The specifications given in the standard “DIN 50929-3 Corrosion of metals - Probability of corrosion of metallic materials when exposed to external corrosion - Buried and underwater pipelines and structural components” developed by the German Institute for Standardization (DIN) are intended to provide a basis for estimating the probability of corrosion of metallic pipelines, vessels and structural components whose external surfaces are in contact with soil or surface water.
The probability of corrosion of these elements is governed not only by the properties of the materials and corrosive substances, but also by their design, dimensions and external electrochemical influences. Since these parameters cannot always be defined with sufficient accuracy, the possible corrosion behavior can only be estimated. Such estimates provide information on the type and extent of corrosion to be expected, as well as a basis for deciding what protective measures can or should be taken. The present standard is based on the information given in DIN 50929-1.
For the purposes of this standard, the concepts defined in DIN 50900 as well as the concepts given in DIN 50929-1 and DIN 30676 are valid. The following definitions will also apply:
The materials covered in this standard are those specified in DIN 50929-1. If other materials are used, expertise is required as to whether and to what extent the specifications of the above standard apply.
The evaluation of corrosive materials is done by examining the parameters in the tables given in the standard and based on the ratings given therein. These ratings are used in various ways for the various types of corrosion and the specified materials.
While unalloyed and low alloyed ferrous materials in contact with soil may undergo uniform surface removal by corrosion, extensive or deep pitting is the rule. Local corrosion events are usually attributed to the formation of corrosion cells or to the action of applied current cathodes. Soils are divided into soil categories based on their corrosivity. Sea and lake beds cannot be assessed on the basis of the information given below.
In the absence of concentration cells, especially aeration cells, free corrosion is almost non-existent. Samples used in field corrosion tests on homogeneous soil to assess soil aggressiveness can reliably simulate homogeneous free corrosion conditions. Removal rates are about 0,01 to 0,1 mm per year and generally decrease over time as coatings form. These conditions also apply to a limited extent to small-sized structures, provided that any risk from impact current cathodes is excluded and the soil is homogeneous. This includes pipelines whose elements are not frictionally bonded in the axial direction and pipelines equipped with high-resistance sheaths that exhibit minor defects.
To estimate the probability of corrosion, the ratings given in the table are used. These ratings are obtained from soil analyses and information on local factors. The total rating is calculated from an equation. This total rating is used in accordance with the table to estimate the probability of free corrosion at the relevant sampling point and to classify the soil, but does not allow for any comprehensive concentration cells that may be present in heterogeneous soils.
There is always an increased probability of corrosion in heavily contaminated soils (soils contaminated with fuel ash, slag, coal chips, coke, garbage, rubble, wastewater) due to concentration cells and where the cells are formed in the presence of impregnated current cathodes.
In short, corrosion, more specifically, pitting corrosion, which occurs excessively in marine environments, leads to a significant reduction in the service life of materials, which causes tremendous economic loss and even environmental disaster and loss of life.
Among the numerous tests, measurements, analyses and evaluations it has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “DIN 50929-3 Corrosion of metals - Possibility of corrosion of metallic materials when exposed to external corrosion - Buried and underwater pipelines and structural components” with its trained and expert staff and advanced technological equipment.
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