Sunday, November 19, 2017

Corrosion Control

Fluid Corrosion

In the selection of materials of construction for a particular fluid system, it is important first to take into consideration the characteristics of the system, giving special attention to all factors that may influence to corrosion. Since these factors would be peculiar to a particular system, it is impractical to attempt to offer a set of hard and fast rules that would cover all situations.

The materials from which the system is to be fabricated are the second important consideration; therefore, knowledge of the characteristics and general behavior of materials when exposed to certain environments is essential.

In the absence of factual corrosion information for a particular set of fluid conditions, a reasonable good selection would be possible from literature based on resistance of materials to a very similar environment. These data, should be used with some reservations. Good practice calls for applying such data for preliminary screening. Materials selected thereby would require further study in the fluid system under consideration.

Steel Corrosion

Steel material, pure metals and their alloys tend to enter into chemical union with the elements of a corrosive medium to form stable compounds similar to those found in nature. When metal loss occurs in this way, the compound formed is referred to as the corrosion product and the metal surface is spoken of as being corroded.

Corrosion is a complex phenomenon that may take any one or more of several forms. It is usually confined to the metal surface, and this is called general corrosion. But it sometimes occurs along grain boundaries or other lines of weakness because of a difference in resistance to attack or local electrolytic action.

In most aqueous systems, the corrosion reaction is divided into an anodic portion and a cathodic portion, occurring simultaneously at discrete points on metallic surfaces. Flow of electricity from the anodic to the cathodic areas may be generated by local cells set up either on a single metallic surface or between dissimilar metals.

Nonmetallic System

As stated, corrosion of metals applies specifically to chemical or electrochemical attack. The deterioration of plastics and other nonmetallic materials, which are susceptible to swelling, crazing, cracking, softening, etc., is essentially physiochemical rather than electrochemical in nature. Nonmetallic materials can either be rapidly deteriorated when expose to a particular environment or at the other extreme, be practically unaffected. Under some condition a nonmetallic may show evidence of gradual deterioration. However, it is seldom possibly to evaluate its chemical resistance by measurements of weight loss alone, as is most generally done for metals.

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Friday, November 17, 2017

Chemical Composition of Carbon Steel

Chemical composition of carbon steel are established by material specifications for each type or grade of material. The elements that are not identified should not be present in more than trace amounts except iron. Iron is the main contain of carbon steels. Other element is present in iron metal as the impurities of element, if too much the trace element will effect to the quality of the end product.

On the real product each carbon steel or metal will have vary of composition after test by heat analysis. This because when taken from the molten heat and given on the certified material test report, the actual composition of the end product might be vary due to the fluctuations that occur during solidification and processing. So for certain grade of steel will have range quality standard to anticipate this problem, and the result of product analysis will somewhat less different.

The range of steel grade in steel composition such as in alloy steel, that give the limited of carbon, manganese and silicon added in limited and varying percentages to the iron base. Even this element percentage is limited by standard, the properties of material are wide ranging. The metallurgical structure and carbon content are major contributor to the overall properties of the different carbon steel material. Steel classified as carbon steel will contain small amounts of other elements, such as chromium, molybdenum, copper, vanadium, niobium (columbium). Phosphorous and sulfur. This element usually already contain on iron as impurities elements.

Each elements that is exist in the base iron steel has some effect on the end properties of carbon steel or alloy steel and how this material will process and react to fabrication. Especially for alloy steel some element deliberately added to the base iron, with the composition depend on the grade of carbon steel. The composition of each grade is discussed in here: Steel Composition

Wednesday, November 15, 2017

Shop Galvanized Paint In Ebay

Galvanized paint contain of zinc on the paint compound. The characteristic of zinc element that this substance have 419.4 oC, can’t dilute in ordinary solvent. Zinc very soluble in hot KOH,  this paint may be modified in order can dilute zinc in cold solution. The quality of this paint that make some type of galvanized spray paint have different price. Many kind of spray paint are sold in online shopping like spray chrome paint and anodized spray paint.

Price of galvanized Spray Paint in E-bay is many kind of type galvanized paint:

  • Aerosol Spray Paint Satin Gloss matt Primer Peelable Galvanized 400. Price £ 5.85. Auto extreme (400 ml spray paint). Use as superior paint finish, color gloss satin and matt finished.
  • Actiion Can ZG 90 Cold Zinc Galvanizing Spray 500 ml. Price £21.45. ZG 90 cold zinc galvanizing spray paint is intended as a repair coating for newly galvanized metal that required repair or re-coating to match the original finish.
  • Hammerite Direct to Galvanized metal Paint Quick Drying smooth Black, volume 750 ml. Price £17.99. Hammerite direct to galvanized metal paint is specially designed to be applied directly to galvanized metal and hard carbon steel without the need for a primer, use as paint act as both primer and topcoat in one applied.
  • Action Can ZG-90 Cold Zinc Galvanizing Paint Aerosol 500 ml. Prize £7.73. Action can cold zinc galvanizing paint. Two button for varied spray pattern and application in exterior windy conditions.
  • Zinc Rich Galvafroid Type Cold galvanizing Paint – High Zinc Rust Inhibitor, volume 1 Ltr. Price £ 28.75
  • Metallic and Enamel for all purpose aerosol spray paint DIY Gloss Matt Primer Graffiti. Price £5.75. Aerosol Spray Paint DIY use for a superior paint finish. Paint factory with volume 200 ml spray stand to heat temperature until 600 oC.

Monday, November 6, 2017

Electropolishing of Stainless Steel

Beside aluminum being electropolished, Stainless steel also need electropolished. To make stainless steel have more corrosion resistance, the hidden properties should be exposed by the process of oxidized the surface of stainless steel. This combines desirable mechanical properties with a known and proven level of corrosion resistance. Stainless steel is one of the most popular alloys to electropolish because it enhances its corrosion resistance properties. The performance of stainless steel alloys are well known and fully documented and despite these known properties and use within an appropriate environment, stainless steels can still fail from corrosion.

The basic steel of stainless steels are iron-based alloys (minimum 50% iron) and have at least 10.5% chromium. The chromium content of this alloy make stainless steel have corrosion resistance. When the chromium is exposed to oxygen, it spontaneously forms a passive oxide layer. This passive oxide layer is very thin, yet it prevents further diffusion of oxygen into the base material and thus prevents corrosion. Stainless steel electropolishing enhances the passive oxide layer by making it thicker, and therefore more resistant to harsh environments.

The detail of this process will discuss more detail later. The common stainless steel that can be electropolished such as follows:

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Sunday, November 5, 2017

Carbon Steel in Different Standard

Carbon steel standard in every country can be have different symbol, but they have similar classification as describe in ASME or ASTM. Carbon steel as ASME can be used as material for high pressure tank like Boiler and Pressure Vessel. Boiler and pressure vessel at room temperature can be have 40 kips per sq in (ksi) or 275 mega-pascals (Mpa) up to 100 ksi (690 Mpa). Material which can use as high pressure strength in application are very limited, material should have minimum tensile strength less than 80 ksi (550 Mpa), this material usually use high carbon steel.

Carbon steel are choose as material for any purpose because of same reason in all of user, the price, the properties and ease of fabrication. Carbon steel composition can be slightly different in each manufacturing but the limitation of their characteristic should include in the range of standard. Material specification of ASME and ASTM are similar in both chemicals and mechanical properties to those of the international specifications listed.

The table below are carbon steel standard comparative International Specifications.

comparation carbon steel standard
comparation carbon steel standard

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