Common Ultrasonic steel plate flaw detection method

Common Ultrasonic steel plate flaw detection method

一、steel plate common flaw and detection method

Steel plate is made of slap rolling ,slap rolling is made of steel ingot rolling or continuous casting,steel plate has common flaw ,they are layered、folding and white spot，flaw is rare to see。

The layered and folding in steel plate is formed in process of rolling ,so they are almost parallel to decks,according to board thickness is different,divide steel plate into thin plate and moderate thickness plate,moderate thickness plate usually uses longitudinal wave detection method of vertical plate of incidence;thin plate usually uses plate wave detection method。

Moderate thickness plate coupling method of vertical detection method has directly touch and water filling coupling method。Adopted probe has single crystal straight probe 、double crystals straight probe or focus probe。Detecting steel plate,Normally adopts multiple bottom wave reflecting methods,only when plate thickness is very big can adopt once bottom or twice bottom wave。

二、choices of probe and scanning method

1、choice of probe including probe frequency 、diameter and structure form

Due to steel plate crystal particle is thinner,for achieving higher resolution,it is better to choose bigger diameter,but as for steel plate with smaller thickness,probe diameter is not suitable to be big,because big probe near field region has long length,is not good for probe。The structure form of probe mainly made sure according to plate thickness,when plate thickness is bigger,commonly choose single crystal probe; plate thickness is thinner can choose double crystal straight probe,because double crystal straight probe has little blind area,double crystal straight probe mainly used for detecting steel plate with thickness is from 6~30mm。

2、choice of scanning method

According to steel plate application and requirement,adopted main scanning methods is respectively complete scan、column line scan、boundary scan and grid scan。

Detecting range and sensitivity adjustment

1,Detecting range adjustment(scanning line requires to have 400mm  range)

δ≤80mm            B5        （instrument is in range of 400mm）

 δ>80mm时          B2～B5Depend on practical condition,but above B2 is must appear

2, sensitivity adjustment

①　Step block method ：

δ≤20mm

②　Flat bottom hole sample

δ＞20mm 

Attention ：

a,  sample steel plate is similar to detected steel material 

b,  sampling steel plate can not have flaw that more than Ф 2 equivalent weight 

c, Ф5 flat bottom hole on the sample is vertical to surface,flat bottom hole is parallel to surface,smooth。③　Bottom wave method

δ＞3N，can use B1 up to 50%

When δ ＞20mm can also use B5 up to 50%,but need to do experimental comparison with Ф5flat bottom hole，make the sensitivity the same。

d, flat bottom hole distance according to JB/T4730-2005 standard graph 2 CBII standard sample requirement