DESIGN OF OFFSHORE OFFSHORE PIPELINES PIPEL INES Materials
Presentation Reference Number Here
L INEP INEPIP IPE E MA MA TERI TERIA ALS
Steel • • • •
Carbon Steel Cost - A$ 1000 - 1500 per tonne Stan Standa dard rd leng length th is 12.2 12.2m m joi joint nts s (40 (40 ft) ft) Main types of line pipe • • • •
Elec Electri trica call Resi Resist stan ance ce Weld Welded ed (ERW (ERW)) Subme ubmerg rge ed Arc Arc Weld Welded ed (SA (SAW) Seamless Spiral welded
Linepipe Line pipe Manufa nufacturi cturing ng ER ERW
Line Lin epip pipe e Manuf nufa actu cturin ring g UO UOE SAW
Carb rbon on Stee teell Lin L ine epi pipe pe • Design co conditions • Max Maximum imum / min minim imu um pr press essure ure • Maximum / minimum temperature • Fabr Fabric icat atio ion n requ requir irem emen ents ts • Corr Corros osiv ivit ity y of of pro produ duce ced d flu fluid ids s • Design Life
• Required Pr Properties • • • • •
Line pipe size Strength Toughness Weldability Corrosion ion Res Resistan tance
Line Li ne Pip ipe e Pro ropert pertii es
Line Li ne Pi Pi pe Ma Mat eri ria al Pr op ope ert rties ies • Toughness • Duct Ductilile e fra fract ctur ure e res resis ista tanc nce e (ma (main inly ly gas lines) • Brit Brittl tle e frac fractu ture re res resis ista tanc nce e (low (low temperature lines) • Test methods • Char Charpy py tes tests ts (sma (smallll sca scale le)) • CTOD (smal smalll sc scale) ale) • Drop Drop Wei Weigh ghtt Tea Tearr Tes Tests ts (lar (large ge scale)
Fittings • Pipeline Fi Fittings • • • • •
Incl Includ udes es;; valv valves es,, flan flange ges, s, ben bends ds,, tees tees,, etc etc Simi Simila larr mat mater eria ials ls sel selec ecti tion on issu issues es appl apply y Shou Should ld hav have e comp compat atib ible le str stren engt gth h to lin line e pipe pipe NonNon-fl flan ange ged d comp compon onen ents ts sho shoul uld d be wel welda dabl ble e Valve Valve materia materials ls shou should ld be be selec selected ted to to ensur ensure e integ integrit rity y of seals and compatibility
Low Lo w Temp Tempe eratu rature re Se Serv rvic ice es • Toug Toughn hnes ess s extr extrem emel ely y impo import rtan antt (eg (eg Arti Artic c ser servi vice ce)) or close to wells with significant Joule Thompson cooling. • Brit Brittl tle e frac fractu ture re is pote potent ntia ially lly cata catast stro roph phic ic • Tran Transi siti tion on temp temper erat atur ure e for for mate materi rial al shou should ld be be low low • For For <-6 <-60C 0C 1-3% 1-3% Nick Nickel el Stee Steels ls may may be be req requi uire red d
Liberty ships
Cor orro rosi sion on Resi sist sta ant Li Line ne Pip Pipe e Materia teriall • “Cor “Corro rosi sion on resi resist stan ant” t” in cert certai ain n env envir iron onme ment nts s • Solid Solid or clad clad / lined lined corr corros osio ion n res resis ista tant nt line line pipe pipe • • • • •
13% Cr (w (welda eldab ble gra grades des) Duple uplex x stain tainle less ss stee steell Supe Superr aust austen enit itic ic stai stainl nles ess s ste steel el Othe thers (t (titan tanium, etc etc)) (flexibles)
Flexi lexibl ble e Pi pe 1. Interlock nterlocke ed stee steel carca carcass ss – resists to
hydrostatic pressure, to radial compression during installation and supports the inner thermoplastic sheath. It is generally manufactured with stainless steel AISI 304 or 316.
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2. Inner nner thermopl thermopla astic shea sheath – promotes
4 3 2 1
sealing, preventing internal fluids (oil, gas or water) from permeating to the external layers. It is manufactured with nylon or a similar material.
3. Interlocke Interlocked d stee steel pressure pressure laye layer: r: resists
to internal and to hydrostatic pressure and to radial compression. It is usually manufactured with carbon steel.
4. Double ouble cross crosswou wound nd tensi tensile le armo armours urs::
resist to axial forces, to internal pressure and to torsion.
5. Externa xternall thermopl thermopla astic shea sheath: protects
the internal layers against external agents, like corrosion and abrasion, to maintain maintain the double crosswound crosswound tensile tensile armours tied and assure the sealing. It is usually manufactured with a polymer, like nylon.
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Good Good for for shor shortt len lengt gths hs / smal smalll to to med mediu ium m dia diame mete ters rs.. Avoid metrology Corrosion resistant Sign Signif ific ican antl tly y mor more e exp expen ensi sive ve than than stee steell for for long long lengths Static or dynamic
WELDING
Pip ipe eli line ne Wel di ding ng
Common Commo n Typ Types es
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Subm Submer erge ged d arc arc weldi elding ng,, SAW SAW (dou (doubl ble e joint ointin ing) g);; Shie Shield lded ed met metal al arc arc weld weldin ing, g, SMA SMAW W (us (usin ing g cell cellul ulos osic ic or or low low hyd hydro roge gen n basic electrodes); Gas metal arc welding, GMAW. Varying bevel preparations. Produ roducti ctivit vity y gene generally rally very very important. impo rtant. Quality also very impo rtant.
Pi peli peline ne Weld ldin ing g
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Weldi elding ng may may be manua anual, l, mecha echani nis sed or or sem semii-au auto tom mati atic. Weld in inspection by by AUT or X-ray Acce Accept ptan ance ce crit criter eria ia base based d on on wor workm kman ansh shiip or or ECA. ECA.
Weld ldii ng CRAs Welding of CRA’s • Carb Carbon on ste steel el weld weldin ing g met metho hods ds can can be be used used • Weldin Welding g rate rates s will will be less less than than carbo carbon n steel steel (2-5 (2-5 times times less) • Weld Weldin ing g cos costs ts will will be be sig signi nific fican antl tly y hig highe her r • Diffe Differe rent nt wel weldi ding ng tec techn hniq ique ues s may may be req requi uire red d • Iner Inertt gas gas pur purge ge on root root • Cont Contro roll of heat heat inpu inputt very very imp impor ortan tantt
PIPELINE CORROSION
Corr orrosi osion on Risk Risk • North Se Sea ex experience • 22% 22% of of inci incide dent nts s are are caus caused ed by corr corros osio ion n • 40% 40% of thes these e resu resulte lted d in LOC LOC (lo (loss ss of of cont contai ainm nmen ent) t) • 80% of LOC incide incidents nts caused caused by intern internal al corros corrosion ion
• Australian experience • Exter Externa nall cor corro rosi sion on in rise riserr spl splas ash h zon zones es – poor poor coati coating ng performance and inspection practices • SRB SRB rela relate ted d int inter erna nall cor corro rosi sion on - untr untrea eate ted d hyd hydro rote test st water and/or infected well fluids • Vara Varanu nus s Isla Island nd expl explos osio ion n bel belie ieve ved d to to be be a resu result lt of pipeline corrosion.
Topics Internal and External Corrosion • Types of Corrosion • Sweet • Sour • Micr Microb obia iall Indu Induce ced d Corr Corros osio ion n
• Corrosion Prevention • Inhibition • Coatings • Cathodic Protection
• Corrosion Monitoring
The Cor orro rosi sion on Pro Process cess •
All corr corrosi osion on proce processe sses s are elec electro troche chemic mical al in natu nature re,, and in gene general ral requ require ire a meta metalli llic c surface in contact with an electrolyte (water). Involve anodic and cathodic reactions. Anodic Anodic rea reacti ction on invol involves ves the the dissol dissoluti ution on of meta metall into the the electr electroly olyte te as posit positive ively ly char charged ged ions. Electr Electrons ons remain remaining ing in in the the metal metal latt lattice ice migr migrat ate e to the the cathod cathode e and and are are discha discharge rged, d, reacting with oxygen and/or hydrogen ions.
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An o di c r eact io n:
M
Mn+ + ne-
→
M stands for a metal and n stands for the number of electrons that an atom of the metal will easily release, i.e. for iron and
steel: Fe
Fe2+ + 2e-
→
Cathodic rea reactions:
O2 + 4 H+ + 4e- 2H2O (oxygen reduction in acidic solution) 1/2 O2 + H2O + 2e- 2 OH- (oxygen reduction in neutral or basic solution) + 2 H + 2e H2 (hydrogen evolution from acidic solution) 2 H2O + 2e- H2 + 2 OH- (hydrogen evolution from neutral water) →
→
→
→
Swee weett Cor Corro rosi sion on Carb Carbon on diox di oxid ide e (CO (CO2) 2) corrosion results when CO2 dissolves in water to form carbonic acid (H2CO3). The acid lowers the pH and sufficient quantities will promote general corrosion and/or pitting corrosion of carbon steel. Corrosion rates depend on: • Part Partial ial pres pressu sure re of CO2 CO2 (Inc (Incre reas asin ing g pre press ssur ure e inc incre reas ases es CR) CR) • pH (lower pH increases CR) • Temper Temperatu ature re (CR increa increases ses with with temper temperatu ature re up to the point point where where stable stable protective films are formed) • Satura Saturatio tion n of of fluid fluid with with iron iron ions ions Fe+ Fe+ (Satur (Saturati ation on decrea decreases ses corros corrosion ion rate) rate) • Flow regime • Hydrocarbon wetting • Inhibitors (inc including glycol)
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Corr Corros osio ion n rate rates s can can be pred predic icte ted d usin using g vari variat ation ions s of De De Waar Waardd-Mi Milli lliam ams s model with correction factors.
Sour ou r Cor Corro rosi sion on Pro Proce cess ss • H2S H2S prod produc uced ed from from some some rese reserv rvoi oirs rs.. • Some Some des desig igns ns con consi side derr poss possib ibilility ity of futu future re H2S H2S production even if not predicted based on reservoir tests. • Dissol Dissoluti ution on of hydrog hydrogen en sulp sulphid hide e into into the water water phase phase • Meta Metall att attac ack k to form form iron iron sulp sulphi hide de and and hyd hydro roge gen n gas gas
Sou ourr Cor Corro rosi sion on Pro Proce cess ss • •
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Hydrog Hydrogen en in the atomic atomic stage stage is prod produce uced d as as part part of the the corros corrosion ion proces process. s. In the presence of H2S it exists for a sufficiently long time at the steel surface to become absorbed into the steel. (The presence of sulfide “poisons” the metal surface reducing reducing the ability for absorbed atomic hydrogen at the metal surface to form H 2, thereby increasing the rate at which atomic hydrogen diffuses into the metal lattice.) Once Once insid inside e the the steel steel the hydrog hydrogen en atom atom is free free,, unles unless s trap trapped ped,, to diffus diffuse. e. Diffus Diffusion ion rate rate depend dependant ant on lattic lattice e dilati dilation on (i.e. (i.e. at highly highly stress stressed/ ed/str strain ained ed zones), solubility (i.e. differences in microstructure), microstructure), concentration (i.e. towards the outer surface) and temperature. If too too much much hydr hydroge ogen n is is pres present ent at too high high stre stresse sses s in in a suscep susceptib tible le microstructure the result will be hydrogen embrittlement cracking and loss of internal integrity. The The trap trappe ped d hydr hydrog ogen en ato atom m will will rec recom ombi bine ne to to mole molecu cula larr gas, gas, and and be be capable of exerting very high internal pressures.
Sour Corr orrosi osion on Sulphide stress cracking, SSC This is a form of hydrogen stress cracking that involves embrittlement of the metal by atomic hydrogen. High strength steel and hard weld zones are particularly prone to SSC. Hydrogen induced cracking, HIC This consists of planar cracking resulting from pressurisation of trap sites by hydrogen. This is typically seen in steels with high impurity levels. Note that HIC may occur without externally applied stresses. When it occurs close to the surface it may result in blistering. Stress oriented hydrogen induced cracking, SOHIC This consists of staggered small cracks formed perpendicular to the principal stress (residual and applied) resulting in a ‘ladder-like’ crack array linking small pre-existing features akin to HIC. SOHIC is facilitated by high hydrogen concentration and local stresses at and above yield strength. Stepwise cracking, SWC This is cracking that connects hydrogen-induced hydrogen-induced cracks on adjacent planes in the steel wall. SWC is dependent upon local straining between the HIC, and embrittlement of the surrounding steels by dissolved hydrogen.
Sour Service Resistance is obtained by keeping the hardness of base metal, heat-affected zones and weld metal at sufficiently low levels, and by improving steel cleanliness.
Micr icrobi obia al Corr Corrosi osion on • Micr Microb obiol iolog ogic ical al ind induc uced ed cor corro rosi sion on (MI (MIC) C) is caus caused ed by by the presence of sulphate-reducing bacteria (SRB). The SRBs feed on fatty acids (present in i n formation water) and a range of hydrocarbons to produce sulphides which are corrosive. • SRBs SRBs can can be be intr introd oduc uced ed thr throu ough gh for forma mati tion on wat water er or or untreated seawater. • Corr Corros osio ion n loc local al to SRBs SRBs caus causes es pitt pittin ing. g. • The The pre prese senc nce e of of SRB SRBs s can can lead lead to rapid rapid pipe pipe wall wall damage. SRBs present in anaerobic conditions cause the majority of MIC failures.
Corr orrosi osion on Cont Control rol Internal
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Proce roces ssing sing of pipe pipeliline ne flui fluid d - ie de-w de-wat ater er Material selection - CS or CRA? Chemical in inhibition Use Use of of cor corro rosi sion on all allow owan ance ce (wi (with th chem chemic ical al inh inhibi ibiti tion on)) Inte Intern rnal al coa coati ting ngs s (no (nott gen gener eral ally ly eff effec ecti tive ve – risk risks s wit with h coating girth welds)
External
• External co coatings • Cathodic pr protection
Corros orrosion ion Inhibit nhibition ion •
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Inhi Inhibi bito tors rs form form film films s whic which h pre preve vent nt water water wett wettin ing g of pipe wall. (flow rate / regime important to ensure film not stripped) Gene Genera rall ass assum umpt ptio ion n is is that that inhi inhibi bito tors rs prov provid ide e ful fulll bottom of line protection when inhibitor system is operating. Residual CR reduced to very low level <0.1mm/year. Corr Corros osio ion n occu occurs rs at full full CR when when inhi inhibi biti tion on system system is not not working working – hence uptime uptime of of CI system critical. Corr Corros osio ion n all allow owan ance ce to allo allow w for for resi residu dual al corrosion and corrosion from inhibitor downtime. do wntime. Corr Corros osio ion n inh inhib ibit itio ion n gen gener eral ally ly does does not not prot protec ectt against against top of line corrosi corrosion on – need to control control condensation rate. Inhi Inhibi bito tors rs corr corros osiv ive e in high high con conce cent ntra rati tion ons. s.
Ext xte ern rna al Cor Corro rosi sion on Con Contr trol ol Exte xt erna rn al Coatings oatin gs Coatings isolate metal from contact with the surrounding environment • Firs Firstt def defen ense se agai agains nstt cor corro rosi sion on • A proper properly ly sele selecte cted, d, appl applied ied,, and inst install alled ed coati coating ng shoul should d provid provide e 99%+ of the protection required, supplemented with cathodic protection Required Properties Properti es of Coatin Coatings gs •
Effe Effect ctiv ive e Elec Electr tric ical al Insu Insula lato tor r
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Effe Effect ctiv ive e Mo Moist isture ure Ba Barrie rrier r
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Eas Ease of App Applilic catio tion to Pip Pipe
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Abil Abilit ity y to to Res Resis istt Dev Devel elop opme ment nt of Holidays with Time
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Abil Abilit ity y to to Wit Withs hsta tand nd Hand Handliling ng,, Sto Stora rage ge,, and Installation
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Resi Resist stan ance ce to Disb Disbon ondi ding ng when when unde underr Cathod Cathodic ic Protec Protectio tion n
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Ease Ease of Repai epairr / Fiel Field d Join Jointt Compatibility
Cathodic Prote rotection ction •
There ar are tw two ty types pes of system tems • galvan galvanic ic where where the the anode anode is is made made from from a more more react reactive ive metal metal than than the the steel, ie anode is sacrificed to protect the steel. • impres impressed sed curr current ent where where the the drivi driving ng volta voltage ge is suppli supplied ed by an an extern external al power source, ie transformer rectifier (TR) unit.
Ho w Do es CP Wo Wo r k How Does Catho Catho dic Protectio n Stop Corrosi on?
Cathodic protection prevents prevents corrosion by converting all of the anodic (active) sites on the metal surface to cathodic (passive) sites by supplying electrical current (or free electrons) from an alternate source. mor e activ active e than than For pipelines usually this takes the form of galvanic anodes which are more steel. This practice is also referred to as a sacrificial system, since the galvanic anodes sacrifice themselves to protect the structural steel or pipeline from corrosion.
In the case of aluminum anodes, the reaction at the aluminum surface is: 4Al => 4AL+++ + 12 e- (4 Aluminum ions plus 12 free electrons) and at the steel surface, 3O2 + 12e- + 6H20 6H20 => => 12OH12OH-
(Oxygen gas converted to oxygen ions which combine with water to form hydroxyl ions) As long as the current (free electrons) is arriving arriving at the cathode cathode (steel) faster faster than oxygen is arriving, no corrosion occurs.
Cathodic Prote rotection ction Sacrific cri ficial ial Anode Ano des s
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Design • Subs Subsea ea usua usualllly y Al/ Al/Zn Zn/In /In allo alloy y or or pure pure zin zinc c • Brac Bracel elet et type type,, stan standd-of off f • Sled mounted Sizing Considers: • Weig Weight ht of of allo alloy y (all (alloy oy capa capaci city ty,, mean mean curr current ent requirements) • Anod Anode e end end of life ife res resiistan stance ce - base based d on on surface area • Anode spacing Issues to Consider : • Curr urrent ent dr draina ainage ge - local ocal struc tructu turres • Inte Interf rfac ace e with with onsh onshor ore e pip pipel elin ine e • Hydrogen damage
Cathodic Prote rotection ction
Typ ypic ica al Extern Externa al Coa oati ting ngs s Coating
Offshore
Onshore
With Concrete Coating
Not suitable
FBE
Good, but needs antislip & extra thickness
Good, but prone to damage
3LPE/PP
Good
Good
Asphalt Enamel
• Surf Surfac ace e prep prepar arat atio ion n is ver very y impo import rtan antt in the the app applic licat ation ion of all coatings
Con oncr cre ete Coatin Coating g
(Not (N ot Corrosi on Re Related) lated)
• For negative buoyancy • For mechanical protection • Various de densities us used (2 (2,240 – 3,400kgs per cubic meter)
• Reinforcement types • welded wire mesh • welded st steel ca cages
• Application Methods • impingement (high velocity spray) • wrap rap (Co (Com mpres press sion ion coa coatt)
Con oncr cre ete Coatin Coating g Cage Reinforcement Installation and Concrete Mixing Cement, Iron Ore, Sand and Water
OD measurement
Anti-Corrosion Coated Pipe
Weighing Machine
Concrete Curing
Sand Berm
Fog Cure
Fie ield ld Jo Join intt Coa Coati ting ng • Cold old tape wr wrap, heat eat shrink sl sleeve eve or FBE • Gene enerally fie fielld jo joint int in infille lled with PU PU foam oam (u (used sed to to use mastic) to provide continuous outside diameter
Fie ield ld Joint Joi nt Coa Coating ting - Tape •
Surfac Surface e prep prepara aratio tion n limi limited ted to clea cleanin ning g and and wire wire brush brushing ing to surf surface ace quality quality SA 3.
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Installat lation time 3-4 minutes.
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Wrapp rappin ing g tape tape fabr fabric icat ate ed from from PVC PVC or polyethylene with a self-adhesive layer. Total thickness 1.5–2.0 mm. The tape tape is cut to size, ize, and and appli pplied ed to the field joint as a cigarette wrap, with the overlap at the top of the pipe. Custo ustoma marry to use use thr three wraps raps,, one one to cover the exposed steel and two (narrow) wraps to bridge the gaps gaps to the the ad adjac jacent ent fac facto torry-ap -applie plied d coatings, overlapping by approximately 50 mm.
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Fie ield ld Joint Joi nt Coa Coating ting - HSS •
Surfac Surface e prep prepara aratio tion n limi limited ted to clea cleanin ning g and and wire wire brush brushing ing to surf surface ace quality quality SA 3.
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Installat lation time 3-4 minutes.
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Heat eat sh shrink rink sleev leeves es are man manufac ufactu turred from radiation-crosslinked polyethylene tape, provided with a self-priming sealant. The total thickness is 1.5–2.5 mm. • Appl Applic icat atio ion n simi simila larr to tape tape,, exce except pt that that there is only one wrap. • Shri Shrink nkin ing g on on to to the the join jointt is is car carri ried ed out out using the yellow flame of a gas torch, applying the heat from the centre of the joint area and outwards. • A typi typica call shr shrin inki king ng rati ratio o is 20 –25% –25% and, and, after shrinking, the overlap to the factoryapplied coating should be at least 50 mm.
Summary • Expe Experi rien ence ce sho shows ws that that cor corro rosi sion on can can be be con contr trol olled led,, but but there will always be some residual risk. • Cohe Cohere rent nt cor corro rosi sion on con contr trol ol & monit monitor orin ing g prog progra rams ms are are part and parcel of the corrosion management. • The The mon monit itor orin ing g met metho hods ds use used d mus mustt alw alway ays s be desi design gned ed to be fit-for-purpose.
