Tuyin tap bao cao Hdi nghj KHCN "30 nam Dau khi Viet Nam: Cff hdi mdi, thach thiic mdi" 287
LY T H U Y E T v A LTNG DUNG CUA KY THUAT DONG DIEN X O A Y
TRONG KIEM TRA KHONG P H A HUY (NDT)
Chu Chat Chinh, Phan Duy Lam, Tran Due Minh Vien Ddu Khi
TOM TAT
Thir nghiem khdng phd hiiy (KPH) bdng phirang phdp ddng diin xody (ECT) Id mpt trong ndm phuang phdp thir KPH dugc quy dinh tgi cdc Tieu chudn Qudc ti vd Viet Nam thupe linh vuc ndy (bdn phuang phdp khdc Id: sieu dm (UT), thdm thdu chdt long (PT). tir tinh (MT) vd chup tia phdng xg (RT). Bdi viit ndy giai thiiu hi thdng vi khdi niem, nguyin ly hogt dpng, cdc irng dung ciia phirang phdp ddng dien xody, cdc ky thudt kiem tra vd khd ndng ung dung phuang phdp ndy vdo diiu kien Viet Nam vi hien nay rdt h cdc dan vi trong nuac vi kiim tra KPH. ki cd Tdng cdng ty Ddu khi Viet Nam, cd logi thiit bi vi thir kiim tra KPH bdng ky thudt ddng diin xody.
K H A I NIEM
Ddng dien xoay trong kiem tra KPH la mdt ky thuat cd the kiem tra khuyet tat cua vat lieu kim loai ca trong qua trinh san xuat va trong qua trinh su dyng vat lieu.
Day la mgt ky thuat cd do chinh xac cao va hoan toan khdng pha buy (vat lieu kiem tra khdng bi pha buy).
Kiem tra nhanh chdng, an toan va hieu qua.
LY THUYET DONG DIEN X O A Y
1. Nguyen ly hoat ddng
Khi mdt ddng dien xoay chieu chay trong mgt cudn day dat sat be mat cua vat lieu dan dien, tu trudng do cudn day se cam ung ra mgt ddng dien xoay tren be mat vat lieu dd (Hinh 1). Bien do va pha eua ddng dien xoay se tae dgng len phy tai cua cudn day va do dd se anh hudng tdi tdng trd cua cudn day (mach dien) do.
Hinhl Hinh 2
28g Ly thuyet va dng dung cua ky thuat ddng di^n xoay trong kiim tra khdng pha huy (NDT)
Mdt vlt nut trong be mat phia dudi cudn day se lam cho ddng dien xoay bj yeu di (do phai di vdng qua vlt nut), khi dd phu tai tac ddng len cudn day cung yeu di va anh hudng cua nd len tdng trd cua cudn day tang len (Hinh 2).
Bien do chi thj (tin hieu) tu vlt niit phy thudc chu ylu vao lugng ddng dien xoay bj roi loan bdi vlt nirt. Hay ndi each khae: chieu sau, bl rdng va chieu dai cua vet nut se xac dinh su thay ddi chi thj cua vet nut.
NIU vlt nut nim ngang ddng dien xoay thi kha nang phat hien se tSng len (Hinh 3).
V^tndt songsong • khdng phSt hifin dugc
vet ndt vudng gdc • phit hien dugc
Hinh 3
2. Cac yeu to anh hu-dng din den ddng dif n xoay - Do dan dien cua vat lieu
- Do tham tu - Tan sd
- Hinh dang hinh hgc - Kha nang tiep can/Lift-off - Do sau tham thau
3. So- dd trd' khang
Day la do thi bieu dien tdng trd cua cac mau thu. True X the hien trd khang cdn true Y the hien cam img dien khang (Hinh 4).
Tuyin tap bao cao Hgi nghj KHCN "30 nam Dau khi Viet Nam: Cff hdi mdi, thach thde mdi" 289
X, sat tir
Dat trong khOng khf
Vft niit trong sit Thep
T VAT LIEU Titanium 4 VAT LIEU KHONG
Ve?t niit trong nh6m
Nh6m
DO dan didn ting len cua vat ki^m tra
• R
Hinh 4. Tong trd cuon day - x
Man hinh cua thilt bj kilm tra ddng dien xoay la cua sd the bien so dd tdng trd (Hinh 5).
Hinh 5. ^^* ^"^ kiem tra vat lieu nhom 4. Cac thanh phan chinh cua thiet bi
- Ket cau cudn day
- Do gia tri tuyet ddi (cudn day don) - Do gia tri so sanh (cudn day ddi) - Dau dd
5. Ung dung cua phu-ong phap ddng dien xoay - Phat hien khuyet tat trong vat lieu - Phan loai vat lieu (do do dan dien)
- Do be day ldp phu khdng dan dien va dan dien Do chieu day vat lieu
- Do do cung
- Kiem tra dng trao ddi nhiet (sit tir va sit khdng tu)
290 Ly t h u y i t va dng dung ciia ky thuat ddng dien xoay t r o n g k i i m tra khong pha huy ( N D T )
6. Dudng kiem tra ASME (Hinh 6)
Hinh 6. Dirdng kiem tra ASTM
a. De ddng, thudn lgi
Keo dau dd qua dng va nhan dugc tin hieu duy nhat tu mdi khuyet tat (Hinh 7).
- Ld thdng
- Ld sau 80% ben ngoai - Ld sau 60% ben ngoai - Ld sau 40% ben ngoai - Ld sau 20% ben ngoai - Mdp
b. Khd khan
- Ong dudng kiem tra dugc dd bdi tam dd va hau het cac sai sd xay ra khi khuyet tat nam canh tam dd (Hinh 8).
- Tin hieu tu tam dd trdn lan vdi tin hieu cua khuyet tat, rit khd xac djnh.
c. Anh huang ciia tdm dd' nhu sau:
Hinh 7
OO&SO b OD Sjppcft ^kit.j Hinh 8
resulting
iivlkil
d. Gidi phdp
Dua vao mot kenh tin hieu de hda tron va loai tru tin hieu cua tam dd.
Tuyin tap bao cao Hdi nghj KHCN "30 nam DjuJ^hi Viet Nam^: Co hdi mdi, thach thuc mdi" 291
e. Kit qud (Hinh 9)
Hinh 9 4. Ky thuat kiem tra cac ong thep tir (thep caebon)
- Can tan sd thap de tham thau
- Cd hai ky thuat kiem tra: Cdng nghe tu trudng xa (RFT) va Cdng nghe tu trudng gin (NFT)
Sy gidng nhau giua hai ky thuat (RFT & NFT) nay la deu su dyng tan sd thap de tham thau vao vat lieu.
a. Ky thuat tir trudng xa (RFT)
Ky thuat tu trudng xa (RFT) la ky thuat phat nhan xuyen qua thanh dng, su dyng cac cudn phat nhan rieng biet each nhau 2,5 lan dudng kinh dng.
RFT phy thudc vao tinh trang cua dng gan cac cudn phat nhan va giua cae cudn dd.
Vi thiet bi chay ben ngoai thanh dng nen cac tin hieu phy thudc nhieu vao ket eau gia dd nhu tam dd gida cac cudn phat nhan.
• Uu diim
Do dugc chinh xac do sau cac khuyet tat. Rat phu hgp de phat hien cac khuyet tat ben ngoai dng.
• Nhugc diim
- Do dac diem thiet ke nen rat khd kiem tra mdt vai em dau dng.
- Rat khd phan biet tin bieu khuyet tat ben trong va ben ngoai.
- Khdng the xac dinh chinh xac cac khuyet tat sat tam dd.
- Khdng the kiem tra dugc vung dudi tam do.
b Ky thugt tir trudng gan (NFT)
Cac cudn day cam bien nam rat gan nhau va day khdng phai la ky thuat xuyen qua thanh dng.
NFT phy thudc vao tinh trang cua dng d gan cac cudn day va phu thudc chut it vao ket cau tam dd vi tin hieu khdng xuyen qua thanh dng.
• Uu diim
- Cd the kiem tra dugc ngay tu dau mep dng.
- Cd sy phan biet rd rang tin hieu giua cae khuyit tat ben trong va ben ngoai thanh ong.
- Kiem tra dugc cac khuyet tat gin va ngay dudi tim dd.
292 Ly thuyit va ung dung eiia ky thuat dong dien xoay trong kiim tra khdng pha hiiy (NDT)
• Nhugc diim
- Khd su dung cho cac khuyet tat ben ngoai vi gdc pha la ngau nhien.
Tdm lai. RFT kiem tra bang ky thuat tu trudng xa cd do chinh xac cao hon ddi vdi cac khuyet tat nhd xa tam dd. NFT kiem tra bang ky thuat tu trudng gin de dang phan tich cac tin bieu han. NFT kiem tra bang ky thuat tu trudng gan phu hgp ban kbi kiem tra cac vung gan va dudi tam dd.
b. Thir nghiem hien trudng
Quyet dinh the nao? Dung ky thuat tu trudng xa hay gan hay dung ca hai?
• Gidi phdp
Su dyng ket hgp ea hai ky thuat tu trudng xa va gan de kiem tra chum dng bang vat lieu tu tinh. Cae man hinh dudi day the bien khuyet tat khe nut 25. 50 va 75% cua thanh dng (Hinh 10).
NF-LF NF-HF NF-VHF
ffinh 10
Remote Field
• Kit qud
- Cac tin hieu NF-LF, NF-HF va RF dua ra cac dai pha rdng rit dl dang eho viec phan tich du lieu. Tin bieu NF-VHF ed do nhay rit kem do tin so cao.
- Mui ten chi ra tin hieu gia tu cudn phat trong diu dd cua ky thuat tu trudng xa.
Cac man hinh dudi day thi hien khuyit tat khe nut 25% thanh trong va 25% thanh ngoai (Hinh 11).
ffinh 11
emote
FieW
Tuygn tap bao cao Hdi nghj KHCN "30 nam DSu khi Viet Nam: Cff hgi mdi, thach thde mdi" 293
• Kit qud
- Trong trudng hgp NF-LF tin hieu dung la cua khe nut 25% thanh ngoai va tin hieu nam ngang la cua khe nut 25% thanh ngoai.
- Tin hieu NF-VHF cho tin hieu phan hdi cua vet nut thanh trong va khong co tin hieu phan hdi cua vet nut thanh ngoai vi su dung tan sd cao.
- Tin hieu RF cho tin hieu chdng len nhau cua 25% vet nut thanh trong va 25% vlt nut thanh ngoai bdi vi su dyng ky thuat xuyen qua thanh dng, do dd khdng phan biet dugc cac khuyet tat giua thanh trong va thanh ngoai.
d. Ket ludn
Bang each ket hgp cam bien tu trudng gan vdi cam bien tu trudng xa, ta cd the cd dugc:
- Kha nang do chinh xac cac khuyet tat gan sat vdi tam dd va tam bgc dng.
- Kha nang phat hien nhiing Id dudi tam dd.
- Kha nang phan biet dugc cac khuyet tat ben trong va ben ngoai thanh dng.
8. Ky thuat mdi - Bien ddi tan sd vdi ma mau a. Sir cdn thiet
Hay xem cac tin hieu dudi day (Hinh 12 va 13):
^ v .A
\\^ Hinh 12a. Tin hieu bao gom tir tinh
••'' Hinh 12b. Tin hieu cua 16 thong
•^ .N Hinh 12c. Tin hieu cua vet nth
- Khdng cd kha nang phan biet giira cae tin hieu nay vdi tan sd don.
- Thiet bi da tan se giup phan biet cae khuyit tat nay.
- Bude tiep theo - Bien ddi tin sd
^ Cac kenh tan sd ao se chi ra cac dau hieu trong cac tan sd khae nhau.
^ Tat ca cac kenh tan sd ao dat chdng len nhau.
^ Dieu nay dua ra mdt dang mau duy nhit eho tung loai khuyit tat.
294 Ly thuygt va dng dung eiia ky thuat dong dien xoay trong kigm tra khdng pha hiiy (NDT)
• • N • • : .
' i . ' v "\ 'V 'i i '^ ) i. ^, ^* t ^\ i, i X 'i "i i 'i v, i ') i
Hinh 13a. Tin hieu bao gom td tinh
Hinh 13b. Tin hieu cua 16 th6ng
I I I
Hinh 13c. Tin hieu cua vet ntrt
\ \
Cdng them mau
Hinh 14: Bien doi tan s6 tir thap den cao
Hinh 15: Bien d6i tan so td cao den thap
ffinh 14a
ffinh 15a
Hinh 16: Bien d6i tan so diem cuoi
ffinh 16a
Hinh 14b
ffinh 15b
ffinh 16b
Tuyin tap bao cao Hdi nghj KHCN "30 nam D5u khi Viet Nam: Co hdi moi, thach thde mdi" 295
b. Lgi ich cda viec bien ddi tdn sd
- De dang phat hien va nhan dang khuyet tat.
- Khdng can thiet phai cd chieu dai toan bg cua tin hieu khuyet tat de phan tich.
KHA NANG UNG DUNG TAI VIET NAM
• Thiet bi kiem tra RFECT rat hien dai. dung chu yeu cho vat lieu sat tu. Hien nay, tai Viet Nam chua cd cdng ty nao mua thiet bi nay. Chua cd ai dugc dao tao bai ban ve ky thuat nay.
• Cac ung dung cy the tai hien trudng hien nay chua cd bdi vi chua cd nhieu ngudi biet ve thiet bi nay.
• Cac nha may lge dau se cd trong tuang lai, do do dau tu bay gid la thich hgp.
• Day la mgt ky thuat hien dai, khd hon cac ky thuat NDT khae nen phai dau tu sdm tu bay gid de 4 - 5 nam sau cd cac chuyen gia gidi ve ITnh vyc nay.
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Hinh 16: Thiet bj kiem tra bang dong dien xoay ECT 48AT
TAI LIEU THAM KHAO
1. ASME V: Boiler and pressure vessel code, non-destructive examination.
2. ASME B31.3: ASME code for pressure piping - Chemical plant and refiner\- piping.
3. ASTM-E709-85. Standard practice for magnetic particle testing.
4. www.russelltech.com.
