Improvement Of Sacrificial Anode Life For

Internal Surface Of Process Vessels

In Upstream of

Oil & Gas Facilities

www.kockw.com

Saleh Al-Sulaiman

Hasan Sabri

Mohammed Abdul-Fatah

Eugene D’souza (Presenter)

Inspection and Corrosion Team,

Kuwait Oil Company

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Presentation Overview

Introduction

Gathering Center Process Overview

Types Of Separators

Separator Construction and Operational Details

Comparison between Separators

Case Study

Results

Conclusions

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The Kuwait Oil Company is one of the major oil producing

companies in the world.

Company mainly executes exploration, drilling, and

extraction of oil and gas within the State of Kuwait.

Oil produced from several oil fields including Burgan,

Ahmadi and Magwa.

Operates 21 Gathering Centers and 4 Booster Stations.

Introduction

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Oil Fields in Kuwait

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Gathering Center Satellite Image

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Serves as a collection (Gathering) location of Crude Oil from wells

Separates the Crude Oil, Gas and Water.

Facilitates Oil Wells Testing

Provides intermediate storage for the Crude Oil prior to pumping to

the Tank Farms

Compresses Tank vapors for condensate recovery

Transports the gas for further compression at the Booster Stations.

Gathering Center (GC)

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Gathering Center Process in Brief

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Wet Separators

Two Phase Separators Three Phase Separators

General Arrangement Drawings

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Operation and function of an Two Phase Separators

The function of a two phase Separator is to separate the associated gas and liquid (oil & water).

The liquid leaves at the bottom of the vessel and gas from top through a mist eliminator to remove small liquid droplets from the gas.

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Operation and function of an Three Phase Separators

The function of a three phase Separator is to separate the associated crude, gas and oily water.

It works on the principle that the three components have different densities allowing the gas being on top, the crude being in the middle and water remains at bottom.

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Comparison between of Two & Three Phase Separator

Two Phase Separator Three Phase Separator

1 The function of a 2-phase

Separator is to separate the

associated gas and liquid (oil &

water)

The function of a 3-phase Separator is to

separate the associated crude , gas and

oily water

2 The liquid leaves at the bottom of the vessel and gas from top through a mist eliminator to remove small liquid droplets from the gas.

It works on the principle that the three components have different densities allowing the gas being on top, the crude being in the middle and water remains at bottom.

3 Oily water resistivity above 1000 ohm-cm.

Oily Water resistivity between 1 to 7 ohm-cm.

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A Case study was performed on a three phase separator vessel which

had been operated for less than year (six months) and found with

sacrificial anodes consumption up to average 85%. The CP design for

this vessel was prepared considering 10 years of service life.

Case Study

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Separator Vessel Design Details

Diameter ID 3,048mm (10 ft)

Length 15,420mm (50 ft)

Heads 2:1 Semi-Ellipsodial

Orientation Horizontal (Saddle mounted)

Process Fluid Crude oil/ Saline water/ Hydrocarbon vapour

Design pressure 9.7 bar (140 psig)

Design Temperature 121 0C (250 0F)

Operating Temperature 60 0C (140 0F)

MDMT -3 0C (27 0F)

MAWP 9.7 bar (140 psig) @121 0C (250 0F)

Design /Construction code ASME (1)/”U” STAMP/API(2)

Internal Coating Phenolic epoxy 3 coat of 100 micron thickness

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Vessel Material Specifications and Internal structure details

Shell (Material/thickness) SA 516 Gr.60N / 18mm UNS K02100

Heads (Material/thickness)

SA 516 Gr.60N / 20mm (nominal) 16.5 (minimum)

UNS K02100

Nozzles SA 106 Gr.B UNS K03006

Flange SA 105N UNS K03504

Nut and Bolts SA193 B8M/SA194 8M SS parts SA193 B7M/SA194 7M CS parts

UNS S31254 SS parts UNS G41400 CS parts

Inlet momentum absorber Inlet device/316L stainless steel UNS S31603

Baffle(s) 2 x Perforated Baffles/316L stainless steel UNS S31603

Coalescer pack(s) 3 x Demisters /316L stainless steel UNS S31603

Mist eliminator 316L Stainless Steel UNS S31603

Vortex breaker(s) Oil & water outlet/SA 516 Gr 60N / Epoxy coated

UNS K02100

Weir plate Carbon steel/ Epoxy Coated UNS K02100

Sludge wash header(s) Carbon steel/ Epoxy coated UNS K02100

Sacrificial anodes Aluminum Alloy -

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Separator Vessel Initial CP Design

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Observations & Findings

As part of routine shutdown program the following three phase separator was

opened for internal inspection, during which the following was observed.

Sacrificial anode installed at 6 o’clock position was completely (100%)

consumed.

Sacrificial anodes installed at 5 and 7 o’clock positions were consumed up to

80%.

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Observations & Findings

Neoprene gasket used for isolating the internal fittings from the

shell was completely deteriorated.

Continuity test revealed all bare internal Fittings and structures

were continuous with the vessel shell.

Vessel shell internal coating was found with blisters between

3 to 9 o’clock positions.

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Reasons for Premature Anode Consumption

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Reasons for Premature Anode Consumption

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Pittings Due to Galvanic Corrosion

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Alternative Approach

Based on the observations and findings and as part of a

remedial action the following plan was implemented.

New CP design considering actual vessel operating

conditions.

Painting of vessel shell internal between 3 to 9 o’clock

positions.

Painting of all internal structures and fittings.

Change of isolating materials from Neoprene gasket to Poly

Tetra Fluoro Ethylene (PTFE) based upon compatibility with

service environment.

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Alternative Approach

New CP design

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Alternative Approach

Coating of Vessel Shell and Internal Fittings/ Structures

The vessel shell between 3 o’clock to 9 o’clock positions and the

bare stainless steel internal structures/ fittings were blasted and

painted with phenolic epoxy three coats of 100 microns each

resulting to 300 microns dry film thickness coating

Coalescer Pack Perforated Baffles Inlet Device Assembly

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Results

After the alternative approach was implemented, the following vessel

was reopened to inspect the internal fittings/structure and anode

condition subsequently two year of operational period of the vessel

during which the following observations were noted:

Drastic reduction in

Anode Consumption

The isolation material

was found in intact

without any

deterioration.

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Conclusion

Conclusion are based on the actual observation and finding mentioned

above. It is evident that the initial Cathodic Protection design and

construction practice required modifications to enhance the life of the

cathodic protection and below are the modifications:

Cathodic Protection Design Considerations

Surface Area considered in the design shall include immersed sections

of vessel shell and internal fittings/structures.

Electrolyte resistivity used for design purpose shall be physically

measured.

Operational temperature of the vessel shall be considered to derive the

actual required current density and to derate the anode electrochemical

capacity.

continued….

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Conclusion

Coating and Isolation Considerations

Application of coating the bare internal fittings/ structures regardless

of its material specifications could reduce the current requirement

drastically in situation of failures in isolation.

The isolating gasket material used to isolate the internal fittings from

the vessel shell shall be compatible with the service environment.

For internal structures where coating is impractical, positive isolation

shall be achieved by isolation gasket or by increasing the coating

thickness at contact locations between vessel and structure.

After implementation of alternative approach the anode consumption

reduced from 54.5 kg per year to 8 kg per year i.e. saving 85.3% of

anode weight per year, resulting in increased anode life.

Sample Chart

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Thank You