Corrosion Contro in Pipelines Using Oxygen Stripping Shankardass

CONRAD

Oilsands Water Usage Workshop 2004

Corrosion Control in Pipelines Using Oxygen Stripping

Champion TechnologiesFebruary 24, 2004

Agenda

Corrosion- The economic impact of corrosion?- What is it?- Why does it occur? - Types of Corrosion

Dissolved Gas – Oxygen- How does it accelerate the corrosion process?- Why is it a problem?

Mechanical Treatment OptionsPros/Cons

Chemical Treatment OptionsHow do they work?

Pros/ Cons

Gas Scavenging- Bisulfite chemistry

Metal Passivation- Phosphate based chemistries

Zinc OrthophosphatePhosphate Esters

Cost of Corrosion - Global Economic Impact

• With new (evolving – stricter) environmental guidelines the requirements on industry to control effluent discharge has increased.

• Industry guidelines are evolving such that zero discharge is the target.

• Lost production and material replacement due to corrosion mechanisms costs billions of dollars annually to industry. These economic losses can be divided into two groups:

• Direct losses• Indirect losses

• Direct Losses – “Increased Costs”Cots of replacement of machinery or their componentsCosts of maintenance/ servicing like repaintingCosts of rebuilding/ constructionEquipment capitalEnvironmental regulationsChemical expensesSafety considerations

• Indirect Losses – “Decreased Revenue”Costs due to shut downLost productionCosts due to loss of efficiencyCosts resulting from catastrophes

Economic Impact - Profitability

Increased Costs

Decreased Revenue

Decreased Profits

Mitigating corrosion is necessary to save costs, time, the environment.

Cost of Corrosion – Local Economic Impact –EUB Statistics - 2002

• Alberta has approximately 320 000 km of energy related pipeline

• EUB conducted 516 inspections on failures/hits in 2002

• 563 corrosion incidents, up from 503 in 2001

• Higher incidents and unsatisfactory inspections due to implementation of Guide-66: Pipeline Inspection Manual

• Failure frequency of 2.5/1000km down from benchmark 5.0/1000km in 1998

• EUB statistics from 2002 show:

Facility suspensions by EUB down from 142 in 2001 to 128 in 2002Cost was greater however, 25.8 million in 2002 compared to 16.3 million in 2001

All Pipeline Failures by Cause

Industry Benchmarks - Alberta Pipeline Information - EUB

50% +

What is Corrosion?The Electrochemical Corrosion Process

• It involves the flow of ions and electrons through liquids and metals, and their interaction across liquid-solid interfaces such as where water and metal meet.

• Corrosion occurs in a corrosion cell. It consists of:

• A metal conductor• The anode, where metal goes into solution• The cathode, which is the reaction site for the electrons• Electrolyte, which completes the electrical circuit

• Water must be present for electrochemical corrosion to occur. If there’s no water, it’s not corrosion.

The Corrosion Cell

MetalMetal

2H2H++ + 2e H+ 2e H22

Fe Fe FeFe++++ + 2e+ 2e

ElectrolyteElectrolyteAnodeAnode

CathodeCathodeee

eeElectron Flow

Electron Flow

Metal Structure

• Metals used for construction and pipeline are inherently inhomogeneous materials. Refined metals have a grain structure made up of microscopic metal crystals. They always contain inclusions, precipitants and sometimes consist of different metallurgical phases. Potential differences on the metal surface are a natural result. These differences are one of the primary causes of corrosion.

• Sometimes there can be no visible change in weight or appearance

• Uniform corrosion, or overall general attack, occurs when anodic and cathodic areas keep shifting. Corrosion then takes place more or less uniformly over the entire exposed surface. The metal becomes thinner and eventually fails. In case of uniform corrosion service life can often be quite accurately estimated on the basis of relatively simple corrosion tests.

• Some corrosion is sudden and unexpected

• Pitting is readily recognised because of pits or holes. This is one of the most vicious forms of corrosion and among the hardest to predict.

• Pitting often starts because of concentration cell effects such as under a permeable deposit. The environment under the deposit becomes exhausted of oxygen, or increases in ion concentration, whereas the surrounding metal away from the deposit is exposed to essentially a constant concentration of oxygen or ions.

• The rate of penetration often accelerates because the pit acts as a crevice and thereby increases the concentration cell effect. An unfavourable ratio of cathode to anode also exists.

Forms of Corrosion?

Localized Pitting

• General corrosion is not a major concern to corrosion risk. Typically flowlines can produce for 15-20 sometime 30 years without failing. However in cases where pitting corrosion is present we can sometimes see failure after 30-days.

Pitting Corrosion

Location of Corrosion Initiation

• Corrosion cells may occur at:

• Points where dissimilar metals connect• Points of internal stress• Places where there are differences in corroded ion concentration• On either side of the bending axis on pieces of bent metal• Stresses from the manufacturing process, or even wrench marks• Places where there are dings, scratches, stress, or other

imperfections have disrupted the uniformity of the metal surface

• Places where there are differences in oxygen concentration

Factors Accelerate the Corrosion Process

• Wherever water and metal meet, corrosion will occur. However, certain factors speed up the rate at which corrosion occurs. These factors include:

• The pH of the water• The presence of dissolved acid gases (CO2, H2S)• Temperature (affects solubility)• Pressure (affects solubility)• Dissolved solids• Velocity of fluid through flowlines• Metallurgy (type of metal)• Dissolved oxygen (O2)• Suspended solids

Suspended Solids

• Suspended solids (slurry/ hydro-transport process), including bacteria, may accelerate corrosion in several ways:

• Solids that settle on metal surfaces can act as cathodes causing concentrated under deposit corrosion

• Layers of deposited solids may also shelter bacteria, some of which produce acid• Solids flowing through tubing can act like a “sandblaster,” stripping away protective

coatings of corrosion by-product (iron carbonate and iron sulfide) as well as corrosion inhibitor from the metal.

Flow Modeling/ Velocity Effects?

Flow Modeling - Importance

• Flow modeling has an impact because we can determine the probability of solids deposition, water hold up areas (high risk/ high consequence). It also has a direct impact on the chemical selection/ dispersibility of the products for adequate treatment.

Unified Flow Pattern Map 24" (610 mm) Line

Gas Velocity (VSG) m/sec0.01 0.1 1 10 100

Liq

uid

Vel

ocity

(VSL

) m/s

ec

0.01

0.1

1

10

100

Stratified Wavy Flow

AnnularFlow

Slug Flow

Dispersed Bubble Flow

Stratified SmoothFlow

Line Conditions

How does oxygen impact corrosion?

How does oxygen impact corrosion?

• Of the three dissolved gases, oxygen is by far the most aggressive of the group. If either or both of the other two gases are dissolved in the water, it drastically increases their corrosivity.

• The higher the concentration of dissolved gases in solution the higher the corrosion tendency.

• Oxygen accelerates the corrosion process in two ways:

First it acts as a “depolarizer”. This means that it will easily combine with hydrogen atoms at the cathode and allow the corrosion reaction to proceed at a rate limited primarily by the rate oxygen can diffuse to the cathode. Without oxygen, the energy it takes to evolve hydrogen gas from the cathode is a major bottleneck in the corrosion reaction and keeps it slowed down.

Second, the oxygen oxidizes the ferrous ions to ferric ions, which forms the insoluble ferric hydroxide (above pH=3).

• Any time there is a difference in the oxygen content of water in two areas of a system, attack will take place preferentially in the area exposed to the lowest oxygen concentration. An oxygen concentration cell. Therefore even solids, scale, corrosion by-product which may cause areas of low oxygen concentration, can cause pitting.

• Dissolved O2 can cause severe corrosion at concentrations of 40 ppb (parts per billion); most operations try to limit the oxygen content to 20-30 ppb in water sources.

• Morphology - Oxygen corrosion has a pitting effect on metal. These pits start small, very deep, with sharp, ice-pick hole-like bottoms – accelerate rapidly.

Oxygen Corrosion

Pitting Corrosion by Oxygen Concentration Cell

FeFe++++

Pipe WallPipe Wall

FlowFlow

Cathodic AreaCathodic AreaAnodic AreaAnodic Area

FeFe++++

FeFe++++

FeFe++++ FeFe++++

HH++

OO22

OO22 OO22OO22

OO22

HH++ HH++HH++ HH++HH++HH++HH++HH++HH++HH++

First it acts as a “depolarizer”. This means that it will easily combine with hydrogen atoms at the cathode and allow the corrosion reaction to proceed at a rate limited primarily by the rate oxygen can diffuse to the cathode.

O2 + 4H+ +4e- 2H2O

Fe Fe2+ + 2e-

Iron atom ferrous ion + electrons


FeFe++++

Pipe WallPipe Wall

FlowFlow

OO22


FeFe++++

FeFe++++

FeFe++++ FeFe++++

OO22

HH++

OO22OO22

OO22


Fe2+ Fe3+ + 1e-

ferrous ion ferric ion+ electron

Second, the oxygen oxidizes the ferrous ions to ferric ions, which forms the insoluble ferric hydroxide (above pH=3).

O2 + 2H2O + 4e- 4OH-

oxygen molecule + water molecules + electrons hydroxyl ions

O2 + 4H+ +4e- 2H2O


FeFe++++

Pipe WallPipe Wall

FlowFlow

OO22


FeFe++++

FeFe++++

FeFe++++ FeFe++++

OO22

HH++

OO22OO22

OO22


hydroxideferricionshydroxylionferricOHFeOHFe

→+↓→+ −+

33 )(3

Oxygen Corrosion

Prevention Options

Materials, Operations, Chemicals

Preventing Corrosion

• Change the metal to corrosion-resistant or non-corroding material, such as a corrosion resistant alloy (CRA) or to a chrome interior.

• Physically treat the metal with a permanent barrier to corrosion, such as hot dip, glass, ceramic, and organic coating or paint.

• Electrochemical cathodic protection, which redirects the corrosion to a weaker galvanic couple, which serves as a “sacrificial anode.”

• Alter the corrosive environment by removing acid gases from the water or de-ionize the water to eliminate its electrical conductivity. Better yet, dehydrate the system and remove the water altogether. Remember, without water you can’t have corrosion.

• Chemicals (Oxygen Scavengers/ Passivators) - Corrosion inhibitors.

Need to determine the root cause of corrosion

• Direct Losses – “Increased Costs”Cots of replacement of machinery or their componentsCosts of maintenance/ servicing like repaintingCosts of rebuilding/ constructionEquipment capitalEnvironmental regulationsChemical expensesSafety considerations

• Indirect Losses – “Decreased Revenue”Costs due to shut downLost productionCosts due to loss of efficiencyCosts resulting from catastrophes

Economic Impact - Profitability

Increased Costs

Decreased Revenue

Decreased Profits

Increase

Profits

Prevention Options

Materials, Operations

• The most common methods of removing oxygen from systems fall in to two categories – mechanical de-aeration (counter current gas stripping towers or vacuum towers) and chemical treatment.

• As a generality, stripping or vacuum towers are used when large quantities of dissolved oxygen are to be removed. Ie. Can handle water flow rates of 10 m3/h.

• Chemical scavengers are used to remove small amounts of oxygen and sometimes for removing the residual after tower de-aeration.

• The final decision is an economic-technical one. Weigh the initial costs of a mechanical set up vs. the costs of a chemical program. The shear volume of chemical required to scavenge or passivate may not be practical.

• The most functional removal of oxygen from water systems uses a combination of mechanical de-aeration to reduce dissolved oxygen to 20-500 ppb, depending on efficiencies in addition to the application of a chemical oxygen scavenger to reduce the dissolved oxygen to < 5 ppb.

Controlling Oxygen Corrosion

A typical 3-stage vacuum de-aeration tower is shown. Efficiently maintained 3-stage

vacuum de-aerators may reduce dissolved oxygen mechanically to < 20-50 ppb.

Residual O2

• Issues surrounding mechanical treatment: − Effectively Remove Oxygen from the System− Good for High Volume Throughput Systems− Up-front Costs/ Maintenance Costs− One Time Set-Up

Gas Stripping: Packed columns/ tray type columns− Maintenance− Fouling with solids and bacteria

Vacuum De-aeration: Vacuum pumps:− De-foamer maybe necessary

Note: the removal of CO2 with gas stripping may also help with the precipitation of calcium scale within the flowlines. This may require the addition of a scale inhibitor.

Controlling Oxygen Corrosion Mechanical Considerations

Prevention Options

Chemical

How do Corrosion Inhibitors Work?

• Oilfield corrosion inhibitors are derivatives of nitrogen groups (amines) and organic acids. Phosphorus and sulfur are also utilized in the synthesis of inhibitors.

• Each molecule of the inhibitor chemical resembles a tadpole, with a “head”and a “tail.” These molecules are electrically charged: the “head” has a positive charge and the “tail” a negative charge.

• The electrical polarity creates an affinity in the molecule for solids, such as metal surfaces of pipelines. As a result, the inhibitor molecules seek out the metal surface and attach themselves to form the protective film.

• Corrosion inhibitors form a protective layer between the metal surface and the water. Without the metal-to-water contact, corrosion cannot take place.

Corrosion Corrosion InhibitorInhibitor

FluidFluid

Pipe WallPipe Wall

HydrocarbonHydrocarbon


Unprotected Cleaned Pipe Surface

Leading pig, 4-5% Oversized Filming pig

Protected Treated Pipe Surface


Surface of Steel Pipe

Inhibitor Adsorbed onto Surface

“Residual” Inhibitor in Water

PRODUCED WATER - FILTERED

Dispersibility Testing

PRODUCED WATER WITH PRODUCTSIMMEDIATELY AFTER ADDITION OF PRODUCTS


PRODUCED WATER WITH PRODUCTSAFTER SLIGHT AGITATION


PRODUCED WATER WITH PRODUCTSAFTER I HOUR


Coupon Treatment

Copper Plating

Protected Surface

Chemical Treatment

Prevention Options

Scavengers - Passivators

Prevention Options

Scavengers

Oxygen Scavengers - Bisulfite

• Oxygen scavengers physically react with the dissolved oxygen.

• Ammonium bisulfite is the most commonly used oxygen scavenger in the oil field. It has good low temperature stability (< -10 0C) and can be further winterized to < - 40 0C. It is the most economical and logistically friendly form of sulfite used for de-oxygenation in the oil field.

• Oxygen scavenger chemicals react stoichiometrically with the dissolved oxygen. Typical treating rates for the scavenger chemistry is 6-10 ppm of scavenger for each ppm measured of dissolved oxygen. Water contains approximately 8 ppm of dissolved oxygen at STP, which is very corrosive.

• Cautions:

• If the source water contains excessive amounts of dissolved barium – the selection of a scavenger may not be the wisest. The barium may react with the sulfate ion causing the highly insoluble barite scale – leads to other problems…

• 2NH4HSO3 + O2 = (NH4)2SO4 + H2SO4 - May Lower pH values


FeFe++++

Pipe WallPipe Wall

FlowFlow


FeFe++++

FeFe++++

FeFe++++ FeFe++++

HH++

OO22

OO22 OO22OO22

OO22


First it acts as a “depolarizer”. This means that it will easily combine with hydrogen atoms at the cathode and allow the corrosion reaction to proceed at a rate limited primarily by the rate oxygen can diffuse to the cathode.

O2 + 4H+ +4e- 2H2O

Fe Fe2+ + 2e-


Oxygen Scavengers

FeFe++++

Pipe WallPipe Wall

FlowFlow


FeFe++++

FeFe++++

FeFe++++ FeFe++++

HH++

OO22

OO22 OO22OO22

OO22


Fe Fe2+ + 2e-


2NH4HSO3 + O2 = (NH4)2SO4 + H2SO4

Oxygen corrosion is normally controlled by the use of oxygen scavenger chemicals, which react stoichiometrically with the dissolved oxygen.

Oxygen ScavengersDo Graphs: Work completed for Hydro-testing Sea Water; Assume a worst case scenario of 8-ppm dissolved O2. Add 100-ppm of the 65% active scavenger package OS2 – Trend dissolved oxygen as a function of time. The method used to measure the dissolved oxygen content was an orbisphere – membrane that measure DO2.

Prevention Options

Passivators

Controlling Oxygen Corrosion Passivators

• Typical oilfield corrosion inhibitors (amines) are not designed to prevent oxygen (O2) corrosion. Oxygen molecules are sometimes able to penetrate the chemical film and attack the metal.

• Cathodic inhibitors tend to form cations similar in charge to H+ ions. These types of inhibitors adsorb strongly to the cathode surface. When this happens the cathode is no longer in contact with the electrolyte and the corrosion current stops.

• Passivating (Anodic) inhibitors form a protective oxide film on the metal surface. Examples of passivators include chromate, nitrate, molybdate, and orthophosphate.

• O2 passivators, which render the metal surface passive

• These chemicals require continuous application to be effective because the oxygen is always in the water.

Oxygen Passivators - Phosphates

• The basic difference between scavengers and passivators:

• Scavengers effectively remove the corroding agent, oxygen, from the electrolyte and by default reduce the corrosion potential on the metal surface. The passivators basically transport the oxygen through the system but reduce the overall corrosion rates by introducing a passivation layer on the metal surface. In effect, corrosion rates are minimized overall.

• Fluid compatibility should also be determined to ensure that there is no increase in the amount of solids precipitated with the addition of chemical. We do not want to increase treatment problems downstream of the chemical injection locations. These products are highly surface active.

• Note: In adequate concentration of passivating inhibitors may actually induce pitting on untreated segments.

Filming MechanismZinc - orthophosphate Zn3(PO4)2

MetalSurface

P O-

O-

O-

O

Fe

Fe

Fe

Fe

Fe

Zn2+

Zn2+

• Zinc Orthophosphate:

• AdvantagesHighly effective corrosion controlCost effective

LimitationsCannot be used above pH 8.1 due to premature zinc precipitation.Divalent zinc ions may help to stabilize interface pads.Depending on discharge techniques, zinc loading is highly toxic to fish and other aquatic organisms.Zinc to phosphate ratios can be adjusted to avoid zinc loading.

P O-

O-

O-

O

Di- phosphate ester – single binding site to Metal Surface

Fe

Fe

MetalSurface

Fe

POO

O

O

POO

O

O

POO

O

O

POO

O

O

Filming Mechanism

Metal Surface

Hydrocarbon Film

Produced Water

InhibitorMolecules

Apolar

Polar

Formation of "Double Layer" Protective Film- Corrosion Inhibitor plus Condensate

Metal Surface

Hydrocarbon Film

Produced Water

InhibitorMolecules

Apolar

Polar


K+

K+• Phosphate Esters• Advantages

Hydrocarbon Chain – Improved EffectivenessSurface Activity may Reduce Friction Cost effectiveMay Reduce Emulsion Stability (Ethoxylation)

Mono phosphate ester – two binding sites to Metal Surface

• New processes enriched mono-phosphate ester –double binding site to Metal Surface

• Improved film persistency

PO

O

OO

Fe

MetalSurface

Fe

PO

O

OO

Fe

Filming MechanismMetal Surface

Hydrocarbon Film

Produced Water

InhibitorMolecules

Apolar

Polar


Metal Surface

Hydrocarbon Film

Produced Water

InhibitorMolecules

Apolar

Polar


K+

K+

No Inhibitor28 days

Inhibited28 days

Pictures of an untreated LPR electrodes. Electrodes were exposed to surface water without corrosion inhibitor. The left picture shows the edge of the electrode with clear sign of crevice attack. The right picture shows the surface with pitting attack

Pictures of an treated LPR electrodes. Electrodes were exposed to surface water dosed with 50 ppm oxygen passivator/ corrosion inhibitor. The left picture shows the edge of the electrode, the right picture shows the surface; no signs of significant corrosion were found.

Oxygen Passivators

Advantages of a Chemical Program

• The basic advantage of a phosphate ester program versus a simplescavenger program or mechanical de-aeration is that we get the benefit of an inhibitor presence to help mitigate corrosion of other types other than O2.

• One other advantage is that the upfront costs are considerably less than setting up a mechanical de-aeration system. The performance can be measured quite quickly with the use of appropriate monitoring tools. Rates can be adjusted easily. All you need is a storage tank/secondary containment, a chemical pump.

Corrosion Control Using Oxygen Stripping

Important Guidelines

• Keep the System Clean• Keep the Water Moving• Eliminate Oxygen

Acknowledgments - References

1. Pipeline Treatment School – Corrosion Fundamentals –Champion Technologies.

2. Common Problems In Oilfield Water Systems –Champion Technologies.

3. Corrosion Inhibitor for Treatment of Carbon Steel Pipelines Transporting Oilfield Waters. W. Veneman. Champion Servo Europe BV. 2002

4. Corrosion Principles, Introduction. Janet Schepers. Champion Servo BV – Champion Technologies.

5. Module 8 – Corrosion. Champion University. Champion Technologies.

Open Forum/ Questions???

CONRAD

Oilsands Water Usage Workshop 2004

Corrosion Control in Pipelines Using Oxygen Stripping

Champion TechnologiesFebruary 24, 2004

Documents

Corrosion Contro in Pipelines Using Oxygen Stripping Shankardass