Operating technology procedure of Magnetic powder detecting

Operating technology procedure of Magnetic powder detecting 

1  Summary

1.1 the procedure is suitable for ASME normative product ferromagnetic material and weld powder inspection。

1.2 magnetic powder testing way is suitable for detecting flaw and other uneven flaw on the surface of ferromagnetic material or around it

1.3the procedure is suitable for magnetic yoke wet powder continuous magnetization technique，this method is only suitable for detecting opening flaw of workpiece surface。

1.4 the procedure must be demonstrated before operating ，make AI satisfied。

2.  worker

2.1 the NDE people who works on magnetic powder detection must be trained 、examined、qualification identified、and approved by Nai jing baose titanium industry co.,ltd  (material no. ：QCD-011)

3.  Generalization 

3.1  in principle ,magnetic powder detecting method means exert ferromagnetic powder on the surface of workpiece tested area,crack or other flaw will lead to normal magnetic field distortion，make magnetic powder on the surface formed certain graph,these graph usually are features of detected flaw。

3.2 the sensitivity of magnetic powder detecting method is the highest regarding to surface defect,and rapidly reduce with the increase of depth from surface;therefore，the method is just suitable for detecting material or the surface of the parts or surface defect。

4.  Magnetization equipment calibration 

4.1 MT equipment adopts CDX-4 type magnetic yoke type flaw detector 

4.2 equipment calibration

4.2.1  check period ：in every area of ammeter magnetization equipment should at least check once a year ;the equipment was repaired about important power source or heavy repair periodically or damaged，it must get calibration ，if the equipment has been not used for at least one year，then it should be checked before using 。

4.2.2  magnetic yoke lifting force calibration

Lifting force uses standard heavy block lifting method to check,alternating  magnetic yoke lifting force should at least be 10lb (44N)(the biggest magnetic yoke interval );direct current magnetic yoke lifting force should as least be 40lb(177N)(the biggest magnetic yoke interval)。

5.  testing medium

5.1 testing medium is thin ferromagnetic powder with high-permeability and low coercivity,its dimension and shape must be easy to form magnetic powder display。

5.2 it should use black magnetic powder HK-1-400 or 350 produced by  yixing  magnetic flux flaw detection material company 。

5.3 the liquid medium of magnetic flow detection ink must be transformer oil、tasteless kerosene or water。The temperature of Magnetic flux detection ink and workpiece surface should not exceed 1350F(57℃)

5.4 the concentration of wet magnetic flux detection ink 

5.4.1 magnetic flux detection ink concentration should according to manufacturers’ recommendation ,using sediment capacity value to check，it is necessary to make sure concentration being certain，if the concentration is not appropriate，,it will affect result of detection seriously 。

5.4.2 apart from manufacturers have other stipulations，non-fluorescent magnetic particle slurry concentration should be 1.2-2.4ml in every 100ml 。

5.4.3  the concentration of magnetic flaw detection ink in the groove usually confirmed by ASTM pear -shape centrifuge tube to measure its sediment value ，for non-fluorescent magnetic flaw detection ink is 1.5ML ; before sampling ,make suspension liquid at least flow for thirty minutes in the recycle  system，to make sure all magnetic powder mixed fully 。Otherwise magnetic powder maybe precipitate in the oil pan filter gauze and along the groove wall or the bottom，take 100ml suspension liquid form flexible pipe and make it precipitate about 30minutes,precipitated volume is indicated value of bath solution ;provided that magnetic powder concentration is too low in magnetic flaw detection ink ，Add enough magnetic powder so as to get needed concentration ；if magnetic powder concentration is too high in magnetic flaw detection ink ,then add enough liquid medium so as to get needed concentration。

5.4.4 if sediment magnetic powder is showed as loose block，not a compact coating，then do second sampling test，if it is still block,it shows magnetic powder has been magnetized,now it needs to replace magnetic flaw detection ink。

6  magnetization process

6.1 magnetic yoke method

6.1.1 adopt direct current 、alternating current  magnetic yoke or permanent magnetic yoke to magnetize a regional area and form a longitudinal magnetic field 

6.1.2  the lifting force of alternating current magnetic yoke should at least be 10 pound (4.5 kilogram)  when the distance between the poles is the biggest。

6.1.3 magnetic field intensity of magnetic yoke can be confirmed by measuring its lifting force。

6.1.4  according to experience ,the magnetic intensity of magnetic yoke can be confirmed by measuring its lifting force。

6.1.5 magnetization direction

Every area should at least have two test respectively ，in the second test ，the direction of magnetic flux line should approximately be vertical with the direction adopted in the first examination area。

6.1.6  be detected area should be restricted at both side of magnetic pole,equal to 1/4 interval of biggest magnetic pole,magnetic pole interval at least has 1 inch lap joint。

7.  Magnetic field intensity 

7.1 using specialized carbon steel copper magnetic field indicator to test the magnetic intensity and direction of accessories surface is whether satisfy the requirements，if copper plate edge has clear magnetic powder lines，then it shows magnetic field intensity is enough。

8. Testing requirements

8.1  surface preparation 

8.1.1 the accessories after welding 、rolling 、casting、forging,normally will get satisfied results,however, uneven surface will mask flaw displaying , then these places need to be polished or machine processing  to do surface preparation

8.1.2  before magnetic powder detesting ,be detected surface and its around at least in the area of 1 inch should be dry ,and no any dirt 、fiber tow、rust scale 、welding flux and greasy dirt or other foreign body that stop detecting。

8.1.3  this can use detergent 、organic solvent、rust remover、descaling liquid、

Remover paint、vapor degreasing、sandblast or ultrasonic cleaning and so on methods to up to the purpose of cleaning。

8.1.4   if on the surface of being detected workpiece exists paintcoat or other covering，then doing demonstrative experiment，and make flaw can be showed by penetrating the thickest place of covering layer，when using magnetic yoke,it should according to the requirements of mandatory appendicesⅠchapter 7 of the V in ASME laws and regulations, verifying the influence of coating thickness 。

8.2   unless drawing or other technical documents has other regulation，any parts should under surface state of finished work ,or ultimate machine processing  state,or magnetic powder flaw detection under ultimate heat treatment state 。

8.3   small opening or groove or hole on the parts ，they should be clogged before detecting to prevent magnetic powder from accessing。

8.4    when detecting ,it should have enough overlaps (at least 10%) ,make sure that detected parts can get coverage under specified sensitivity。

8.5   after-sales-services area on the detected workpiece ,it should be re-inspecting according to original detecting procedure。

8.6  observing brightness of the surface on the detected workpiece must be at least 50fc(500lx)  。

9. Displaying assessment and  qualified standard

9.1 magnetic powder displaying assessment 

After a period of saving Magnetic powder ,it will display magnetic line ,not all of displayed are flaws, due to rough surface (such as at the edge of heat-affected zone), permeability has changed and other reasons, it will produce similar flaw 。

Only have been confirmed as mechanical flaw displaying ,and displaying dimension is more than 1/16inch(1.6mm) and then can be thought effective displaying;

a . Linear display means its length is more 3 times than width

b. Facial form displaying means the length of roundness and oval is equal to 3times of width。 

 C.  Suspicious 、controversial display should be retested to decide whether they are effective display。

 D.  Main area where be accumulated discontinuous magnetic powder covering is not allowed，retest to these area。

9.2  qualified standard  (according to the first fascicule appendix 6 of Ⅷ volume )

Apart from special material appoints to use more strict standard，usually adopts as follow qualified standard 。

All detected surface are not allowed to have as follow flaw displaying：

a.  Effective linear display 

b. The dimensions should more than 3/16inchs (4.8mm)effective facial form display 

C.edge interval on the direct line is equal to or less than 1/16inch(1.6mm) that four or more effective facial form。

D. Flaw displaying maybe more than flaw itself，but use displaying dimension as the base of qualified assessment 。

10.Demagnetization

When the remanence has impact on parts processing or usage ,the parts should be in time do demagnetization after magnetic powder detecting。 

11. cleaning

  When Magnetic powder material hinders subsequent processing or usage,it should be cleaned after detecting。

12. Recording and reporting 

12.1 operator must record detected details and results,it also can use adhesive tape 、photo、or other methods as permanent recording if necessary。

12.2  NDE report should be authorized by operator，and checked by NDE II level or III level inspection person ,and approved by appointed NDEIII then submit AI recognition