Applied Production Technology - Fundamentals of Corrosion Engineering
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Transcript of Applied Production Technology - Fundamentals of Corrosion Engineering
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Applied Production Technology
Fundamentals of Corrosion Engineering
Objectives
Introduction to: Types of corrosion which may occur in downhole environments
Methods to prevent corrosion
Methods to nd corrosion
Provide enough background knowledge to allow you to question Corrosion
ecisions in an intelligent manner!
Contents
"eneral corrosion principals
Corrosion e#pected in $il and "as facilities
Prevention Materials selection guidelines
Monitoring and measuring
Applicable Applications NonNACE
%PI &CT ' I($ ))*+, (teel Pipes for Casing and Tubing of -ells
%PI +% ' I($ ),./0 -ellhead and Christmas Tree 1quipment
%PI )2 (ubsea -ellhead and Christmas Tree 1quipment
Applicable Applications of NACE !National Association of
Corrosion Engineers" M3 ,)2& ((C resistant metallic materials for oileld equipment
3P ,.2& (election of metallic materials to be used in all
phases of water handling for in4ection into oil5bearing
formations
M3 ,)2+ Metallic materials for sucker rod pumps for
corrosive oileld environment
TM ,)22 6ab testing of metals for resistance to specic
forms of environmental cracking in 7/( environments
3P ,/20 7andling and proper usage of inhibited oileld
acids 3P ,/*) Care8 handling and installation of internally
plastic5coated oileld tubular goods
3P ,)9+ %pplication of Cathodic Protection for e#ternal
surfaces of steel well casings
)
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Electrochemical cell
igure ): (chematics of electrochemical cell
* We can test this prediction by adding a few chunks of mossy zinc to a
beaker of concentrated hydrochloric acid. Within a few minutes, the zinc metal
dissolves, and signicant amounts of hydrogen gas are liberated.
The reaction has some of the characteristic features of oxidation-reduction
reactions.
t is exothermic, in this case giving o! "#$.%& kilo'oules per mole of zinc
consumed.
The e(uilibrium constant for the reaction is very large )*c+ x "#/, and
chemists often write the e(uation for this reaction as if essentially all of
the reactants were converted to products.
0n)s/ 1 21)a(/ 0n1)a(/ 1 2)g/
t can be formally divided into separate oxidation and reduction half-
reactions.
3xidation4 0n 0n11 e-
5eduction4 211 e- 2
/
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6y separating the two half-reactions, the energy given o! by this reaction
can be used to do work.
7ccording to the rst law of thermodynamics, the energy given o! in a
chemical reaction can be converted into heat, work, or a mixture of heat andwork. 6y running the half-reactions in separate containers, we can force the
electrons to 8ow from the oxidation to the reduction half-reaction through an
external wire, which allows us to capture as much as possible of the energy
given o! in the reaction as electrical work.
We can start by immersing a strip of zinc metal into a " 9 0n1ion
solution, as shown in the gure below. We then immerse a piece of platinum wire
in a second beaker lled with " 9 2:l and bubble 2gas over the ;t wire. 0n1half-cell.
This half-cell therefore picks up a positive charge that interferes with the transfer
of more electrons. The reduction of 21ions in the 2>21half-cell leads to a net
negative charge as these 21ions are removed from the solution. This negative
charge also interferes with the transfer of more electrons.
To overcome this problem, we complete the circuit by adding a ?-tube
lled with a saturated solution of a soluble salt such as *:l. @egatively charged
:l-ions 8ow out of one end of the ?-tube to balance the positive charge on the
0n1ions created in one half-cell. ;ositively charged *1ions 8ow out of the other
0
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end of the tube to replace the 21ions consumed in the other half cell. The ?-
tube is called a salt bridge, because it contains a solution of a salt that literally
serves as a bridge to complete the electric circuit.
#eneral Corrosion Principles
1lectrochemical in nature:
Involves the transfer of electrons
3equires electron path and ionic path
3equires two half reactions:
Production of electrons e e/; ; /e5
%llows consumption of electrons/7; ; /e5 7/
Must consider two aspects: Thermodynamics < willingness to corrode
Measured using potential di=erence >voltage?
@inetics < rate of corrosion
Indicated by electrical current Aow
Increases with concentration ' temperature ' Auid velocity
Thermodynamics
Pourbai# diagrams
or particular conditions these demonstrate the stability of metals
They suggest di=erent methods of mitigating corrosion
6ower potential 3aise p7
3aise potential
They do not say anything about the kinetics or rate of corrosion
igure /: Pourbai# diagram
.
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Ae!g! heavy cold
working such as tong marks?
&
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igure 0: "alvanic series of metals in seawater
*The Galvanic Series of Metalscan be used to determine the likelihood of a
galvanic reaction, andgalvanic corrosion or bimetallic corrosion, between two
di!erent metals in a seawater environment.
The most @oble, metal lower in the Balvanic Ceries, will be the cathode while the
less noble, higher in the Galvanic Series, will act as an anode and it will
corrode.
The seawater galvanic series is used also to approximate the probable galvanic
e!ects in other environments for which there are no data.
2owever galvanic corrosion is a function of several di!erent factors that needs
to be carefully evaluated when assessing the likelihood to have galvanic
corrosion.
+
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We suggest you to have a look also at our Balvanic :orrosion pageand also
at Balvanic :orrosion Documents
The table below reports the :orrosion potentials or Balvanic Ceries of metals in
8owing sea water at ambient temperature.
The unshaded symbols show ranges exhibited by stainless steels in acidic water
such as may exist in crevices or in stagnant or low velocity or poorly aerated
water where Ctainless Cteel become active, while the shaded areas show the
potentials of Ctainless Cteel when is in passive state.
Electrochemical %easurements
1lectrochemical measurement whether done in the lab or in the eld8 requires
three electrodes!
(ample 3eferences
%u#illiary
They are used to determine:
Corrosion rates
Current required for Cathodic Protection
PolariEation behaviour
igure .: 05electrode scheme electrochemical measurement
FDo e#planation
Types of Corrosion
2
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igure &: Garious types of Corrosion
&nusual Types of Corrosion
3ing5worm corrosion
6ocaliEed corrosion around bo# end
-ireline attack >also in coated tubing?
Internal scratches along the tubular corrode rapidly Caliper track corrosion
(imilar to wireline attack but caused by the feelers of the caliper
tools
(ucker rod failure
$ften caused by pitting8 then fatigue
Tong damage
May lead to localiEed corrosion
igure +: -ireline damage
'hat ma(es 'ells special)*
"eometry There are usually concentric strings of casing
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irect corrosion monitoring is diHcult8 preferably non5intrusive >or
its usually high cost? To certain e#tent the annulus environment can be controlled
Completion designs are determined by:
Tubing siEe required for Aow performance
Mechanical integrity >principally tension8 burst and collapse? 6ife e#pectancy >typically the time to a workover8 usually ), years?
Tubing8 casing and 4ewellery to be considered
%cidisation for stimulation may be a factor8 or hydraulic fracturing
Potential Corrosion $ites in a +ell
igure 2: Potential corrosion sites in a well
*External Casing Corrosion
External casing corrosion can occur for a number of reasons, such as exposureto water zones, di!erences in formations the casing passes through, or when thecasing acts as an anode to other metals in the area )such as surface e(uipmentand other wells/. :ementing the casing can prevent some of this corrosion, andsome wells are completely cemented for this reason. :athodic protection )seethepreventionpage/is another common method to reduce corrosion.
Internal and Annulus Corrosion
:orrosion in the annulus between the casing and the tubing is dependant on thetype of 8uid in this area. When a well is completed with a packer, as in theillustration above, this 8uid is usually a combination of drilling mud, brine and
possibly produced oil or gas. The composition of this 8uid determines the typesand the amount of corrosion. ;acker 8uids can be designed to meet thecorrosion mitigation needs of a particular well, for instance, using oil baseddrilling mud can help prevent corrosion in the annulus. f the well is completedwithout a packer, the annulus space is lled with wet gas above the 8uid leveland produced 8uids below. The composition of the 8uids and the gas can cause
corrosion, especially if acid gasses are present. )see the section on 2Cfor moreinformation
*
http://octane.nmt.edu/WaterQuality/corrosion/prevention.aspxhttp://octane.nmt.edu/WaterQuality/corrosion/H2S.aspxhttp://octane.nmt.edu/WaterQuality/corrosion/H2S.aspxhttp://octane.nmt.edu/WaterQuality/corrosion/H2S.aspxhttp://octane.nmt.edu/WaterQuality/corrosion/prevention.aspxhttp://octane.nmt.edu/WaterQuality/corrosion/H2S.aspx -
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,nternal Casing Corrosion
Internal casing corrosion can occur in the absence of a packer or if the
packer fails
-ater can condense at cool areas on the casing and 7/( and'or C$/cancorrode the steel
The tubing wouldnt necessarily be corroded at the same area because
Auid travelling along it may keep its temperature above the dew point!
Factors ,n-uencing Corrosion
%ggressive species
-ater plus
$/ C$/
7/( Cl5
$thers
Pressure
Temperature
lowrate
p7
Jicarbonate
Jacteria
"alvanic couples
i=erential concentration
ew point Inhibitor
Coating ' lining
Corrosion rates $pecies dependency
igure 9
Common Corrosion .eactions
(weet Corrosion C$/ ; e ; 7/$ eC$0 ; 7/ 7alf reactions:
C$/ ; 7/$ /7; ; C$0/5
e e/; ; /e5
(our Corrosion
7/( ; e e( ; 7/ 7alf reactions:
7/( /7; ; (/5 /7; ; /e5 7/ isassociation in water
e e
/;
; /e
5
),
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The Types of Corrosion Caused
(weet
"eneral corrosion >calculated using (hell 7ydrocor8 or Petronas
Corrosion %nalyEer? Pitting < leaks8 grooves
(caling (our
7ydrogen Induced Cracks
(ulphide (tress Cracking >especially K 9,LC?
Jlistering
Chloride
Pitting
(tress corrosion cracking of corrosion resistant alloys >especially
above 9,LC?
%itigation %ethods 1ngineering
Permanent solution particularly for corrosion which can cause rapid '
sudden failure Increases C%P1
$perating
%dds to $P1
3equires condence in operations and commitment
Operations
3emove the corrosive species
ownhole dehydrationN
In4ection of chemicals to prevent or remove 7/(
Inhibit
Continuous
Jatch
Cathodic Protection >for casing? Impressed >continuous or pulsed for casing protection?
(acricial
,nhibitor Application/ 0atch
Tubing displacement and squeeEe treatments
Inhibitor Aowed through tubing or displacement8 the tubular is lled and the well shut5in! -ith
squeeEe8 the inhibitor is in4ected through the tubular into the
reservoir! Typically shut5in for a day
Inhibitor residuals monitored at wellhead
%nother treatment is necessary when ppm falls below a pre5
determined level May require one treatment every 0 or . months
(queeEe protects below the packer
))
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igure ),
-eighted inhibitors
Intended to fall to rat hole and slowly release 1ncapsulation
Inhibitors encapsulated in polymer gel are introduced into the well8
either in a basket or in the rat hole!
igure ))
,nhibitor Application/ Continuous
Through the production annulus
Into the casing through a valve positioned in a side pocket
Its possible to in4ect into specic region of the string
Can simply ll the annulus with inhibitor and in4ect through a gas lift valve8
but lacks control!
oesnt protect below the packer
igure )/
Casing Cathodic Protection
Osually requires quite large currents
Is diHcult to directly measure the e=ect of applying current
$ften attenuation calculations are used to give a comfortable
feeling Casing pressure survey may be used to measure success8 provided
enough baseline data e#ists
3emote wellhead measurements are often used Can cause interference with Aowlines8 other wells or surface equipment!
or this reason wellheads require good electrical insulation >also to
prevent galvanic problems?
"roups of wells are usually protected simultaneously
To ensure CP to the bottom of the casing8 current is sometimes pulsed!
1Corrosion Control %ethods !for oil2eld"
Cathodic Protection
(acricial %node Impressed Current Cathodic Protection
)/
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Protective coatings
Chemical inhibitors
Plastic or cement liners
Ose of special alloys
3emoval of corrosive gases
ehydration
%ultilateral 'ells
I"O31 )0
Completions and %ultilateral Team
%dvanced completion design
Multilateral well technology
Casing e#iting using milling ' e#plosives
Dovel multilateral 4unction designs
1#pandable systems8 monobore completions8 slim wells Materials selection ' new materials ' preparation of standards
Materials advice
Testing procedures ' Industry standards
Dew Coiled5tubing technology %morphous bonding
Ose of C3% with orbital TI" NNNNN
M6 database ' newsletter ' website
issemination of latest completions technology
7ttp:''swwri4!siep!shell!com'cc'dw'cmlt'home!htm
3inetics
1vans diagram and related Potential'Current graphs
Illustrates the speed of a reaction
Illustrates how e#posure to di=erent environments can create a galvanic
cell
Can be used to demonstrate how changes in the environment may a=ect
the corrosion rate
Can be determined for simulated conditions and used in the materials
selection process
Illustrates a way to measure corrosion Binstantaneously in the eld!
I"O31 ).
E log , for Cathodic Protection E4uipment
-ell casings may need cathodic protection
$btaining 1 lg I data is an accepted method of determining current
requirements
BInstant o= reading should be used
The reference electrode should be remote from the wellhead
Dote the similarity between this wet up and that shown earlier regarding
determination of corrosion rate and G5I graphs!
)0
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I"O31 )&
3esults look similar to lab tests on small coupon
The change in gradient as the Tafel portion of the slope is reachedgives an
indication of current
7owever it is only an indication and should be supported by other
techniques to provide greater condence
I"O31 )+
%onitoring 5 %easuring
(plit into two categories
Intrusive
Those which require production to stop
Don5intrusive Can be done without interrupting Aow
ownhole calipers! Mechanical8 magnetic8 ultrasonic
Gideo cameras
ownhole CP logging tools
-eight loss coupons
1lectrochemical techniques >6P38 1I(8 potentiodynamic?
7ydrogen probes
1lectrical resistance probes
ield signature monitoring
Intelligent pigging of pipelines Conventional non5destructive techniques e!g! OT
%onitoring 5 %easuring/ ,ntrusive
ownhole calipers8 mechanical8 magnetic8 ultrasonic
Gideo cameras
-eight loss coupons ' 1lectrical resistance probes
1lectrochemical techniques >6P38 1I(8 potentiodynamic?
ownhole CP monitoring using logging tools >casing potential prole tool?
Inspection of recovered tubing
Pressure testing
I"O31 )2
F@inley mechanical caliper tool >www!kinley!com?
I"O31 )9
F@inley caliper < ingers
).
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I"O31 )*
F@apuni caliper corrosion
I"O31 /,
F@apuni caliper corrosion
<rasonic Corrosion ,nspection Tools >http:''www!connect!slb!com?
I"O31 /)
3otating pulse5echo transducer gives 0+,L coverage
7igh resolution5focused transducer quanties even small defects on bothinternal and e#ternal casing surfaces!
Precise rst echo time gives accurate and detailed internal radius
measurement!
(econd time echo gives casing thickness
Internal and e#ternal surface echo amplitudes give a qualitative visual
image of casing condition
-ell site presentation is corrected for tool e#5centraliEation e=ects
etailed e#amination of both inner and outer casing surfaces8 ranging in
diameter from . to )0 0'9 in
Multinger calipers can e#amine only the internal surface and may evendamage the casing! lu# leakage instruments presently o=er limited
accuracy and coverage!
"ood resolution of the OCI tools is due to the very high transducer
frequency of / M7E! The signal is however attenuated by the bore hole
Auid8 and for best results brine8 oil or very light muds should be used >no
solids?
6ogging rate is ./& to 0,,, ft'hr depending on sampling rate
Dot much use if solids are present in the Auids >noise?
I"O31 //
The OCI takes )9,L highly focused measurements during each revolution
of the ultrasonic sensors!
It has up to & rotations every inch of travel inside the casing and can
measure pits and other anomalies down to diameters of appro#imately 9
mm on either the inside and outside surfaces!
Casing Potential Pro2le E4uipment
% casing potential prole is a measurement of the di=erence in potential
between two points inside the casing not a measure of the casing to soilpotential which is indicative of the likelihood of corrosion!
)&
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Typically the contacts are 0 to ), meters apart with wires brought up to
surface and connected across a voltmeter!
The tool is moved along the inside of the casing with potential di=erence
measurements taken as needed!
I"O31 /0
Casing Potential Pro2le .esults
It is usual to run the tool without CP to get baseline data and then with CP
% positive shift indicates current Aow up the casing
In the e#ample from the diagram8 the entire casing appears to be
receiving current
Dote that the tool does not indicate the casing to soil potential and
therefore does not provide direct information about e#ternal corrosion
I"O31 /.
Corrosion %onitoring Application 6imits
I"O31 /&
7o+nhole Corrosion %onitoring
I"O31 /+
%onitoring 5 %easuring/ Non,ntrusive
-ellhead and remote CP monitoring >e#ternal casing?
Inspecting tubulars retrieved for some other purpose
Iron8 Mn or bacterial counts
Inhibitor concentration monitoring
%nnulus pressure monitoring
Monitoring of Aowlines and'or other surface equipment using conventional
methods to infer well conditions 1lectrical resistance probes
1lectrochemistry OT etc
%itigation %ethods
Corrosion allowance
3emove the corrosive species
Prevent ingress ' gas blanket
(cavenge
@ill bacteria
Cathodic Protection
Impressed current >continuous or pulsed for casing protection?
(acricial
3esistant materials
(olid Corrosion 3esistant Materials >C3%?
)+
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Clad C3% >low alloys to nickel alloys?
Coatings ' linings
Composite materials >bre reinforced plastics?
Inhibitors
% combination of these methods
$+eet 5 $our Corrosion/ 7amage
(weet corrosion
Pitting < pin hole
leaks eep grooves along
wetted areas of gas
lines < may lead to
rupture $ften accompanied
by severe scaling (usceptibility increases
with: Increasing pp>C$/?
Increasing velocity
Increasing
Temperature Presence of
particulates
(our corrosion
7ydrogen Induced Cracking
(ulphide (tress
Cracking (tep5wise cracking
Jlistering
7ydrogen5assisted
ductile failure
e( dust can also block gasline lters
(usceptibility increases with:
Increase pp>7/(?
Increasing hardness'strength
ecreasing p7'temperature
Increasing stress >residual or
applied?
$+eet 5 $our Corrosion/ Prevention
)2
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(weet corrosion
ehydration
Corrosion resistant materials
)0 Cr or better
Don5metallic
Ose inhibitor
Prefer continuous
application Jatching is possible
3equire test to
determine most
e=ective Deed to ensure it gets
to correct location Coat ' line
Insert line into
new'e#isting line>particularly for water
disposal? Coat with "31'J1'P1
>sometimes used ofr
downhole equipment?
(our corrosion
ehydration
3esistant materials
((C D%C1 qualied
materials < bear in
mind the potential forother kinds of failures 3equest qualication:
slow strain and ripple
strain tests now used %pply inhibitor
Coat'line >isolate from
environment? 3emove hydrogen sulphide
>use D%C1 criteria?
I"O31 /2
Factors ,n-uencing the Choice of %aterials
Mechanical properties required
imension and strength of material governed by well characteristics
Corrosion allowances are not normally used
3equire life cycle cost >often emphasise is on cape#?
Corrosion which may cause sudden failure >e!g! (CC8 ((C? must be
designed out! Cost of failure >o=shore vs onshore?
-orst case composition8 pressure8 temperature and Aow velocity of Auids
i=erences between tubing'casing'wellhead Internal and e#ternal
Condence in ability to operate within boundary conditions
7ow accurate is the well data >esp! during engineering phase?
Can inhibition continuity be guaranteed
-ill water breakthrough occur8 will 7/( level increase with age
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NACE %. 89:;8< Criteria for $our $ervice !=