¿Cómo se puede clasificar la corrosión de las tuberías?

Pipeline corrosion is classified into two types: internal and exterior. Internal corrosion is induced by the contents of the pipeline, such as acids, which erode the inside surface. External corrosion is caused by interactions between the pipe's exterior surface and its surroundings, such as soil or water. External corrosion is influenced by soil composition, moisture levels, the presence of stray electrical currents, microorganisms, and pipe coatings. Mechanical engineers can pick optimal materials and preventative measures to maximise pipeline integrity and longevity by taking these corrosion triggers into account.

La corrosión uniforme en tuberías puede ser interna, en casos como reinyección de aguas producidas en campos de petróleo, para mantenimiento de presión del yacimiento o recuperación secundaria; lo cual puede ser originada por dos causas: - Presencia de bacterias sulfato reductoras. - Presencia de oxígeno en el sistema. Para el caso de bacterias sulfato reductoras, se deben utilizar químicos biosidas, generalmente aminas cuaternarias. Para el caso de presencia de oxígeno, se debe revisar detalladamente el sistema, pues debería ser un circuito cerrado, por lo tano sí llegare a existir oxígeno en el sistema de reinyección, es porque está entrando aire por alguna parte de los equipos de superficie.

Uniform corrosion in pipelines, often encountered in my experience, is significantly influenced by the nature of the fluids being transported. Typically, these fluids are either oil products en route to processing facilities or final products destined for distribution, as well as gas products transported on a national scale. The corrosion characteristics and rates vary notably between these types. For oil, the primary corrosive elements are hydrogen sulfide (H2S) and Total Acid Number (TAN) levels. In the case of gases, the corrosion is predominantly driven by the presence of acidic gases within the streams. This understanding is crucial for effective pipeline management and maintenance strategies.

One of the most dangerous corrosion in multiphase gas/condensate pipelines is a localized corrosion which occurs on top half of the pipeline that is called TLC (Top of Line Corrosion) in stratified flow regimes. There are some contributing factors in this type of corrosion such as water condensation rate, presence of organic acids such as HAc, low flow rates and low gas velocities (less than 4-5 m/s). For monitoring this kind of corrosion there is only one way: intelligent pig running. No way to understand if this kind if corrosion is active in your pipeline except intelligent pigging. Corrosion coupons and ER probes installed at the end of the pipeline cannot help you to recognize it.

Generalmente, cuando se presenta corrosión por picadura, es normal percibir la aparición de los agujeros o picaduras muy cerca unas de otras, esto hace que el material metálico adquiera una apariencia superficial rugosa. Estas picaduras inicialmente son difíciles de percibir, ya que su característica es tener picaduras de dimensiones muy pequeñas, tanto que aparentan ser simples manchas y del tamaño de la punta de una aguja. Sin embargo, son éstas mismas las que son capaces de realizar un ataque muy acelerado generando la perforación de las estructuras metálicas.

Pitting corrosion is a localized form of corrosion by which cavities or "holes" are produced in the material. Pitting is considered to be more dangerous than uniform corrosion damage because it is more difficult to detect, predict and design against. Corrosion products often cover the pits

In my experience, the interplay between intergranular and erosion corrosion can accelerate the degradation process, especially in challenging environments like sour services. Intergranular corrosion weakens the metal at grain boundaries, making the pipeline more susceptible to the physical wear caused by erosion corrosion. Conversely, erosion strips away protective surface layers, exposing new areas to corrosive attacks and intensifying intergranular corrosion. This synergistic effect creates a vicious cycle where each type of corrosion exacerbates the other, leading to rapid deterioration of the pipeline. Addressing this requires selecting corrosion-resistant materials, and implementing robust designs.

There are 3 main factors, causing SCC of metals. Stresses (applied stress, residual stress, etc.), high enough temperature and "specific corrodent". The specific corrodent for each and every metals is unique. Certain metal will only be affected by certain corrodent. Two famous examples are caustic soda for carbon steel and chloride for stainless steel. The appearance of Oxygen in the system will accelerate the SCC to occur.