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  1. PRESERVATION & PREVENTION FROM CORROSION Prepared By: Engr. Syed Ali Raza Naqvi [STE] 1
  2. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 2  The act, process, or result of preserving something: such as the activity or process of keeping something valued alive, intact, or free from damage or decay.  Preservation is the act of maintaining, protecting or keeping something in existence.  Preservation assists in keeping information accessible and useful over time. Conservation treatments help to ensure the longevity of objects that have value for their content, so information can be learned from them as artifacts. [1]  Any thing which is affected by its environment and surrounding must be protected to extend its lifetime such as, food products, chemicals, metals , machines etc.
  3. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 3 As more and more new oil and gas reserves are developed in more challenging and remote locations, increased transportation difficulties and thus increased long-distance pipeline constructions have been seen. Large pipe volumes are often required on a single pipeline project, and thus pipe coating activities may take place several months or even years before the coated pipes are loaded out for installation. Storage of coated pipes for an extended period, especially in the tropical environment, can lead to deterioration of pipe ends and coatings, undercutting (or corrosion creep) of external anticorrosion and/or flow assurance coatings, and rust formation of pipe ends due to accumulation of moisture, dust and debris on external and internal surfaces. Moisture and rust weakens the bonding of the anti-corrosion base layer, often being fusion bonded epoxy (FBE), to the steel substrate. Over time, disbandment can occur, particularly at the cutback of thick three layer and multi-layer polyolefin coating or insulation systems due to high residual stress [2]
  4. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 4 Several factors will affect the deterioration of pipe ends and end disbandment of pipe coatings during long term storage:  Type of coating and adhesive: Properties of different types of coating components affect their ability to withstand deterioration and end disbandment, including moisture absorption, density, hardness and elasticity, tensile strength, coefficient of thermal expansion, stress relaxation, thermos oxidation/UV and heat ageing resistance, etc.  Thickness and cutback configuration of the mainline coating: At pipe coating cutbacks, stress concentration is related to coating thickness and cutback angle. The higher the pipe coating thickness and more acute cutback angle, the higher the residual stress concentration2 . As moisture and rust weakens the bonding strength of the base coating layer to the steel substrate, over time the coating will disbound at the cutback once the resultant shrinking force from the stress concentration exceeds the adhesive force of the coating-steel interface.
  5. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 5  Quality of the factory applied coating: End disbandment of a pipe coating can be a result of already poor adhesion due to improper surface preparation or improper decontamination in the plant coating process, improper application resulting in too high interface porosity, coating formulation with too easy to absorb moisture, too low application temperature for the FBE, etc. Aside from selection of the coating material which may be specifically required by the client, the other factors are the applicator's responsibility.  Storage conditions of coated pipes prior to pipeline installation: Water absorption and rust formation can occur with coated pipes stored for several weeks or longer periods prior to construction, particularly at a hot, high humidity and salty environment (i.e. tropical and marine).
  6. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 6 Corrective and preventative measures can be taken in order to mitigate the deterioration of pipe ends and end disbandment of pipe coatings. These measures include: o Design and select a pipe coating system which can be thinner, less absorbent to moisture, more UV and thermal stable, and is less or not constrained by the shrinkage-stress factor. o Select pipe coaters who have better demonstrated process capability and track records to produce high quality pipe coatings and to deliver an effective preservation program for long term pipe storage. o Review and improve related coating application processes for the selected coating system: for examples, to tighten up surface preparation and application temperature control in order to enhance the adhesive strength of the coating to the substrate, to apply multiple layers for thick coating systems in order to reduce stress build-up, and to make correct cutback configuration and FBE toe in order to reduce/minimize the stress concentration. o Brushing back the disbanded coating until sound and tightly adhered coating, and then apply a suitable field joint coating or temporary protective system prior to pipe installation. o Develop and implement an effective temporary preservation method and program, in order to protect the pipe end cutback and the pipe coating during long term storage.[2]
  7. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 7  Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual destruction of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.[3]  Corrosion is the deterioration of a material as a result of its interaction with its surroundings and can occur at any point or at any time during petroleum and natural gas processing. Although this definition is applicable to any type of material, it is typically reserved for metallic alloys.[4]
  8. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 8  It is generally accepted that ten unique types of corrosion exist. Unfortunately, identification of a specific type of corrosion mechanism often occurs only in forensic analysis after a component fails.  Design considerations must account for corrosion using corrosion resistant materials, or by increasing the bulk of a material with a known corrosion characteristic to account for loss during its service life.  Actuarial science and economics govern this choice in the design phase, but corrosion failures often arise in service operations not anticipated in the design phase.  There are numerous remedies in existence to counteract specific corrosion mechanisms and increase the service life of specific components.[5]  Corrosion is primarily an electrochemical process. Michael Faraday established this principle in the early nineteenth century, and it is still fundamental to an understanding of the problem and to corrosion prevention.
  9. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 9 As corrosion most often occurs in aqueous environments, we now explore the different types of degradation a metal can experience in such conditions:  UNIFORM CORROSION Uniform corrosion is considered an even attack across the surface of a material and is the most common type of corrosion. It is also the most benign as the extent of the attack is relatively easily judged, and the resulting impact on material performance is fairly easily evaluated due to an ability to consistently reproduce and test the phenomenon. This type of corrosion typically occurs over relatively large areas of a material’s surface.  PITTING CORROSION Pitting is one of the most destructive types of corrosion, as it can be hard to predict, detect and characterize. Pitting is a localized form of corrosion, in which either a local anodic point, or more commonly a cathodic point, forms a small corrosion cell with the surrounding normal surface. Once a pit has initiated, it grows into a “hole” or “cavity” that takes on one of a variety of different shapes. Pits typically penetrate from the surface downward in a vertical direction. Pitting corrosion can be caused by a local break or damage to the protective oxide film or a protective coating; it can also be caused by non-uniformities in the metal structure itself. Pitting is dangerous because it can lead to failure of the structure with a relatively low overall loss of metal
  10. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 10  CREVICE CORROSION Crevice corrosion is also a localized form of corrosion and usually results from a stagnant microenvironment in which there is a difference in the concentration of ions between two areas of a metal. Crevice corrosion occurs in shielded areas such as those under washers, bolt heads, gaskets, etc. where oxygen is restricted. These smaller areas allow for a corrosive agent to enter but do not allow enough circulation within, depleting the oxygen content, which prevents re-passivation. As a stagnant solution builds, pH shifts away from neutral. This growing imbalance between the crevice (microenvironment) and the external surface (bulk environment) contributes to higher rates of corrosion. Crevice corrosion can often occur at lower temperatures than pitting. Proper joint design helps to minimize crevice corrosion.  INTERGRANULAR CORROSION An examination of the microstructure of a metal reveals the grains that form during solidification of the alloy, as well as the grain boundaries between them. Intergranular corrosion can be caused by impurities present at these grain boundaries or by the depletion or enrichment of an alloying element at the grain boundaries. Intergranular corrosion occurs along or adjacent to these grains, seriously affecting the mechanical properties of the metal while the bulk of the metal remain intact. An example of intergranular corrosion is carbide precipitation, a chemical reaction that can occur when a metal is subjected to very high temperatures (e.g., 800°F - 1650°F) and/or localized hot work such as welding. In stainless steels, during these reactions, carbon “consumes” the chromium, forming carbides and causing the level of chromium remaining in the alloy to drop below the 11% needed to sustain the spontaneously-forming passive oxide layer. 304L and 316L are enhanced chemistries of 304 and 316 stainless that contain lower levels of carbon and would provide the best corrosion resistance to carbide precipitation.
  11. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 11  STRESS CORROSION CRACKING (SCC) Stress corrosion cracking (SCC) is a result of the combination of tensile stress and a corrosive environment, often at elevated temperatures. Stress corrosion may result from external stress such as actual tensile loads on the metal or expansion/contraction due to rapid temperature changes. It may also result from residual stress imparted during the manufacturing process such as from cold forming, welding, machining, grinding, etc. In stress corrosion, the majority of the surface usually remains intact; however, fine cracks appear in the microstructure, making the corrosion hard to detect. The cracks typically have a brittle appearance and form and spread in a direction perpendicular to the location of the stress. Selecting proper materials for a given environment (including temperature and management of external loads) can mitigate the potential for catastrophic failure due to SCC.  GALVANIC CORROSION Galvanic corrosion is the degradation of one metal near a joint or juncture that occurs when two electrochemically dissimilar metals are in electrical contact in an electrolytic environment; for example, when copper is in contact with steel in a saltwater environment. However, even when these three conditions are satisfied, there are many other factors that affect the potential for, and the amount of, corrosion, such as temperature and surface finish of the metals. Large engineered systems employing many types of metal in their construction, including various fastener types and materials, are susceptible to galvanic corrosion if care is not exercised during the design phase. Choosing metals that are as close together as practicable on the galvanic series helps reduce the risk of galvanic corrosion.
  12. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 12  CONCLUSION In aqueous environments, metals may be exposed to not only uniform corrosion, but also to various types of local corrosion including pitting, crevice, intergranular, stress, and galvanic corrosion. In areas where corrosion is a concern, stainless steel products offer value and protection against these threats. Stainless’ favorable chemical composition makes it resistant to common corrosives while remaining significantly more affordable than specialty alloys such as titanium and Inconel® alloys. Stainless steel is a highly alloyed, low-carbon steel with a high (at least 11%) chromium content. When exposed to an oxygenated environment, the chromium reacts to form a passive oxide layer on the metal’s surface, slowing further and providing a self-healing quality, which helps resist uniform and local corrosion. Nickel helps to stabilize the increasing SCC resistance. Manganese, in moderate quantities and in association with nickel, will perform many functions attributable to nickel and helps prevent pitting. The addition of molybdenum (the additional element in Type 316 SS that increases its performance with respect to Type 304 SS), helps increase resistance to pitting and crevice corrosion. Reduced levels of carbon, such as those found in 304L and 316L will help prevent intergranular corrosion. Lastly, nitrogen, although a major element of stainless steel’s composition, increases pitting resistance. Choosing stainless steel can help greatly the risk of corrosion and yield long-term savings by avoiding the costs associated with reinstallation of inferior products. [6]
  13. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 13 What Causes Corrosion? o The simplest cause of corrosion is contact. That can be when metal comes in contact with all kinds of things, including water, oxygen, grime, or other metal. Any of these elements can set off the problem, but each kick- starts corrosion for different reasons. o Corrosion is a chemical reaction that plagues metals. The problem starts when a piece of metal loses electrons and is weakened. Those electrons are encouraged to leave when the metal is in contact with an electrolyte, like water, and electron-greedy materials. o Suddenly, the metal is vulnerable to other destructive chemical reactions. The result can be things such as rust, cracks, and holes. o Unfortunately, there’s more bad news for pipes. Pipe corrosion is also self-perpetuating, which means corrosion gets worse once it starts. However, there are ways to keep corrosion from creeping into piping or non-piping surfaces.
  14. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 14  Here are five ways to fight off corrosion: [7] 1. For Pipes, Watch Your Water Water is a major corrosion causer. Especially in copper piping, too low of a pH level can hurt the pipe’s lining. The EPA recommends you make sure your water’s pH hovers between 6.5 and 8.5. You’ll also want to monitor the oxygen levels in your water. Oxygen leads to rust, and it can cause buildups and blockages. Another good idea is to keep water temperatures low when possible. Hotter water tends to be more corrosive. 2. Keep Pipes Clean Microbiologically induced corrosion (MIC) happens when metals are exposed to corrosive bacteria. It’s smart to clean pipes to prevent MIC, especially when pipes are in contact with sulfides regularly. You can use inhibitors or biocides to keep fluids clean. Another option is to consider chemical treatment for water or other liquids.
  15. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 15 3. Add Protection to All Metals Protective linings or special coatings can prevent corrosion in pipes as well as other surfaces. That includes things such as beams, joints, and bolts. For instance, galvanization works by adding a layer of zinc to metallic surfaces such as steel or iron. It’s also wise to use a sealant to keep corrosive bacteria from settling into joints or crevices in the first place. 4. Keep Structures Stable Friction, jiggling, and bouncing wear on metal. When openings start to form, corrosive material sets in, and it can lead to crevice corrosion. A good way to prevent crevice corrosion is to use a restraint . Things such as U-bolts, straps, and clamps cut down vibrations that can lead to corrosion. 5. Protect Against Metal-to-Metal Contact Not all metals get along. Galvanic corrosion happens when one metal pulls electrons from another metal. The result is a weakened section and a compromised structure. The best way to protect against metal-to-metal corrosion is to insulate the metal. For piping, consider installing insulators, such as wear pads or Pipe shoes. Insulators add a buffer between metals, so the metal stays durable longer.
  16. Prepared By: Engr. Syed Ali Raza Naqvi [STE] 16 [1]. [2]. [3]. [4]. [5]. [6]. [7].