Corrosion resistance of pneumatic valve material selection

in the corrosive medium under the condition of pneumatic valves, anti-corrosion chemical equipment is the key place, if not properly choose the metal materials chemical pneumatic valves, slightly careless, light damage to the equipment, or caused by accidents and even cause disaster. According to the statistics, the destruction of the chemical equipment about % is caused by corrosion, so in chemical equipment selection should first pay attention to the science of material selection. Usually there is a myth that stainless steel is 'a universal material', no matter what medium and environmental conditions with the stainless steel, this is not correct, is very dangerous.
here for some commonly used chemical media talk about corrosion pneumatic valve material selection of key points.
。 Sulfuric acid medium
as one of strong corrosive medium, sulfuric acid is an important industrial raw material is very versatile. Corrosion of different concentration and temperature of sulfuric acid on the material difference is bigger, the concentration in the % above, temperature less than ℃ concentrated sulfuric acid, carbon steel and cast iron has good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, is not used as pump pneumatic valve materials; Ordinary stainless steel such as ( CrNi、( CrNiMoTi also limited use for sulphuric acid medium. So transport of sulfuric acid pump pneumatic valve usually use high silicon cast iron ( Casting and machining is difficult, high alloy stainless steel, Alloy manufacture. Fluorine plastic has good acid resistance, the use of pneumatic valve fluorine-butterfly pump ( F is a more economical choice.
。 In HCl medium
most don't HCl corrosion resistant metal materials ( Including all kinds of stainless steel material, high molybdenum silicon also can only be used for ℃, % HCl below. And metal materials contrary, the vast majority of non-metallic materials of HCl has good corrosion resistance, so the lining rubber and plastic pump ( Such as polypropylene, fluorine plastic is the best choice of transportation HCl.
。 Medium HNO
general metal corrosion and damage, mostly in HNO quickly stainless steel is the most widely used HNO resistant material, all concentration on room temperature HNO has good corrosion resistance, it is worth mentioning the molybdenum stainless steel ( Such as, the corrosion resistance of HNO L not only no better than ordinary stainless steel ( Such as, and sometimes even better. For the high temperature HNO, usually with titanium and titanium alloy materials.
。 Acetic acid medium
it is one of the strongest material corrosion in organic acids, ordinary steel in all concentration and temperature of severe corrosion of acetic acid, acetic acid proof material is stainless steel, stainless steel containing molybdenum can also apply to high temperature and dilute acetic acid steam. For high temperature and high concentration of acetic acid or contain other corrosive medium such as strict requirements, can choose high alloy stainless steel or fluorine plastic pump.
。 Alkali ( NaOH
steel is widely used in ℃ below, % concentration of NaOH solution, there are also many petrochemical plant in ℃, while % the following USES the ordinary steel, while the corrosion increases, but the economy better. Ordinary stainless steel for corrosion resistance of lye no significant advantages compared to cast iron, as long as the medium for allowing a small amount of iron added, stainless steel is not recommended. For high temperature and alkali liquor with titanium and titanium alloy or high alloy stainless steel.
。 Ammonia ( Ammonia hydroxide
most metal and non-metallic liquid ammonia and ammonia ( Hydroxide in the ammonia corrosion is very slight, only copper and copper alloy should not be used.
。 Brine (
ordinary steel in sodium chloride solution of sea water and sea water, salt water corrosion rate is not high, in the coating protection should be used in general; All kinds of stainless steel has a very low uniform corrosion rate, but may be localized corrosion caused by chloride ion, usually adopt stainless steel is better. Above, aluminum bronze butterfly pneumatic valve.
。 Alcohols, esters, ketones, ethers,
common alcohol medium with methanol, ethanol, ethylene glycol, etc. , ketone, such as medium, ethyl esters medium are various, such as, ethers media such as methyl ether, butyl ether, their basic no corrosive, commonly used materials are applicable, the specific selection should also according to the requirements of the dielectric properties and related make reasonable choice. In addition it is worth noting that the ketone, ester, ether has solubility to a variety of rubber, when choosing sealing material to avoid mistakes.
there are many other media can not cover here, anyhow when select material should not be arbitrary and blind, or use for reference the experience of mature should refer to more related information.