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The recommendations concern anticorrosion protection
by zinc-rich coatings inner and outer surfaces of ground-based and buried
vertical welded cylindrical tanks made of carbon steel with capacity of
400 m3 and more, intended for petroleum storage.
Paint-&-varnish coatings based on compositions ZINOTAN,
ZINEP, ZVES and ALUMOTAN produced by FMP, which are recommended for anticorrosion
protection of petroleum storage tanks were tested by various branch bodies
and institutions. The result of this testing was Lloyd's Register Certificate
¹ MATS/1515/1. Coatings based on ZVES composition are effectively applied
for petroleum storage tanks protection since 1983.
1. Zinc-rich coatings properties.
Due to the high content of metal zinc (from 83 up to 93 mass. %) zinc-rich
coatings possess a number of properties, which predetermine their use
for anticorrosion protection of petroleum storage tanks.
Zinc-rich coatings are conductive and can provide cathode steel protection.
Zinc-rich coatings don't accumulate static electricity, they don't sparkle
when stroked.
Stretching durability of zinc-rich coatings is identical
to the durability of the protected metal, which results in the coating
uniformity at the tank compression and expansion due to temperature
drops during exploitation.
Zinc-rich coatings are uninflammable, they refer to the group of materials
which don't spread fire on the surface.
Zinc-rich coatings preserve high anticorrosion properties in any atmospheric
conditions, in fresh and sea water, in petroleum and petroleum products.
2. Corrosion medium characteristics.
Tanks used for petroleum storage are exposed to intensive
corrosion destruction during exploitation. The level of petroleum corrosion
activity depends on the content of sulphureous compounds and mineral salts
water solutions, which is determined by the oilfield occurrence, petroleum
production way and others.
| Tank construction elements |
Working medium characteristics |
Aggressive impact of the medium |
| Tank inner surface |
| Roofing and upper part of the pontoons |
a) Constant impact of the gas-air medium saturated with corrosion
agents (Í2S, CO2);
á) Condensation of hydrocarbons and moisture. |
medium aggressive |
| Upper belt |
Alternating impact of corrosion mediums – liquid and gaseous (air),
containing vapours of volatile aggressive components (Í2S,
CO2) |
medium aggressive |
| Middle belts and lower parts of the pontoons |
Constant or long impact of liquid medium (petroleum), access of
oxygen is limited |
low aggressive |
| Bottom and lower belt |
à) Impact of water condensate with petroleum and petroleum products
emulsion, which represent weak solutions of acids, salts, oxygen
saturated, ðÍ 5,5 - 8,5;
b) Abrasive impact of mechanical admixtures |
medium aggressive |
| Tank outer surface: |
| Tank walls and roofing |
à) Complex impact of ambient factors: temperature drops, relative
humidity, precipitation, solar radiation;
á) Impact of corrosion active gases (Í2S, CO2)
as a result of possible leakages;
â) impact of operating mediums (petroleum) in case of their getting
on the surface;
c) contact with soil |
medium aggressive |
* If content of hydrogen sulphide in concentration
is more than 10 mg/l or there are hydrogen sulphide and carbonic acid
in all proportions the level of the aggressive impact increases by one
step.
3. Recommended systems of coatings
Scheme of tank anticorrosion protection is chosen in
correspondence with its technological function, taking into account economical
effectiveness of the chosen zinc-rich material and conditions of its application.
3.1 Tank inner surface:
| Working medium |
Painted elements of the tank construction |
Zinc-rich material |
Number of layers |
Thickness, µm |
| Raw petroleum |
Whole tank surface |
ZINOTAN |
3 |
120-160 |
| ZINOTAN+ALUMOTAN |
2+2 |
| ZINEP |
3 |
| ZVES¹ 2 |
3 |
| Raw petroleum at the absence of aggressive components
(ÑÎ2, H2S) in the atmosphere |
Roofing and two upper belts |
ZINOTAN |
2 |
80-120 |
| ZINOTAN+ALUMOTAN |
1+2 |
| ZINEP |
2 |
| ZINOTAN |
2 |
| Other belts |
ZINOTAN |
3 |
120-160 |
| ZINOTAN+ALUMOTAN |
2+2 |
| ZINEP |
3 |
| ZVES ¹ 2 |
3 |
| Processed petroleum |
Roofing, three upper belts, lower belt and bottom |
ZINOTAN |
3 |
120-160 |
| ZINOTAN+ALUMOTAN |
2+2 |
| ZINEP |
3 |
| ZVES ¹ 2 |
3 |
| Other belts |
ZINOTAN |
2 |
80-120 |
| ZINOTAN+ALUMOTAN |
1+2 |
| ZINEP |
2 |
| ZINOTAN |
2 |
| Processed petroleum at the absence of aggressive components
(ÑÎ2, H2S) in the atmosphere |
Lower belt and bottom |
ZINOTAN |
3 |
120-160 |
| ZINOTAN+ALUMOTAN |
2+2 |
| ZINEP |
3 |
| ZVES ¹ 2 |
3 |
| roofing and other belts |
ZINOTAN |
2 |
80-120 |
| ZINOTAN+ALUMOTAN |
1+2 |
| ZINEP |
2 |
| ZINOTAN |
2 |
Expected service life of the systems - 8-10 years.
Actual service life of ZVES coating on the operating projects is already
more than 10 years.
3.2 Outer tank surface:
| # |
Primer
|
Preferable top enamel*
|
|
Name
|
Number of layers
|
Thickness, µm
|
| 1 |
ZINOTAN
|
2
|
80-90 *
|
ALUMOTAN
|
|
ZINEP
|
2
|
ALUMOTAN
|
| 2 |
ZVES # 1
|
3
|
ALUMOTAN, PAES
|
| 3 |
ZVES # 2
|
2
|
4. Application method
4.1 Surface preparation
Zinc-rich composition is applied to a prepared surface.
Surface preparation includes:
Removing dirt, friable and scaling off rust with scrapers, metal brushes,
etc;
Degreasing;
Removing of oxides up to grade Sa2.5 ÈÑÎ 8501-1:1988. The best result
is reached by blast cleaning of the metal till surface roughness Rz ~
20% of total thickness of the coating;
For outer surface mechanical cleaning up to grade St2-St-3 as per ISO
8501-1:1988 is admissible. But in this case the expected service life
of the coating can be reduced;
Removing remnants of blast cleaning material and dust;
If necessary repeat degreasing.
Zinc-rich material application should be conducted
not later than 6 hours after the surface preparation was finished.
4.2 Coating application
Before beginning of the painting it is necessary
to check the ambient conditions (temperature and relative humidity),
absence of grease and secondary corrosion products on the steel surface.
During application it is necessary to stir the paint
periodically in order to avoid zinc powder sedimentation.
Zinc-rich material application is conducted by spraying
(pneumatic or airless), by brush or roller in few layers with natural
inter-layer curing. Application of every next layer is admissible.
after the previous one is fully cured. Application
of top layers not earlier than 24 hours after the last layer of the
primer was applied (PAES, ALUMOTAN - after 2 hours).
After the painting coating quality control is conducted
by the following:
Appearance - visually;
Thickness - by magnet thickness gauges;
Adhesion - latticed cut test.
Finally the painted tanks should be filled with the
operating medium not earlier than after 7 days.
| Zinc-rich material |
1 layer thickness, µm |
Net consumption for 1 layer, g/m2 |
|
| ZVES # 1 |
20-30 |
160 |
| ZVES# 2 |
30-40 |
200 |
| ZINEP |
40-60 |
260 |
| ZINOTAN |
30-40 |
250 |
* Actual consumption is determined by method and
conditions of application.
By toxicity and fireproofness zinc-rich materials
are similar to paint-&-varnish materials containing organic solvents.
While handling them it is necessary to observe rules and regulations
of branch norms and requirements.
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