Cathodic Protection

Shared : Amazon produce their own Ipad version with cheaper price : USD199 ONLY!!

2011-09-29T21:38:00.001-07:00

HIGH-TECH - Amazon offers a tablet more basic than the iPad but much more affordable ...

From correspondent during the launching in Los Angeles

It's not the heat, it's dynamite. Wednesday, Amazon unveiled the Kindle Fire, a 7-inch tablet that will be sold from November 15 to U.S. $ 199 (no date for Europe). An ultra-aggressive price-two times cheaper than the iPad, which reflects the ambition to Amazon: Kindle Fire to a mass product, where Acer, Asus and Archos have failed with their offer mid-range .

Read more..

http://kindlefirespec.blogspot.com/

aluminium anode 1480 np for offshore cathodic protection

2010-07-27T20:54:00.000-07:00

Aluminum Anode

Aluminum anodes are one type of sacrificial anodes in cathodic protection systems that are used generally in offshore industries for metals corrosion protection.

These anodes are in 4 types as follow.

AP& NP types are used more than other types in marine industries at present due to existence of mercury as a poisonous material for sea ecosystem in LP & GP types.

For offshore pipeline bracelet anode is used that is installed pipe round.

Dimension specification of these anodes is variable due to pipe size and purchaser order.

Cathodic Protection Cad Drawing

2010-07-27T20:41:00.000-07:00

Dear readers,

Please e-mail me at izardy2000@yahoo.com if you need my assistance to draw cathodic protection system schematic in CAD both in 2D and 3D according to your design.

Thanks and regards

Izardy

Resistivity measurements for Design : SOIL RESISTIVITY TYPICAL DATA

2010-04-30T00:47:00.000-07:00

MATERIALPermafrost
Dry Asphalt
Wet Asphalt
Dry Concrete
Wet Concrete
Composite dry GAP
GAP compound with 30% water by mass

RESISTIVITY (ohm-meter)

3500 - 4000
E6 2 * 10 - 30 * 10E6
10,000 to 6 * 10 e6
1200-28000
21-100
0032
0015

Resistivity measurements for Design : MEASUREMENT OF SOIL RESISTIVITY- RESISTIVITY PROFILE

2010-04-26T00:37:00.000-07:00

For resistivity profile at a given point, using the Wenner method with a spacing between test electrodes growing. In general, for every two readings are taken spacing resistivity in directions perpendicular to each other.

The resulting graph charting the average of the measurements of resistivity (R) versus distance between electrodes (a) is called the apparent resistivity profile of the terrain.

Resistivity measurements for Design : MEASUREMENT OF SOIL RESISTIVITY- SCHLUMBERGER METHOD

2010-04-23T22:29:00.000-07:00

Schlumberger method is a modification of the Wenner method, since it also uses 4 electrodes, but in this case the central electrode gap or potential (a) is kept constant, and measurements were made by varying the electrode gap external electrodes from internal multiples distance (na) of the basic separation of internal electrodes (a).

The configuration and the expression of the resistivity for this method of measurement is shown in Fig.

Schlumberger method is useful when you need to know the resistivity of deeper layers, without the need for many measurements such as the Wenner method. It is also used when measuring devices are not very smart. Only recommended to make measurements at 90 degrees so that the readings are not affected by underground structures.

Resistivity measurements for Design : MEASUREMENT OF SOIL RESISTIVITY.

2010-04-18T20:22:00.000-07:00

The soil resistivity is measured primarily to find the depth and thickness of the rock in geophysical studies and to find the optimal points to locate the land network of a substation, electronics, power plant or RF transmitter. It may also be used to indicate the degree of corrosion of underground pipelines.

In general, places with low resistivity tend to increase corrosion.

At this point it is necessary to clarify that the measurement of soil resistivity is not a requirement to make a mesh ground. While designing a land of great size, it is advisable to find the area of lower resistivity to achieve efficient fixtures.

The profile of the soil resistivity determines the resistance value of the land and the depth of our ground system.

To measure soil resistivity requires a terrómetro (called in other countries: telurómetro) or land Megger four terminals.

The most commonly used devices, according to its principle of operation, may be of 2 types: the kind of compensation balance to zero and the direct reading.

The terrómetros should inject a current frequency of 60 Hz is not to prevent voltages and currents are measured that are not due to the device but to electrical noise. For example, if we are near a substation or line in service, and we to make measurements of resistivity and ground resistance, a unit of 60 Hz, these systems will induce currents on the ground due to 60 Hz electromagnetic fields and give an incorrect reading.

Similarly happens when the test electrodes are poorly connected or have false contacts, give false signals of current and voltage. If currents are different from those sent by the device, it will read other voltage and current signals are not adequate.

These devices also suddenly have oscillations in their readings and you can not read them.

A smart device, has been shielded conductors, coaxial cable, has filtering systems, analysis and measures what it is, but this information is analyzed, filtered and then the clear. For example, a measurement to a signal of 100 Hz and measured, then sends another signal of 150 Hz and re-measure and can continue sending other high frequencies until values will be similar, forms and obtain a statistical average.

The terrómetros are analog or digital and should contain 4 rolls of 14 AWG cable normally. For fast winding is recommended to build a winder system to help reduce the time of measurement. They also bring 4 electrode material hard enough to be driven into the ground with mallet. They are of an approximate length of 60 cm and a diameter of 16 mm. In addition to this it is necessary to have a non-metallic tape 50 m away.

The terrómetros have four current terminals 2 (C1, C2) and 2 potential (P1, P2) and are numbered in the apparatus P1 P2 C1 C2. The terrómetros must be certified and tested in the field with a strength before making measurements.

As the measurement is obtained by a timely terrómetro, measurements must be made in a sense, in another 90 degrees to the first, and in the direction of the diagonals. In the measurement of ground resistivity is common to find very different values, caused by the geology of the area, so it is common practice for a table with readings, eliminating the values that are 50% above or below the arithmetic average of all values captured.

Resistivity measurements for Design : EARTH AND RESISTIVITY

2010-04-15T20:12:00.000-07:00

The most important factor of resistance to earth is not the electrode itself, but the resistivity of the soil itself, so it is known requirements for calculating and designing the grounding systems.

The soil resistivity is the property that has it to conduct electricity, also known as specific resistance of the ground. In their measurement, we average the effects of the different layers that make up the ground under study, as these are often not uniform in composition, resulting in what is called "apparent resistivity" as for the interest of this work will be known simply as "Ground resistivity.

The NOM-022-STPS-1999 defines the term resistivity, as the resistance offered by the passage of the current field cube one meter on each side.

According to the NOM-008-SCFI-1993, The dimensional representation must be expressed in Ohm-m, whose meaning is used internationally.

The soil resistivity varies widely across the globe, to be determined by:

Soluble salts
Composition of the land itself
Stratigraphy
Grit
Moisture content
Temperature
Compaction

SOLUBLE SALTS

The soil resistivity is mainly determined by the amount of electrolytes, that is, by the amount of moisture, minerals and dissolved salts. As an example, for values of 1% (by weight) of salt (NaCl) or greater, the resistivity is almost the same, but for values less than this amount, the resistivity is very high.

COMPOSITION OF THE LAND

The composition of the ground depends on the nature of it. For example, the normal clay soil has a resistivity of 40-500 ohm-m which buried electrode rod 3 m will have a resistance to ground from 15 to 200 ohms respectively. However, the resistivity of a rocky terrain is 5000 ohm-m or higher, and try to get a grounding resistance of 100 ohms or less with a single rod electrode is virtually impossible.

STRATIGRAPHY

The site is obviously not uniform in its layers. In the 3 m length of a typical electrode rod, at least there are two different soil layers. In XX are examples of different profiles of resistivity.

GRANULOMETRY

Influences enough about the porosity and moisture retaining power and the quality of contact with the electrodes by increasing the resistivity with the largest grain size of the earth. For this reason the resistivity of the gravel is higher than that of the sand and that it is greater than that of the clay.

MOISTURE CONTENT

The water content and humidity have a significant influence. Its value varies with climate, season, depth and the water table. For example, the soil resistivity increases considerably when the moisture content is reduced to less than 15% of the weight of it. But a higher moisture content above 15%, because the resistivity is nearly constant. And, it may be the case that in the dry season, a field can have such a resistivity that can not be used in the land system. Therefore, the system must be designed taking into account the resistivity in the worst cases.

TEMPERATURE

As the temperature decreases the resistivity of the field increases and this increase is most noticeable when it reaches 0 ° C, to the point that, as the greater the amount of water in a frozen state, is reduced movement electrolytes which influence the resistivity of the earth

COMPACTION

The soil resistivity decreases with increasing compaction. It is therefore always seek to place the electrodes in the more compact as possible.

AC Mitigation : Zinc Anode

2010-04-11T01:00:00.000-07:00

It is important to review the use and design of a system of gradient control wire with an engineer experienced with this system, since the yield depends on the structure of multiple layers of the earth.

For the inductive interference, gradient control wires additional grounding for the pipeline and the reduction induced by the suction tube potential. At the same time, raise local ground potential, thus drastically reducing the potential for contact and coating stress voltages.

For drivers interference, gradient control wires to moisten the soil near the pipeline may increase while increasing the potential of piping, providing lower contact stress and decreasing coating stress voltages.

The life expectancy of zinc anode in this application would be fairly long and generally be determined by zinc anode as a cathodic protection system projected. The most common sizes of zinc anode mitigation and AC are standard.

Zinc anode protection can provide an important means to mitigate the potential gradients along a pipe. Importance should also be placed on reducing the potential sites of the valve, the measuring stations, the pig launchers and receivers and other facilities accessible to worker safety.

The most common size zinc anode grounding mats are standard. Reference should be made to NACE Standard RP0177 (latest revision) - Recommended Practice AC Mitigation and Lightning Effects on Metallic Systems and corrosion control. In addition, ANSI / IEEE 80 specifies the design safety criteria for determining maximum acceptable touch and step voltages during fault conditions.

Finally, during fault conditions in the high voltage line, the system must ensure that the pipeline coating stress voltages remain within acceptable limits to prevent damage to the layer and damage to the steel pipe. coating damage may occur in the range of 1000 - 2000 volts for asphalt-based coatings and in the range of 3000 - 5000 volts for polyethylene pipe and fusion-bonded epoxy.

Resistivity measurements for Design : MEASUREMENT OF SOIL RESISTIVITY-WENNER METHOD

2010-04-10T22:03:00.000-07:00

n 1915, Dr. Frank Wenner of the U.S. Bureau of Standards developed the theory of this test method, and the equation that bears his name.

In order to measure soil resistivity is necessary to insert electrodes into the soil 4. The four electrodes are placed in a straight line and the same depth of penetration, resistivity measurements depend on the distance between electrodes and soil resistivity, and conversely do not depend significantly on the size and material of the electrodes, although it depends on the kind of contact is made with the earth.

The basic principle of this method is the injection of a DC or low frequency through the earth between two electrodes C1 and C2 while the potential which is measured between two electrodes P1 and P2. These electrodes are buried in a straight line and equally spaced between them. The ratio V / I is known as the apparent resistance. The apparent resistivity of the ground is a function of the resistance and geometry of the electrode.

The figure shows schematically the arrangement of the electrodes, where the current is injected through the outer electrodes and the potential is measured across the inner electrodes. The apparent resistivity is given by the following expression:

If the gap buried (B) is small compared to the distance between electrodes (A). So A> 20B, the following simplified formula can be applied:

The resistivity obtained as a result of the equations represents the average resistivity of a field of a hemisphere of radius equal to the separation of the electrodes.

As an example, if the distance between electrodes is 3 meters A, B is 0.15 m and the reading of the instrument is 0.43 ohms, the average resistivity of the ground at a depth of 3 meters is 8141 ohm-m according to the equation and of 8105 ohm-m according to the simplified formula.

It is recommended to take readings at different locations and 90 degrees from each other so they are not affected by underground metallic structures. And that they get the average.

Cathodic Protection : The Scope of Work

2010-04-10T20:06:00.000-07:00

A highly effective method to mitigate external corrosion on pipelines and tank bases in contact with soil or other electrolytes, the cathodic protection. Two systems for providing cathodic protection to a structure, either by impressed current or sacrificial anodes. Both require specialized installation and inspection, and that a malfunction would affect environmental damage and even fatalities.

Design and installation of cathodic protection systems includes:-

• Studies of soil resistivity
• Location and diagnosis of anode beds, rectifiers and anodes sacrifice
• finite element calculations
• Troubleshooting attenuation
• Evidence of formal power

Interference detection and mitigation

• Currents static with other cathodic protection systems
• Urban systems
• High Voltage Alternating Current
• telluric currents
• Monitoring and diagnosis of systems in operation
• Performance Evaluation
• Problems with electrical isolation and short
• Mapping of potential
• Inspection of short interval (CIS)
• Leak Detection direct current (DCVG)

And organization of information security

• Systems and safety manuals for the operation of cathodic protection
• Organization of records of field inspections, repairs and modifications
• Implementation of executive summaries

CP Project Implementation: Task to Be Considered (Equipment &Documentation supply)

2010-01-28T19:08:00.000-08:00

Cathodic Protection installer must ensure all the equipment required to execute the project are available. This equipment includes:-

i. Machineries
ii. Power supply
iii. Tool box
iv. Testing Equipments
v. Spare parts

Most of the client required factory acceptance test before CP equipment brought and installed at the construction site. Throughout the production, client might need to access to the factory periodically to check:-

i. Manufacturing progress
ii. That the equipment conforms to their specifications
iii. To be present during factor testing.

Factory test reports, anode material chemical analysis, the certificates of approval for electrical equipment to be used in hazardous areas, etc., shall be supply to the client which is also included in the final report.

The final report shall consist of:

• A detailed description of the installation

• Drawings and the operating and maintenance instructions

• The as built drawings

• The equipment list with references and manufacturer addresses

• The list of spare parts for two years of operation, with complete references

• The operating procedures

• The complete list of measurements taken before and during the starting up phase

• The reports stating the agreements taken with the COMPANYS of the neighbouring structures (duly signed by the various parties concerned) on the corrective measures to be taken for any interference of these structures

• The results of the enquiry and the permission of the local authorities if the installations are to be in countries where such installations are subject to special legislation

CP Project Implementation: Task to Be Considered (Administrative Formalities)

2010-01-21T19:06:00.000-08:00

If local legislation requires that an enquiry takes place before a cathodic protection system is installed, the legal file shall be prepared before the project execution.

The file shall be transmitted to the competent administrative body. The project execution shall be hold until the results of enquiries obtained to avoid problems in the future.

Any questions from the administrative body regarding the property which might be involved in the installation of the cathodic protection system must be answered in a proper technical way.

Information and documents required for the land and rights of way of the project owner facilities must be obtained, these documents include:-

• Extracts of land survey maps

• Delimitation on the land survey maps of the land to be acquired and the temporary and/or permanent rights of way to be acquired.

CP Project Implementation: Task To Be Considered (Study – Pt2)

2010-01-14T18:55:00.000-08:00

Study – Pt 2

The preparation of a detailed study report comprising:

• An analysis of all information gathered and measurements taken, and an estimate of corrosion risks

• Justified design hypotheses, particularly for the insulation values of the coatings, and for ageing

• A technical-economical discussion of the various possible solutions

• Design notes justifying the sizing and layout of equipment: anodes, transformers-rectifiers, cables, etc. Unless otherwise specified, the cathodic protection system will be designed for a service life of 25 years minimum

• A list of materials, including assembly accessories, and the corresponding technical specifications

• A list of possible suppliers.

• Schematic diagrams

• Detailed equipment diagrams

• Detailed installation drawings, indicating:

- The location of insulating joints

- Electrical bonding to be installed

- Special insulations to be installed

- The layout of different types of equipment and the relevant installation procedure

- Wiring diagram for electrical equipment.

• Instructions proper to installations, indicating all precautions to be taken. Particular emphasis shall be placed on the construction of:

- Ground beds

- Connections on anode circuits

- Insulations between protected and non protected parts

- Insulations between parts protected by different systems

- Insulations between parts protected by the same system, which must be separated temporarily for various operational reasons, such as routine checking of the quality of the coating, etc.

- Influence correctors between the work to be protected and neighbouring works

- Reference electrode installations at fixed points.

As a general rule, the location of electrical equipment in hazardous areas shall be avoided. If this is impossible, the use of equipment corresponding with the safety classification of the area in question will be specified.

CP Project Implementation: Task To Be Considered (Study – Pt1)

2010-01-07T18:53:00.000-08:00

A cathodic protection project shall include all of the tasks listed below:-

i. Study
ii. Administrative Formalities
iii. Equipment Supply

Study – Pt 1

• The site survey, the collection of all relevant information, the measurements required for the estimation of corrosion risk and the evaluation of coating materials

• The collection of all documents and information concerning the design of the structure to be protected, its size, and those of its characteristics which are likely to influence the design of the cathodic protection system

• The collection of all documents and information concerning the environment of the work: the presence of nearby metallic structures whether cathodically protected or not, the presence of works likely to emit stray currents, the presence of high voltage cables or transmission lines, electric power stations, transformer stations, etc., which, if faulty, may damage cathodic protection installations, coatings, or the structures itself

• The collection of all information concerning the availability of electrical power for the supply of cathodic protection installations.

To be continue on the next post…

Impressed Current Cathodic Protection - Pipeline

2009-12-03T22:22:00.000-08:00

Most of the underground pipeline nowadays installed with Cathodic Protection System. Either Impressed Current System or Sacrificial Anode System together with the existing coating system.

A basic Impressed Current Cathodic Protection for pipeline will require the following materials.

1. Anodes (made of inert metals)
2. Cables
3. Test Post
4. Transformer Rectifier

Diagram of a basic Impressed Current Cathodic Protection for pipeline shall be as the folowing:-

Design of an Impressed Current Cathodic Protection for pipeline is determined base on the following parameters:-

1. Length of the Pipeline
2. Pipeline Coating Type
3. Soil Resistivity
4. Groundbed location
5. Consideration of nearby existing ICCP system
6. Metal crossing
7. High Voltage AC transmission line
8. River crossing

The output size of the ideal transformer rectifier to be used is base on the requirement of cathodic protection current and groundbed soil resistivity range . In order to determine groundbed resistivity, site survey has to be carried out . Soil coring and 4 pin method are usually used, however soil coring method does provide more precise result. Deep well groundbed normally used soil coring method, on the other hand 4 pin method used for shallow type groundbed.

If the groundbed have high soil resistivity range, usually if more than 5 ohm, other suitable location of groundbed have to be determined. Low resistivity location usually near the wet area. Low soil resistivity range area is required to minimized the voltage output from transformer rectifier since
V = IR (as per Ohm's law)

The installation of test post depends on the clients requirements, normally test post have to be installed at every 2km interval of pipeline (depends on the total length of pipeline), pipeline crossing, river crossing, road crossing, drain point, and end of pipeline.

Usually , transformer rectifier will be installed near to the AC power source and near to the groundbed it self . This is normally done to safe the cable usage which can minimize the cost. A junction box sometime installed at the drain point to control current supply to the anode , this junction box can also be used as the pipeline potential measurement point which also considered as a test post.

A very simple technique to know whether the whole stretch of pipeline protected (more than -950mV wrt Cu/CuSO4 reference electrode) is by measuring the potential at the end point of pipeline. Adjustment shall be done at Transformer Rectifier output if results indicates under-protection or over-protection reading.

Infrastructure Corrosion Control

2009-11-07T10:37:00.000-08:00

Material loss due to deterioration cause by electrochemical reaction is one of the biggest challenges to our aging infrastructure nowadays. In a simple word, these steel based infrastructures facing the corrosion problem.As per studies from several governments, it costs more than $400 billion of loss annually due to corrosion problem in the US alone.

With science and technology, we can actually prevented these huge amount of loss. One of the proven science and technology methodology that can extend the life of our steel based infrastructure is cathodic corrosion protection. Cathodic protection system usually installed to the pipes, storage tanks, vessels and even underground embedded steel piling. The environment can also be protected from the pollution of hazardous materials, liquid or gases due to the loss of materials from corrosion process. Corroding materials can also cause injury due to sharp edges produced and somemore those rusty surface of infrastructures projected ugly scenary to the surrounding environment.

Electrochemical reaction took place when a metallic structures are place in electrolytes (soil or waters). There will be anodic and cathodic areas on the surface of the structure due to the reaction with the environment. Corroding areas known as anodic (lose current) while the area which is not corrode known as cathodic(gain current). The above explaination make researchers thinks that the whole structure of a metallic body can be protected from corrosion, if it become cathodic (gain current).

Cathodic protection works when there's an external source of DC current supplied to the corroding structures.Let say if an underground pipeline receive an external DC current it'll become cathodic. An external DC current source can be from sacrificial anode (for example Magnesium, Zinc, Aluminium) or impressed current from transformer rectifier. Sacrificial anodes are metals which have higher tendency to release electron compared to steel. Impressed current system is when a transformer rectifier force current to flow via an inert metal. The induced DC current will replaced current release to the corroding structure, therefore no corrosion occured. Cathodic corrosion protection can only work if there are anode, cathode, electrolyte and a metallic path.

The replacement cost of an infrastructure which is not installed with cathodic protection are very high compared to the maintenance by using cathodic protection system. Therefore, a cathodic protection specialist offered a system which is cost effective . These can be accomplished by a proper cathodic protection system design, procedures and research. The cathodic protection techniques had been discoverd and commerciallized since 1930's .

The National Association of Corrosion Engineer (NACE) is and organization recognized around the world for their expertised in corrosion control. They conducted training and certification for players in the industry.

The following industries are served by professional from NACE:

* Power and Energy
* Independent and General Contractors
* Architectural and Engineering Firms
* Water and Wastewater Municipalities
* Oil and Gas Industries
* The Federal Government
* Alternative/Clean Energy
* Lite Rail Systems (DC) and High Speed Trains
* Mobile Home Parks
* Service Stations
* All other Infrastructure and Industries
* Above and Below Grade Storage Tanks (Water, Chemical, Petroleum, etc.)

Some of the structures that can be considered for cathodic protection may include but are not limited to the following:

* Above Grade & Buried Pipelines of All Types (DIP, CCP, PCCP, Carbon Steel, PVC, etc.). Chemical, Petroleum and Water Pipes
* Marine Structures such as Mooring Dolphins, Sea Walls, Pipe Piles, Offshore Platforms and more
* Reinforced Concrete Structures
* Submerged (Internal) and Soil-Side Surfaces for Storage Tanks
* Lite Rail Systems and High Speed Trains
* Well Casings
* Intake Structures, Water Boxes and Other Structures at Power Plants
* Clarifiers, Trash Racks, Sludge Thickening Tanks and Other Structures at Water and Wastewater Treatment Plants
* Submerged Pumps and Piping at Pump Stations
* Electrical Grounding Systems at Satellite Towers and Other Locations
* Buried cables
* All Other Related Metallic and Reinforced Concrete Structures

Cathodic corrosion protection is the proven techniques for decades though the process can't be seen from the naked eye. Cost of replacement of a metellic infrastructure due to corrosion problem can be minimized by a proper maintenance and installation of cathodic protection system. An effective cathodic protection system is when it was installed together with the best coating system in the market.

Type of Corrosion - Video

2009-10-29T09:18:00.000-07:00

Corrosion and Prevention

2009-10-28T00:09:00.000-07:00

Corrosion

The tendency of metals to return to their natural condition is known as corrosion process, the deterioration of metals by abandoning their current physical form due to the electrochemical reactions.

The electrochemical reaction occur with the existence of electrolytes, conductor and metals. In high humidity environment, with the presence of liquid/water in atmosphere this electrochemical reaction occurred on steel structures. The same process applies on structures immersed in the water or buried underground.

Metals corrosion occur due to the tendency to be more thermodynamically stable with the combination of oxygen in the atmosphere. The materials then metallurgical transformed to a different state with the supply of electric, chemical or heat work.

Oxidation is a chemical process where metals oxidized. Oxidation of a metal occurred when it discharge electrons. The rate of electrons discharge depends on the metals' affinity with oxygen, gold and platinum hardly discharge since they have low affinity with oxygen. An example of metal with high affinity of oxygen is iron.

There are 3 types of corrosion:-

i. Generalized corrosion

This type of corrosion mostly effect on the surface of metals and the metal lost can be considered slow, usually classified as non severe and depends on the contact with electrolytes and types of electrolytes contacted.

ii. Localized corrosion

The localized corrosion occurred on a specific location within the metal structure. It cause cavity formation. These cavities known as ulcers, craters, pittings, or criccas depends on their size and depth. Localized corrosion can be classified as severe since it have the tendency to penetrate. The cricca or fissure can be intergranular or transgranular, depending if it follows the edge of the grain or through it.

iii.Selective corrosion

Selective corrosion produces the preferential dissolution of a certain part of the metal that, for chemical or metallographic reasons, proves to be more easily attackable.

We can speak of cristalographic, intergranular or interdendritic corrosion, if the corroded material results in certain crystalline species in the grain borders or the immediately adjacent zone.

Another form of selective corrosion, the dealloying, happens when the preferential dissolution of one of two components of an alloy is verified, leaving an inconsistent and frothy residue of the other metal in the alloy.

Corrosion control and prevention:

There were few method use to control and prevent corrosion in the industry.

i. Some contractors use special construction materials resistant to corrosion.

ii. Use paint specially produce for corrosion protection, eg:- International Paint, Belzona etc

iii. Cathodic protection system.

iv. Corrosion inhibitor.

v. Anti corrosive system

Cathodic Protection System Transformer Rectifier

2009-10-19T18:16:00.000-07:00

There are a lot of cathodic protection system transformer rectifier manufacturer in the market. In Asia, one of the well known manufacturer is EEME Singapore. Other manufacturers are Corrosion Electronics, Willet Manufacturing,Corrpro and Universal Rectifier. There are various type of transformer rectifier:-

i. Oil cooled type

ii. Air cooled type

iii. Explosion proof type

iv. Solar powered type

v. SCADA intergrated type

The above type of transformer rectifier usually selected by considering the requirement from the Owner of a project, adaptability with the surrounding (where the T/R to be installed) and accessibility.

Cathodic Protection System Test Post

2009-10-10T22:27:00.000-07:00

There are several numbers of cathodic protection test post. The test post are use by considering the surrounding area where it supposed to be installed. If the test post is required to be installed within access road the flush type test post shall be use.

If it to be installed in bushes, big fink type shall be considered.The big fink shall be in orange color in order to make them easy to be seen during the inspection.

And in Africa they used test post where the length is quite big. They use this kind of test post to avoid it being covered with the long grass (which sometime exceed to 2 meter long). And to avoid it damaged from being burned (when season change there, nomad sometime did burn the dry grass)

Other type of test point shall be as the following.

i. Pigeon house type
ii. Flushed cast iron type

Cathodic Protection Survey Works

2009-09-30T20:01:00.000-07:00

Cathodic protection survey works includes: -

i.Soil resistivity survey

-Soil resistivity survey shall be carried out in order to design a new CP system for underground pipelines.

-Soil resistivity survey usually carried out by using Wenner 3 pin method or by using soil box.

-The instrument to be use is soil resistance meter.

ii.Current drainage survey

-Current drainage survey is to determine the amount of current to be required by using temporary ICCP system.

-This method can be a guideline during design documentation.

iii.Pipeline potential survey

-Pipeline potential survey shall be carried out to determine the existing potential level of pipeline.

-As per NACE standard, the protection level for metallic structure with reference to Cu/CuSO4 reference electrode is –0.950V. Therefore the protection level shall be in the range of –0.950V to –3.000V.

-Pipeline potential shall not be below than –0.950V to avoid corrosion or above-3.000V to avoid coating disbondment.

-Other types of reference cells are Zinc and Ag/AgCl that is usually use to measure potential of submerged metallic structures.

iv.Close Interval Potential Survey

-CIPS is the method to measure the effectiveness of ICCP system for the entire length of pipeline.

-CIPS will be carried out with the condition there must be numbers of test post or pipeline riser.

-In CIPS the operator establishes an electrical connection to the pipeline by means of a trailing wire.

-This coated copper wire unwinds from a spool as the operator walks the length of the pipeline.

-The pipeline potential is measured with a set of reference electrodes at ground level, positioned directly over the pipeline, at intervals of about 1 meter. (depend on the client’s requirement)

-During CIPS, CP transformer rectifier for the pipeline must be interrupted at certain ON and OFF period by using current interrupter to minimize the IR error.

-CIPS result can be analyzed to determine coating defects, unknown metallic crossing or the existence of stray currents.

v.Direct Current Voltage Gradient (DCVG) Survey

-DCVG is another method to determine coating defect for the buried pipeline.

-This technique not only locates but also determines the size of the coating defect.

-The technique is fundamentally based on measuring the voltage gradients in the soil above a cathodically protected pipeline.

-A distinctive feature of this technique is that even small defects can be located accurately, with a claimed accuracy of about 10 cm (4 inches).

-A voltage gradient is established in the soil surrounding a defect, in the coating of a pipeline with an impressed current CP system.

-The highest gradient is recorded in close proximity to the defect.

-In the DCVG methodology, the DC input signal used to measure the voltage gradient is pulsed.

-A sensitive milli-voltmeter and two copper-copper sulfate reference electrodes (placed about one meter apart by the operator) are typically used for measuring purposes.

-Apart from locating defects, their sizing is also important in order to prioritize excavation and repair. Based on DCVG measurements it is possible to compute a so-called %IR value.

-Four defect categories, related to the %IR computation, have been proposed. This defect classification is empirical and is also dependent on the soil resistivity.

A Brief Note : Sacrificial Anode System

2009-09-18T00:07:00.000-07:00

Sacrificial Anode Cathodic Protection (SACP) system is another method of metallic structures corrosion protection. SACP system used galvanized anodes and the installation process is quite straight forward compared to ICCP system. Normally, clients will decide to choose either system base on cost and maintenance consideration.

Galvanic anodes such as Magnesium, Zinc and Aluminum will be selected by considering the surrounding environment.

i. Magnesium anodes usually installed in the groundbed with soil resistance more than 3000 ohm.cms. Anode cable from the groundbed will be routed to the CP test post. Two (2) numbers of single core copper cable to be attached to the protected structure by thermit welding or pin brazing method. These cables will also routed to the CP test post. One of the pipeline cable will be terminated at the same terminal where anode cable to be terminated. Another pipeline cable will be use to measure pipeline potential.

ii. Zinc anodes can be installed for onshore and offshore purpose, for onshore purpose zinc anode can only be installed if the soil resistivity is below than 1500 ohm.cms. Installation method is the same as elaborated for Magnesium anodes. However for offshore purpose and internal tank protection Zinc anodes are directly attached or weld to the protected structure by its metal core.

iii. Aluminum anode usually installed for offshore and internal tank protection. Aluminum anode metal core will be welded directly to the surface of the protected structure.

A Brief Note : Impressed Current System

2009-09-17T23:54:00.000-07:00

Impressed Current Cathodic Protection (ICCP) system usually installed for the following structures: -

i. Underground pipelines
ii. Tank bottom
iii. Tank internal (waste water tank)
iv. Submarines structures

ICCP system utilized numbers of impressed current anodes and transformer rectifier to energize the system. Impressed current anodes will be installed in groundbeds. There are two types of anode groundbeds:

i. Deep well groundbed
ii. Shallow horizontal groundbed

Anode cables from the groundbed will be routed and terminated at transformer rectifier positive terminal. One number of single core copper cable will be attached to the pipeline by thermit welding or pin brazing method. This cable will be routed and terminated at transformer rectifier negative terminal.

There will be numbers of test post and junction box for potential measurement purpose of the protected structures.

Materials Engineering E-Books

2009-09-09T09:37:00.000-07:00

List of materials engineering e-book for your reference (links will be updated):-

1. Materials for Engineering, 3rd edition
2.Hand book of Material Selection
3. Materials Handbook
4. Corrosion Science and Technology
5. Pipeline Corrosion and Cathodic Protection
6. Peabody's Control of Pipeline Corrosion
7. Electrochemistry and Corrosion Science
8. Corrosion and Protection

Introduction to Cathodic Protection

2009-09-07T21:40:00.000-07:00

1.1 Corrosion is a natural process where metal deteriorated through electro-chemical reaction when exposed to its natural surrounding. Corrosion process took place with the existence of the following elements: -

i. Oxygen
ii. Electrolytes
iii. Iron, Steel etc

1.2 By eliminating one of the above elements, there will be no corrosion re-action.

1.3 Corrosion occurs when there is the existence of anodic and cathodic sites within a metal surface. The cathodic and anodic site is determined with the concentration of oxygen.

1.4 An underground pipe that passes from clay to gravel will have a high oxygen concentration in the gravel region and almost no oxygen in the impermeable clay. The part of the pipe in contact with the clay becomes anodic and suffers damage. A similar situation is found where a pipe passes under a road. The section under the road (which is the more difficult to get at for repair) is oxygen deprived and will suffer the greatest damage.

1.5 The anodic part of a metal structure (high oxygen concentration) slowly deteriorate when it actually protect the cathodic part (low oxygen concentration) of the structure by throwing current to this particular area (cathode).

1.6 The above process can be controlled by applying external source of DC current to the metallic structure. This method is known as cathodic protection system.

1.7 Cathodic protection system normally applied with coating and corrosion inhibitor to increase the metallic structure resistance against corrosion.

1.8 There are two type of cathodic protection system: -

i. Impressed Current Cathodic Protection (ICCP) System
ii. Sacrificial Anode Cathodic Protection (SACP) System

1.9 ICCP system used impressed current anode where the current is impressed from external DC source (transformer rectifier).

1.10 SACP system used metal with higher potential (Zinc and Aluminum) than the protected structure (M.S Pipeline, tanks, etc). These metals known as galvanic anode. The following example is an anode installed to underwater metallic structure.

Type of Corrosion

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Type of Corrosion	Material System	Driving Force	Control Point	Remarks
General Corrosion	All metals in atmospheric environment	* Atmospheric * Temperature	* Painting * Hot dip galvanize	Seldom lead to failure
Intergranular Corrosion	Al Alloys,Ni-Cr Austenitic SS	* Third phase precipitate * Temperature	* Heat treatment * Welding during fabrication	* Lost of strength and ductility * Severe attack can lead to failure
Galvanic Corrosion	Galvanic coupling materials	Different metal in electrolytic solution	* Proper design * Rivetting *Insulating coupling material	Moderate effect but can be detrimental for a long period
Crevice Corrosion	Metal to Metal/Non Metal in Electrolyte	* Small gap in electrolyte * Stagnant fluid	* Proper design * Gasketing material * Proper drainage practice	Moderate effect but can be detrimental for a long period
Pitting	Stainless steel and aluminium in chloride or bromide environment	* Surface irregularities * Presence of Cl or Br Ion * Chemical composition * Temperature	* Surface quality control * Proper welding practice * Proper material handling	Severe attack can lead to failure
Erosion Corrosion	Carbon steel, stainless steel in flowing fluid containing abrasives	Synergy effect of passive film breakdown by abrasive and localized corrosion	Corrodent; turbelency Corrodent impingement in elbow and tees	Severe attach can lead to failure
Stress Cracking Corrosion	Stainless steel, carbon steel in high pH > 9.3	* Microstructure * Temp. region * Existance of residual stress * Suitable pH * Presence of H2S chloride ion	H2S content and temperature control	Found in gas and liquid pipelines
Biological Corrosion	All metal in environment with:- * Sulfate reducing bacteria	* pH 6 – 8 * temp. 20 deg C to -45 deg C	Application of organic coating	-

Gas and Microbes Corrosion

2009-08-18T19:03:00.000-07:00

Corrosive gases in Oil & Gas industry are Oxygen, Carbon Dioxide & Hydrogen Sulfate. Micro bacterial activities which produce corrosive gases also develop the corrosion process. The following graph indicates the corrosion rate with the existence of Oxygen, Carbon Dioxide & Hydrogen Sulfate.

Oxygen dissolved in water is one of the primary causes of corrosion in the oil field. When oxygen is present,the most common types of corrosion include pitting corrosion and uniform corrosion.

Carbon dioxide systems are one of the most common environments in the oil field industry where corrosion occurs. Carbon dioxide forms a weak acid known as carbonic acid (H2CO3) in water, a relatively slow reaction.

Hydrogen sulfide is a weak acid when dissolved in water, and can act as a catalyst in the absorption of atomic hydrogen in steel, promoting sulfide stress cracking (SSC) in high strength steels.

Microbes fall into two basic groups, aerobic and anaerobic. These two groups are based on the kind of environment they prefer, either with or without oxygen. Slime formers form a diverse group of aerobic bacteria. Common anaerobic bacteria include Sulfur/sulfate reducing bacteria (SRB's) and organic acid formers.

Sulfate-reducing bacteria (SRB) are anaerobic bacteria which metabolize sulfates (SO4
2-) and produce sulfuric acids or H2S, thus introducing hydrogen sulfide into the system. SRB colonies can also form deposits that are conducive to under-deposit corrosion (crevice corrosion.)

Corrosion Factors

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Corrosion occurred due to the following factors:-

1. Metallurgical factors, due to fabrication, field installations etc.:

1.1 Compositions
1.2 Microstructures.
1.3 Inclusions.
1.4 Precipitations.
1.5 Heat treatment.
1.6 Mechanical rolling and tempering.
1.7 Welding
1.8 Work hardening.
1.9 Fabrication, installation and external stress, strain factors.

2. Environmental factors.

2.1 Concentration Cells.
2.2 Environmental induced SCC, SSC, HIC etc.
2.3 Microbial MIC etc
2.4 Temperature induced corrosion.
2.5 Mechanical environmental induced erosion, fretting, cavitation etc.
2.6 Galvanic, CP and Impressed current anodic dissolution, stray current, cathodic embrittlement etc.

Further explaination can be referred from books or others online references. The above only indicates some basic knowledge :).

Pourbaix Diagram (Iron)

2009-08-17T00:07:00.000-07:00

Pourbaix Diagram is a Potential vs pH Diagram. Three oxidation states of iron (0, +2 and +3) are represented on this diagram. The stability regions for the
oxidized iron states are shown only within the stability region of H2O. Equilibrium between species separated by vertical lines are dependent on pH only.

The +3 oxidation state is the only stable one in environments in which the oxidation level is controlled by atmospheric O2. This is the reason the Earth’s crust contains iron oxides, which developed only after the appearance of green plants which are the source of O2.

Iron is attacked by H+ to form H2 and Fe(II); the latter then reacts with O2 to form the various colored Fe(III) oxides that constitute “rust”.

Notes: Diagram taken from wikipedia

Fundamental of Corrosion : Basic Theory

2009-08-13T08:13:00.000-07:00

Corrosion of metal is mostly electrochemical reaction composed of two half cell reactions, an anodic reaction and a cathodic reaction. The anodic reaction releases electrons, while the cathodic reaction consumes electrons. There are three common cathodic reactions, oxygen reduction (fast), hydrogen evolution from
neutral water (slow), and hydrogen evolution from acid (fast).

Fundamental of Corrosion : Electrochemistry

2009-08-12T01:05:00.000-07:00

In order to understand electrochemical, we must have basic knowledge of the followings:-
1. Atoms
2. Molecules
3. Acid and Bases

The explanation on how an electrochemical cell work involved the above 3 basic knowledge. (which is quite easy to understand with some quick reference on theinternet, remember u have wikipedia :)?)

In electrochemical, oxidation and reduction process took place. Oxidation is a process where neutral iron atom release electron to form positive ion of iron.

The release electron will bond with non metallic atom and forming negatively charge non metallic ion. Because the charge of these ions has become smaller (more
negative charges) the ion or atom which has gained the electron(s) is said to have been reduced.

The following is an example of the electrochemical process.

When two metal samples is connected with a wire and the electricity measured through the connecting wire, we find that one of the electrodes becomes different
in potential than the other and that the corrosion rate of the copper decreases while
the corrosion rate of the zinc increases.

By connecting the two metals, we have made the copper a cathode in an electrochemical cell, and the zinc has become an anode.

The accelerated corrosion of the zinc may be so much that all of the oxidation of the copper stops and it becomes protected from corrosion. We call this method of corrosion control cathodic protection.

Reaction at copper become:-

2H+ + 2e- --> H2 (reduction), receive electron release by copper
Cu(2+) + 2e --> Cu (reduction) ,receive electron release by zinc via connection cable

Reaction at zinc become:-

Zn --> Zn2+ + 2e- (oxidation), free electron

Standard Reduction Potential :-

The potential of a voltaic cell as a whole will depend on the half-cells that are involved. Each half-cell has a known potential, called its standard reduction potential (Eº). The cell potential is a measure of the difference between the two electrode potentials, and the potential at each electrode is calculated as the potential for reduction at the electrode. That’s why they’re standard reduction potentials, not standard oxidation potentials.

On this reduction potential chart, the elements that have the most positive reduction potentials are easily reduced and would be good oxidizing agents (in general, the nonmetals), while the elements that have the least positive reduction potentials are easily oxidized and would be good reducing agents (in general, metals).

Fundamental of Corrosion : Metal Corrosion

2009-08-11T23:45:00.000-07:00

As referred from Wikipedia, Corrosion can be defined as the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings.

Other simple and clear definition of Corrosion is the degradation of a material due to a reaction with its environment.

Material on the above definition includes metals, polymers (plastics, rubbers,etc.), ceramics (concrete, brick, etc.) or composites mechanical mixtures of two or more materials with different properties.In Petrochemical and O&G industries, we are focusing on metal corrosion.

Corrosion of metal occurred when the electrochemical process took place. What is electrochemical process ? As referred from Wikipedia,

"Electrochemical is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution."

Metal corrosion can be classified into two which is:-

1. wet aqueous (Our scope will be on wet aqueous corrosion.)
2. dry high temperature corrosion (will not be discussed)

Corrosion of metal take place when they are use within the environment where they are chemically unstable.

All metals exhibit a tendency to be oxidized, some more easily than others. The driving force that causes metals to corrode is a natural consequence of their temporary existence in metallic form. To reach this metallic state from their occurrence in nature in the form of various chemical compounds (ores), it is necessary for them to absorb energy by smelting, refining processes. These stored up energy later return by corrosion, the energy required to release the metals from their original compounds.

Introduction

2009-08-11T22:55:00.000-07:00

Hello guyz, I'm creating this blog with the hope that it can be a good reference on topics regarding corrosion and how to control corrosion. However, I'll be focusing more on Cathodic Protection system since this is my area of expertise. If you are one of those who need assistance for the design/maintenance/refurbishment of CP system you can alwiz contact me via e-mail or just leave your comment here. I'm providing consultancy/design/CAD drawing on cathodic protection system as well with considerate charges :).

Through my work experience, I'd designed,installed and commissioned cathodic protection system within Malaysia and countries like Sudan, Myanmar, Singapore and Brunei. Well it's nothing compared to other CP engineers out there :) (who haven't started their own blog yet).

Currently, I'm attached to a company involved with marine/offshore items/equipments installation and maintenance. I'm handling corrosion protection division, which include CP and coating system, thinking of to include NDT service within the division. Though, I also need to assist my company on other works and services such as SBM maintenance, submarine hose installation, fendering system etc.

If there's any enquiries or comments regarding my posting, please do leave comment or email me.

-Thanks-