INTRODUCTION
The
tanks are vessels
constructed for acceptance, storage, technological
possessing and transportation of different liquid
and semi fluid products independently on their form, material,
situation and
construction. The conditions for their exploitation are different. They
can be
vertical and horizontal, aboveground, semi underground and underground,
to carry
static and dynamic loads to work under vacuum and over pressure,
upon the
wind, seismic and temperature influences.
The
biggest part from this group engineering facility which are widely used
in almost all industrial sectors are the Aboveground Steel Vertical
Tanks,
which are the sheet constructions with cylindrical form.
View of Aboveground Steel Vertical Tanks
In Bulgaria
intensive construction of Aboveground Steel Tanks began in the 60
years of 20th century, and the necessity for such
facilities provoked their introduction. So a trend for
growing of the total storage tank volume is imposed and
developed. The consequences of this trend have the two
connected directions: total increase of
the tank construction annually and increase of the single volume V1. In chronological aspect, the tank
construction has the following
three periods:
(I) Formation – tanks have
relatively small volumes (V1 ≤
2000 m3), done according to foreign projects and workshop
constructions. This period is from 1900 to 1950 year. Typical
representative: steel
tank for which is used the German project and delivery and with volume V1
= 1 000 m3, constructed in the Bourgas port in 1917
year.
(II) Establishment
– During the period after
1950, and it can be said that the period ends in 1980. The tanks with
considerable volumes have been constructed (V1 = 5 000
÷
50 000 m3), according to our typical or
individual
projects: of КИПП
"Хранпроект" ( for light oil products which volume is V1 ≤
5000 m3)
in 1967 and of НИППИЕС "Енергопроект" (for fuel oil with V1≤ 10000 m3)
from 1970. The improvements of the theoretical methods optimization and
automation of the tanks projects have been made. The construction of
the steel tanks was
industrialized through implementing of the facilities for rolls sheets
production in НХК "Бургас" and later in ЗЛМК "Септември". Typical
representatives of this
period
are steel tanks in НХК "Бургас", НХК "Плевен" (now "Плама"), Thermal
power
plant "София", Thermal power plant "Тр.
Костов", Thermal power plant
"Пловдив", ОЦ "Земляне", ОЦ "Люлин" and different production plants in
our
country
( Stara Zagora, Bourgas, Sliven, Iliantzi etc.) with volume up to
10 000 m3
– with roll method of erection, and from 15000 m3 to 50 000 m3
– sheet
by sheet technology for erection.
(III) Technical inspection, repairing works and
reconstruction – The
extreme values of two trends in tank construction in our country(MAX VΣ
and
MAX V1) are reached in the period between 1975 – 1979. On
the other
part the period of use of the steel tank is accepted to be B = 25
years.
Obviously
we are in the period in which the normal term for exploitation of the
steel
tanks is expiring or even is expired.
So the
next period
must be the period of the intensive and responsible technical
inspection,
repairing and reconstruction of steel tanks in our country.
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