Tuesday, November 28, 2017

Steel Weld-ability or P Number

P Number of steel is an indicator of weld-ability. The standard codes of weld-ability is refer to ASME standard that is approached to qualifying of welding procedures and welders/welding operators. For the purpose of specific toughness testing, each set of P number materials is subdivided into groups. The P Number of number materials are divided into groups 1 through 4, which loosely reflect the strength levels of the materials, as follows:

  • Group 1: materials with a minimum tensile strength requirement less than 485 Mpa.
  • Group 2: materials with a minimum tensile strength form 485 Mpa to less than 550 Mpa.
  • Group 3: materials with a minimum tensile strength from 550 Mpa to less than 620 Mpa.
  • Group 4: materials with tensile strength properties of more than 620 Mpa.

The purpose of P number is to establish qualification of material group based on weld-ability.

Effect of Chemical Composition on Weld-ability

Chemical composition of steel can affected the ability to be welding. The presence of certain chemical in the final micro-structure can effect to the weldability of steel. Weld-ability generally explain by means of a continuous transformation (CCT) diagram, which is formed by two sets of curved CCT diagram. Chemicals contain like carbon, manganese, chromium and molybdenum suppress the start of austenitic stainless steel, decomposition to lower temperature. Too much carbon contain on steel make more difficult to be welded, but contain metal like chromium, manganese or others make the steel easily to be welded. This is normal like the characteristic of metal generally.

The Quality of Welding

The characteristic of every kind of steel can different on welding apply, the increasing of temperature during welding change the crystal form, there is a limit temperature of each kind of steel to change the Chrystal form, Sometime the formed new crystal can have very bad behavior like easily to crack and even easily to corrode because of high temperature is applied during welding. So welding operator should understand the characteristic of each kind of steel and how they treat welding in order don’t break the crystal structure. Time and temperature of welding electrode will determine the quality of welding, more less a crystal structure change during welding, more better the quality of welding. The quality of welding can be seen under X-Ray, if the quality of welding is bad then the x-ray result showing porous picture. Good quality of welding will showing a solid picture of X-ray result.

Welding on Carbon Steel and Stainless Steel Result:

Here are example result of welding result on carbon steel:

carbon steel welding 1
carbon steel welding 1

carbon steel welding 2
carbon steel welding 2

The example result of welding on stainless steel:

stainless steel welding 1
stainless steel welding 1

stainless steel welding 2
stainless steel welding 2

Wednesday, November 22, 2017

Physical Properties of Carbon Steel

There are two properties of steel, physical properties and chemical properties of carbon steel. Physical properties of carbon steel are such as follows:

  • Mean coefficient of linear thermal expansion; the ratio of the change in length to the original length at a reference temperature, To, per degree of temperature change, where To is normally room temperature. If lo is the length at To and alpha, α is the mean coefficient of linear thermal expansion, the length at temperature T, lt is given be this formula:

Lt = lo [1 + α (T – To)]

  • Linear thermal expansion; the change in length over a specific temperature range per 30.5 m.
  • Modulus of elasticity (E); 1. The measure of rigidity or stiffness of a material; the ratio of stress below the proportional limit to corresponding strain. 2. The slope of a stress strain curve in the range of linear proportionality of stress to strain. This known as Young’s modulus.
  • Thermal conductivity; the quantity of heat transmitted, k, due to unit temperature gradient, in unit time under steady conditions in a direction normal to a surface of unit area and when the heat transfer is solely dependent on the temperature gradient.
  • Thermal diffusivity; the constant in heat conduction equation describing the rate at which heat is conducted through a material. It is linked to thermal conductivity, k, specific heat, Cp, and density, , through the equation.

 Thermal diffusivity = k/Cp.⍴

  • Electrical resistivity; a measure of how strongly a material opposed the flow of electric current.

Electrical resistivity = ⍴ = RA/L

  • Specific heat: the amount of heat, Cp, measured in calories, required to raise the temperature of one gram of substance by one degree Celsius.
  • Density: the mass per unit volume of a solid material
  • Specific gravity: the ratio of the density of a substance to the density of water.
  • Shear modulus (G): The ratio of shear stress to the corresponding shear strain for shear stresses below the proportional limit of the material. Value of shear modulus are usually determined by torsion testing. Shear modulus is also known as the modulus of rigidity.
  • Melting point: melting point is the temperature at which a metal change from solid to liquid; temperature at which the liquid and solid are at equilibrium.
  • Poisson’s Ratio: the absolute value of the ratio of transverse (lateral) strain to the corresponding axial strain resulting from uniformly distributed axial stress below the proportional limit of the material.
physical properties of carbon steel
physical properties of carbon steel

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.

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