Lack of Side Fusion UT Signal Interpretation, A Scan Manual Ultrasonic Testing

Manual UT is carried out in following steps (1) Scanning. (2) Identification of indications (3) Classification (Planner/Nonplanner) (4) Evaluation (nonrecordable/recordable/Accept or Reject).

Even though it is not simple to spot a flaw, you need to make a good examination by taking note of its location in the weld, moving the probe around the flaw, and observing the signal's shifting on the screen. However, the most difficult aspect of MUT is interpreting and specifying defects like crack, lack of side fusion, Porosity etc. Sometime even experience Inspectors struggle to denote the Defects.

The shape, amplitude, and time-spread of a reflector, as displayed on the MUT display unite, can provide hints about the nature of a flaw Like a SPECULAR reflector, which has a mirror-like face and reflects all sound back to MUT Probe, provided if the probe and flaw are positioned as near to 90° as possible. A sidewall fusion flaw is nearest to this ideal.

Porosity, on the other hand, can be thought of as an abundance of tiny spherical reflectors that cause energy to reflect everywhere. Porosity is considered a Diffuse reflector.

In addition, the person performs MUT examination should also have basic knowledge of the welding process, and should have information regarding weld preparation, weld dimensions, size of root gap and other aspects of welds. For instance, the Slag is unlikely in a TIG weld and lack of sidewall fusion is not likely in the middle of the weld metal.

Conclusion can be drawn by combining obtained data from MUT screen with a weld profile sketch.

Before going into details let’s see what Lack of side wall fusion is

The Lack side wall fusion can be defined as no union/fusion between the weld metal and the parent metal

To further Explain this Topic, ?let’s assume we have a 30mm thick single Vee butt weld, which contain weld imperfection, 20mm depth from top surface, with 5mm height and 200mm Length.

During weld scan we move UT probe back-forth up transversally from weld toe to standoff distance up one and one-half (1 ?) times?of full skip length of the beam bath. This to cover weld full weldment (like weld cap, weld root including Heat affected zone). Here in animation, you can see sound pulse are hitting the back wall and making a V shape progression, this is nothing but sound beam path at full skip distance. Sound pulse are hitting the back wall and making a V shape progression

By looking at Animation, you can imagine that weld will not be fully scan without Transverse and Lateral Scan at appropriate scanning speed. If there is no reflector/defect in weld than there will not be any amplitude rise in Flaw detector display Unit. only grass (nose) coming from surface will be seen at time base.?

Now we will evaluate Amplitude response of lack of side wall fusion with respect to various probe position. Here we can see, The High amplitude signal from "A" on second leg of the full skip, and at Position "C" within half skip obtained at 153 and 66mm range, respectively. At both position (A and C) sound beam is hitting at the middle of defect. At position B the primary beam is hitting on top ligament of the defect and at Position "D" Primary beam is hitting on bottom ligament of the defect. In both the instance the probe angle is such that the beam is not perpendicular to the defect. Therefore, at Position "B" and "D" Low amplitude signals is Received at the range of 58mm and 161mm respectively from defect. Defect Size: Defect from Top Surface 20mm Defect Height=5mm Length=200mm.

For Lack of side fusion, the best response is received while lateral movement. To interpret the echo response, mark the position where the best response is being received. As we move the probe toward the defect the amplitude will start rising, at start of defect you can see amplitude is approximately 50% (6db) of full signal response height. As we will keep moving the probe then max signal response will be received. Base on this best response all evaluation and sizing will be done.

As probe move at the end of the defect the amplitude will start decreasing. Mark the Probe position when the Amplitude reach at 6db or 50 % of full amplitude response. This will be used to measure the length of the defect.

Further to evaluate whether the identified defect is lack of side fusion. Place the probe where the best response was received, give swivel or rotational or orbit movement if echo falls rapidly then the defect is Lack of side wall fusion.

The reason is that, in Lateral movement the sound beam remains perpendicular to the defect and amplitude held stable. However, as the probe swivel or orbited as shown in animation, the sound reflector angle changed and full echo response does not reach to Probe crystal eventually no response or low amplitude appears on flaw detector display.

To Sum up,

• Lack side wall fusion poor echo response received on opposite side.
• Echo large, single, narrow at time base when side wall.
• Poor echo from opposite side.
• Confirm by skip scan.
• Probe Movement Rotate or orbit, echo falls rapidly.
• Lateral or traverse echo height held.
• Generally, depth is measured by 20dB drop method and the length is measured either by 6dB or 20dB drop method.