Applied Production Technology - Fundamentals of Corrosion Engineering

7/24/2019 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


4/19

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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6/19

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

))


12/19

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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14/19

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

).
http://www.kinley.com/http://www.kinley.com/


15/19

I"O31 )*

F@apuni caliper corrosion

I"O31 /,

F@apuni caliper corrosion

&ltrasonic 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!

)&
http://www.connect.slb.com/http://www.connect.slb.com/


16/19

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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17/19

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


18/19

(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

)9


19/19

NACE %. 89:;8< Criteria for $our $ervice !=