Protective coatings for pipes

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FIELDS OF USAGE

ATMOSPHERIC METAL STRUCTURES

PETROLEUM PRODUCTS TANKS

STEEL SHEET

PIPES

PORT INSTALLATION

Pipes

These recommendations cover anticorrosion protection of the internal and external surface of steel pipes, used in the industrial and civil engineering; in petroleum, gas and chemical industries, as well as in housing and communal services.

Zinc-rich composition ZFES and aluminium-rich composition PAES are certified and introduced in branch standards for anticorrosion protection of the internal surface of the ship piping.

Table 1. Characteristics of ZRC produced by FMP

The name of ZRC	The type of film former	The number of packages	Appearance of the coating	Zn content in dry coating	Thermal stability, ⁰C, up to
ZFES	Modified ethyl-silicate	2	Mat, dark-grey	91-92	150
ZINOL	Thermoplastic polymer	1	Mat, smooth light-grey	95-96	150
ZINOTAN	Polyurethane varnish	1	Smooth grey	83-86	150
ZINEP	Epoxy pitch	2	Smooth, Grey	86-89	150
ZINOTERM	Modified silicon-organic pitch	1	Mat, smooth light-grey	90-95	350

Properties of compositions and the peculiarities of work with them are given in the recommendations and technological instructions of "Fine Metal Powders" for every material.

Table 2. Protection systems recommended for the internal surface of the pipes.

Medium		No	ZRC	Number of layers	Total thickness, µm	Net consumption per 1 m² of the coating, g	Expected service life of the coating, years, at least
Raw oil, water-oil emulsion, presence of abrasive material		1 2 3	ZFES # ZINOTAN ZINEP	3-4 3-4 2-3	100-140 100-140 100-140	690 590 600	5
Clear petroleum products, fuels, mineral oils, natural and liquefied hydrocarbon gases	up to 150⁰C	1 2 3	ZFES#2 ZINOTAN ZINEP	2-3 2-3 2	80-120 80-120 80-120	580 490 500	8
	up to 350⁰C	1	ZINOTERM	2	80-120	600	3
Sea water and fresh water, including potable water	cold	1 2	ZFES # 2 ZINOL	3-4 3-4	100-140 100-140	690 780	5
	hot	1	ZFES # 2	3-4	120-160	800
	overheated vapour	1	ZINOTERM	2-3	100-140	720
Aggressive gases SO₂, CO₂,H₂S	up to 150⁰C	1 2	ZINOTAN ZINEP	2-3 2	80-120 80-120	490 500	5
Aggressive gases SO₂, CO₂,H₂S	pH=5-9	1	ZINEP	3	100-140	600	5
Aggressive liquids (solutions of salts, acids, alkalis, subterranean waters	pH=5-9	1	ZINEP	3	100-140	600	3
	pH=1-12	1	ZINOTAN	3-4	120-140	640	3

*Service life mentioned above corresponds to the abrasive blasting preparation of the surface, deterioration of the quality of preparation results in reducing service life of the coating. Expected service life of the coating determines assumed durability of protective paint-&varnish system till the first overhaul of the coating. It is calculated on the basis of intensive corrosion tests and experience of practical usage. Expected service life is not a legally determined guarantee period.

**Actual consumption of paint depends on the method of application, conditions of painting as well as the dimensions of the pipes. In practice it is advisable to specify consumption before the beginning of work by means of test painting.

***The number of layers mentioned above refers to application of the coating by spraying.

Table 3. Protection systems of the external surface.

Service conditions of the pipe external surface	#	System							Expected service life, years, at least
		Primer*				Finishing layers		Total thick-ness of the systems
		ZRC	number of layers	Total thickness, µm	Net consumption per 1 m² of the coating, g	Name of the paint	Number of layers	Total thick-ness of the systems
Atmospheric conditions	1	ZFES #2	2	80	460	ALUMOTAN, Vinicolor-62	1-2	150	10
	2	ZINOL	2	80	520	ALPOL, Vinicolor-62	2	150
	3	ZINOTAN	2	80	390	ALUMOTAN, Vinicolor-62	1-2	150
	4	ZINEP	2	80	400	ALUMOTAN, Vinicolor-62	1-2	150
Soil	1 2 3 4	ZINOTAN ZINEP ZFES #2 ZINOL	3 2-3 3-4 3-4	100-140	590 600 690 780	Insulating coatings, including bitumen, polyethylene, polyvinyl-chloride strips and polyethylene sticky, enamel-ethylene coatings. Heat insulated foam-polyurethane coatings			5-10 depending on soil type

*Application of ZRC as independent coatings is possible in case there are no specific colour requirements in respect of the decorative properties of the coating. The total thickness of the coating must not be less than 120 µm, but not more than 250 µm.

**ZINOL-Vinicolor (Vinicolor-62) system is used when there is no heavy mechanical duty.

Methods of application

1. Surface preparation

ZRC is applied on prepared dry metal surface. The preparation includes:

Remove dirt, loose and laminated rust.

Degreasing: there must not be any oil or other impurities on a clean cloth after wiping the metal surface.

Removal oxides to grade Sa 2,5 to ISO 8501-1:1988. Abrasive blasting units of injected type are used for this purpose. Various types of extensions for this unit allow to use this method to a wide range of pipe diameter over 50 mm (the upper limit is not restricted). Application of mechanical methods is permissible when abrasive blasting cleaning is not possible. They are: cleaning with the help of mechanized tool (for the pipes of a small diameter - disc, end and face rotating wire brushes, for the pipes of a big diameter - corner pneumatic machines) and heat treatment (with a gas torch, live vapour). In these case shortening of the service life of the coating is possible, especially in medium- and high-aggressive mediums.

If corrosion or oil traces are found on the processed surface before the coating application, the surface must be cleaned and degreased again.

The surface prepared for painting must be dry, dust-free, of grey (from light-grey to dark- grey) colour. The time interval between the surface preparation and the coating application must not be:

more than 6 hours outdoors (provided that there is no moisture condensation on the surface and any surface contamination is excluded);

more than 24 hours indoors ( at the temperature not less than +200 C and relative humidity not more than 65%).

Application of the coating.

Conditions of application.

ZRC	Temperature of application, ⁰ C	Relative humidity, %	Drying time for one layer, min
ZFES	-15 - +40	optimum 50-80	at 20⁰ C – not more than 30 (shortens with increasing the temperature)
ZINOL	-15 - +40	not more than 90	at 20⁰ C – not more than 30 (shortens with increasing the temperature)
ZINOTAN	-15 - +50	40-98	at the humidity more than 85% 180 min (increases with decreasing humidity)
ZINEP	+5 - +40	not more than 90	at 20 C – not more than 90 min (decreases with increasing the temperature)
ZINOTERM	-15 - +40	not more than 80	at 20 C – not more than 30 (shortens with increasing the temperature)

ZRC are applied by airless and pneumatic spraying, with a brush, a roller, by dipping, jet glazing. Optional methods of application of the coating on the internal surface of the pipes are given in table 5.

At any method of application it is necessary to take into account inclination of all compositions to zinc powder particles sedimentation. So constant stirring of compositions should be performed.

Besides, it is necessary to consider that methods connected with repeated usage of one and the same paint quantity lead to premature jellification of two-package compositions ZFES and ZINEP, also of ZINOTAN.

Second layer is applied after the first layer is dry. The curing between the layers is considered satisfactory if pressing the finger (in clean rubber glove) during 5 sec. doesn't leave a trace. In closed capacities and places difficult to access the curing time increases by 1,2 - 1,5. In order to accelerate the curing it is possible to blow the internal surface of the pipe by dry clean air heated up to 60⁰C.

ZINOTERM coating should be previously cured (by heating at 1500C within 3 hours) before aggressive liquid factor is introduced.

To wash the equipment and the tools it necessary to use solvents recommended in technical documentation for each material.

Welding of the objects with 1-2 layers of ZRC (total thickness 30 - 40 µm) is admissible only if the premises are ventilated properly. The most preferable welding is electro-welding. After the welding is finished the scum and welding dust should be thoroughly cleaned off the seam, then the coating is applied.

Coating quality control

At estimating the coating quality, the appearance, thickness and adhesion are checked. The checking of the characteristics is conducted on a number of pipes from the batch (not less then 2) on the outer surface and in accessible places of the inner surface, also on the samples, which are threaded on one of the painted pipe end with the help of a transition muff.

The appearance of the coating is estimated visually. There shouldn't be any admixtures, cracks or scaling on the surface. Traces of seizure by hoisting gear are admissible. Thickness of the coating is estimated by portable magnet gauges with a special nozzle for the pipes. Coating thickness control is conducted not less then in three profiles along the pipe and not less than in four points of each profile. Coating thickness is checked upon the curing of each layer. The final approving is given after the system of coatings is cured.

Coating adhesion is checked not earlier than after 24 hours by lattice cut test from the butt-ends as far as possible from the pipe end. Adhesion should be not more than 2 points. After the test is done, the place of testing is painted with the same material.

Safety measures

Methods of the coating application to inner and outer surfaces of pipes of different diameters.

Application method	Process and equipment	Advantages	Disadvantages
Spraying (pneumatic, airless)	Outer and inner surfaces of pipes of large diameters are painted by universal equipment. Inner surface difficult to access requires using special automated equipment with nozzles. Application equipment for painting inner and outer surfaces is enumerated in table 6.	High efficiency, high quality of the coating, small quantity of the paint-&-varnish material waste.	Expensive method (by investments). Efficiency is reached only when a large quantity of the pipes is painted. Necessary control of painting equipment and washing the supplying pipes.
Dipping into tub with paint	The tube is dipped horizontally into the tub and is rotated.	Simultaneous painting of the inner and the outer surfaces.	Large wastes of paint-&-varnish materials, especially for 2-package compositions. Thickness unevenness and forming of leakage. One-layer application.
Pouring in	The material is poured into the pipe which is fixed at a slight angle, The paint is supplied manually or with a tube, The paint is flowing down distributing freely on the surface. The lower end of the pipe can be stopped up with a plug, in order to distribute the paint evenly, the pipe should be rotated, To accelerate the process special holders allowing to [paint a few pipes simultaneously are used. The method can be applied to horizontally located pipe, which is stopped with plugs from both ends and is rotated or rocked. Extra paint is either poured off or pressed out by air flow/	Simplicity	Paint-&-varnish material wastes.Blanks.Thickness unevenness.Leakagesone-layer application
Painting with piston	The paint is poured over the piston, which is located in the upper part of the vertically fixed pipe, the piston together with the column of paint is moved down.	Simplicity	Heterogeneity of coating composition thanks to the high density of the stuff, streaming down. One-layer application. Thickness unevenness and leakages due to the pipe diameter changing
Glazing	A device with holes for supplying paint is moving inside the horizontally fixed pipe; brushes of the device distribute the paint evenly on the surface. Either the device or the pipe rotates.	Respectively even coating, painting of surface imperfections, absence of leakages	Necessity of setting up of a mechanical line, washing of supplying tubes and equipment.
Painting with plugs	The paint is poured between two plugs fixed inside the pipe, then the plugs are moved through the pipe either with air flow or with a mechanical traction. One of the variants of this method is pulling the pipe through a fixed painting device, which is supplied with paint at constant speed.	Simplicity	Unevenness of the coating due to pipe diameter changing, possibility of leakages.

Paints are toxic and fire-dangerous materials, which is caused by the properties of solvents composing the paint. During paint application safety measures generally accepted in paint-&-varnish industry should be fulfilled.

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