predicting cp system performance buried piping, structures and … · 2013-01-30 · • the...

SOFTWARE & SERVICES © BEASY 2013

Helping Engineers Control Corrosion & Cracks

1

BEASY SOFTWARE & SERVICES© BEASY 2013


Predicting CP System Performance Buried Piping, Structures & Tanks



2

CP Protection Of Buried Piping, Structures & Tanks• The design verification of CP

systems applied to underground facilities including storage tanks, buried piping, equipment bases, grounding systems, reinforced concrete and other underground structures is complex challenge

• Space limitations may restrict installation of anodes in certain areas and shielding effects from buried structures may affect the distribution of the protective current



3

CP Protection Of Buried Piping, Structures & Tanks

• Modelling provides a tool to ensure adequate protection by evaluating ground bed design options and locations to mitigate the effect of interference and shielding



4

CP Protection Of Buried Piping, Structures & Tanks

• In this case study the impact of nearby storage tanks is predicted on the performance of the CP system and the pipeline potentials



5

Overview

• The modelling study aims to verify the protection provided including the interference & shielding between the CP systems and structures

• 3 tank bases

• 3 Pipelines with different coatings

• Sections of the pipelines are over-ground

• ICCP Anodes supplied by either constant current or voltage rectifiers

• Grounding rods

• Tank Bottom ICCP Grid

• Rod ICCP anodes

• Cable anode (sacrificial)



6

Three Different Soil Resistivity's Are Considered

The use of sub-regions is one method of defining

both horizontal and vertical variation of resistivity.

Region 3

ρ3

Region2ρ2

Region 1

ρ1

NorthInternal region Dimensions

300m 300m 5m

External region Dimensions

2000m 2000m

200mDivided into two regions:•North•South



7

Pipelines Locations

East

North

Pipeline1 Pipeline2 Pipeline3

North regionResistivity Value3

South regionResistivity Value2

Inner regionResistivity Value1



8

Coating Degradation Model

• The coating breakdown factor is a function of coating properties, operational parameters, and time

• As a simple engineering approach, bf can be expressed as:

• Bf = a + b * t

• Where “t” (years) is the age of the coating

• And “a” and “b” are constants that depend on coating properties and the environment

• When bf = 0, the coating is 100% electrically insulating



9

Coating Breakdown Factors

• For this example, we have used constants “a” and “b” with values:

• a = 0.02

• b = 0.008

• Pipeline 1 in the model has a new coating, so that the breakdown factor is 0.02

• Pipeline 2 has a 10 year old coating system, so the breakdown factor for it is 0.1

• Pipeline 3 has a 20 year old coating system, so the breakdown factor for it is 0.18



10

Layout Of Tank Farm Region

East

North

Zone depth = 5 m



11

Tank Layout & CP System

Tank 1

Tank 2

Tank 3

Tank bottoms uncoated bare steel

Diameter

Tank 1 40 m

Tank 2 50 m

Tank 3 50 m



12

CP System Configuration

Sacrificial cable

anode

Ground rod 1

ICCP Tank

grid anode 1

ICCP cylindrical anode 2

Ground rod 2

Ground bed 3

ICCP plate anode 3



13

CP System Configuration

Anode type Depth Dimension Impressed Current

1 Tank ICCP anode grid

1m Diameter 8.3 mm

Length 34m

CASE1 20A

CASE 2 125A

2 ICCP vertical cylindrical anode

1m to 10m

Diameter 25 mm

Length 9m

CASE1 25A

CASE 2 125A

3 ICCP anode 3m Thickness 40 mm

300mm x 300mm

CASE1 25A

CASE 2 125A

4 Cable sacrificial anode.

4m Diameter 5mm

Length 120m

MAGNESIUM polarisation curve and Magnesium

resistivity applied.



14

Viewing Different Components Of The Model Using BEASY GID

Different components can be easily viewed simply by clicking on different layers



15

Model 1 ScenarioHigh Soil Resistivity

Pipeline Electrical Resistance

Ω / m

Pipeline 1 1.41E-05

Pipeline 2 7.78E-06

Pipeline 3 3.76E-05

Cable anode 2.25E-03

Soil Resistivity

Ω - cm

Region 1 Tank Area

20000

Region 2

South

40000

Region 3

North

35000



16

Predicted Potentials: Pipelines & Tanks

The initial design is insufficient to provide protection. This is shown by the colours of the potential contours



17

Optimising The CP Design

By increasing the current supplied by the anodes and improving their location using the model results the protection provided can be improved



18

Value

• The study demonstrated the ability of the model to predict the protection provided by the CP systems to the structures including the interference and shielding caused by the array of complex underground structures

• By varying the CP design options in the model the optimum design and its robustness can be identified

• Changes in the coating performance and the degradation of the CP anodes over the life of the asset can also be simulated to predict the "whole life" protection provided by the CP system



19

Value

• While the initial design is important the monitoring of the system performance over its life is essential to ensure adequate protection is maintained

• Standard survey methods can be difficult to apply and interpret due to the variation in the depth of the piping and interference from nearby structures

• Modelling provides a tool to interpret the potentials obtained during surveys in these complex situations



20

Contact Details

• For further information contact

• Computational Mechanics Inc

25 Bridge Street

Billerica, MA 01821

Tel 978 667 5841 email [email protected]

• C M BEASY Ltd

Ashurst Lodge

Ashurst, Southampton, UK

Tel +44 2380293223 email [email protected]

predicting cp system performance buried piping, structures and … · 2013-01-30 · • the...

Documents