Chng m u/1 Vt liu thp s dng ngoi khiB tng v thp l hai vt liu chnh c s dng trong kin trc ngoi khi (offshore). Thng th nh thu chnh s l bn chu trch nhim mua sm v kim tra cht lng vt liu, tuy nhin, trong vi trng hp c th , v du nh ng ng du kh (pipeline) chng hn, vt liu s do bn khai thc ch nh hoc cung cp.Vt liu s dng trn cc kin trc ngoi khi phi duy tr c bn vng trong mi trng v ti khc nghit, bao gm kh nng khng n mn (corrosion) v xi mn bi cc tc ng ca mi trng bin khai thc, duy tr c tnh di tc ng ca sng, gi, nhit , ti trng ... Do vy, vt liu s dng ngoi khi phi tha mn, v chu kim sot bi cc yu cu php nh (statutory) v chun nh (Rules, standards). Cng ngh ch to (fabrication)1Cng ngh ch to bao gm ngun lc (Thit b, phng php, qui trnh, ti chnh), nhn lc, trnh v k nng qun l.

l nhn t c tnh quyt nh i vi cc kin trc ngoi khi; bi l cc kin trc, cu kin ny cn bo m duy tr tnh nguyn vn trong iu kin ti kch thch c bin v tn s kh d bo kt hp vi tc ng ca mi trng khai thc c th lm suy gim c l tnh ca vt liu 2kh nng thay i trng thi ph hy ca vt liu, pht sinh cc tn tht cp t vi nh n mn tinh gii, nt do tc ng ca hydro (HIC - Hydrogen Inductive Crack), suy gim kh nng khng rch (CTOD) ...

. Cc thch thc i vi nh thu ch to cc kin trc ngoi khi bao gm: phc tp v ln ca cc cu kin t ra cc yu cu nghit ng cc khu vn chuyn, o kim v lp t.

K thut ch to (ct, nh hnh, hn ...) cn c kim sot nghim ngt v chnh xc, bin dng nhit, ng sut d

Qun l tin v kim sot cht lng yu cu k nng v tin cy cao.

1.1 Ch tiu nh gi s ph hp ca thpCc ch tiu c bn cn xem xt i vi thp s dng ngoi khi bao gm:Gii hn chy ti thiu {Minimum yield strength)

bn ko ti thiu (Minimum ultimate strength)

dn di khi t (Minimum elongation at rupture)

dai Charpy nhit thp (CVN toughness at low temperatures)

c im c tnh theo phng b dy (Through-thickness mechanical properties)

Tnh hn (Weldability)

c im khng mi (Fatigue endurance)

Thnh phn ha hc (Chemical composition)

Vin Du Kh M (API - American Petroleum Institute), Vin Kt Cu Thp M (AISC - American Institute for Steel Construction), v ng Kim Na Uy (DNV - Det Norske Veritas) l cc t chc pht hnh nhiu ti liu hng dn thc hnh (recommend practice), cc b qui tc (rules / code) v tiu chun (standards) lin quan n kin trc thp s dng ngoi khi. 3Cc tham kho khc TCVN 7230-2003 Fixed Offshore platform-Rules for Classification and Construction Materials , TCVN 72290-2003_Fixed Offshore platform-Rules for Welding and Fabrication. BS EN ISO 19902:2007+A1:2013

Nh thu (contractor) khng ch chu trch nhim v mua sm vt liu theo ng cht lng yu cu, m h cn phi cn nhc n gi c, ngun cung cp, iu kin v thi gian giao nhn Bn cnh , cc cn nhc v k thut nh dung sai b dy v kch thc phi, tnh hn sao cho ph hp vi iu kin cng ngh sn c cng khng km phn quan trng. i vi cc cu kin s dng ng (tubular member) th dung sai v mo (out-of-roundness) v ng knh ng v chiu di ng cung cp li c tc ng mnh n chi ph thi cng. Vi cc h thng ng du kh trn bin (submarine pipeline) th dung sai v chiu di ng c ngha quan trng hn so vi h thng ng trn b (cross-country pipeline) 4L do rt n gin v cc phng tin hn v ri ng bn t ng ngoi khi, khng th vn hnh vi chiu di ng sai lch qu ln, hoc c kch thc ngu nhin.

.Thp ch to cho cc kin trc khai thc vng kh hu lnh (vng cc) cn ch c bit n kh nng duy tr dai nhit thp v tnh hn, vt liu hn (consumable) cn phi c cn nhc k lng nhm bo ton kh nng ti v bn vng ca mi hn v vng ln cn trong mi trng kh hu khc nghit. Tiu ch quan trng chn la vt liu hn ph hp l bo m bn v do theo yu cu thit k, quan trng hn l phi kim tra xc thc s tng thch (compatible) gia vt liu p (filler metal) v vt liu c hn (base metal) v c hai kha cnh nhit luyn (heat treatment) v n mn (corrsion). xc thc s ph hp ca vt liu p v qui trnh hn (WPS - Welding Procedure Specification), bo co xc thc cht lng qui trnh hn (PQR - Procedure Qualification Record) ngoi cc th nghim theo thng l cn phi thc hin thm cc th nghim b sung nh CTOD hoc cc phng php nh gi khng rch (fracture test) c yu cu bi qui chun p dng. B lng v ai c cng lc s dng trong kin trc ngoi khi ngoi th nghim xc thc bn ko, cn b sung th nghim bo m dai th va Charpy (CVN).1.2. Phn cp cu kinCc cu kin (members) s dng trong kin trc ngoi khi c phn cp theo cc tiu ch sau: Cu kin chnh yu (Primary Structural Member) - bao gm cc cu kin v cc thnh phn c vai tr chnh yu bo m tnh nguyn vn v an ton ca ton b kin trc.

Cu kin th cp (Secondary Structural Member) - bao gm cc cu kin , thnh phn c vai tr bo m tnh nguyn vn cc b ca kin trc. Khi xy ra s c i vi cc cu kin th cp, s khng dn n tnh nguyn vn v an ton ca kin trc.

Cu kin c dng (Special Members) - l cc b phn ca cu kin chnh yu nm cc v tr c bit nh :Cc nt, khp, khu vc c vai tr chuyn ti hoc lc tc ng.

Cc v tr c s tp trung ng sut cao.

Cc v tr kh tip cn kim tra.

Cu kin ph tr (Ancillary Members) - l cc cu kin ph tr th yu khng thuc nhm cc cu kin nu trn.

Cc v d .Danh mc cu kingin boong (Deck)Chn (Jacket)

Chnh yu (Primary)Tr (Leg), cc dm chnh (truss) cc x (plate girders)Chn (Legs), ct (piles), Cc nt lin kt (braces)

Th cp (Secondary)Np (stringers), tn sn (floor plates)Cc nt lin kt th cp (Minor braces), chng va / chng sng (caissons), gi ng, dy dn (conductor supports)

c dng (Special)Cc nt lin kt gia tr v dm / x (Nodes), neo dy chng buc, cn cu (lifting padeyes)Cc nt lin kt chn / ct vi dm / x (Nodes), Neo dy chng buc (padeyes)

Ph tr (Ancillary)H lan (handrails), sn (platforms), gi (supports)Cu dn (Walkways), Chng va (bumpers) v dn hng (guides)

1.3. TIU CH CHN LA THPKt cu gin khoan c nh thng c ch to t thp c bn trung bnh, gii hn chy di 350 MPa. Nhm thp ny c a chung do cc nguyn nhn sau:S hiu bit v c im k thut v kinh nghim ch to ca nh sn xut

Thng tin v c im k thut, cng ngh ch to c cng b rng ri bi cc nh sn xut v cung cp thp.

c ph duyt bi hu ht cc t chc kim nh, cp php khai thc.

1.3.1. Phn cp, Nhm & Hng 5- Tc gi xut khng chuyn ng cc thut ng nhm trnh nhm ln. - Grade : thng c hiu l phn cp thp theo chun nh, - Group l phn nhm thp theo ng dng ring, trong khi, - Class : phn cp thp theo tiu ch ring.

1.3.1.1 Phn cp theo bn (Grade) Thp dng ch to cng trnh ngoi khi dng tm, thp hnh, thp hp cn nng, lng tr cun ngui, dm x hn v ng ... c phn lm 4 cp nh sau: Thp thng (MS - Mild Steel)

Thp thng c dng (SMS - Special Mild Steel )

Thp bn cao (HS - High Strength Steel)

Thp bn cao c dng (SHS - Special High Strength Steel)

Thp thng (MS)a) Thp thng (MS) dng tm, thp hnh, tm dng lm ng yu cu phi bo m cc ch tiu k thut qui nh bi ASTM A 36, Yu cu k thut ca thp kt cu.b) Thp dng lm ng du kh khng hn (seamless line pipe} c th s dng lm cu kin ng c ng knh ngoi nh hn 508 mm. v d nh h lan (handrails), cc khung sn (grating supports), cu dn (walkways) ... Cn tha mn cc ch tiu qui nh bi API 5L Cp (Grade) B hoc ASTM A 53 cp B.c) Thp thng phi c gii hn chy ti thiu khng thp hn 250 MPa.Thp thng c dng (SMS)Thp thng c dng (SMS) dng tm ngoi yu cu phi ph hp vi ASTM A 36, chng phi c cn luyn t phi thp lng hon ton (fully killed), v bo m mn ht t nht l cp 6 theo tiu chun qui nh bi ASTM E 112.Thp bn cao (HS)a) Thp tm bn cao (HS) cn tha mn yu cu qui nh bi API 2H phn cp 50 hoc ASTM A 633 phn cp C.b) Thp hnh (HS) cn tha mn yu cu ASTM A 633 phn cp D.c) Cc phn cp thp ny phi cn luyn t phi thp lng hon ton v c mn ht khng thp hn cp 6 theo chun ASTM E 112.d) Ch s carbon tng ng tha mn qui nh bi API 2H phn cp 50.e) Ring thp ng bn cao c ng knh ngoi nh hn 508 mm phi p ng cc yu cu qui nh bi API 5L.Thp bn cao c dng (SHS)Hai cp thp bn cao c dng c s dng trong kin trc gin ngoi khi bao gm : SHS-50 ph hp vi API 2H phn cp 50 hoc ASTM A 633 phn cp C, l thp hp kim thp bn cao (HSLA) cn luyn thng ha (Normalized Rolling) tha mn cc tiu ch b sung qui nh bi cc mc S-1 , S-4 v S-5 qui chun phn cp API 2H. Phn cp thp ny c cn luyn t phi thp lng hon ton tun th qui trnh cn thng ha t mn ht khng thp hn cp 6 theo chun ASTM E 112.

Thp tha mn yu cu ASTM A 5786ASTM A 578 Straight Beam Ultrasonic Examination of Plain and Clad Steel Plates for Special Applications

, v ASTM A770. Khim khuyt pht hin bng php kim tra siu m phi c nh gi t yu cu mc II v phm vi tm sot l 100% tm kho st. Cc yu cu b sung S1 v S4 cng phi tha mn.

Ch s carbon tng ng ti a khng vt qu gi tr qui nh bi API 2H phn cp 50.

Ghi ch : Khi thit k cc kin trc thp, nh thit k thng trnh a ra mc thp c th nh SS41 , CT34 , S235 ...Thay vo cc qui chun phn cp c tnh ph qut nh ASTM, API, EN 14025 ...l cch tip cn thng dng. iu ny th hin trit l v quan im nh thu (contractor) l ngi quyt nh v chu trch nhim ton b i vi cng trnh, sn phm do mnh ch to.1.3.1.2. Phn nhm cht lng (Group) 7Theo API 2A WSD Recommended Practice for Planning, Designing and Constructing Fixed Offshore PlatformsWorking Stress Design

Nhm I : thp carbon trung bnh c gii hn chy ti thiu n 280 MPa (40ksi8Ksi - kilo pound per square inches

). Hm lng carbon tng ng (CE9CE - Carbon Equivalent : mt ch s c lng tnh hn da trn thnh phn ha hc ca thp, trong tc ng ca cc nguyn t hp kim n tnh hn c qui i tng ng vi % C thm vo.

) di 0.40%. Thp nhm ny c th hn tt vi mi qui trnh hn ph hp vi AWS D 1.1 10American Welding Society Steel structure Welding Code.

Nhm II : thp c bn trung bnh vi gii hn chy trn 280 Mpa (40 ksi) n di 360 Mpa (52 ksi)_. Hm lng carbon tng ng n 0.45% hoc cao hn. Nhm thp ny khi hn phi s dng qui trnh hn gim hydro (low hydrogen welding process).Nhm III : thp bn cao c gii hn chy trn 360 MPa (52 ksi). Thp nhm ny ch c s dng khi cc vn sau y c xc thc v ph duyt bi cc bn lin quan : Tnh hn v qui trnh hn.

Cc vn lin quan n tnh mi c th pht sinh trong iu kin khai thc, v

Kh nng tn tht dai tc ng ca cc bin php cng ngh cn thit nhm tha mn yu cu khng rch (fracture control) trong qu trnh hn.11Nung s b (preheat) ,gi nhit (intermediate temperature), PWHT (post weld heat treatment)

.

tin cy ca qui trnh gim st,

ng sut v nhit thc t khi khai thc.

1.3.1.3. Phn hng (Class) Cn nhc n dai CVN thch ng vi mi trng v iu kin ti, thp c phn cp nh sau:Cp C : thp c nhn bit qua lch s ng dng v khai thc thnh cng nhit trn ngng ng bng, ngoi tr cc trng hp khng yu cu th va. Thp cp C c s dng ch to cc cu kin chnh (primary member) nm trong gii hn b dy cho php, khi ch to khng phi nh hnh hoc nh hnh vi mc bin dng va phi 12Bin dng do gy ra khi nh hnh khng ng k (low strain)

. Mc tp trung ng sut thp, ti gn nh tnh (quasi-static) 13Chu k tng gim ln hn 1s.

v c cc cu kin ph tr (redundancy)14Cc cu kin ny phng khi c s gy / rch cc b s ngn cng trnh khng sp

. Cu kin chnh bao gm: Cc (piling), cc nt kt ni (jacket brace) v chn (leg), x boong (deck beam) v tr (boong).

Hng B : thp s dng ch to cc cu kin dy, khai thc khu vc c nhit thp, lun b cng ko (restrain), tp trung ng sut, ti va p, v khng c cc cu kin ph tr, hoc cc cu kin ph tr yu cu phi bo m dai CVN. Thp cp B cn bo m dai CVN ln hn 20J (15 ft-lbs) i vi thp nhm I, v 34J (25 ft-lbs) i vi thp nhm II nhit thp nht m mi trng khai thc c th t n. Thp cp B c lit k trong ti liu ny ch tha mn yu cu dai CVN nhit t 10 n 0C ( 50 n 32F) vi tiu ch nh gi dai qui nh bi ASTM A673 cp H.

Hng A : thp s dng ch to cc cu kin khai thc mi trng ng bng v cc tc ng c th gy ra trong qu trnh khai thc c th gy ra cc tn tht n c l tnh ca thp. Thp ny cn bo m dai CVN theo yu cu song nhit th phi thp hn nhit thp nht ca mi trng khai thc t 2030C. Khong chnh lch ny nhm mc ch ngn nga s lan truyn cc yu t gy t gy dn t cc khim khuyt c kch thc tng i, ng thi bo m vt liu c c im cn thit ngn chn s pht trin ca vt nt trn ton b dy. Thp cp A cp trong ti liu ny ch bo m dai 20 n 40C. Tn sut th dai nhm mc ch xc thc vt liu cp A cn phi c th hin r trong n hng v c bn cung cp thp thc hin theo tng m cn (heat / lot number).

1.4. S DNG THP BN CAO TRONG KIN TRC NGOI KHI Nh cp, thp bn trung bnh di 350 MPa cn luyn theo qui trnh thng ha (normalized) l loi thp ch yu c dng ch to cc cu kin thp hn trn cng trnh bin. Bng 1.4 lit k cc mc thp thng dng c s dng cc hng mc chnh yu. S ci tin n t cc nh sn xut v cung cp thp ch yu l cc bin php tng bn song vn bo m tnh hn (weldability) thng qua vic ci tin cc qui trnh cn luyn hoc nhit luyn (Qui trnh cn kim sot c nhit - TMCP - Thermo-Mechanical Controled Process hoc ti v ram - Q&T - Quenching and Tempering. Bng 1.4 Thp bn cao dng trong kin trc ngoi khi bn (MPa.)Cn luynng dng

350 (X52)Thng haTMCPKin trc thpKin trc thp & ng ng

450 (X65)Q & TTMCPKin trc thpng ng

550 (X80)Q & TTMCPKin trc thp & Chng buc ng ng

650Q & TGin nng (jack up)Chng buc (Mooring)

750Q & TGin nng (jack up)Chng buc (Mooring)

850Q & TGin nng (jack up)Chng buc (Mooring)

1.4.1 Cn nhc & kinh nghim s dng thp bn caoTrong thp nin gn y xu th s dng thp c bn cao, gii hn chy t 400 Mpa n 450 MPa ngy cng tng cao trong thit k kt cu gin (platforms) v thng tng (topsides). Cc li ch mang li t vic tng sut bn trn khi lng v cc hiu qu gi thnh c c nh cc hot ng tip th, cnh tranh ca cc nh sn xut thp, tuy vy, cng khng loi b c nhng e d ca ch u t v nh sn xut khi p dng chng cho cc kt cu c nhy ph hy mi cao - Cc cu kin hn ch to t thp ng chng hn. iu ny cho thy kin thc v c im k thut ca thp v kinh nghim tch ly t khai thc c vai tr quan yu hn trong chn la vt liu ch to so vi cc hiu qu kinh t c th c t vic p dng cc loi vt liu mi. i vi cc gin t nng (jack-ups) th hiu qu gim trng lng t vic s dng thp bn cao gii hn chy 500 n 800 Mpa rt n tng; cc ng dng nhm thp ny ch to chn (legs), cc thanh rng (rack) v cc bnh rng (pinion) k c cc ng cm neo (spud) cho thy s ng n ca cc nh thit k; d vy th cc hng mc ch to bng nhm thp ny vn phi chu s gim st nghim ngt ca cc qui chun k thut theo tn sut 5 nm mt ln phi c a ln kh (dry-dock) kim tra sa cha bt c vt nt v tn tht no c pht hin. D sao th qui nh ny cng khng th ngn cn vic tin phong p dng thp bn cao vo cc cng trnh m kh nng a chng ln kh kim tra sa cha l bt kh thi (Gin Harding nm 1996 v Siri nm 1998 v sau ny l Elgin- Franklin). Thp bn cao cng c dng ch to cc cu kin chng buc cho gin khoan ni kiu TLP (tension leg platform) v h thng neo ca cc gin khoan di ng na chm kiu MODU (semi-submersible module offshore drilling unit). Mt lng ln cc ti nghin cu gn y c thc hin lin quan n thp bn cao; cc nghin cu ny cung cp cc d liu quan trng v c im v cc tc ng ca mi trng khai thc n cc thuc tnh ca thp. Tuy nhin, hu ht u th hin lng thng tin rt hn ch v tc ng lu di ca mi trng bin (c bit iu kin khc nghit) n cc cu kin ch to bng thp bn cao. Cc nghin cu cng cha a ra cc chng minh tin cy v nhy nt do hydro tng cng di tc ng ca vi khun kh sulphate - SRB : Sulphate Reduction Bacteria - hin hu trong mi trng du kh, din bin mi v kh nng khng rch ca thp bn cao trong mi trng bin, p ng ca thp trong mi trng nhit p sut cao ... Thc t l hu ht cc qui chun, tiu chun thit k (v kim nh) u gii hn vic p dng cc h thc v chun mc trong phm vi thp c gii hn chy di 500 MPa. y thc s l mt ro cn k thut quan trng cha th vt qua; bt chp lng thng tin v d liu nghin cu ngy cng phong ph, ch mt phn nh trong s c cng nhn bi h thng qui chun v tiu chun. N lc gim trng lng v tng hiu qu kinh t thng qua tng t s bn / trng lng v gim thiu khi lng hn l tin chnh thc y ng dng thp bn cao. Tuy nhin do cc hn ch cp, ngy nay chng c s dng ch yu ch to cc hng mc thuc kin trc thng tng (topsides) hoc trn cc thit b nng h. T l p dng nng t 10% n 40% l khch l ng k.Cc nh ch to trong thi gian gn y cng tng cng s dng thp bn cao vo cc cu kin kch thc nh, nh p ng cc iu kin tho gi kim tra, sa cha hoc thay mi nh k theo yu cu ca qui chun. Ch yu chng c s dng nhng cu kin khng hn, cc cu trc khng b nh hng nhiu bi mi trng khai thc, nhng ni c th gim st thng xuyn cc tn tht do mi ...Tuy vy, thp s dng vn b gii hn gii hn chy khng qu 450 MPa, bt chp cc tin b gn y t lnh vc sn xut thp c th cung cp v bo m tnh hn, cng nh c im khng mi ca thp c gii hn chy n 550 MPa.Hin nay, Thp c bn cao hn 550 MPa (c gii hn chy n 700 MPa.) thng l thp Q&T c s dng ch to cc cu kin trn gin di ng t nng, vn khng thng xuyn ngm nc bin v thun li khi a vo kh kim tra sa cha nh k. cc gin ny, thp bn cao c th c s dng ch to khung chn (nng h, yu cu gim trng c ngha quan trng i vi hiu qu vn hnh, khai thc). i th th mi n nguyn ca khung chn c thit k vi 3 hoc 4 c cu dc mang thanh rng phc v cho thao tc nng gin; cc c cu dc ny lin kt vi nhau bng cc ng ngang v ng ging cho nh cc nt lin kt gn trn c cu dc. Thng c cc thanh ging cho b sung (span breakers) kt ni cc ging chnh (main braces) im gia vi mc ch tng cng cng chng vn xon. Cc thanh rng (rack) c ch to t thp tm c b dy kh ln t 150 n 250 mm. Mi c cu dc c dng v tr c ng knh t 800 n 1200 mm, ch to t thp tm dy t 35 n 80 mm. Do vy, thp s dng trong trng hp ny phi bo m tnh hn tt, dai (toughness) v do (ductility) l hai ch tiu c tnh quan trng cn bo m. iu ny buc cc nh cung cp thp phi p dng cc qui trnh nghim ngt kim sot thnh phn hp kim v qu trnh ti v ram sau khi cn. Thc t th cc loi thp c cp bn cao (>550 MPa) ch thc s c nh gi sau khi chng c s dng trn cc gin t nng c nh lp vng bin bc (Harding - 1996, Siri - 1998 v Elgin - 2001). Trn cc gin ny, tnh trng mi do ti, tn tht mi do n mn, ha dn hydro t ra cc thch thc khin cho vic ng dng i tr cn phi c cn nhc cn trng.Gin TPG 500 ca Php l mt thit k x l tt cc hn ch khi s dng thp bn cao. Gin ny c ch to hon chnh trn b v c ko ni n khu vc khai thc; ti cc chn gin c cm xung y bin v gin c nng ln sn sng khai thc. Cch3 lm ny loi b nhu cu s dng cu bin hng nng phc v cho lp t v nh gim chi ph u t ng k. Li ch th hai ca loi gin ny l kh nng ti s dng cc hng mc, cu kin, bi v chng c th c h xung v ko n vng khai thc mi. Vi mc ch ngn nga cc tn tht n tnh khng mi do hn, gin s dng cc nt lp ghp ch to t thp rn (sn xut bi Creusot-Loire), thit tr nh vy gip gim s tp trung ng sut, v ng sut d vn rt kh loi tr i vi cc nt kt cu c ch to t phng php hn. i vi gin Harding th phn chm di 110 m c ch to bng b tng nhm loi tr nguy c do ha dn hydro gy ra bi vi khun kh sulphate c trong lp bn di y bin. gin t nng c nh Siri, cc cu kin chn c ch to t thp cp bn 690 MPa. c dy t 65 n 110 mm. Gin Elgin chn c ch to t thp cp bn 500 MPa, bao gm cc c cu tr v ging. Thanh rng c ch to t thp 700 MPa. Song phn cm xung y bin c ch to t thp c bn trung bnh (350 MPa.) theo truyn thng. Mc ch vn l ngn nga nguy c ha dn hydro do vi khun kh sulphate. Cc ng dng khc ca thp bn cao bao gm cc cu kin neo cc cu trc ni kiu gin TLP. in hnh l khung chn chu cng (vertical tension legs) neo cht vo tm nn nm y bin. ng dng u tin dng ny c trin khai m Hutton vng bin Vng quc Anh. Gin c 16 chn chu cng, mi chn c ch to t cc ng thp 3.5% NI, Cr, Mo, V dy c gii hn chy ti thiu 795 MPa. Cc nt kt ni ca chn c lm t thp rn v kt ni ch yu bng cc khp vn ren (screw coupling). Thp c dng l thp c bn cao nht tha mn dai x rch (Fracture toughness), khng nt tt c trng hp n mn do ng sut ln mi do n mn. La chn ghp ni bng cc khp vn ren nhm khc phc cc thiu st v d liu c s d bo cng nng khng mi ca cc mi hn ng. Mc ch l bo ton tnh nguyn vn ca cu trc ng tui th d kin khi tht k. Trc khi la chn thp nh sn xut tin hnh mt lng ln cc th nghim xc nhn tnh ph hp ca thp c chn. Kt qu l gin hot ng 20 nm v cha gp bt c tn tht ng k no i vi h chng ko (tether) Thc t th cc gin TLP c ch to t thp tng bn s dng hp kim to kt lng t vi (micro-alloy) tng bn kt hp vi qui trnh cn c nhit c kim sot (TMCP) - X70 vn c s dng rng ri trong h ng ng du kh c trin khai nhiu khu m, c Na Uy ln Vnh Mexico. Gin Heidron l mt v d; cc chn cng khai thc su 270 m c cu trc t ng lm t thp c gii hn chy 500 MPa. ng knh 1 m dy 38 mm, cc mi hn c kim tra th va chun 60J nhit -40 C. Cc gin hot ng su ln hn nh Auger TLP - 872m lp nm 1994; Mars TLP su 896 m lp nm 1996 ...s dng thp gii hn chy 415 MPa dy 76mm t thp ci thin tnh hn TMCP. 1.4.2 Thp s dng ch to kin trc thng tng (topsite)Thp s dng ch to kin trc thng tng c phn thnh 5 cp nh bng di y. Thp cp ST2 c th dng thay cho ST1 v ST4 c th dng thay ST3Bng 1.4.2 V d s dng thp ch to kin trc thng tngCp thpDng phiB dyTiu chunphn cpPhn cpcht lngng dng

ST1Thp tm Thp tm Thp hnh Thp hp hnThp hp khng hn T 50 mmT > 50 mmallallallEN 10025EN 10025EN 10025EN 10219EN 10210S355J2S355NLS355J2S355J2HS355J2HCu kin chnh

ST2Thp tm Thp tm Thp hnh Thp hp hnThp hp khng hnT 50 mmT > 50 mmallallallEN 10025EN 10025EN 10025EN 10219EN 10210S355J2S355NLS355J2S355J2HS355J2HCu kin chnh c yu cu nng cao kh nng chu bin dng theo phng thng gc b mt. tha mn EN 10164 Cp Z35.

ST3Thp tm Thp tm Thp hnh Thp hp hnThp hp khng hnT 50 mmT > 50 mmallallallEN 10025EN 10025EN 10025EN 10219EN 10210S420NS420NLS420NS420NS420NCu kin chnh

ST4Thp tm Thp tm Thp hnh Thp hp hnThp hp khng hnT 50 mmT > 50 mmallallallEN 10025EN 10025EN 10025EN 10219EN 10210S420NS420NLS420NS420NS420NCu kin chnh c yu cu nng cao kh nng chu bin dng theo phng thng gc b mt. tha mn EN 10164 Cp Z35.

ST3-SThp tmAllEN 10225S420G1+Q S420G1+MCu kin chnh

ST4-SThp tmAllEN 10225S420G1+Q S420G1+MCu kin chnh c yu cu nng cao kh nng chu bin dng theo phng thng gc b mt. tha mn EN 10164 Cp Z35.

ST5-SThp tmThp tmThp hnhThp hp hnThp hp khng hnThp mallEN 10025EN 10025EN 10025EN 10219EN 10210EN 10067S235S235S235S235S235S235Cu kin th cp

1.4.3. C TNH CA THP BN CAO1.4.3.1 LOI THP V QUI TRNH CN LUYN bn ca thp c kim sot bng cu trc t vi c hnh thnh t thnh phn ha hc v qui trnh nhit m phi thp tri qua theo qui trnh sn xut. Thp s dng trong cc kin trc ngoi khi c thm yu cu v p ng tt tnh hn. i vi thp c b dy t 30 n 100mm) c yu cu phi bo m dai tt v loi tr hu ht cc nguyn nhn ph hy dn v yu cu bo ton bn cao tng ng cc khu vc chu nh hng ca nhit hn.Nhng yu cu kh n gin v hp l song vic p ng chng thc s l mt thch thc i vi nh sn xut thp, bi v iu kin p ng tt mt yu cu ny thng gy tc ng tn hi n yu cu khc. Bng 1.4.3.1(A) di y lit k phm vi bn v qui trnh cn luyn tng ng i vi thp bn cao dng trong cc cu kin khc nhau ca cng trnh ngoi khi. D thy rng (v c l do hiu rng) hu ht cc hng mc c ch to bng cc mc thp c bn trung bnh cn luyn theo qui trnh thng ha (normalized) hoc c nhit c kim sot - TMCP. i vi thp c b dy ln, qui trnh truyn thng (normalized hoc TMCP) thng khng tha mn yu cu bn cao, khi thp Ti v ram (Quenching & Tempering) c gii thiu. Cc hn ch ca vic p dng thp t cc qui trnh cn luyn ng vi cp bn v dy c trnh by bng 1.4.3.1(B). Bng 1.4.3.1(A) ng dng thp v qui trnh cn luyn yu cung dngPhm vi bn (Mpa. gii hn chy)Qui trnh cn luyn

Jacket & Topsite350-:-500Thng haQ & TTMCP

Pipeline350 -:-550X52 -:- X80TMCP

Jack-up & Mooring500 -:- 850Q & T

Bng 1.4.3.1(B) Qui trnh cn luyn thp bn caoThng ha p dng thp c gii hn chy 800 MPa.800 MPa500 MPa400 MPa

(2) TMCP l g ?TMCP l vit tt ca cm t The Thermo-Mechanical Controlled Processing, c dch l qu trnh (cn) kim sot c nhit, cng ngh cn ci tin t qu trnh cn c kim sot (CR) . TMCP to ra thp c mn cao bng cch kim sot c thnh phn ha hc phi, mc bin dng, nhit cn v (nung duy tr - nu cn thit), tc lm ngui cui qu trnh. Cc bin php c kim sot nghim ngt to ra thp c mn ht, dai v bn cao. Hnh 1.4.3 (2) m t cc qui trnh cn TMCP khc nhau c cp di y:Cn c nhit - Thermo-Mechanical Rolling (TMR) - Thp mn ht c cn th nhit ln hn nhit kt tinh li (recrystallisation) v sau tip tc cn nhit (di nhit kt tinh li) khi thp bt u kt lng to pha t cu trc austenite, i khi nhit m pha ferrite hnh thnh mt phn (trng hp cc c nhit lng tnh - TMCP - DP). Qu trnh ny ph v cu trc ht austenite, to ra cc x lch c kim sot. khi autenite chuyn ha hon ton s c ht mn theo yu cu. Thng th qu trnh cn to bin dng ln c thc hin nhit bt u to pha ferrite (Ar3) v tip tc duy tr vi mc bin dng thp hn nhit trc khi austenite chuyn ha hon ton. Sau thp thnh phm c lm ngui trong khng kh to bn cn thit. The1p TMR gm 3 qui trnh nh m t hnh 1.4.3 (2).

Lm ngui tng cng (AC -Accelerated Cooling). Thp sau khi cn c nhit (TMR hoc cn c kim sot CR) t yu cu mn s c thi kh hoc phun nc c kim sot lm ngui theo tc xc nh. Qui trnh 4, thp c cn c nhit n di nhit Ar3 sau lm tin hnh lm ngui tng cng.

Qui trnh 5, thp TMR kt thc nhit cao hn Ar3, sau lm ngui tng cng.

Qui trnh 6, thp CR (kt thc cn trn nhit kt tinh li) sau lm ngui tng cng.

DQT - Direct Quenching and Tempered (DQT) - Thp TMR c ti trc tip (Direct Quench) trong qu trnh cn sau c nung li v ram t yu cu c tnh. Gm hai qui trnh:Qui trnh 7 : TMR DQT.

Qui trnh 8 : CR DQT.

Cc nhn t nh hng n c tnh 15C tnh bao gm bn (gii hn chy, chnh gia gii hn chy v bn ko), do (ductility) , dai (toughness).

ca thp TMCP ph tuc vo thnh phn ha hc , s hin din ca cc nguyn t vi lng (Al, Nb, V) v qui trnh cn luyn.

Hnh 1.4.3(2)(3) Cc qui trnh cn thng dngHnh 1.4.3 (2) cng m t qui trnh cn thng thng bao gmAR - As Rolled : phi cn trong phm vi kt tinh li (cn nng) sau lm ngui t nhin. p dng cho cc loi thp xy dng thng dng khng c yu cu nghim ngt v dai. bn ch yu c quyt nh bi thnh phn ha hc (C, Mn, Si). (qui trnh 9)

N - Normalised : Thp c cn luyn t phi thp c thnh phn ha hc c kim sot (S, P) hoc c hp kim ha bng cc hp kim vi lng (microalloyed) sau khi cn c nung n nhit thng ha v lm ngui. mn ht v kt qu l dai s ty thuc vo thnh phn vi lng, nhit thng ha v thi gian duy tr (soaking time) nhit thng ha. (qui trnh 10)

CR - Controlled Rolling :Bao gm :qui trnh 11 tng t nh TMR song mc bin dng nhit di nhit kt tinh li (cold working) t hn v nhit kt thc cn cao hn.

qui trnh 12 l qui trnh cn thng dng song c thi gian tr hon phi cn kt tinh li trc khi thc hin lt cn hon tt.

1.4.3.2 NH HNG CA THNH PHN HA HC V C IM LUYN KIMThp ng cp X70 (gii hn chy 450 MPa) c ng dng ch to cc ng ng du kh t nhiu nm trc. Mc thp ny chng t kh nng xc lp dai v tnh hn nu thp c cn luyn t phi thp thnh phn ha hc v cc qui trnh cn c kim sot ng n phi hp vi qu trnh lm ngui tng cng ...y l kinh nghim thnh cng qu gi c th p dng i vi thp bn cao.Cc nguyn l luyn kim lm tng kh nng tha mn cc yu cu c tnh ca thp bn cao bao gm: Gim hm lng carbon s lm tng tnh hn v dai

Gim c ht (cu trc ferrite / v (hoc) bainite) c tc ng tng c bn v dai.

C ch lm mn ht c th dng cc nguyn t hp kim vi lng (microalloyed) nh Nb - Nobium, V-Vanadium hoc Al - Nhm kt hp vi qui trnh cn c nhit c kim sot - TMCP.Gim cc tp cht phi kim (S, P, O) s gip tng dai, c bit khi c yu cu bo m dai ton b chiu dy thp, ng nht. Ni cch khc phi thp phi c tinh luyn lu hunh v phospho v kh oxy trit .

Ti u hm lng cc nguyn t Ni, Cr, Mo v Cu s gia tng kh nng tng bn do kt lng to ra kh nng nng cao gii hn bn.

Cn nh l ch mt thay i nh v thnh phn hp kim hoc cc tham s qui trnh cn luyn (nhit , mc bin dng, tc ngui) cng c th nh hng nghim trng n c tnh (bng 1.4.3.2(A) - cho thy s ci tin ca ba cp thp tiu chun in hnh 355,450 v 690 MPa). D rng tng nhm thp ring "c" v "mi" u p ng cng tiu ch phn cp - Gii hn chy ti thiu, chng ta thy rng nhm "mi" c s ci tin ln trong vic phi hp gia bn v dai (Cv) cng nh tnh hn (CE=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15). Kt qu t c chnh l nh s dng hp kim ha vi lng v x l nhit.Hnh 1.4.3 (1) m t tng quan gia bn v hm lng carbon tng ng ca thp TMCP.

Nhng ci tin v c tnh, c bit l dai v tnh hn gip gia tng ng k tim nng khai thc thp bn cao. Tuy nhin, cc k s ch to v cc nh thit k khng an tm lm v thc t (do cc tc ng nhy cm ca qui trnh sn xut thp) l cng mt phn cp thp, sai lch v gii hn chy kh cao (khong 100 MPa - tng ng vi 20% gi tr nh ngha). Sai lch ny dn n cc h ly khi trin khai cng tc hn lm cho mi hn trn kt cu tr nn kh d on (bn hn - overmatching) hoc (km bn hn - undermatching) so vi kim loi c bn (base metal). Bn cnh , tc ng ca qu trnh cn luyn bn, dai v tnh hn cng khin cho vic kim sot cht lng thp ch to c yu cu khe khc hn; cha k n vic p dng cc ch tiu khc nhau i vi b dy v kch thc tm khc nhau. Trong trng hp ny, cc t chc kim nh c c s a ra cc yu cu gim st khe khc hn. Chnh iu ny c th lm lu m li ch v hiu qu gi thnh m thp bn cao c th cung cp.Bng 1.4.3.2(B) , 1.4.3.2(C) v 1.4.3.2(D) cung cp thnh phn hp kim in hnh tng ng vi cc qui trnh cn luyn / nhit luyn i vi thp s dng trong ch to cng trnh ngoi khi. Chng ta c th tham kho tiu chun v vt liu ch to gin khoan do DNV khuyn ngh (DNV OS-B101). Nhn chung th bn ca thp gia tng khi kh nng bin cng (hardenability) gia tng di tc ng ca cc nguyn t hp kim (c tnh bng cc h s tng ng thng qua biu thc tnh hm lng carbon tng ng - CE). xem hnh 3.4. Tuy vy, ng vi mi qui trnh cn luyn th tc ng tng bn c khc nhau. iu ny dn n kh nng tng bn thp song vn duy tr cc thnh phn hp kim sau cho chng c CE thp nht; ngha l p ng tnh hn tt nht. Ni cch khc qui trnh cn luyn phi hp vi vic kim sot thnh phn hp kim phi cn l liu php chun ha to ra cc mc thp va d hn va bo m bn cao, v do dai tha mn cc yu cu thit k. Thp p ng tnh hn tt c ngha l cc nguy c gy tn tht c tnh nh kch thc ht, chuyn bin cu trc, kt lng hydro vng nh hng nhit (HAZ) c nhy thp i vi vic tay i tham s qui trnh hn (nng lng hn (heat input), tc ngui (t8/5 : thi gian lm ngui t 800 xung n 500 C ), nhit nung s b (preheat) v nhit gia cc lp hn (interlayer / intermediate temperature). V ch tiu dai th thp c gii hn chy cng cao, dai cng km (kh nng ph hy dn cao).

Bng 1.4.3.2(A). Tc ng ca thnh phn hp kim, qui trnh cn luyn n c tnh & tnh hn ca thep Grade 355, 450 v 690Mc ThpQui trnhThnh phn ha hcGii hn chy MPa dai CVNTnh hnCE

BCMnSiNiCrMoCuSPAlV

Grade 355BS434050DThng ha 0.201.350.300.0160.0150.0236070J @ -40C0.43

BS7191355EMZThng ha (*)0.111.500.400.150.150.0050.0150.03380>200J @ -40C0.39

BS436050DTMCP0.071.490.210.380.020.0020.0080.02280200J @ -30C0.36

Grade450Q1NQ&T0.180.40.33.01-:-1.80.0150.0050.020.0255080J @ -85C0.81

BS7191450EMZQ&T (*)0.111.490.30.520.110.0010.0100.03480300J @ -40C0.40

Dillinger450TMCPTMCP0.091.500.30.0010.0070.030.04500300J @ -30C0.35

Grade690Q2NQ&T0.110.420.233.401.480.460.030.0010.0120.0260.08550-:-69080J @ -84C0.81

OX812Q&T (*)0.110.890.261.180.460.380.150.0030.0080.070.01690100J @ -80C0.52

SE702Q&T (*)0.00270.1251.050.251.40.50.450.20