Significance and Use
5.1 High pressure fluids being pumped in all oil field applications often stress iron pipes where subsequent failure can lead to injury to personnel or equipment. These forgings are typically constructed from 4700 series low carbon steel with a wall thickness in excess of 1.25 cm [0.5 in.], dependent on the manufacturers' specification. The standard method to certify that these iron segments can withstand operational pressures is to perform dye penetrant (PT) or magnetic particle penetrant (MT) tests, or both, to reveal defects (cracks and corrosion). As these methods are subject to interpretation by the human eye, it is desirable to employ a technique whereby a sensor based system can provide a signal to either pass or fail the test object. To that end, the acoustic emission (AE) method provides the requisite data from which acceptance/rejection can be made by a computer, taking the human out of the loop, providing that a human has correctly programmed the acceptance criteria. Most of these pipe segments are not linear, thus a 3D defect location method is desirable. The 3D source indication represents the spatial location of the defect without regard to its orientation, recognizing the source location is only approximate due to sound propagation through the part and water bath.
5.2 The immersed 3D approach is found to be preferable due to the large number of parts to be examined. The 3D system is easily replicated and standardized in that all sensor locations are fixed to the exterior of the fluid bath. Multiple parts may be easily placed into an assembly, allowing all to be examined in a single test, thus accelerating throughput. Attaching a minimum of eight AE sensors to the tank enhances the probability that a sufficient number of AE hits in an event will occur, allowing for an approximate location determination. When an indication of a defect is observed, the subject part is identified by the spatial location allowing it to be removed for further examination, or rejected for service. An immersed test configuration is shown in a and b.
FIG. 1 (a) Immersion Bath With Permanently Attached AE Sensors on Exterior (Circles)
FIG. 1 (b) Photo of Part Under Test (continued)
5.3 The non-immersed examination is equally effective in detecting defects, but requires more time to assemble in that sensors must be attached to the part for each examination. Moreover, the fluid fill and air purge times are much longer than in the immersed bath immersion. The non-immersed test layout and photo are shown in a and b. Note the sensors are indicated with the symbol x.
FIG. 2 (a) Is the Layout, With sensors 1–4, of A Typical Non-immersed Test as is Shown in the Photo (b)
FIG. 2 (b) Sensors 1–4, of A Typical Non-immersed Test (continued)
1.1 This practice is no longer being updated but is being retained for historical value as it represents the only AE practice using hydrostatic testing in which the sensors are not in direct contact with the part.
1.2 In the preferred embodiment, this practice examines immersed low carbon, forged piping being immersed in a water tank with the acoustic sensors permanently mounted on the tank walls rather than temporarily on the part itself. The pipes are monitored while being internally loaded (stressed) by hydrostatic means up to 1000 bar.
1.3 This practice examines either an immersed pipe, or non-immersed pipe being stressed by internal hydrostatic means to create acoustic emissions when cracks are present. However, the non-immersed method is time consuming, requiring placement and removal of sensors for each pipe inspected, while the immersed method has sensors permanently mounted, providing consistent sensor coupling to the tank-eliminating reinstallation. The non-immersed method is not recommended for the specified reasons and only the immersed method will be discussed throughout the remainder of the practice. This is similar to pressure vessel testing described in Practice , but uses hydrostatic means not included in that standard.
1.4 This Acoustic Emission (AE) method addresses examination for monitoring low carbon, forged piping systems being internally loaded (stressed) by hydrostatic means up to 1000 bar [15,000 psi] while being immersed in a water bath to facilitate sensor coupling.
1.5 The basic functions of an AE monitoring system are to detect, locate, and classify emission sources. Other methods of nondestructive testing (NDT) may be used to further evaluate the significance of acoustic emission sources.
1.6 This practice can be used to replace visual methods, which are unreliable and have significant safety risks.
1.7 This practice describes procedures to install and monitor acoustic emission resulting from local anomalies stimulated by controlled hydrostatic pressure.
1.8 Other methods of nondestructive testing (NDT) may be used to further evaluate the significance of acoustic emission sources.
1.9 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.
1.10 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.