AE Example

EXAMPLE AE EXAM

Testing Overview

Acoustic emissions are elastic energy waves that are spontaneously released by a material undergoing deformation. Acoustic emission testing is defined as a “passive” inspection method for monitoring the dynamic internal stress redistribution within a material that occurs when an external stress is imposed on a component. The stress can be either a hydrostatic, pneumatic or thermal. In an acoustic emission test a network of piezoelectric transducers are attached to the exterior of a vessel. These sensors convert mechanical energy such as elastic waves into an electric impulse that is transmitted by cable to the AE Instrument.

As the vessel is stressed, the AE instrumentation collects signals. Parameters from each emission are measured and then stored within the system data logger. Data from each sensor is stored on separate channels along with the exact time when the event was detected. These data are analyzed both during and after the test. Acoustic emission serves an important function in the oil, chemical, paper and petrochemical industries, to name a few. It is a global non-destructive examination technique, which provides a measure of the structural severity of a defect. As such, it is complementary to other non-destructive examination methods such as radiography, ultrasonic, and visual which are used for examination of local areas. Prior to the development of acoustic emission, hydrostatic test was the principal global test. This Inspection method is designed to detect structurally significant defects and damage in vessels that can occur during fabrication and under normal operating conditions. This test will only detect defects that are stressed during the course of the test. Defects in unstressed areas and passive defects (structurally insignificant during the applied load) will not generate AE.

Some of the defects that can generate AE are as follows:

• Crack Growth • Fiber breakage • Stress corrosion micro cracking / liner matrix failure • Delaminations • Entrapped air pockets / Manufacturing flaws

• Inadequate design for the applied stresses.

Introduction

All NDEI Acoustic Emission Reports have the following information included:

• Introduction: Scope & Exceptions

• Requirements: Test Parameters & Loading Method

• Evaluation Criteria: ASTM Guidelines

• Results: Conclusions & Recommendations

• AE Data Graphs: Counts & AE Activity Samples

The following example is based on an FRP Style Vessel in accordance with ASTM E1067*

*Please note that NDEI always uses the most current revision of the ASTM E1067 standard

(This report is Generic and is created solely for the purposes of an example for our perspective customers)

INTRODUCTION

This vessel was examined in accordance with the standard practice ASTM E1067 for Acoustic Emission (AE) monitoring of fiberglass-reinforced plastic (FRP) tanks/vessels under atmospheric pressure to determine structural integrity.

This practice is limited to tanks-vessels designed to operate at an internal pressure no greater than 1.73 MPa absolute [250 psia, 17.3 bar] above the static pressure due to the internal contents. It is also applicable for tanks-vessels designed for vacuum service with differential pressure levels between 0 and 0.10 MPa [0 and 14.5 psi, 1 bar].

The following criteria was utilized for the overall evaluation of this vessel:

ASTM E1067 Non Mandatory Criteria X1.2

Exceptions:

No exceptions to the ASTM standard were necessary for the completion of the acoustic emission examination.

Requirements

INSPECTION PARAMETERS

Following the ASTM E1067-18 standard procedure and once the sensors and connection cables were in position, the system was connected and verified using a mechanical pencil PENTEL 0.3 mm. Three lead breaks were performed at 4.0 inches from the center of each sensor.

The results of this test were recorded and used to verify the performance and calibration of each channel. (Appendix B)

PRE-TEST BACKGROUND CHECK

To establish emission levels that can be attributed to the normal background noise emission that is extraneous; the vessel was monitored ten (10) minutes prior to the start of the loading sequence.

TEST TERMINATION

Departure from a linear count / load relationship should signal caution. If the AE count rate increases rapidly with load, the vessel shall be unloaded, and the test terminated. A rapidly (exponentially) increasing count rate indicates uncontrolled, continuing damage, and is indicative of impending failure. Test termination is solely at the discretion of the inspection technician.

LOADING METHOD AND SEQUENCE

To perform a successful acoustic emission test, the vessel must be subjected to programmed increasing stress levels, while being monitored by the acoustic emission testing equipment. The guidelines recommended in the ASTM E1067-18 procedure require that the vessel must be tested at a maximum of 100% of the operating level. The inspection analysis is valid only to the achieved load level. This vessel was previously filled to maximum capacity and was conditioned per Section 8.2 - Table 1 and Section 11.2 – Figure 1 of the ASTM E1067-18 Standard.

Evaluation Criteria

EVALUATION CRITERIA

(In-Service Vessel)

No 1. EMISSIONS DURING LOAD HOLD PERIODS:

PASS = No hits after 2 minutes > Am

The significance of these criteria is that continuing emissions during the hold can indicate a continuing yield or damage due to creep or a growing defect. These criteria can show the presence of a significant defect when the total number of hits during each load hold is increasing with the increasing load level.

No 2. LARGE AMPLITUDE HITS:

PASS = < 5 hits with amplitudes greater than the reference amplitude of 76 Db

Large amplitude hits often indicate the presence of a growing crack, fiber breakage, or significant structural damage.

No 3. CUMULATIVE DURATION:

PASS = < N_d/2

N_d in accordance with ASTM E1067-18 A2.5, is equal to 130 times (x) the average of 10, 0.3-mm (2h) lead pencil breaks for each of the two lead break locations (i.e. #1 in the direction of the fibers, #2 at 45 degrees to the direction of the fibers at a distance from the sensor to equal the decibel value of A_m).

*This criterion is subjective to the specific material utilized for construction. This criterion is a measure of overall damage during a load cycle.*

No 4. FELICITY RATIO:

PASS = > 95% previous load

The criterion ratio is important for in service vessels. The felicity ratio provides a measure of the severity of previously induced damage.

Result Example