Non Relevant Ultrasonic Indications

 Non relevant Ultrasonic Indications can usually be identified as one of the following:

  1. Electrical Interference
  2. Interference form the transducer (search unit)
  3. Interference form the surface of the specimen
  4. Interference caused by mode conversion of the sound beam
  5. Interference caused by the shape of the specimen
  6. Interference caused by material structure


Electrical interference can be caused by improper electrical connections of sound energy from the interface between the wedge and test specimen surface.

ultra sonic testing services

In Immersion Testing, Air bubbles either on the transducer or specimen can cause reduced signal amplitude form the back surface and at times also from the front surface.

Surface Interface

A small amount of surface wave energy is usually transmitted in all directions around a transducer as shown below.

If the transducer is near the edge of a plate, a signal may appear on the CRT.

ultra sonic testing

 

When inspecting with shear waves, it is possible to detect a surface discontinuity with the small amount of surface waves generated (see below).

ultra sonic testing inspection

You can determine if the reflection is from a surface wave by running your finger along the surface in front of the transducer.

If the reflection is due to surface waves, the amplitude of the pipe will drop on the CRT. When your finger is between the transducer and the interface producing the signal, surface wave indications may not be cause for rejection, but they should be evaluated.

Interference can be caused as a result of mode conversion in the test specimen as shown below.

However all of these reflections can be ignored as they will appear on the CRT after the first back reflection.

ultra sonic testing

The shape of the specimen can cause false indications as shown below.

ultrasonic test indications

The Ultrasonic operator should always know the configuration of the part so that these false indications can be identified.

To verify a possible false indication, the operator should try to locate the discontinuity from a different location on the specimen.

A non-relevant indication may occur when using a transducer with a large beam spread as shown below.

This indication is easily identified as it is always behind the first back reflection of the part and would probably be continuous along the surface of the part.

ultrasonic test

In the situation above, a plastic shoe machined to the diameter of the part usually reduces the excessive beam spread.

A large grain size may also cause “Noise” or “Hash” on the CRT screen. Abnormally large grains may result in total loss of back reflection. A lower examination frequency may help alleviate this problem.

ultrasonic test ndt services

During weld inspection, non-relevant indications my result from reflections from the crown and the root of the weld and possibly from the heat affected zone.

ultrasonic testing ndt

Any indication on the CRT screen that is unusually consistent can be suspected as being non-relevant.

As is shown above, the reflection from the root and crown of the weld may appear for the entire length of the weld. If the non-relevant signal is coming from the crown of the weld, it can often be identified by placing your finger wet with couplant over the suspected area.

If the sound beam is striking the crown, it will be dampened by your finger, a surface examination, PT or MT, can be used to reduce the possibility of a surface crack causing the reflection.

For best Non destructive Testing  Inspection services  and other Material testing services in Coimbatore and NDT certification , QC training contact us at https://aqcinspection.com/

Visit our technical and career updates at our Blog site https://advancedqualitycentre.blogspot.com . https://ndtcenter.blogspot.com

Location: 116-B, 5th St Ext, 5th Street Extension, Doctor's Colony, Gandhipuram, Tamil Nadu 641012, India

Comments

Post a Comment

Popular posts from this blog

Discontinuities in Ultrasonic Testing in NDT

Image
 This blog will discuss types of discontinuities that can be evaluated with the ultrasonic testing in NDT method. Discontinuities can be divided into three general categories inherent, processing and service Inherent discontinuities are usually formed when the metal is molten. Inherent wrought discontinuities relate to the melting and solidification of the original ingot before it is formed into slabs, blooms and billets. Inherent cast discontinuities relates to the melting, casting and solidification of a cast article. Usually caused by inherent variables such as inadequate feeding, gating, excessive pouring temperature or entrapped gases. Processing discontinuities are usually related to the various manufacturing process such as machining, forming, extruding, rolling, welding, heat treating and plating. Service discontinuities are related to the various service conditions such as stress, corrosion, fatigue and erosion. During the manufacturing process, many disco
Read more

NDT on Shafts

Image
  Non Destructive Testing,NDT on Shafts is considered essential , because the shafts are mostly made as load bearing structures, any defects such as cracks will propagate more during acting of load and eventually will cause failure. The most possible defects in shafts are Cracks and Pipes , which is shown below The Non Destructive methods preferred for defect detection on raw material shafts are Ultrasonic Testing, Magnetic Particle testing / Eddy Current Testing / Magnetic Flux Leakage method. We have not discussed about other NDT methods such as Liquid Penetrant testing & Radiographic testing because for raw material inspection. These methods will be cost effective for raw material testing  ( i.e. most costly and labor intensive, also there is possibility of missing out the cracks in radiography testing due to orientation of crack ) The Defect wise identification method is given as below  , Internal Defect ( Piping ) – Ultrasonic Testing Surface Defects  (C racks) – Magnetic Part
Read more

Standards for Welding Positions

Image
  Standards for Welding Positions : It is very important for the Weld Inspector  to know the position , or location of a joint relative to the horizon, because it may determine what welding process, methods, and techniques can be used. Welding is usually easiest when the welder can work on a joint located on a flat, horizontal surface, such as on a table or bench. However, joints in the field may be located in a variety of positions relative to the welder and to the horizon, as shown below.  1)  Welding positions – AWS D1.1, European Welding Standard EN 287 – 1, ASME IX: 2) Welding Positions – Butt, Fillet and Piping Welds: Flat Butt Weld Position – 1G In this position, the axis line of the weld must  not incline more than 15°  from the horizon and the face of the weld must be on top. Welders often refer to the flat-position welding by the nonstandard term  downhand welding. Horizontal Butt Weld Position – 2G In this position, both plates are perpendicular to the bench top, but the axi
Read more