What is UFDT (ultrasonic flaw detection test)? Why this done in LPG spheres? What is the principle behind?

Answer 1

#ULTRASONIC TESTING (UT)

The fundamental principles of ultrasonic testing of metallic materials are similar to radar and related methods of using electromagnetic and acoustic waves for detection of foreign objects. The distinctive aspect of UT for the inspection of metallic parts is that the waves are mechanical, so the test equipment requires three basic components.

* Electronic system for generating electrical signal.
* Transducer system to convert the electrical signal into mechanical vibrations and vice versa and to inject the vibrations into and extract them from the material.
* Electronic system for amplifying, processing and displaying the return signal.
Very short signal pulses are induced into the material and waves reflected back from discontinuities are detected during the receive mode. The transmitting and detection can be done with one transducer or with two separate transducers (the tandem technique).

Unlike radiography, UT in its basic form does not produce a permanent record of the examination. However, more recent versions of UT equipment include automated operation and electronic recording of the signals.

Ultrasonic techniques can also be used for the detection and measurement of general material loss such as by corrosion and erosion. Since wave velocity is constant for a specific material, the transit time between the initial pulse and the back reflection is a measure of the travel distance and the thickness.

DETECTION PROBABILITIES AND FLAW SIZING :

The implementation of NDE (nondestructive examination) results for structural integrity and safety assessment involves a detailed consideration of two separate but interrelated factors.

* Detecting the discontinuity.
* Identifying the nature of the discontinuity and determining its size.
Much of the available information on detection and sizing capabilities has been developed for aircraft and nuclear power applications. This kind of information is very specific to the nature of the flaw, the material, and the details of the test technique, and direct transference to other situations is not always warranted.

The overall reliability of NDE is obviously an important factor in a safety and hazard assessment. Failing to detect or undersizing existing discontinuities reduces the safety margin while oversizing errors can result in unnecessary and expensive outages. High reliability results from a combination of factors.

* Validated procedures, equipment and test personnel.
* Utilization of diverse methods and techniques.
* Application of redundancy by repetitive and independent tests.
Finally, it is useful to note that safety assessment depends on evaluating the largest flaw that may be missed, not the smallest one that can be found.

#For basic principle,please click on:
http://www.olympusndt.com/en/applications-and-solutions/introductory-ultrasonics/introduction-flaw-detection/

Answer 2

Ultrasonic vibrations are sent into the material and are reflected back from the opposite surface. Measuring the elapsed time from sending to receiving, the instrument calculates the thickness. If the instrument detects a crack, thin place, fissure, void-in-weld etc. then the tank is abnormally weak in that one place.

Answer 3

Ultrasonic testing can be used on welds as one method of detecting flaws.

Ultrasonics can also be used to find laminations in the plate from which a vessel is made. It is best to do this prior to fabrication.

Answer 4

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