Ultrasonic weld detection

Ultrasonic weld detection

With wide application of steel structure in industry and civil use，steel frame is 

less area、large span 、beautiful shape and so on features.steel frame is high order statically indeterminate structure that bearing pulling force and use screwball and steel pipe pole bolt combination。Its steel tube and shrouding cone head group weld quality is key factor of whole security。The diameter of pipe is usually  Φ32～180mm，wall thickness is 3～14mm,due to thin tube wall，sonic path distance is short,Serious divergency and more clutter ,it is difficult to use normal nondestructive ultrasonic detecting method，GB11345-89 is not suitable,how to be efficient to do necessary detection on bar weld?according to 3G/T3034.2-96 《bolt-sphere joint steel frame ultrasonic flaw detection and quality classification method 》to talk about space frame pole weld ultrasonic detecting application。

一、solution and technology parameter selection

（一）instrument selection 

Industrial ultrasonic testing is divided into A、B、C three kinds according to their designed principle，type A ultrasonic detecting equipment exists interface echo amplitude and distance on screen ,using echo amplitude to show reflection strength，so called amplitude modulation mode; type B 、C  ultrasonic detecting equipment reflect interface ultrasonic pulse echo signal amplitude strength by light luminance 。Combine with various kinds of scanning techniques to form two-dimensional image。Suitable for volume type workpiece flaw detection,have wide application on medical area。Due to industrial ultrasonic detection has a lot of workpiece ,affected by shape appearance and flaw characteristics，so type A ultrasonic Detecting equipment is in leading position in industrial ultrasonic detection。Aim at space frame pole weld structure feature,so choose type A ultrasonic detecting equipment,and require higher resolution and higher pulse width，horizontal linearity is not more than 1%,vertical linearity is not more than 5%,and surplus sensitivity is enough , initial pulse width is less than 2.5m。

1.Probe type:usually adopting plane single crystal transverse wave probe, advantages:scanning area is big,high efficiency ;disadvantage : much noise wave, low sensitivity。 It also can use focused transverse wave probe,advantage :high sensitivity ,noise wave is little,waveform is clear;disadvantage:cost too much ,scanning area is small,low efficiency。

2. Frequency :due to thin tube wall ,normally use higher frequency ,4～6MHz,good for improving directivity of probe，improving resolution。

3. Chip dimension :it should not be too big,and require high accuracy when assembling chip,normally use 6×6mm。

4. Refraction angle value:due to thin tube wall,flaws are located in near-field region，big error ，so adopting big angle of refraction ,normally use 72°.

Tube wall thickness (mm)（mm） 4～6  ＞6～8 ＞8～14

Selection of angle  (°)（°） 70～72 67～70 63～67

5.Leading edge:for assuring scanning the whole root of weld in one-time,normally require that leading edge length is lower than 10mm,usually use 5～8mm

6. Wedge :for assuring probe has good contact with outer wall of tube，often add probe wedge，process it into hook face that match with outer wall of tube ,make coupling effect best。

7. Coupling agent :usually use chemical paste，due to its low cost with certain consistence and good adhesiveness ,it also can choose engine oil.

8 specimen :main function is adjust time base line proportion and detect probe actual K value leading edge。According to standard to choose CSK-1C specimen,contrast specimen RBJ-1

(二)  adjusting instrument

1. Time base line proportion : due to thin wall tube ,normally adopting reference block level 1:1. The solution has two kinds:one is take advantage of standard specimen CSK-1C: aim probe at two  φ2 cross bore with different depth，make echo height respectively correspond to horizontal scale 。Solution two :take advantage of contrast specimen RBJ-1 :put probe fore and after movement ,use a wave and second wave detecting hole φ2,make the highest wave of two sides respectively correspond to horizontal scale