STATE STANDARD OF THE USSR
Unified system of corrosion and aging protection
ZINC COATING HOT
Date of introduction 01.07.90
This standard establishes General requirements (hereinafter — requirements) for protective coatings applied by hot — dip galvanizing (hereinafter-coatings) on structural steel, including high strength, steel structures, products of shaped rolled and sheet steel, sets of pipes, large diameter pipes, bent or welded before coating, containers, steel wire products, fasteners, processed in the total mass, steel and cast iron castings, forgings, stamped steel products, as well as to the base metal and coating quality control methods.
This standard does not apply to continuous coatings.
1. REQUIREMENTS TO THE BASE METAL
1.1. Requirements for the design of products to be galvanized
1.1.1. The structures shall not contain pockets, closed cavities and air bags; all cavities shall be accessible for unhindered entry and exit of liquids, molten zinc and gases.
Hollow products and products of complex shape are subjected to trial galvanizing.
It is not allowed to apply coatings on products with closed cavities in order to avoid explosion.
1.1.2. Welding of structural elements should be butt seams either bilateral or unilateral seam with jelly.
It is not allowed to zinc products with welded lap joints.
1.2. Base metal surface requirements
1.2.1. On the surface of the base metal is not allowed rolled scale, burrs, pores, inclusions, welding slags, the remains of the molding mass, graphite, grease, metal chips, marking paint.
1.2.2. On the surface of cast products should not be pores and shrinkage shells.
1.2.3. The welds should be uniform, dense and continuous along the entire length.
Pores, fistulas, cracks, slag inclusions, weld filler joints are not allowed.
1.2.4. Sharp corners and edges of products, except for technically reasonable cases, shall be rounded off by radius not less than 0,3 mm.
1.2.5. The surface of products to be hot-dip galvanized, shall be cleaned by degreasing, followed by etching or blasting treatment, followed flyaway.
The degree of surface cleaning from scale and corrosion products - 1 according to GOST 9.402.
2. COVERAGE REQUIREMENTS
2.1. Appearance of coating
2.1.1. At external inspection the surface of the zinc coating should be smooth or rough, the coating should be solid.
The color of the coating from silver-shiny to matte dark gray.
2.1.2. On the surface of the product should not be cracks, nicks, blisters.
2.1.3. The presence of zinc deposits is unacceptable if they prevent Assembly. Grains hartsink diameter of not more than 2 mm, Rabina surface, with light gray spots and color of a tint, risks, scratches, traces of capture lifting fixtures without destroying the coating to the base metal are not defects.
It is permissible to restore uncovered areas if they are not wider than 2 cm and make up no more than 2% of the total surface area. Unopened areas are protected by a layer of zinc-containing paint coating (minimum thickness of 90 microns, the mass fraction of zinc in the dry film of 80 — 85 %) or thermal spraying of zinc (minimum thickness of 120 microns).
2.2. Coating thickness
The thickness of the coating must be at least 40 microns and not more than 200 microns and is determined by the operating conditions of galvanized products and regulatory and technical documentation for a particular product.
2.3. Adhesion strength
The coating has a satisfactory adhesion if it can withstand the tests according to the methods given in paragraph 4.4.
3. THE REQUIREMENTS FOR CONTROL OF BASE METAL AND COATING QUALITY
3.1. Before coating 2-5 % of the products from the party, but not less than three, and for products of a single production - each product is controlled for compliance with PP. 1.1, 1.2.
3.2. Semi-finished products (wire, pipes, etc.) are subjected to input control for compliance with the requirements of regulatory and technical documentation for the supply and the requirements of PP. 1.1, 1.2.
3.3. The applied zinc coating is subjected to control in appearance, thickness and strength of the coupling.
Control placing each batch galvanized products. For the party take a unit of production or cargo, consisting of one or more products of the same type and size, belonging to the same order, if they are coated in one shift and in the same bath.
3.4. Control of the appearance of coatings is carried out on 100% of the products.
3.5. Control of thickness and durability of coupling expose:
1) the elements of steel structures up to 1 %, but not less than 2 units from the party;
2) welded units in the amount of up to 5%, but not less than 1 piece from the party;
3) threaded fasteners in the amount of up to 0.5 %, but not less than 3 pieces from the lot.
Allowed the use of statistical methods of control GOST 18242.
Control of coating thickness by metallographic methods may be performed on the same part of the party.
3.6. Products on which quality control was carried out by destructive methods are allowed to be presented for acceptance after the restoration of the coating.
3.7. Control of coating thickness
3.7.1. Control of the coating thickness is carried out before its additional treatment (chromating, application of preservative lubricants, etc.).
3.7.2. The thickness of the coating is controlled on the surface, but having knurling and thread at a distance of not less than 5 mm from the ribs, corners, holes and places of contact with the device. The thickness of the coating on the threaded fasteners of control on the bolt heads and the ends of the screws.
3.7.3. Measuring tool for non-destructive testing of the coating thickness should have a measurement error of not more than ±10 %.
3.8. If unsatisfactory results of checking the thickness and adhesion of a second control twice the number of parts.
When unsatisfactory results are repeated over the entire batch galvanized products is rejected.
3.9. Control of the composition of the hot dip galvanizing bath at the request of the customer is carried out before removing the products from the bath.
4. CONTROL METHOD
4.1. Appearance control
The appearance of the coatings is controlled by visual inspection with the naked eye under illumination of at least 300 Lux at a distance of 25 cm from the controlled surface.
4.2. Control of coating thickness
4.2.1. Magnetic method
The method is based on the registration of changes in the magnetic resistance depending on the thickness of the coating. Magnetic thickness gauges are used as measuring devices.
For the result of measuring the thickness of the coating take the arithmetic mean of at least five measurements at the edges and in the middle of the controlled surface of one product.
The relative error of the method ±10 %.
4.2.2. Metallographic method (arbitration)
The method is based on the measurement of the coating thickness on the cross section using metallographic microscopes of different types.
The sample for the manufacture of the loop is cut from galvanized products.
The thickness of the zinc coating measured on the cone in three or more points uniformly distributed on a line segment with a length of about 1 cm For the result should be the arithmetic mean of all measurements.
The relative error of the method ±10 %.
4.2.3. The average thickness of the coating (NDS) in micrometers determined by nondestructive methods or by the gravimetric method according to the difference between the masses of the sample before and after receiving or before and after removal of coatings according to GOST 9.302.
To remove the coating, a solution is used: 3.2 g of antimony chloride or 2 g of antimony trioxide is dissolved in 500 cm3 of hydrochloric acid, a density of 1.19 g / cm3, CH. a., according to GOST 3118 in a volumetric flask with a capacity of 1 dm3 and brought to the mark with distilled water according to GOST 6709.
The relative error of the gravimetric method ±10 %.
4.3. Control of the chemical composition of zinc melt-according to GOST 19251.1, GOST 19251.2, GOST 19251.3, GOST 19251.5.
The mass fraction of zinc in the working volume of the bath should be at least 98 %.
4.4. Control of adhesion strength of coatings
4.4.1. Method of applying grid scratches (thickness of coatings up to 50 µm)
On the cleaned surface of the controlled coating with a tool with a steel tip at an angle of 30° (the hardness of the metal tip should be higher than the hardness of the coating), four to six parallel lines are applied to the depth of the base metal at a distance from 2.0 to 3.0 mm from each other and perpendicular to them. The lines are drawn in the same direction. The adhesion strength is satisfactory if there is no peeling of the coating on the controlled surface.
4.4.2. Dyeing method
For the method of kravanja used steel and brass brushes with a wire diameter of 0.1 — 0.3 mm and a rotation speed of the brushes — 1500 — 2800 min-1.
The surface of the coating is not less than 15 s. after dyeing on the controlled surface should not be observed swelling or peeling of the coating.
4.4.3. Heating method
When using the method of heating coated parts or specimens-witnesses heated to (190 ± 10) °C, kept at a given temperature for 1 h and cooled in air. No swelling or peeling of the coating is allowed on the controlled surface.
4.4.4. Rotary hammer impact method
The flat surface of the product with a thickness of the base metal of at least 3 mm is cleaned of dust, mechanical impurities and degreased with organic solvents.
A rotary hammer weighing 212.5 g is mounted on the flat surface of the product so that the hammer head falls vertically on the horizontal surface of the product. Produce at least two hammer blows so that the distance between the parallel prints was 6 mm, and the distance from the edge of the print to the edge of the product was not less than 13 mm.
1. DEVELOPED AND SUBMITTED to the State construction Committee of the USSR
S. V. Marutyan, kand. tech. (head of the topic), S. A. Klochko, L. N. Pavlova, S. G. Gutnik, L. M. Belousova