Ultrasonic detection on seamless steel and T type welding joint

Seamless tube usually means the steel that external diameter i slower than 100mm,mostly adopts perforation method or extrusion method。In the detection of seamless tube,mostly adopt eddy current automatic detection，magnetic powder and ultrasonic manual detection is complementary。 Here I want to talk about ultrasonic detection part。 Traditional seamless tube detection has three methods:use inclined probe to scanning along with axial and circumferential ;thick walled tube can use double crystal probe to scan,thin wall tube can use hygrophanous method to use straight probe to scan。

If everyone detects tube stock personally and will find traditional method has a fatal weakness,that is efficiency is too low。 Usually can just detect few,  this schoolbook detecting way Is eliminating gradually in practical production，it is good for human to have infinite wisdom,keep summarizing experience from production,and improving original techniques,ultimately inventing a high efficient method to detect seamless tube。This method is based on no upgrading on detecting device,only improvement on detecting methods and make results produce big change。Pull ultrasonic detection back to mainstream position, as follows we will use ultrasonic detector with proprietary intellectual property rights to share this magic method with everyone。

At first,the materials that needed are:a seamless tube  two inclined probe lines,SCK-1A sample,make two angle probe with same dimension angle,leading edge back to back together,and produce a qi block with same model,a bottle of coupling agent ,half kilogram engine oil,a red pen,paper。

Firstly,well connect two probe lines,and respectively insert two probes sockets,start up,bear this in mind,set the probe into “signal” not double or “receive and dispatch” ,the reason is :not all probe with two crystal are double probe,two crystal in double crystal probe is receive and send。But our special probe needs they can work independently。Then SCK-1A adjusts leading edge of one probe,zero point and K value,because two probes are totally in same,so well set a probe parameter and another one is set well too。After doing these,paint coupling agent onto probe and set together with Qi block,the coupling agent between probe and Qi block should be coupling agent with good sound transparent property。,don’t choose liquid engine oil,the reason you can think by yourself。Until now our preparation are done。

Of course,we set flaw detection sensitivity，because seamless tube is not allow to appear flaw,so DAC curve is eliminated,straightly adjust gain to max value that without noise wave,suggesting to set 80-90db is reasonable。Some clients requires to ignore little flaw,now only choose antitheses to adjust sensitivity,let client use line to cut off to open a groove on the surface of seamless tube,width is determined by customer,and use this groove to set sensitivity,and paint engine oil on seamless tube。Put probe with Qi block on seamless tube and we can see that they fit very well。Sway from side to side in circumferential direction in low amplitude ,along with axial direction do sawtooth moving，appearing wave signal then use red pen to mark ,means this period should be judged to be waste。After The whole seamless tube scanning,use paper to clean workpiece and coupling agent on probe surface,flaw detection job is end。

At last do simple e­xpression on principle。Actually a lot of people who read until now have understood，ultrasonic wave enters tube stock and do launch in tube stock,using two inclined probes are aim to make probe launch ultrasonic from double directions so as to cover whole tube stock,and improve efficiency。Equal to one machine do two jobs。 So when tube diameter is smaller,a flaw will display two flaw signal on the screen,the reason is the ultrasonic that launched by two probes catch this signal,due to beam path is different,they will appear in different position on the screen。On the tube stock with big diameter,due to energy attenuation,at a circumferential section even though use two probes is also hard to completely cover the whole tube stock，now need to move probe 1/4 pipe diameter and will completely cover as well。

Steel structure flaw detection is another application that will often meet in flaw detection。Its features are complex structure,multiple welding joint,big volume,and welding joint are T type weld.

T type welding joint can be thought as a common welding joint，we often read much introduction on T type welding joint from many kinds of books。At the same time we familiar with theory,in practical flaw detection will meet many problems。Firstly we have a look at how does book say。

We should know T type weld firstly, as picture,horizontal is called pterygoid lamina,because it looks like wing,so it called pterygoid lamina。Vertical is called sternum,because it is inserting in the middle of pterygoid lamina,so it called sternum。Common flaw in T type weld is the same as other weld, have air hole ,slag inclusion,crack,lack of penetration and not fused 。There is another T type weld exclusive flaw is called avulsion。Avulsion is sternum bearing force and generate a horizontal breakage,it will not appeared in welding joint area，,only appear out of welding joint,T type welding joint flaw detection are take advantage of three operative surface，five position to scan。However,it is difficult for us to detect on five points to one T type welding joint in practical flaw detection.there are two main reasons，if sternum thickness is below 5mm,in the blind area of probe,there is no possibility to do flaw detection from sternum,in theory it is possible to do flaw detection on pterygoid lamina,but there are a lot of difficulty in practical operation,basically belong to no way to detect。 In addition,in domestic steel structure industry,due to cost reason,the sternum that below 8mm basically don’t have groove ,when welding , in root of sternum ,both sides make two welding joint,don’t need to think that they definitely have pack of penetration。But due to these thin sternum are not load,so it will not appear big problem。This is also give us enlighten in practical work,in practical flaw judge,there is a assessment standard called”national conditions” should be taken into consideration。

The secondly is structure problem。Practical T type weld are not isolated welding joint， a workpiece always  complex and full of dozens 、hundreds of welding joint,big and heavy,no way to rotate。 So in practical flaw detection,it will be good if make sure three point detection。Detecting direction mainly is no fused,lack of penetration and tear。 Detecting position is mainly detect on fusion line and sternum central position。

In addition,in practical flaw detection it is easy to ignore welding angle reflection。In T type weld ,only in pterygoid lamina use probe to scan will catch this signal,the reason is generated by welding angle structure 。The structure of T type welding angle is similar to organic glass in CSK-1A,namely no matter use inclined probe in  what angle will catch this signal 。Its signal feature is high intensity,smooth amplitude is narrow。Due to beam path ,flaw signal must appear before welding angle reflected signal。Now only use inclined probe as straight probe will easy to eliminate flaw 。

At last share a doohickey with you ,sometimes when we detect T type weld have no way to see sternum,now we can take advantage of welding angle reflection to positioning sternum。 Method is respectively find welding angle and reflected wave in pterygoid lamina ,and make them displayed in same position on one screen,then the center of two probes is the center of welding joint，and use inclined probe triangulation location to make sure the width of sternum。