Hydrogen

Hydrogen - fuel gas without color, taste and smell. Under normal conditions, 14.5 times lighter than air. Under normal conditions, the hydrogen density is 0.09 g / l. Among the gases is the easiest and has the highest thermal conductivity. Soluble in many metals (iron, nickel, platinum, etc.), slightly soluble in water. In the liquid state exists in the temperature range of -252,8 ° C to -259,2 ° C.

Hydrogen is the most common in the universe, making up the bulk of stars and interstellar gas. On Earth, is contained in the form of compounds (17% in the number of atoms, 1% mass fraction in the crust), only a small amount of it present in the atmosphere in the form of a simple substance (about 0.00005% by volume).

Hydrogen is obtained by chemical methods, the most common of which are:

• transmission of water vapor over red-hot coke (t = ~ 1000 º C): H 2 O + C ↔ H 2 ↑ + CO;
• the interaction of water vapor and methane (t = ~ 1100 º C): 12SN 4 + 5H 2 O (vapor) + 5O 2 → 29n 2 ↑ + + 3SO 9SO 2 ;
• electrolysis of distilled water, the formal reaction: 2H ​​2 O → 2H 2 ↑ + O 2 ↑; because almost clean water does not conduct electricity, it added electrolytes, for example, KOH;
• electrolysis of aqueous solutions of chloride salts: 2NaCl + 2H 2 O → H 2 ↑ + 2NaOH + Cl 2 .

According to GOST R 51673-2000 pure hydrogen gas (including those used for thermal processing of metal) is made of three kinds: the higher, the first and second. Balloon with hydrogen, is painted in dark green, with the inscription "Hydrogen" in red (PB 10-115-96, GOST 949-73).

Hydrogen is supplied in standard steel tanks with a capacity of 40 and 50 liters at a pressure of 14.7 MPa (Standard 949), seamless steel cylinders with a large volume (1,000 liters) at a pressure of 39.2 MPa (GOST 12247), by pipeline, as well as in special large tanks of gas - gas tank, usually under pressure of not more than 10 MPa.

Hazards and safety precautions when working with hydrogen

• hydrogen mixed with oxygen and air (detonating gas) fire and explosion hazard, and for hydrogen-air mixture concentration limit of flame spread is 4.12% -75% by volume, for a mixture of hydrogen and oxygen - 4.1% -96% of volume;
• Auto-ignition temperature of the mixture of hydrogen and air - 510 º C, a mixture of hydrogen and oxygen - 450 º C;
• daylight hydrogen flame is almost not visible, so it is necessary to use a special detection sensors;
• liquefied hydrogen in contact with skin causes severe frostbite, the evaporation of liquefied hydrogen may form explosive mixtures and fire;
• High pressure hydrogen is able to provide a narcotic effect;
• at high concentrations of hydrogen, causing oxygen deprivation and suffocation, while working in its environment is necessary to use insulating gas masks, and the rooms are equipped with ventilation.

The use of hydrogen in welding and cutting
Hydrogen has received limited application:

• for atomic-hydrogen welding (usually steel and aluminum thickness of 5-10 mm);
• as fuel gas for gas welding (usually steel, aluminum thickness to 5 mm) and cutting;
• as an additive to argon, nitrogen plasma treatment.

In recent years, interest in hydrogen for the flame machining of metals increases due to the emergence of mobile devices, providing production of hydrogen-oxygen mixture in the hydrolysis of water. The decomposition of the water electric current generated oxygen and hydrogen in the ratio of β = 1:2, but this is the flame of oxidation and ensures the quality of the welding process of steels. That the flame was normal (β = 0,25-0,4) gas mixture in the bubbler water electrolysis-enriched vapor generator hydrocarbons - gasoline, acetone, alcohol, etc. When using gasoline flame temperature is 2600 ° C. Feedstock to produce hydrogen and oxygen is 5-35% solution of KOH in distilled water.

Hydrogen-oxygen welding performed mostly left way. As a filler material used welding wire Sv08GS, Sv08G2S, Sv10GS, Sv10GSM. Doping of silicon and manganese deoxidation of the metal provides a weld pool required because of an excess of oxygen. For the hydrogen-oxygen welding and cutting apparatus and produced a variety of installation - "The League", "Energy", "Moscow", etc.

Photos. The devices League-12 and League-02 for hydrogen-oxygen welding, brazing and cutting by water electrolysis

This type of flame treatment of metals does not require gas cylinders, environmentally friendly, reduces operating costs.

See also:
gas (oxygen) welding
oxygen cutting technology

Welding materials:

welding electrodes welding wire welding flux for arc welding carbon dioxide helium

argon protective gas mixture acetylene propane-butane IAF