sp60-18 rev3 cathodic protection
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SPECIFICATION
SP-60-18 Revision 3
CATHODIC PROTECTION
VALIDITY OF SPECIFICATION
This document will be valid by directly printing the document from Sasol Intranet and
validated by a registered Sasol Intranet user by completing the table below.
Validity automatically expires 3 months after verification. Reinstatement of a document
takes place by verifying pertinence and completing the next line in the table. If the
document is found to be obsolete, it shall be destroyed or marked as such.
It is forbidden to use obsolete or expired documents.
Sequence
Number
Control
Number
Initials
and
Surname
Signature
Date
of
Verification
Expiry
Date
1 2003-12-12
2
3
4
5
6
7
8
This Specification is protected by copyright and is the sole property of Sasol. The information is proprietary to Sasol and is for the sole useof the identified project or defined scope of work. Any unauthorised use, disclosure or copying or any other means of duplication orreproduction, is prohibited.Copyright 2003. Sasol. All rights reserved.
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SASOL SPECIFICATION SP-60-18
CATHODIC PROTECTION
Originator : (SIGNED)
DG ROSS
Reviewer : (SIGNED)
DFM GOODWIN
Approved by : (SIGNED)JP NELL Date : 16 MARCH 1988
ISSUE DATE: APRIL 1988
For interpretation of the Specification, the following person(s) can be contacted:
GH Mller, BAR Machado, J Piorkowski, T Erasmus
SUBSEQUENT REVISIONS
A Revision Description sheet is included to assist in identifying the changes.
Rev No Issue Date Proposed By Reviewed By Approved By Date
2 Aug 2000 DG Ross BAR Machado C Thirion 5 June 2000
3 Oct 2003 T Erasmus BAR Machado C Thirion 26 Nov 2003
This Specification is protected by copyright and is the sole property of Sasol. The information is proprietary to Sasol and is for the sole useof the identified project or defined scope of work. Any unauthorised use, disclosure or copying or any other means of duplication orreproduction, is prohibited.Copyright 2003. Sasol. All rights reserved.
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Revision 3
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SASOL SPECIFICATION SP-60-18
CATHODIC PROTECTION
TECHNICAL COMMITTEE OF SPECIFICATION SP-60-18, Revision 3
NAME DEPARTMENT AND / OR COMPANY
BERGH, G (Gerhard) Sasol Infrachem Water Systems
COOKE, JH (Jack) Electrical and Integrity, Natref
ERASMUS, T (Theuns) Electrical Engineering, Sasol Technology
HAYNES, GJ (Gerald) Sasol Technology Consultant
HOLLER, RK (Rolf) Electrical and Integrity, Natref
LOMBARD, ER (Sias) Electrical Engineering, Sasol Technology
MACHADO, BAR (Tony) Electrical Engineering, Sasol Technology
MLLER, GH (Grant) Electrical Engineering, Sasol Technology
OOSTHUIZEN, PC (Pieter) Sasol Oil
WILKINSON, W (William) Reliability, Sasol Synfuels
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SASOL SPECIFICATION SP-60-18
CATHODIC PROTECTION
REVISION SHEET
REVISION 3
Specification SP-60-18, Revision 2 is revised in its entirety.
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CATHODIC PROTECTION
Subject to SASOLs review of the report and acceptance of the conceptual design proposal, the design
specialists scope of work should then be extended to cover:
a. The additional site survey in order to permit the preparation of a detailed cathodic protection
design complete with a detailed technical specification and bill of quantities. The latter shall
permit the procurement or a Request For Quotation (RFQ) document to be issued to enable
cathodic protection construction contractors to carry out the cathodic protection installation.
b. The necessary liaison with the engineering contractor of the process plant, transmission or
distribution pipeline which is to be cathodically protected, so as to ensure the inclusion of all
cathodic protection field installation details in the final plant / pipeline engineering drawings.
c. The site supervision, quality control and commissioning of the completed cathodic protection
system.
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CATHODIC PROTECTION
PAGETABLE OF CONTENTS
PAGE
1 GENERAL.............................................................................................................................. 1
1.1 SCOPE ........................................................................................................................ 1
1.2 LEGAL REQUIREMENTS........................................................................................ 2
1.3 ABBREVIATIONS .................................................................................................... 2
1.4 DEFINITIONS............................................................................................................ 9
1.5 PRECEDENCE......................................................................................................... 17
1.6 MATERIAL REQUIREMENTS .............................................................................. 17
1.7 GUARANTEE PERIOD........................................................................................... 17
2 REFERENCE DOCUMENTS............................................................................................ 18
2.1 SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTH
AFRICAN BUREAU OF STANDARDS (SABS) CODES OF PRACTICE AND
SPECIFICATIONS................................................................................................... 18
2.2 SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTHAFRICAN BUREAU OF STANDARDS / INTERNATIONAL
ELECTROTECHNICAL COMMISSION (SABS IEC) SPECIFICATIONS.......... 21
2.3 SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTH
AFRICAN BUREAU OF STANDARDS / INTERNATIONAL
ORGANISATION FOR STANDARDISATION (SABS ISO) STANDARDS....... 21
2.4 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME)
STANDARDS........................................................................................................... 22
2.5 AMERICAN SOCIETY FOR THE TESTING OF MATERIALS (ASTM)............ 222.6 AMERICAN PETROLEUM INSTITUTE (API)..................................................... 23
2.7 NATIONAL ASSOCIATION OF CORROSION ENGINEERS (NACE)
RECOMMENDED PRACTICES............................................................................. 23
2.8 BRITISH STANDARDS INSTITUTION (BS) SPECIFICATIONS....................... 24
2.9 RAL DEUTSCHES INSTITUT FR GTESICHERUNG UND
KENNZEICHNUNG RAL-FARBEN ................................................................... 25
2.10 DEUTSCHES INSTITUT FR NORMUNG (DIN)................................................ 25
2.11 INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC)PUBLICATIONS...................................................................................................... 25
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PAGE2.12 INTERNATIONAL ORGANISATION FOR STANDARDISATION (ISO)
STANDARDS........................................................................................................... 25
2.13 SWEDISH STANDARDS INSTITUTION (SIS) STANDARDS............................ 26
2.14 SASOL SPECIFICATIONS, DATA SHEETS AND STANDARD DRAWINGS.. 26
3 CP SYSTEM REQUIREMENTS....................................................................................... 28
3.1 SPECIALIST CP CONSULTANT AND CP CONTRACTOR ............................... 28
3.2 ON SITE INVESTIGATIONS / SURVEY .............................................................. 29
4 CATHODIC PROTECTION DETAILED DESIGN REQUIREMENTS...................... 39
4.1 GENERAL CONSIDERATIONS ............................................................................ 39
4.2 COATINGS AND CP............................................................................................... 39
4.3 CHOICE OF CP SYSTEM....................................................................................... 41
4.4 DETAILED CP DESIGN CALCULATIONS.......................................................... 42
4.5 SPECIAL DESIGN CONSIDERATIONS ............................................................... 47
5 CONSTRUCTION, DRAWINGS, RECORDS AND COMMISSIONING.................... 48
5.1 CONSTRUCTION, TESTING AND INSPECTION ............................................... 495.2 COMMISSIONING, AS-BUILT DRAWINGS AND RECORDS .......................... 51
5.3 SPARE PARTS......................................................................................................... 55
5.4 INSTALLATION, OPERATION AND MAINTENANCE MANUALS ................ 55
6 CP ACCEPTANCE CRITERIA ........................................................................................ 55
6.1 ACCEPTANCE CRITERIA..................................................................................... 55
6.2 ASSESSING THE IR FREE STRUCTURE-TO-ELECTROLYTE
POTENTIAL............................................................................................................. 57
7 OPERATION AND MAINTENANCE OF THE CP SYSTEM ...................................... 59
8 CATHODIC PROTECTION MATERIALS AND THE INSTALLATION
THEREOF............................................................................................................................ 61
8.1 GENERAL................................................................................................................ 61
8.2 MANUAL TAP CHANGE AND AUTOMATIC THYRISTOR CONTROLLED
TRANSFORMER RECTIFIER UNITS ................................................................... 61
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PAGE9 ELECTRICAL CONSTRUCTION ................................................................................... 63
9.1 GENERAL................................................................................................................ 63
9.2 OUTPUT CONTROL............................................................................................... 65
9.3 METERS AND MONITORS ................................................................................... 66
9.4 SURGE PROTECTION............................................................................................ 67
9.5 WIRING AND BUSBARS....................................................................................... 68
9.6 COLOUR CODING AND LABELLING................................................................. 69
9.7 CABLE ENDS AND TERMINALS......................................................................... 71
9.8 EARTHING .............................................................................................................. 72
9.9 SPARES.................................................................................................................... 72
9.10 COMPONENT LAYOUT ........................................................................................ 73
9.11 AUXILIARY AC SUPPLY...................................................................................... 74
9.12 CABINET CONSTRUCTION.................................................................................. 74
9.13 COATING................................................................................................................. 76
9.14 INSPECTION AND TESTING ................................................................................ 76
9.15 DOCUMENTATION................................................................................................ 78
9.16 GUARANTEE .......................................................................................................... 78
9.17 MANUFACTURER QUALIFICATIONS ............................................................... 78
10 CONCRETE PLINTHS ...................................................................................................... 78
11 CORROSION RESISTANT SILICON IRON ANODES ................................................ 79
11.1 GENERAL CONSIDERATIONS ............................................................................ 79
11.2 GENERAL ANODE DETAILS ............................................................................... 80
11.3 CHEMICAL COMPOSITION.................................................................................. 82
11.4 QUALITY CONTROL AND TESTING.................................................................. 82
12 TYPICAL IMPRESSED CURRENT ANODE INSTALLATION DETAILS............... 83
12.1 DEEP VERTICAL AND SHALLOW VERTICAL ANODE GROUNDBED
SYSTEMS................................................................................................................. 83
12.2 HORIZONTAL AND DISTRIBUTIVE ANODE GROUNDBED SYSTEMS....... 84
12.3 MIXED METAL OXIDE (MMO) / PRECIOUS METAL OXIDE (PMO)
ANODES .................................................................................................................. 85
12.4 ANODE DIMENSIONS AND TITANIUM SUBSTRATE GRADES.................... 86
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PAGE12.5 ANODE LOADING AND OPERATING PARAMETERS..................................... 88
12.6 ANODE CABLE CONNECTION............................................................................ 89
12.7 CHEMICAL AND PERFORMANCE TESTING OF ANODES............................. 90
13 IMPRESSED CURRENT CARBONACEOUS ANODE BACKFILL MATERIAL .... 91
13.1 INTRODUCTION AND GENERAL CONSIDERATIONS.................................... 91
13.2 CHEMICAL COMPOSITION.................................................................................. 92
13.3 PARTICLE SIZE DISTRIBUTION (PSD) .............................................................. 92
13.4 SHIPPING AND PACKAGING............................................................................... 93
14 CATHODIC PROTECTION CABLING.......................................................................... 93
14.1 INTRODUCTION .................................................................................................... 93
14.2 GENERAL PROPERTIES OF INSULATING COMPOUNDS.............................. 94
14.3 CABLE AND CABLE INSULATION COMPLIANCE.......................................... 95
14.4 CP CABLE REQUIREMENTS................................................................................ 96
14.5 CABLE INSTALLATION AND IDENTIFICATION............................................. 97
15 EXOTHERMIC WELDING / PIN BRAZING CABLE CONNECTION DETAILS ... 9715.1 CABLE CONNECTIONS TO PIPES AND REPAIR TO COATINGS .................. 97
15.2 SURFACE PREPARATION.................................................................................... 98
15.3 PIN BRAZING / EXOTHERMIC WELDING......................................................... 98
15.4 TESTING.................................................................................................................. 99
15.5 WELD POWDER / CABLE COMBINATION........................................................ 99
15.6 PRECAUTIONS..................................................................................................... 100
15.7 REINSTATEMENT OF THE COATING SYSTEM ............................................. 101
16 PERMANENT REFERENCE ELECTRODES.............................................................. 101
16.1 GENERAL CONSIDERATIONS .......................................................................... 101
16.2 MANUFACTURER QUALIFICATIONS ............................................................. 101
16.3 PERMANENT REFERENCE ELECTRODE (PRE) CONSTRUCTION ............. 101
16.4 PERMANENT REFERENCE ELECTRODE (PRE) STABILITY........................ 103
17 CATHODIC PROTECTION TEST POINTS................................................................. 103
17.1 INTRODUCTION .................................................................................................. 103
17.2 LOCATION OF TEST POSTS / STATIONS ........................................................ 10417.3 TYPICAL CP TEST POSTS .................................................................................. 105
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PAGE18 SOLID STATE DC DECOUPLING DEVICES ............................................................. 108
18.1 INTRODUCTION .................................................................................................. 108
18.2 ELECTRICAL CONSTRUCTION ........................................................................ 109
18.3 ENCLOSURE CONSTRUCTION ......................................................................... 111
18.4 INSPECTION AND TESTING .............................................................................. 111
18.5 DOCUMENTATION.............................................................................................. 112
18.6 GUARANTEE ........................................................................................................ 112
18.7 MANUFACTURER QUALIFICATIONS ............................................................. 112
19 INSULATING FLANGE MATERIALS ......................................................................... 113
19.1 GENERAL CONSIDERATIONS .......................................................................... 113
19.2 MATERIAL SPECIFICATIONS ........................................................................... 113
19.3 IDENTIFICATION / LABELS, OPERATING INSULATING FLANGE, NO
ATTACHMENTS TO PIPEWORK PERMITTED .............................................. 115
19.4 MONOLITHIC INSULATING JOINTS................................................................ 115
19.5 INTERNAL PIPE LINING FOR COOLING WATER SERVICE ........................ 116
20 HIGH POTENTIAL SACRIFICIAL MAGNESIUM ANODES (SOIL USE)............. 120
20.1 GENERAL CONSIDERATIONS .......................................................................... 120
20.2 MAGNESIUM ANODE CHEMICAL COMPOSITION....................................... 121
20.3 HIGH POTENTIAL MAGNESIUM ANODE PHYSICAL PROPERTIES .......... 121
20.4 ANODE CABLE AND CABLE CONNECTION.................................................. 122
20.5 ELECTROCHEMICAL PROPERTIES ................................................................. 123
20.6 TESTING AND REVIEWAL................................................................................. 123
20.7 TYPICAL INSTALLATION DETAILS ................................................................ 123
21 AC MITIGATION EARTH ELECTRODE.................................................................... 124
21.1 ZINC TUBE MATERIAL SPECIFICATION........................................................ 124
21.2 ZINC TUBE DIMENSIONS .................................................................................. 125
21.3 ZINC TUBE CHEMICAL COMPOSITION.......................................................... 125
21.4 HARDNESS MEASUREMENTS.......................................................................... 125
21.5 METALLOGRAPHY............................................................................................. 126
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SASOL SPECIFICATION SP-60-18
CATHODIC PROTECTION
1
1.1
1.1.1
a.
b.
c.
d.
e.
1.1.2
1.1.3
GENERAL
SCOPE
This Specification defines the minimum and mandatory requirements governing the design,
application, installation and commissioning of a Cathodic Protection (CP) system for the
following:
Pipelines, process, fire water, cooling water and utility piping, as well as pipes located
inside chambers;
Pipeline casings (cased crossings);
On-grade storage tank bottoms and the internal surface of storage tanks;
Well casings;
Water boxes of heat exchangers,
installed inside and / or outside the SASOL plant(s) battery limits.
In the event of any detail that is not fully addressed in this specification and that is warranted
to be carried out by the contractor, the work shall be performed in accordance with the
relevant applicable codes and best recognised engineering practices in the CP industry. The
contractor shall develop detailed specifications, procedures and method statements required
to perform the CP design during the engineering phase of work and this shall be submitted to
SASOL for review and approval prior to construction, supply and / or installation work.
The specification covers the general requirements of the CP system. CP may be achieved
through the use of Sacrificial Anode CP (SACP) or Impressed Current CP (ICCP).
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1.1.4
1.1.5
1.2
a.
b.
c.
d.
e.
1.3
AC interference mitigation may be achieved through the use of pipeline-earth grounding
systems, in conjunction with solid state DC decoupling devices. It must not adversely affect
or interfere with the CP system.
The details and extent of the plant or structure equipment required to be cathodically
protected, the site / locality and the meteorological data shall be both specified and supplied
by SASOL and / or the main contractor.
LEGAL REQUIREMENTS
The SASOL factories are subject to the statutory requirements of the following Acts and all
CP installations shall meet the requirements of these Acts:
The National Environmental Management Act (NEMA) - Act 107 of 1998;
The Occupational Health and Safety Act with Regulations - Act 85 of 1993;
The Mine Health and Safety Act - Act 29 of 1996;
The Minerals Act - Act 50 of 1991;
The National Water Act - Act 36 of 1998.
ABBREVIATIONS
The following CP abbreviations have been used:
A Ampere
A / m Ampere per metre square
AC Alternating Current
AFC Approved For Construction
A.hr / kg Ampere hours per kilogram (Electro-chemical Consumption Rate)
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Al Aluminium
API American Petroleum Institute
A.y Ampere-years
AQL Acceptable Quality Level
ASME American Society of Mechanical Engineers
ASTM American Society for the Testing of Materials
Br Bromine
BSI British Standards Institute
C Carbon
CD Current Drainage
CIP Close Interval Potential
COC Certificate of Compliance
CP Cathodic Protection
Cr Chromium
Cu Copper
CuSO4 Copper Sulphate
Cu-Ti Copper - Titanium
DB Distribution Board
DC Direct Current
DCVG Direct Current Voltage Gradient
DIN Deutsche Institut fr Normung
ECTFE Ethyl Carbo Tetra-Fluoro-Ethylene
EPR Earth Potential Rise
ETFE Ethyl Tetra-Fluoro-Ethylene
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Ex Hazardous Classified Equipment
EXW Exothermic Welding
F Fluorine
FBE Fusion Bonded Epoxy
Fe Iron
Fe-Si Silicone Iron
FDU Forced Drainage Unit
GC Grounding Cell
g / ml grams per millilitre
GIS Geographical Information System
GPS Global Positioning System
H2SO4 Sulphuric Acid
HDPE High Density Polyethylene
HMWPE High Molecular Weight Polyethylene
HVTL High Voltage Transmission Line / High Voltage Power Line
Hz Hertz
ICCP Impressed Current Cathodic Protection
ID Inner Diameter
IEC International Electrotechnical Commission
IJ Insulating Joint
IF Insulating Flange
IP Ingress Protection
IR Ohmic Voltage Drop
ISO International Organisation for Standardisation
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IrO2 Iridium Oxide
kg kilogram
kg / m kilogram per cubic metre
kPa kilopascal
kV kilovolt
kV / mm kilovolt per millimetre
kW kilowatt
LCD Liquid Crystal Display
LMPE Low Molecular Weight Polyethylene
m metre
mA / m Milli-ampere per Square Metre
Mg Magnesium
mH Milli-henry
m Milli-ohm
mA Milli-ampere
MIC Microbial Induced Corrosion
Mil Thousandth of an Inch
MMO Mixed Metal Oxide
MMP Maximum Meter Point
MMWPE Medium Molecular Weight Polyethylene
Mn Manganese
Mo Molybdenum
MON Monitor
MOV Metal Oxide Varistor
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MPa Megapascal
mV Milli-volt
mV / C Milli-volt per Degree Celsius
NACE National Association of Corrosion Engineers
NDU Natural Drainage Unit
NDT Non Destructive Testing
NPS Nominal Pipe Size
OD Outer Diameter
OMM Operation and Maintenance Manual
OWS Oily Water Sewer
PC Printed Circuit
PCB Polycarbonate Based
PDF Portable Document Format
PE Polyethylene
pH Level of Acidity or Alkalinity
PIV Peak Inverse Voltage
PMO Precious Metal Oxide
PO Purchase Order
PPI Probable Performance Index
PPM Parts Per Million
PRE Permanent Reference Electrode
PSD Particle Size Distribution
psi Pounds Per Square Inch
P-TP Plant Test Post
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PTFE Poly-Tetra-Fluoro-Ethylene
PVC Poly-Vinyl-Chloride
PVDF Poly-Vinylidene Fluoride
QCP Quality Control Plan
Pub Publication
RE Reference Electrode
RFQ Request For Quotation
RMS Root Mean Square
RP Recommended Practice
R-TP Recording Test Posts
SAACE South African Association of Consulting Engineers
SABS South African Bureau of Standards
SACP Sacrificial Anode Cathodic Protection
SANS South African National Standards
SEM Scanning Electron Microscope
Si Silicon
SI System International
SIS Swedish Standards Institution
SP Specification
SPIR Spare Parts Interchange-ability Record
SRB Sulphate Reducing Bacteria
SS Stainless Steel
SS-DCD Solid State - Direct Current Decoupling Device
STDD Standard Drawing
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SWA Steel Wire Armour
Ta Tantalum
Ta2O5 Tantalum Oxide
TDS Technical Data Sheet
Ti Titanium
TP Test Point / Test Post
TP-R Reference Monitoring Test Post
TRU Transformer Rectifier Unit
V Volt
+VE Positive Terminal
-VE Negative Terminal
XLPE Cross-linked Polyethylene
Zn Zinc
% IR Percentage Ohmic Voltage Drop
% Percentage
C Degrees Celsius
F Degrees Fahrenheit
micro
m micro metre
s micro second
.m micro Ohm metre (unit of measurement for resistivity)
Ohm
cm Ohm Centimetre
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1.4 DEFINITIONS
ANAEROBIC Oxygen deficient environment.
ANAEROBIC BACTERIA Also called sulphate reducing bacteria. A type of bacteria
which corrodes steel and is present only in the absence of
oxygen (anaerobic). When they are present, the protective
potential must be raised to -0,95 V.
ANODE DISTRIBUTIONCABINET
A steel cabinet containing a bulbar to which is joined theanode cables as well as the main anode groundbed ring main
cable(s).
ANODIC GRADIENT Gradient arising in the soil due to the current flow through
the soil from the anode(s).
ANODE GROUNDBED An anode groundbed consisting of a number of impressed
current anodes joined to a common positive rectifier cable.
The anodes are encapsulated in coke to increase their life and
decrease the resistance to earth. The anode groundbed is onaverage 100 m to 150 m long and a minimum of 2,5 m deep.
APPROVAL OR
APPROVED BY SASOL
Written agreement or authorisation by SASOL. All requests
for approval shall be submitted in writing and any proposed
deviation from the specified requirements shall be fully
explained and motivated.
ANODE (IMPRESSED
CURRENT)
Any buried or submerged metal (or graphite) which is
connected to the positive terminal of a transformer rectifier
and serves to introduce current into the earth. CP anodes
normally consist of a silicon iron alloy, containing 14% to
17% silicon, and measuring 1,1 m long and 0,075 m
diameter. Centrifugally cast tubular anodes have proven to
be the most reliable and effective anodes at SASOL.
Generally an anode is defined as any metal in which current
flows from it to the electrolyte.
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ANODE (SACRIFICIAL) A metal which is more electro-negative in potential than
steel and which when buried or immersed confers protection
to the latter when electrically connected to it. For buried
pipelines sacrificial anodes generally consist of magnesium.
ANODIC AND CATHODIC
AREAS
See Corrosion.
BONDING CABINET A steel cabinet used to bond two or more pipelines
electrically.
BYPASS CURRENT The current drained from a pipeline to a railway line, when
the latter is at very negative potential. Under such conditions,
the transformer rectifier temporarily shuts down.
CATHODE (IMPRESSED
CURRENT)
Any buried or submerged metal which is connected to the
negative terminal of a transformer rectifier. Generally a
cathode is defined as any metal in which current flow is
always from the earth to the cathode.
CATHODIC PROTECTION An active electrochemical method of corrosion protection in
which all areas of a metallic surface are rendered cathodic.
CLOSE POTENTIAL
SURVEY
A technique whereby the pipe potential is measured every
metre along the length of the pipeline.
COKE An electrically conducting form of carbon. It is used in
granular form to surround each individual anode in order to
form one long extended anode, termed the anode groundbed.
It decreases the resistance to earth and increases the life ofthe individual anodes.
COKE BREEZE An inferior carbonaceous backfill material generally termed
metallurgical coke or coke breeze. It nominally contains less
than 85% fixed carbon and high amounts of sulphur and ash.
CONTINUITY BOND An electric cable welded to both sides of a potentially
insulating joint, such as a coupling or flange, in order to
ensure the electrical continuity.
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CONTRACTOR /
MANUFACTURER
Company engaged to perform the work covered by the
specification (successful supplier or bidder).
CORROSION An electrochemical process resulting in metal dissolution
and degradation. A buried or submerged metal forms anodic
and cathodic areas on its surface with consequent flow of
electric current between them. Corrosion occurs at the anodic
areas.
DATA SHEETS All necessary drawings, tabulations, sketches and relevant
documentation which SASOL will submit with a RFQ or PO,
to clearly indicate the technical, electrical and physical
requirements of the equipment, together with information
that is required to be submitted by the manufacturer.
DC DECOUPLING
DEVICE
A solid state device used for two main purposes. One is to
disconnect two metal systems, of which one is under CP and
the other is not, while at the same time permitting continuity
in any AC circuit, for example an earthing system connectedto a pipeline via this device. The other use is as a surge
arrester whereby it blocks DC voltages up to several volts,
but readily passes current at higher voltages (e.g. AC fault
currents and lightning). Its operation does not depend on the
moisture content of the soil, is easily inspected, tested and
more reliable than a polarisation cell or grounding cell.
DEEP WELL GROUND-
BED
One or more anodes installed vertically in a column, the top
most anode being at a nominal depth of 15 m or more below
the earths surface.
DRAIN POINT That part of the pipeline connected to the negative terminal
of the TRU.
EARTHING The technique of using a buried electrode in order to
decrease the voltage to earth of a particular structure.
ELECTRODE An electrode is a solid electrical conductor which discharges,
or picks up, current from an electrolyte.
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ELECTRODE
(REFERENCE
ELECTRODE [HALF
CELL])
The voltage difference between an electrode and the
electrolyte cannot be measured in absolute terms, but only
with respect to a special reference electrode, whose own
potential does not alter regardless of the solution in which it
is immersed. A reference electrode is also referred to as a
half cell. In CP of buried pipelines, a copper / copper
sulphate reference electrode (Cu / CuSO4) is used.
It consists of a copper rod in a saturated copper sulphatesolution, all housed in a suitable polymer housing and
possesses a porous plug at the bottom to permit current to
flow, enabling one to take potential measurements.
ELECTROLYSIS
(ELECTROLYTIC
CORROSION)
Electrolysis or electrolytic corrosion refers to the corrosion
caused by stray electric currents flowing in the ground. 1 A
flowing for 1 year corrodes 9 kg of steel.
ELECTROLYTE A medium, usually liquid, in which the flow of electric
current is by means of cations and anions. Typicalelectrolytes are water and its solutions, acids, etc., and the
soil.
EXOTHERMIC WELDING The universal method of welding a copper cable to a steel
surface. The method is quick and simple and generates far
less heat than brazing or arc welding, which would otherwise
damage the coating and lining. Pin brazing / stud welding is
a newer and quicker method, which generates far less heat
than exothermic welding, but is very costly in comparison.
FORCED DRAINAGE
UNIT
A transformer rectifier using the railway line as the anode is
referred to as a forced drainage unit.
FOREIGN SERVICE A structure lying or buried in the ground belonging to
another owner. Typical examples are pipelines, cables,
railway lines and electricity pylons.
GALVANIC CORROSION A form of corrosion caused by one metal in electrical
contact with another and at different natural potentials or
separated in the galvanic series.
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HALF CELL Another name for reference electrode. See Electrode.
HOLIDAY A defect in the structure coating system also referred to as
coating defects.
HOLIDAY DETECTOR An instrument for detecting coating defects.
HYGROSCOPIC A material that has a high affinity for water.
INORGANIC Compounds composed of elements other than carbon. A few
simple compounds of carbon including carbon monoxide,
carbon dioxide, carbonates and cyanides, are generally
considered inorganic.
INSULATING JOINT /
FLANGE
A joint which is electrically insulating. An insulating flange
normally consists of an insulating gasket, insulating bolt
sleeves and insulating washers. An insulating joint is a
complete joint consisting of insulating epoxies embedded in
a spigot and socket type joint. An insulating joint nominally
cost six to eight times more than an insulting flange.
METAL OXIDE
VARISTOR
A metal oxide varistor is an electrical device used as a
voltage arrester. It has a high resistance at low voltages and
low resistance at high voltages.
MONOLITHIC JOINT Immovable (flange-less) electrical insulating fitting rated to
handle the operating pipe pressure.
NATIVE STATE Natural state or potential of a pipeline or structure.
NATURAL DRAINAGEUNIT
A unidirectional bond from a pipeline to an electrifiedrailway line. It permits current flow only when the rail is at
negative potential and consists of one or more diodes, fuses,
surge arresters, etc. It is a passive device requiring no
external source of power.
NATURAL POTENTIAL Also called the corrosion potential. It is the potential of
steel buried in the ground without receiving current from an
external source.
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OVER PROTECTION When the pipe potential is too negative, the coating may be
damaged in the sense that it becomes detached from the steel
pipe, also referred to as cathodic disbondment. There is no
universal agreement as to what the maximum negative value
should be, but the most commonly accepted value of -2,5 V
is used, where no stray currents are present. This potential
must exclude the IR error associated with normal potential
measurements.
PIPE INVERT DEPTH Depth of ground cover from surface to the bottom of the
pipe.
PIPE OVERT DEPTH Depth of ground cover from surface to the top of the pipe.
PIPE POTENTIAL The voltage difference between a pipeline and a reference
electrode inserted in the ground (also known as pipe-to-soil
potential).
POLARISATION The change in metal potential upon passage of current. The
normal potential of steel in the ground is about -0,5 V and if
current enters it via the electrolyte the potential will become
more negative, say -1,0 V.
Polarisation can take place slowly over weeks or months, by
which the potential becomes even more negative and the
current required diminishes. The latter depends on the
coating quality.
POLARISATION CELL A DC electrolytic varistor / decoupling device. It consists of
two metal plates in a suitable electrolyte. The cell passes AC
at all voltages but blocks DC below a certain voltage, but
conducts above a certain voltage limit. By choosing different
metals and electrolytes a number of different blocking
voltages may be achieved. The steady state AC is generally
limited to 0,01% of the maximum surge current. The cells
need constant toping up and cleaning and are not as reliable
as a solid state device.
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PROTECTION LIMITS The limits in pipe potential between which a cathodically
protected pipe should operate. The lower limit is -0,95 V for
complete corrosion protection of the steel substrate, and the
upper limit is -2,5 V in order to avoid coating damage. The
value of -2,5 V is often impossible to adhere to in the
presence of stray currents.
PROTECTION
POTENTIAL
The minimum IR free pipe potential in order to achieve
protection. It varies from metal to metal. The protectionpotential for steel ranges between -0,85 V to -0,95 V
depending on the oxygen content of the electrolyte.
RAIL RECORDING The potential of the rail (fluctuation) recorded over time.
REVIEWED/REVIEWAL A formal 5-day hold period on the planning schedule while
SASOL reviews / considers the relevant information or
proposed deviations; all communication to be confirmed in
writing
SILICON IRON ANODES See Impressed Current Anode.
SOIL AND PIPELINE
VOLTAGE GRADIENTS
The voltage gradients arising in the soil in the immediate
vicinity of coating defects, as the current flows (CP or DC
traction) to the bare steel (coating defect) through, the soil.
SOIL RESISTIVITY The specific electrical resistance of the soil. The lower the
resistivity, the higher the corrosivity of the soil. It is
commonly measured on site by a technique called the
Wenner Four method.
STRAY CURRENTS (DC) The flow of DC electric currents in the ground which follow
a course other than that intended. The most frequent cause of
DC stray currents is from electrified railway lines, and of a
fluctuating nature. Another source is that from adjacent CP
systems.
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TEST POINT Consists of a cable welded to the pipe or cleated to the
inside of a chamber wall and connected to an insulated
stainless steel stud protruding through the wall. It permits a
quick and vandal resistant method of measuring the pipe
potential. The potential measurement will however, contain
the IR error.
TEST POST A free standing post protruding about 0,6 m above the
ground and containing a cable welded to the pipe andextending to the top in a suitable terminal. It permits the
ready determination of the On pipe potential at any
location.
TRANSFORMER
RECTIFIER UNIT
An electrical apparatus which converts AC voltages to low
DC voltages.
UNDER- PROTECTION When the pipe is only partially protected, which is indicated
by a potential of between -0,7 V to -0,85 V.
VIKING JOHNSON
COUPLING
A flexible coupling used to mechanically join two sections
of steel, plastic or concrete pipe materials.
VOLTAGE SURGES Also called voltage transients. A voltage, higher than
normal operating voltage, generally of short duration, which
enters the transformer rectifier or natural drainage unit
(NDU), either from the AC or DC side. It does great
damage unless measures are taken to contain it.
WENNER FOUR
ELECTRODE METHOD
A soil resistivity test method covered in ASTM G57,
utilising four electrodes spaced equidistant to one another.
The electrode separation distance equates to the average
depth measured in the soil. Current is injected into the outer
two electrodes and the potential drop is measured between
the inner two electrodes and the resistivity is then calculated.
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1.5 PRECEDENCE
Any conflict between the technical requirements stated in the RFQ or PO and the technical
requirements of this Specification shall be referred to SASOL for clarification. The
precedence of purchase documents is as follows:
a.
b.
c.
d.
1.6
1.7
The technical requirements specified in the RFQ or PO including terms, conditions
and legal requirements;
Data sheets;
This Specification;
Documents referenced in this Specification.
MATERIAL REQUIREMENTS
The material requirements shall detail all of the necessary drawings, tabulations, sketches,
technical data, materials specification and relevant documentation which will be issued with
a RFQ and / or PO.
The latter shall clearly indicate the technical, electrical, metallurgical and physical
requirements of any equipment, together with the information that is required to be
submitted by the manufacturer.
GUARANTEE PERIOD
The contractor shall guarantee the CP system for a 36 month period, which shall commence
from the date of commissioning.
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2 REFERENCE DOCUMENTS
Where reference is made to a code, specification or standard, the reference shall be taken to
mean the latest edition of the code, specification or standard, including addenda,
supplements and revisions thereto.
2.1 SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTH AFRICAN
BUREAU OF STANDARDS (SABS) CODES OF PRACTICE AND SPECIFICATIONS
SANS 10086-1 / SABS 086 The installation, inspection and maintenance of
equipment used in explosive atmospheres Part 1:
Installations including surface installations on mines
SANS 10089-2 / SABS 089-2 The petroleum industry Part 2: Electrical
installations in the distribution and marketing sector
SANS 10108 / SABS 0108 The classification of hazardous locations and the
selection of apparatus for use in such locations
SANS 10121 / SABS 0121 Cathodic protection of buried and submerged
structures
SANS 10142-1 / SABS 0142-1 The wiring of premises Part 1: Low-voltage
installations
SANS 10199 / SABS 0199 The design and installation of an earth electrode
specifications
SANS 122 / SABS 122 Pressure-sensitive adhesive tapes for electrical
purposes (Metric units)
SANS 1700-7 /SABS 1700-7 Fasteners Part 7: External drive hexagon bolts and
screws Section 1 - 10: Hexagon head bolts - Product
grades A and B
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SANS 1700-14 / SABS 1700-14 Hexagon nuts Section 1: Style 1 - Product grades A
and B
SANS 1700-7-2 / SABS 1700-7-2 Fasteners Part 7: External drive hexagon bolts and
screws Section 2: Hexagon head bolts - Product
grade B - Reduced shank (shank diameter
approximately equal to pitch diameter)
SANS 1700-7-3 / SABS 1700-7-3 Fasteners Part 7: External drive hexagon bolts and
screws Section 3: Hexagon head bolts - Product
grade C
SANS 1700-7-4 / SABS 1700-7-4 Fasteners Part 7: External drive hexagon bolts and
screws Section 4: Hexagon head screws - Product
grades A and B
SANS 1700-7-5 / SABS 1700-7-5 Fasteners Part 7: External drive hexagon bolts andscrews Section 5: Hexagon head screws - Product
grade C
SANS 1700-14-1 / SABS 1700-14-1 Fasteners Part 14: Hexagon nuts Section 1: Style 1 -
Product grades A and B
SANS 1700-14-2 / SABS 1700-14-2 Fasteners Part 14: Hexagon nuts Section 2: Style 2 -
Product grades A and B
SANS 1700-14-3 / SABS 1700-14-3 Fasteners Part 14: Hexagon nuts Section 3: Product
grade C
SANS 1700-14-4 / SABS 1700-14-4 Fasteners Part 14: Hexagon nuts Section 4: Hexagon
thin nuts (chamfered) - Product grades A and B
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SANS 32 / SABS EN 10240 Internal and / or external protective coatings for steel
tubes - Specification for hot dip galvanized coatings
applied in automatic plants
SANS 1411-1 / SABS 1411-1 Materials of insulated electric cables and flexible
cords Part 1: Conductors
SANS 1411-2 / SABS 1411-2 Materials of insulated electric cables and flexible
cords Part 2: Poly-Vinyl-Chloride (PVC)
SANS 1411-3 / SABS 1411-3 Materials of insulated electric cables and flexible
cords Part 3: Elastomers
SANS 1411-4 / SABS 1411-4 Materials of insulated electric cables and flexible
cords Part 4: Cross-linked Polyethylene (XLPE)
SANS 1411-5 / SABS 1411-5 Materials of insulated electric cables and flexible
cords Part 5: Halogen-free, flame-retardant materials
SANS 1411-6 / SABS 1411-6 Materials of insulated electric cables and flexible
cords Part 6: Armour
SANS 1507-1 / SABS 1507-1 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to
1900 / 3300 V) Part 1: General
SANS 1507-2 / SABS 1507-2 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to 1900
/ 3300 V) Part 2: Wiring cables
SANS 1507-3 / SABS 1507-3 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to 1900
/ 3300 V) Part 3: PVC distribution cables
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SANS 1507-4 / SABS 1507-4 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to
1900 / 3300 V) Part 4: XLPE distribution cables
SANS 1507-5 / SABS 1507-5 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to
1900 / 3300 V) Part 5: Halogen-free distribution
cables
SANS 1507-6 / SABS 1507-6 Electric cables with extruded solid dielectric
insulation for fixed installations (300 / 500 V to 1900
/ 3300 V) Part 6: Service cables
SANS 555 / SABS 555 Unused and reclaimed mineral insulating oils for
transformers and switchgear
SANS 1149 / SABS 1149 Flat and taper steel washers
2.2
2.3
SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTH AFRICAN
BUREAU OF STANDARDS / INTERNATIONAL ELECTROTECHNICAL
COMMISSION (SABS IEC) SPECIFICATIONS
SANS 60079-10 / SABS IEC 60079-10 Electrical apparatus for explosive gas
atmospheres Part 10: Classification of
hazardous areas
SOUTH AFRICAN NATIONAL STANDARDS (SANS) AND SOUTH AFRICAN
BUREAU OF STANDARDS / INTERNATIONAL ORGANISATION FOR
STANDARDISATION (SABS ISO) STANDARDS
SANS 121 / SABS ISO 1461 Hot dip galvanized coatings on fabricated iron and steel
articles - Specifications and test methods
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2.4 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) STANDARDS
ASME B31.4 Liquid transportation systems for hydrocarbons, liquid petroleum gas,
anhydrous ammonia and alcohols
ASME B31.8 Gas transmission and distribution systems
2.5
AMERICAN SOCIETY FOR THE TESTING OF MATERIALS (ASTM)
ASTM A325 Standard specification for structural bolts, steel and heat treated, 120 /
105 psi minimum tensile strength
ASTM A694 Standard specification for carbon and alloy steel forgings for pipe
flanges, fittings, valves and parts for high-pressure transmission
service
ASTM B265 Standard specification for titanium and titanium alloy strip, sheet andplate
ASTM B338 Standard specification for seamless and welded titanium and titanium
alloy tubes for condensers and heat exchangers
ASTM A518 Specification for corrosion resistant high silicon iron castings
ASTM B571 Standard practice for qualitative adhesion testing of metallic coatings
ASTM D149 Standard test method for dielectric breakdown voltage
ASTM D229 Standard test method for rigid sheet and plate material used for
electrical insulation
ASTM D293 Standard test method for sieve analysis of coke
ASTM D709 Standard test method for laminated thermosetting materials
ASTM D732 Standard test method for shear strength of plastics by punch tool
ASTM D785 Standard test method for Rockwell hardness of plastics and electrical
insulating materials
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ASTM D1248 Polyethylene plastic moulding and extrusion materials
ASTM D2000 Standard classification system for rubber products
ASTM D3222 Standard specification for unmodified Poly-Vinylidene Fluoride
(PVDF) moulding extrusion and coating material
ASTM E186 Standard reference radiographs for heavy walled (51 to 114 mm) steel
castings
ASTM G57 Method for field measurement of soil resistivity using the Wenner
Four Electrode method
2.6
2.7
AMERICAN PETROLEUM INSTITUTE (API)
API Std 620 Design and Construction of Large, Welded Low-Pressure Storage
Tanks
API Std 650 Welded Steel Tanks for Oil Storage
API RP651 Cathodic Protection of Aboveground Petroleum Storage Tanks
API RP1632 Cathodic Protection of Underground Petroleum Storage Tanks and
Piping Systems
API RP2003 Protection against Ignitions Arising out of Static, Lightning and Stray
Currents
NATIONAL ASSOCIATION OF CORROSION ENGINEERS (NACE) RECOMMENDED
PRACTICES
NACE RP0169 Control of external corrosion on under ground or submerged, metallic
piping systems
NACE RP0177 Mitigation of alternating current and lightning effects on metallic
structures and corrosion control systems
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NACE RP0186 Application of cathodic protection for well casings
NACE RP0193 External cathodic protection of on-grade carbon steel storage tank
bottoms
NACE RP0285 Corrosion control of under ground storage tank systems by cathodic
protection
NACE RP0286 Electrical isolation of cathodically protected pipelines
NACE RP0388 Impressed current cathodic protection of internal submerged surfaces
of steel water storage tanks
NACE RP0572 Design, installation, operation and maintenance of impressed current
deep groundbeds
NACE RP0575 Recommended practice for design, installation, operation and
maintenance of internal cathodic protection system in oil treating
vessels
NACE Pub10A190 Measurement techniques related to criteria for cathodic protection of
underground or submerged steel piping systems
2.8
BRITISH STANDARDS INSTITUTION (BS) SPECIFICATIONS
BS 171 Specification for power transformers
BS 1016 Method for analysing and testing of coal and coke
BS 1591 Specification for corrosion resisting high silicon iron castings
BS 1872 Specification of electroplated coatings on tin
BS 6001 (ISO 2859-1) Sampling procedures for inspection by attributes
Part 1: Specification for sampling plans indexed by acceptable quality
levels (AQL) for lot-by-lot inspection
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BS 7361 Cathodic Protection
Part 1: Code of practice for land and marine applications
2.9
2.10
2.11
2.12
RAL DEUTSCHES INSTITUT FR GTESICHERUNG UND KENNZEICHNUNG
RAL-FARBEN
RAL Specification for Colours for Identification, Coding and Special Purposes
DEUTSCHES INSTITUT FR NORMUNG (DIN)
DIN 30676 Design and application of cathodic protection of external surfaces
DIN 50918 Corrosion of metals, electrochemical corrosion tests
DIN 50925 Verification of the effectiveness of the cathodic protection of buried
structures
DIN 50929 Probability of corrosion of metallic materials when subject to corrosion from
the outside
INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC) PUBLICATIONS
IEC 60038 Standard voltages
IEC 60144 Degree of protection of enclosures for low voltage switchgear and control
gear
INTERNATIONAL ORGANISATION FOR STANDARDISATION (ISO) STANDARDS
ISO 2325 Method for analysing and testing of coal and coke
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ISO 2859-1 Sampling procedures for inspection by attributes
Part 1: Specification for sampling plans indexed by Acceptable
Quality Levels (AQL) For Lot-by-Lot inspection
ISO 8501-1 Preparation of steel substrates before application of paints and
related products
Part 1 to 3 and supplement 1994
ISO 13 623: 2000E CP monitoring plan
2.13
2.14
2.14.1
SWEDISH STANDARDS INSTITUTION (SIS) STANDARDS
SIS 05 59 00 Pictorial visual standards for surface preparation for the painting of steel
surfaces
SASOL SPECIFICATIONS, DATA SHEETS AND STANDARD DRAWINGS
Specifications
SP-40-3 Spare parts requirements
SP-50-6 Coating and wrapping of under ground steel pipe
SP-50-7 Design of under ground gravity sewers
SP-60-1 General electrical specification
SP-60-4 Low voltage switchgear and motor control centres
SP-60-10 Power and control cables rated 600 / 1000 V
SP-60-35 Earthing systems
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SP-60-37 Classification of hazardous locations and the selection of apparatus for use in
such locations
SP-60-47 Requirements for electrical engineering documentation
SP-90-32 Minimum requirements for SASOL engineering drawings
SP-90-37 End of job documentation deliverables
2.14.2
2.14.3
Data Sheets
E979 Spare Parts and Interchange-ability Record (SPIR)
Standard Drawings
STDD-6005CA Electrical CP general assembly G-026 to G-028
STDD-6005CB Electrical CP general assembly G-030
STDD-6005CD Electrical CP connection assembly G-034 to G-036
STDD-6005CN Electrical CP manual output transformer rectifier
STDD-6005CP Electrical CP details of thermit weld
STDD-6005CQ Electrical CP insulating flange
STDD-6005CR Electrical CP junction box test point
STDD-6005CS Electrical CP cabling at tanks located in tank farms
STDD-6005CT Electrical CP schematic diagram of variable voltage DC decoupler
STDD-6005CU Electrical CP encapsulating of anode head
STDD-6005CV Electrical CP electronic controller
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STDD-6005CW Electrical CP data logger post
STDD-6005CX Electrical CP potential test point details
STDD-6005CY Electrical CP insulating joint details
STDD-6005CZ Electrical CP high potential magnesium and cable connection details
3
3.1
3.1.1
3.1.2
3.1.3
CP SYSTEM REQUIREMENTS
SPECIALIST CP CONSULTANT AND CP CONTRACTOR
SASOL and / or the main contractor shall appoint a specialist sub-consultant in order to carry
out a detailed site survey, to permit the drafting of both a conceptual and detailed CP design,
should they be warranted. The detailed design shall only be carried out upon the reviewal of
the conceptual design by SASOL.
The design of the CP system shall be carried out by a SASOL approved consultant. The CP
consultant shall be completely independent as defined by the Southern African Association
of Consulting Engineers (SAACE). The main contractor shall assist the CP consultant with
drawings to permit the AFC drawings to be issued. The CP consultant shall prepare and
submit to the main contractor / SASOL a detailed list of all materials and equipment required
permitting the relevant RFQ document to be formulated.
The CP construction contractor shall install the CP field installation elements, concurrently
with the construction of the associated process plant and / or pipeline. The CP consultant
shall provide field engineering support and site supervision necessary to ensure the integrity
of the as-built CP installation. The CP consultant shall prepare a quality control plan for the
progressive checkout and acceptance of the CP installation and assist the main contractor in
its implementation.
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3.1.4 The CP consultant shall assist in the checkout, testing and commissioning of the installation
and the marking-up of AFC drawings to reflect the as-built status. He shall also submit a
final commissioning report in accordance with the requirements stipulated below.
3.2
3.2.1
a.
i)
ii)
iii)
iv)
ON SITE INVESTIGATIONS / SURVEY
The following surveys shall be carried out by the CP consultant prior to commencing with
the design:
Soil Corrosivity Survey
Distribution / transmission pipelines
Soil resistivity measurements shall be conducted nominally every 250 m along
the pipeline route in accordance with the Wenner Four Electrode Method, as
stipulated in ASTM G57 at pipe invert depth. Where corrosive areas are
encountered or at locations where temporary CP will be required or where it isto be anticipated, measurements will be conducted every 50 m or as required.
Alternatively, an electromagnetic soil conductivity meter may be used, on long
remote pipelines. Measurements shall be carried out every 50 m at pipe invert
and overt depth.
Soil samples shall be taken at pipe invert depth or proposed burial depth along
the pipeline route nominally every 1000 m. The samples shall be analysed and
assessed in accordance with DIN 90529 Part 1 to 3, in order to determine thePPI of the proposed or existing buried steel pipe.
The presence and probable magnitude of SRB shall be assessed every 1000 m
and / or at corrosive locations where the soil resistivity is less than 30 m.
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b. Petrochemical plants
i)
ii)
iii)
iv)
v)
3.2.2
a.
i)
ii)
Soil resistivity measurements shall be conducted accordance with the Wenner
Four Electrode Method, as stipulated in ASTM G57. The measurements shall be
carried out in a 50 m x 50 m grid section at a depth of 0,5 m, 1,5 m, 2,5 m and
3,5 m per grid section.
Soil samples shall be taken at pipe invert depth or proposed burial depth across
the site in accordance with BS 6001: Part1. The samples shall be analysed and
assessed in accordance with DIN 90529 Part 1 to 3, in order to determine the
PPI of the proposed or existing buried steel pipe.
The presence and probable magnitude of SRB shall be assessed per 50 m x
50 m grid section, but only where the soil resistivity is less than 30 m.
Where on-grade carbon steel storage tank bottoms are encountered, all of the
items described in Section 3, of NACE RP0193, shall be evaluated in full for
both new and existing tanks, in order to determine whether or not CP will be
required.
Redox measurements will not be carried out, as they are difficult to perform and
assess under normal site conditions.
Stray Current Survey
Distribution / transmission pipelines
The presence and magnitude of DC traction stray currents shall be assessedprior to installation of the pipeline and / or after installation of any transmission
pipeline. In the absence of a pipeline, rail recordings and pipe to soil and
pipeline voltage gradient recordings shall be conducted at the foreign service(s).
This, however, shall only be conducted upon approval from the foreign
service(s) owner.
On long transmission pipelines, the possible presence and magnitude of telluric
(magnetic interference effects from solar storms and flares) effects, shall also be
determined.
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iii) All foreign service(s) shall be identified, as well as foreign CP system(s) which
may influence (positively and / or negatively) the SASOL system. Where
possible, the GPS co-ordinates shall be obtained and the data entered into the
existing SASOL GIS. Operating data shall be obtained from the railway
authority, including the polarity, operating voltage and power of the overhead
catenary.
iv)
b.
i)
ii)
iii)
Where transmission pipelines are located in close proximity of HVTL, where
resistive and / or capacitive and / or inductive coupling may occur, tests shall be
conducted in order to determine the extent of the interference. All of the
relevant data pertaining to the supply authority shall be obtained, as well as the
soil resistivity at a depth in the vicinity of the HVTL towers representative of
pipe invert and overt depths along the affected pipeline route. All data relating
to the power line transpositions shall be obtained, as well as the distance
between the pipeline and HVTL, including angles of convergence, divergence
and all earthing (earth mat or point) details.
Petrochemical plants
Tests shall be conducted to determine whether the adjacent CP systems will
introduce any form of stray current into the new plant.
The tests shall include but not be limited to obtaining natural potentials with all
of the CP system(s) de-energised. Measurements shall also be obtained with the
neighbouring CP systems re-energised one-by-one. The neighbouring TRU(s)
shall also be pulsed at a 1,1 Hz frequency and the pipe potential signal (On -
Off) influence be recorded, mapped and modelled.
Once the above surveys have been carried out, definitive recommendations can
be made as to whether CP is required or not. A conceptual CP design report
shall be issued to SASOL for reviewal, should CP deemed to be required. As
soon as the conceptual CP design has been reviewed by SASOL, the following
additional tests shall be carried out.
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3.2.3
a.
i)
ii)
iii)
iv)
v)
vi)
Anode Groundbed Survey
General considerations
When designing and / or selecting to use ICCP, consideration must be given to the
proper use and selection of the anode groundbed(s).
The groundbed location shall be determined early in the design process because its
location may affect the choice of which groundbed type may be best suited to a
particular application. The following factors should be considered when choosing a
groundbed location:
Soil resistivity and moisture content;
Interference with other structures;
Electrical shielding by structures;
Availability of power supply and site accessibility;
Vandalism or other damage (e.g. operational damage);
Purpose of the groundbed and availability of Right-of-Way or servitudes.
Horizontal (conventional) anode groundbeds are normally used to distribute the
protective current over a broad area of the structure requiring protection. These are
frequently called remote groundbeds because the structure is outside the anodic
gradient of the groundbed caused by the discharge of current from the anodes to the
surrounding soil. They may be continuous or discrete in construction as detailed in
Figure 1 and 2.
FIGURE 1 SHALLOW CONTINUOUS HORIZONTAL ANODE GROUNDBED
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FIGURE 2 SHALLOW DISCRETE HORIZONTAL ANODE GROUNDBED
b.
i)
ii)
iii)
Anode Groundbeds
Distributed Anode Groundbeds (2,5 m to 15 m deep) are used to reduce the
potential for interference effects on neighbouring structures. They are also used
to protect sections of bare or poorly coated structure. They are extensively used
in congested areas where electrical shielding may or will occur, if other types of
groundbeds are considered.
Deep Vertical Anode Groundbeds (30 m deep) are remote to the structure by
virtue of the vertical distance between the anode and structure. Deep anode
groundbeds therefore achieve results similar to remote horizontal (surface)
groundbeds. A deep anode groundbed is an appealing choice when space is not
available for a horizontal groundbed or when the surface soil has a high
resistivity and the deeper strata exhibit low resistivity. They should however,
not be used where electrical shielding can occur in congested plant areas.
Shallow Vertical Anode Groundbeds (15 m but 30 m deep) are commonly
used where space is limited and shielding might occur, as well as to mitigate
costs associated with a distributive anode groundbed system as shown in
Figure 3.
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FIGURE 3: DISTRIBUTIVE, DEEP AND SHALLOW VERTICAL ANODE BED
ARRANGEMENT
c.
i)
ii)
Distribution / transmission pipelines
Preference shall be given to remote horizontal continuous or discrete anode
groundbed systems. Where servitude and / or Right-of-Way problems exist,
deep vertical anode groundbed systems shall be employed.
Where horizontal anode beds are to be installed, the soil resistivity shall be
measured at 20 m intervals along the entire length of the active anode bed
length at the proposed anode installation depth.
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iii) Soil resistivity measurements shall also be conducted at two, three, four and
five times the equivalent depth of the proposed anodes, at the beginning, half
way to the centre, centre, halfway between the centre and end and end of the
proposed anode bed, using the Wenner Four Electrode Method, as per
ASTM G57.
iv)
v)
vi)
d.
i)
ii)
iii)
The minimum distance between the pipeline and anode bed shall be two and
half times the length of the anode bed.
Where deep vertical anode groundbeds are required, the soil resistivity shall be
measured at a depth of 2 m, 4 m, 8 m, 16 m, 32 m, etc., until the final depth of
the proposed deep vertical anode groundbed is attained, using the Wenner Four
Electrode Method, as per ASTM G57. The values will be rechecked upon
drilling of the bore hole.
The minimum burial depth of the vertical anode bed (i.e. excluding the active
length) shall be determined according to the resistivity data obtained from the
bore hole, but shall nominally be two and a half times the active length of thebed.
Petrochemical plants
In uncongested areas, deep vertical anode groundbeds shall be the preferred
choice of anode groundbed systems.
In congested areas where electrical shielding can occur, only shallow vertical
and / or distributive anode groundbed systems shall be employed.
In both instances, the soil resistivity shall be measured at the active anode depth
of the proposed shallow vertical / distributive anode groundbed, using the
Wenner Four Electrode Method, as per ASTM G57. The values will be
rechecked upon the drilling of a test hole.
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3.2.4 Current Drainage (CD) Survey
a.
b.
c.
d.
e.
f.
g.
A CD test is conducted in order to calculate the total current required to confer
complete protection to the structure / pipeline. This is of utmost importance as the
current requirements determine the rating and number of TRUs required and the size
and rating of the anode groundbed(s). The current required is also used in order to
determine both the number and distribution (in conjunction with the soil resistivity
data) of the sacrificial anodes required.
This survey cannot generally be carried out on new structures / pipelines or during the
construction of a new process plant or during construction of new on-grade steel
storage tank(s), as construction schedules generally preclude such testing.
On existing pipelines and / or tanks the CD survey must be carried out.
During a CD survey, one essentially sets up a temporary CP system and injects a
known current into the structure(s) requiring protection via a suitable anode
groundbed. The latter may be a convenient fence or steel rods driven into the groundand the former may be a portable DC power source such as a car battery, AC
generator connected to a rectifier bridge, etc.
The pipe potential is measured along the pipeline / structure before (natural potential),
and after injection of current (On potential). The current is adjusted until adequate
protection is achieved over a meaningful length of pipe or meaningful area of the
structure requiring protection.
It must also be appreciated that the On potentials of the structure / pipeline will also
vary as a result of temperature variations and due to the fact that the On potentials
also contain a voltage drop as a result of the current flowing through the soil /
electrolyte.
From the magnitude of current required and the length of pipe and / or surface area of
the structure protected and taking into consideration the abovementioned variations,
one may proceed towards preparing a CP design based on the current requirements.
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3.2.5
a.
b.
c.
Electrical Continuity Survey
This survey is generally conducted on old pipelines where the method of construction
may not be fully documented and on newly constructed OWS lines. The survey entails
measuring the voltage drop along the pipeline(s), with CP current flowing.
A break in electrical continuity is indicated by a voltage drop and complete electrical
continuity is indicated by a direct short measured between the two points with
current flowing in the pipeline as shown in Figure 4a and 4b.
This survey is obligatory, as any break in electrical continuity will result in corrosion
occurring downstream of the break.
FIGURE 4a and 4b: CONTINUITY BONDED CHAMBER / FLEXIBLE COUPLING
FIGURE 4a:
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FIGURE 4b:
3.2.6
a.
b.
c.
d.
Other CP Requirements
All other aspects pertinent to the installation of a CP system shall be addressed. Theseinclude, but are not limited to the following:
Location of a suitable power source (public, plant and / or remote);
Location of river, rail and / or road crossing where casing will be required;
Location of test stations / points for CP, AC mitigation, foreign crossings, Insulating
Flanges (IF) or Insulating Joints (IJ);
Location of in-line valves, chambers, block valves, etc., etc., etc.
Once all of the above surveys have been carried out, a detailed CP design report will be
submitted to SASOL for reviewal.
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4 CATHODIC PROTECTION DETAILED DESIGN REQUIREMENTS
4.1
4.2
4.2.1
4.2.2
4.2.3
GENERAL CONSIDERATIONS
CP is perhaps the most important of all approaches to corrosion control. By means of an
externally applied electric current, corrosion may be reduced to virtually zero and the metal
surface may be exposed to a corrosive environment without any deterioration for an almost
indefinite period of time. CP is also one of the most economically viable methods available
in abating the corrosion process of submerged metallic structures.
COATINGS AND CP
Coatings (e.g. tape wrap systems, bitumen fibreglass, Fusion Bonded Epoxy (FBE), etc.)
applied to metal surfaces can be extremely effective in containing the corrosion of the steel
substrate in many environments.
However, no freshly applied coating is entirely free from defects and there will always be
small areas of steel which are exposed directly to the corrosive environment. It is possible to
reduce, but not eliminate these defects, by paying attention to workmanship. In practice it
becomes increasingly expensive to achieve fewer and fewer defects due to the need for high
quality inspection, detection and the repair of individual defects.
The coating provides the initial barrier against the corrosive environment and CP provides
protection at the coating defects. This apparently ideally complementary behaviour occurs as
a result of the low resistance path offered by the defects, as opposed to the high resistance
path offered by the coating.
A coating will deteriorate both chemically and mechanically during its lifetime. These results
in an increase in both the number of defects and the current required in order to protect the
newly exposed steel surface areas (defects).
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The defects will once again provide a low path of resistance and the CP current will flow to
it and provide protection, providing that it is of sufficient magnitude. This naturally implies
that the CP system must be designed such that it has sufficient reserve in order to provide the
necessary additional current.
4.2.4
4.2.5
In general, the choice of the coating system falls outside the scope of the CP Consultant.
However, the coating system must be compatible with the choice of CP utilised to protect the
structure.
Specification SP-50-6 must be complied with in full and any deviations must be reviewed by
SASOL prior to carrying out the work.
As a guideline, the protective coating system efficiencies should comply with the following:
COATING SYSTEM EFFICIENCY (%)
Three Layer FBE / Polypropylene > 98,5
FBE > 97,5
Polyethylene Tapes > 96
Cold Applied Mastics or Enamels > 95
Internal Pipe and Tank Linings > 94,5
Bitumen Fibre Glass Coatings > 92
External Epoxy Paint Coatings > 90
No Coating System 0
4.2.6
The pipeline shall be backfilled in accordance with ASME B31.4 / 8. This implies a selected
pipeline backfill material (size less than 9 mm) free from sharp objects, rocks, stones or any
other material which may damage the coating system. Pipelines located in the same trench
should nominally be separated by at least one and a half times the diameter of the largest
pipe, in order to prevent shielding.
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4.2.7 Where concrete encasement of the pipe is required, such as at river crossings, the reinforcing
steel shall be electrically isolated from the steel pipe. The pipeline shall be wrapped as per
Specification SP-50-6 prior to being concrete encased.
4.2.8
4.2.9
4.2.10
4.3
4.3.1
4.3.2
All buried pipelines when entering, passing through or leaving a chamber, reservoir, or any
concrete structure shall ensure a minimum clearance of 50 mm from the steel reinforcing and
the pipe or pipe puddle flange and shall be completely wrapped / coated as per Specification
SP-50-6 in the concrete covered section.
Pipeline sections which will be located inside chambers that may become flooded from time
to time or which will be continuously flooded, shall be wrapped / coated as per Specification
SP-50-6. Sacrificial magnesium anodes shall be employed to protect the pipeline or pipe
section in these chambers.
A DCVG survey shall be conducted on all transmission and distribution lines afterconstruction, in order to assess the condition of the coating subsequent to construction. The
pipeline construction contractor shall be responsible for the repair of all major defects
identified during the DCVG survey. Some 10 % of the defects will be exposed in order to
delineate defects and compare them to the DCVG % IR values prior to prioritising defects
for repair.
CHOICE OF CP SYSTEM
CP may be achieved by means of ICCP or SACP. The choice of which system to use shall be
based on both technical and economic factors.
ICCP utilises a TRU, which is supplied by a 230 V, 400 V or 525 V AC supply and produces
a low voltage direct current. The negative terminal of the TRU is connected to the structure
(tank / pipe), which becomes the cathode, and the positive terminal to an anode or a series of
anodes buried in the ground. This set-up is generally termed an anode groundbed.
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Current flows from the anode to the cathode through the electrolyte (soil or ground), and
provided it is of an adequate magnitude, protection will be attained.
4.3.3
4.3.4
4.4
4.4.1
a.
b.
c.
d.
e.
f.
g.
h.
i.
A SACP system does not need an external source of power. It exploits the difference in
potential of various metals in the galvanic series and generates its own voltage, much like a
battery. For example, magnesium possess a natural potential of -1700 mV and steel a natural
potential of -500 mV with regard to a saturated copper / copper sulphate reference electrode.
Therefore, the two combined will produce a driving voltage of approximately 1200 mV.
If the structure is subject to moderate to sever