Preface to the Third Edition electrical cable sizes xxxii. Measuring technology 132 3.7.2 Carrying out an intensive measurement 135 (a) Determination of the pipe/soil potential 135 (b) Determination of AU values 136 3.8 References 137 4 Corrosion in aqueous solutions and soil 139.
PRINZ
Range of cathodic protection resistance and potential distribution of current demand in the case of overprotection Cathodic protection in narrow gaps Current and potential distribution within a tube. Here, too, the shortening and removal of less important parts of older publications has had to be done to make room for newer information.
VON BAECKMANN
The editors of the German edition of the Handbook of Cathodic Corrosion Protection would like to thank Gulf Publishing Company for their great interest in the translation of this work. The publishers are grateful to the authors for their dedicated assistance with subsequent drafts of the translation.
Constants, and Symbols
R' resistance per unit length, resistive load Qnr^Qknr1 Rm ultimate tensile strength (UTS) N mm"2 Rp polarization resistance Q. 7ac amount of anodic (a) or cathodic (c) region as well as corresponding total currents.
Electrical Cable Sizes
Corrosion Protection for Buried Pipelines
It was reported that natural gas is used for lighting in the Middle East and China. In the initial phase of the city gas supply, cast iron pipes were used for electricity lines, the connections of which were sealed with tarred rope, oak wood or lead.
Corrosion Protection by Painting
The technique of iron casting only reached Europe towards the end of the 14th century. Paints and varnishes made from coal tar were used in America after about 1860 to protect iron and steel in shipbuilding, but were originally used only to coat the interior surfaces of iron ships.
History of Cathodic Protection
At the end of the 1920s, publications on cathodic protection of pipelines became known in Europe. The technology has developed in recent years from local cathodic protection to the cathodic protection of the underground installations of entire power stations and industrial installations (see Chapter 12).
Development of Stray Current Protection
Thompson for the Brooklyn streetcar in an attempt to move the stray current directly back to the rails without harmful effects [63]. Deliberate stray current drainage was already installed at a sub-rectifier in Germany in 1895 during the electrification of the Aachen railway.
Corrosion Protection by Information
The state of the art in 1987 was published in "Survey of standards, technical rules and regulations in the field of corrosion, corrosion testing and corrosion protection," together with the most important DIN standards and some other regulations in the DIN 219 [71] .
Corrosion and Electrochemical Corrosion Protection
Corrosion Processes, Corrosion Damage, and Protective Countermeasures
The most important are uniform corrosion, pitting, pitting, crevice corrosion, intergranular corrosion and those with associated mechanical impact - stress corrosion and corrosion fatigue.
Electrochemical Corrosion
- Metallic Materials
- Mixed Electrodes
In the metallic state, atoms donate part of their outer electrons to the electron gas that permeates the entire volume of the metal and is responsible for good electrical conduction (105 S cm"1). Materials consisting of elements in main groups 4 to 6 of the periodic table suffer from weight loss due to corrosion due to the formation of volatile hydrides.7 The time dependence of the changes in the measured values is important in determining J(U) curves.
This is the general case where the current densities of the partial reactions vary across the electrode surface. In free corrosion, the potential of the local cathode changes to £/c(-/e) and the potential of the local anode to t/a(/e) due to the internal polarization of the cell. The reason for this is that the total current potential curves for the homogeneous Cu and Fe regions intersect at negative currents.
Local corrosion is generally the result of the formation of heterogeneous mixed electrodes where the change in the local partial current-density-potential curves may be the result of the material or the medium. A primary current distribution can be obtained from the laws of electrostatics by integration of the Laplace equation (div grad.
Potential Dependence of Corrosion Extent
- Almost Uniform Weight Loss Corrosion
- Stress Corrosion
- Hydrogen-Induced Corrosion
- Corrosion Fatigue
- Limits of Applicability of Electrochemical Protection Processes If the products of electrolysis favor other types of corrosion, electrochemical
A slight underprotection can lead to a large increase in the corrosion rate due to the steep JA(U) curve. Aluminum and its alloys are passive in neutral waters, but can suffer pitting corrosion in the presence of chloride ions, which can be prevented by cathodic protection. Since OH~ ions are formed in neutral media in the cathodic partial reaction according to Eq. 2.
These limiting potentials are strongly influenced by the alloying elements in the steels and the composition of the medium [4]; in particular, the corrosion rate in the passive zone is reduced by Cr. Such surface films can also be affected by chemical reagents in the medium so that the corrosion rate-potential curve can shift significantly. If there is no protective current, the material quickly assumes a resting potential in the zone of active corrosion.
The sensitivity is very high within cathodic overprotection and is independent of the composition of the medium. Resistance can occur if the passive film itself has a fatigue strength (e.g. in neutral water [105]).
- Critical Protection Potentials and Ranges
Fundamentals and Practice of Electrical Measurements
- The Electrical Parameters: Current, Voltage, and Resistance In all electrical measurements, current and voltage measuring instruments with
- Reference Electrodes
- Potential Measurement
- Application of Potential Measurement
- Application of Protection Criteria
- Current Measurement
- General Advice for Measurement of Current
- Pipe Current Measurement
- Measurement of Current Density and Coating Resistance
- Resistivity Measurement
- Resistivity Measuring Instruments
- Measurement of Specific Soil Resistivity
- Measurement of Grounding Resistance
- Location of Faults
- Location of Heterogeneous Surface Areas by Measurements of Field Strength
- Quantities to be Measured and Objectives of Intensive Measurement Technique
- References
Ohmic protection current voltage drops were included exclusively in the procedures described above for non-IR potential measurements. An interruption of the protective current is detectable at the next protective station as a change in pipe/ground potential. The switch-on potential must be measured in the vicinity of the foreign cathode structure.
This corresponds to the sum of the parallel earthing resistances for public holidays (see section 5.2.1.2). 3-13 Determination of a pipeline's protective current density and coating resistance (explanation in the text). The first harmonic of the cathodic protection rectifier in the bridge circuit (100 Hz) produces.
Between this and the end of the pipeline, there are four pipe flow measurement points. It uses the inductive effect of the electromagnetic field of an audio frequency current flowing in the pipeline. Local concentrations of the current density develop in the region of a defect and can be determined by field strength measurements.
3-23 Locating the position of a pipeline with pipe location: (a) Position setting, (b) Depth setting.
Solutions and Soil
HEIM AND W. SCHWENK
- Action of Corrosion Products and Types of Corrosion
- Determining the Corrosion Likelihood of Uncoated Metals
- Corrosion in Aqueous Media
- Enhancement of Anodic Corrosion by Cell Formation or Stray Currents from dc Installations
- Corrosion Due to ac Interference
- References
-4)], and Jx is the rate of transport of a partner in the reaction leading to the formation of the surface film. In the presence of dissolved ions, the ion charge on the metal surface can be neutralized by the migration of counterions to the reaction site. It is a consequence of the action of different pH values in the aeration cell that these cells do not arise in well-buffered environments [4] and in fast-flowing waters [5-7].
The arrows represent the current density of the anode and cathode partial reactions at a given instant. 4-3 Schematic representation of the partial current densities in corrosion in free corrosion (a-c) and with the formation of cells with foreign cathodic structures (d). Rating numbers, Z, are given according to data on individual characteristics from which a further judgment can be made using the sum of the rating numbers.
The data in Table 4-1 show the significant influence of the electrical resistance of soil. The intensity of cell action depends on the aeration of the foreign cathodic structures [25-27] and on the surface ratio (i.e. the ratio of cathodic to anodic surface areas) [18].
Coatings for Corrosion Protection
Objectives and Types of Corrosion Protection by Coatings
- Organic Coatings
- Cement Mortar Coatings
- Enamel Coatings
- Metallic Coatings
Typical thick coatings are bituminous materials [3] and polyolefins [e.g. polyethylene (PE) [4]], combinations of thick coating resins [e.g. EP tar and polyurethane (PUR) tar [2]. All organic coatings exhibit varying degrees of solubility and permeability to components of the corrosive medium, which can be described as permeation and ionic conductivity (see sections 5.2.1 and 5.2.2). Corrosion protection requires certain requirements to be met, including electrochemical factors [1] (see section 5.2).
Cement coatings are usually used as liners for water pipes and water tanks, but occasionally also for external protection of pipelines [7]. Cement is not waterproof, so electrochemical reactions can take place on the surface of the object to be protected. Due to the similar processes occurring at the interface between cement and object and reinforcing steel and concrete, data on the system iron/.
The corrosion protection can only fail due to defects in the enamel layer and due to corrosion of the enamel (see section 5.4). Metal coatings are applied in special cases where the protective effect must be ensured by the coating metal or its corrosion products.
Properties of Organic Coatings
- Electrical and Electrochemical Properties .1 Review of the Types of Reactions
In the case of free corrosion at the edge of voids and in the case of cathodic protection on the entire exposed surface (ground), oxygen reduction and production of OH~ ions takes place according to the equation. OH" ions are in a position to react with the adhesive groups in the coating and thus migrate under the coating. This is due to pores or voids in the coating and poorly coated fittings and defects in the coating of girth welds where the metal is exposed to the environment.
The presence of alkali ions and the permeability of H2O and O2 are required to form OH" ions in the cathodic partial reaction, as in equation 2. Blisters are apparently statistically distributed and their formation is related to pathways of increased ion conductivity in the coating material. In case of loss of adhesion to larger area than in the right picture in fig.
It can also be recognized by the drying tendency of the areas near the anode (see section 7.5.1). The dissolution in free corrosion depends on the formation of vent cells which produce OH~ ions in the cathodic region according to Eq.
