#asnt #UT Level-2, Level III, Level-2 #pcn Level 2 BiNDT, #ultrasonictesting (UT) defects Signal Interpenetration, Lack of sidewall
british institute of non-destructive testing
Fusion
Defects in The weld region (sidewall/body)
Slide-1
Hi there, this video I would explain, how to interpret UT indications obtained from weld imperfection. And I will talk about interpretation practice and technique which are used in UT to categorise the weld defect as a lack of side wall fusion. And briefly I will touch the amplitude response from the defect at varies position of UT transducer.
Slide-2
Here we have 30mm thick single vee butt weld,
which contain weld imperfection, 20mm depth from top surface, with 5mm height and 200mm Length.
Slide-3
Now we move to actually scanning, in Manual UT for weld scan we move UT probe back-forth up transversally from weld toe to standoff distance up 1 and half 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 heating the back wall and making a V shape progression, this is nothing but sound beam path at full skip distance.
Now you can imagine that weld won’t fully scan if there won’t be any Transverse and Lateral Scan at appropriate scanning speed
If there is no reflector / defect in weld than there won’t be any amplitude rise in Flaw detector display Unit. only grass (nose) coming from surface will be seen at time base.
Slide-4
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
Slide-4
Lack of Fusion.
For Lack of side fusion, the best response is received while lateral movement.
To inter pret 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.
Here you see
For 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.
Measurement
For depth use 20dB. For length use 6dB or 20dB.
Causes
The principal causes are too narrow a joint preparation, incorrect welding parameter settings, poor welder technique and magnetic arc blow. Insufficient cleaning of oily or scaled surfaces can also contribute to lack of fusion. These types of imperfection are more likely to happen when access to the joint is restricted.
Joint preparation
Too narrow a joint preparation often causes the arc to be attracted to one of the side walls causing lack of side wall fusion on the other side of the joint or inadequate penetration into the previously deposited weld bead. Too great an arc length may also increase the risk of preferential melting along one side of the joint and cause shallow penetration. In addition, a narrow joint preparation may prevent adequate access into the joint or encourage flooding the joint with moulting weld metal. For example, this happens in MMA welding when using a large diameter electrode, or in MIG, MAG