APPLICATION OF ACOUSTIC EMISSION TESTING DURING HYDROSTATIC TEST TO ENSURE INTEGRITY OF VESSEL SECTION WITH SUPPORT STRUCTURES

Sarath S1, Pragnesh J Patel1, Dharmik Dave1, P Raghavendra1, Dhiren J Kothari1,V N Rao2 1NDE Department Heavy Engineering Division, Hazira Manufacturing Complex, L&T, Surat – 394510 Gujarat, India http://www.ndt.net/?id=21211 2Physical Acoustics India Pvt. Ltd 222, Arcadia, Hiranandani Estate,Thane (West) 400607 Maharashtra India

E-mail: [email protected],[email protected], [email protected]@larsentoubro.com, [email protected],[email protected] More info about this article: Abstract The capability of Acoustic Emission (AE) Testing to detect and locate emission sources caused by surface and internal discontinuities in the vessel walls, welds, and attached components, makes it an effective tool in assessing volumetric integrity during the pressure test of a vessel. It acts as an excellent supporting technique for other methods when employed as a primary examination method during hydrostatic or pneumatic testing. ASME Boiler and Code section VIII Division 2 calls for acoustic emission testing during hydrostatic test or pneumatic test, as per Article 12 of Section V, if specified in the Users Design Specification. Acoustic emission monitoring is preferred during pneumatic testing, primarily to ensure safety by providing early warnings of any significant defect growth which might occur during the pressure test. Apart from addressing safety concerns, it also helps in detecting and locating any areas of AE activity that require further investigation. AE Testing is thus becoming more popular in the recent scenario especially in the manufacturing sector.

This paper discusses the application of Acoustic Emission Testing in reactor vessel with complex structural attachments, for ensuring the full volumetric integrity during Hydrostatic test. AE Test has been carried out by Mistras Group inc-Physical Acoustics Corporation (PAC) AE instrument with MONPAC technology employing intensity analysis method for evaluation of the defects. The paper describes in detail about the code requirements, pressurization sequence followed and the This paper also explains the methodology adopted for evaluation and the test results obtained.

Keywords: Acoustic Emission, Hydrostatic Test, ASME, complex structural attachments, Pressure vessels.

411 Non-Destructive Evaluation 2016

Introduction Acoustic Emission Testing (AET) is a non-destructive testing method that uses acoustic emission phenomenon. Material under inspection is applied with external load.A sudden movement in discontinuity produces a stress wave, which radiatesout into the structure and excites a sensitive piezoelectric transducer. As the stress in the material is raised, many of theseemissions are generated. The signals from one or more sensors are amplified and measured to produce data for displayand interpretation.

While other methods detect existing geometrical discontinuities, AET detects movements. Another key aspect in AET is that the signal used for detection is originated in the material itself and not given by an external source. Of all the advantages of AET one of the most highlighted one is that is provides full volume inspection in a single loading operation. It acts as an excellent supporting technique for other nondestructive testing methods when employed as a primary examination method during hydrostatic or pneumatic testing. In manufacturing sector, ASME Boiler and Pressure Vessel Code section VIII Division 2 calls for acoustic emission testing during hydrostatic test or pneumatic test, as per Article 12 of Section V, if specified in the users design specification.

This paper discusses the application of Acoustic Emission Testing in gasifier reactor with complex structural attachments, for ensuring the full volumetric integrity during Hydrostatic test. The specific reactor is one of the critical components designed for an internal pressure of 57 Kg/cm2 at 3430 C. The reactor fabricated out of carbon steel (SA 542M) material consists of a conical section with numerous brackets attached externally as given in fig 1. Taking into consideration the criticality of the joints and the additional stresses generated due to the external attachments,AET was performed specifically for this conical section to ensure the complete structural integrity.

Fig. 1: Conical section with external attachments

412 Non-Destructive Evaluation 2016

Instrumentation and methodology adopted:

AET was carried out in line with ASME Section V article 12 and IPACTM MONPACTM procedure using a Physical Acoustic SAMOS testing system. MONPAC technology is experience based and was developed using Physical Acoustics AE sensors and test equipment. This system is able to efficiently and reliably detect propagating defects: cracking, overstress, corrosion etc. It does not give information on defect size but grades the activity (from įinsignificant‖ to įintense‖) and gives recommendations for the extent of any follow-up inspection. The MONPAC TM Intensity chart is used to determine the MONPACTM grade of individual sensor channels. The grading is based on severity & history of the acquired acoustic emission hit data and was developed by correlation of AE data with inspection results on tests from more than 2000 metal VESSELs. Each MONPAC TM grade has an associated recommendation.

The intensity data is only valid for tests run with MONPAC TM certified instrumentation to MONPAC TM procedures.Location is primarily įzonal‖ and indicates the active area.Location by time arrival is sometimes possible where sources are intense and this gives a more localized search area. The method does not identify manufacturing defects if they have not propagated during subsequent service. However, significant manufacturing defects, including embrittled welds, may be identified during hydro test.

Sensors and sensor location:

AE sensors (PAC model R15I/DT15I), were positioned in triangular location array at the locations shown in sensor location diagram, and tested in-situ following mounting. A total of 29 sensors were mounted in the vessel after carrying out sensor verification check and attenuation study to ensure coverage of the entire conical section.

413 Non-Destructive Evaluation 2016

Fig2:AE sensor location on the reactor component with external attachments.

Results:

AE data acquired during vessel pressurization in two cycles. Pre-decided pressurization sequence was followed as per the reference code section.

Following the test, the data was analyzed and extraneous noise was removed from the data. MONPACTM ZIP INTENSITY analysis carried out to evaluate the severity of emission received at each sensor.The noise sources were identified and removed from the data prior to analysis and evaluation .Emission reaching three or more sensors was located by triangulation and any sources obtained were analyzed.

During 1st Loading AE signals were observed mainly due to Vessel Stress Relief, Vessel Expansion and Vessel Support Movement.

414 Non-Destructive Evaluation 2016

Fig 3:Load and AE activity (Amplitude and energy) Vs Time during 1st loading

Fig 4:Location graph for the conical section

415 Non-Destructive Evaluation 2016

During the 2nd Loading AE test data registered few C-grade clusters apart from the AE signals generated due to continuation stress relief, vessel expansion, vessel support movement and hex mesh.

Fig 5:Load and AE activity (Amplitude and energy) Vs Time during 2nd loading

416 Non-Destructive Evaluation 2016

Fig6: MONPAC TMseverity evaluation during second loading

Fig 7:Location graph for the conical section during 2nd loading

Fig 8:Location graph for the conical section during 2nd loading

Refer fig.7for the location of the clustered AE signals observed in the conical section. The C grade-AE clusters registered in AE test recommends additional investigation by other NDE methods on the clustered locations on the long seams of the cone.

417 Non-Destructive Evaluation 2016

Conclusion:

No AE location clusters were formed by AE sensors mounted on top ring & the base ring. This rules out AE indications from Gusset to cone weld & Lug support welds.Follow up NDE(HS UT and UT) was performed on the longitudinal welds on cone where AE location clusters were observed. TOFD and HSUT did not reveal any indications from the weld and this assured the soundness of the weld pressure boundaries in the conical section.It is thus concluded by the method of elimination that, the indications are from the hex mesh beneath the long seam welds which wereinstalled post weld heat treatment to the limiting bars. This specific case reveals how sensitive AE is and at the same time shows the numerous possibilities of AE source. Thus it demands an in-depth knowledge of the component to be AE tested, the fabrication process involved and the environmental conditions during test for effective interpretation of the AE signals.

References:

1]A case study for crack detection within a cylinder using acoustic emission testing,Gerald Lackner , Rene Dusek Tüv Austria Services Gmbh; Institute For Technical Physics Deutschstrasse 10, 1230 Wien, Austria

2]Evaluation Of Acoustic Emission Behavior Under Hydrostatic Test In Api 5l X70 Steel Pipe,H. Hanafi,N. JamaludinS, Abdullah,M.F. YusofDepartment of Mechanical & Material EngineeringFaculty of Engineering, National University of Malaysia43600 UKM, Bangi, Selangor, Malaysia

3]Defect Detection By Acoustic Emission Examination Of Metallic Pressure Vessels , Franz Rauscher ,Vienna University of Technology, Vienna, Austria

4] Acoustic Emission Examination of Metallic Pressure Vessel during Pressure Testing,ASME section V Article 12

418 Non-Destructive Evaluation 2016