors The
in-service hydrogenation reactors 4# and 5# are single-layer stainless steel reactors designed by Luoyang Institute and manufactured by First Heavy Industries in 1993. During the comprehensive inspection in 2004, a deep crack was found on the outer surface of the upper manhole weld of 4#, and two cracks were found on the outer surface of the upper and lower head ring seams of 5#. The above cracks were welded and repaired by qualified units entrusted by the user. After passing the inspection, the pressure test (air pressure) was carried out, and the acoustic emission detection was carried out at the same time. The typical acoustic emission signal spectrum is shown in Figures 5 and 6. It can be seen from Figures 5 and 6 that there are many signals in the boosting stage, which are related to the mechanical noise caused by the catalyst loaded in the reactor and the pressurization rate, and are difficult to shield. They are only used as reference during analysis. When the pressure is maintained for 30 minutes under the highest loading pressure, the acoustic emission signal gradually decreases, and the characteristic parameters such as amplitude, count, and energy are low, showing an obvious convergence trend. According to the comprehensive rating of strength and activity of JB/T7667 standard, they are all Class I and Class II sound sources, and do not need to be retested by conventional non-destructive testing methods or other methods. This shows that the reactor is stable under a pressure of 13.3MPa.

Figure 5. Location of acoustic emission sources during the pressure increase stage of R001A from 5.7 to 9.3 MPa

Figure 6 Acoustic emission source positioning for R001A 10.4～13.3 MPa pressure increase and pressure maintenance for 30min Figure
3 Calibration of positioning source and re-inspection of conventional non-destructive testing
After calibrating the centralized positioning sound source in the detection process of 5 hydrogenation reactors, and conducting macroscopic inspection, magnetic particle re-inspection or penetration re-inspection and ultrasonic inspection at the same time, no active dangerous defects were found. Analysis of the reasons The centralized positioning sound sources recorded in these tests all come from the pressurization process, the mechanical noise of the inlet and outlet pipes, and the catalyst in the reactor. In other words, the positioning sound source signal recorded by the acoustic emission test is not caused by active defects, but by external factors such as mechanical noise. 4 Conclusion (1) As a dynamic non-destructive test, acoustic emission testing can be carried out at the same time as the equipment pressure test to detect dangerous defects of the equipment. (2) There are many containers for special media in the petrochemical industry, which cannot be opened for normal inspection. The use of acoustic emission online detection technology, supplemented by conventional detection methods, can effectively prevent the occurrence of container failure accidents (3) New hydrogenation reactors are qualified and shipped out of the factory, and the hydrogenation reactors in use are safely put into use.