What Is Winterization? Requirements For The Basic Design of Winterization Systems
What Is Winterization? Requirements For The Basic Design of Winterization Systems
What Is Winterization? Requirements For The Basic Design of Winterization Systems
Basic Principle:
Process piping where the pour point or solidifying point of the internal fluid is
higher than the lowest ambient temperature shall be winterized. Unless otherwise
specified, the fluid temperature shall be maintained above the solidifying point or
at least 10°C above the pour point.
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For liquid sulfur lines, steam jacket piping or electric heat tracing shall be applied to
maintain the fluid temperature between 118 °C and 158°C.
For highly viscous fluids such as asphalt and bitumen, the fluid temperature shall be
maintained, applying steam tracer piping or steam jacket piping, at the temperatures
exceeding the pour point +10°C or temperatures giving a kinetic viscosity of 300 cst
(Allowable maximum viscosity during the use of centrifugal pumps) or lower, whichever is
higher.
Appropriate measures to prevent fluids from temperature drop are taken for piping in
which fluids are always flowing (on-stream) while the plant is being operated. The
necessity of winterization, therefore, should be studied for the case where the plant stops
operating.
Tank yards have many items of piping, in which fluids are not always flowing (not on-
stream). Care should be taken on this point.
Every size of piping should be steam traced and hot insulated regardless of liquid
temperatures.
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Vents and drains provided for the line should, in principle, be hot insulated; the
requirement of steam tracing should be according to the line conditions.
Such lines should be sloped so as not to form pockets and should also be provided with
steam purge connections to completely empty the inside; otherwise, they should be only
hot insulated.
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(1) Lines always on-stream
(a) The upstream side of the lines of orifice plates or control valves, in which vapor
could possibly condense, should be hot insulated.
(b) Lines, in which condensate is likely to solidify or is corrosive, should be steam
traced.
(c) Lines, in which condensate is likely to freeze or coagulate due to
depressurization during shutdown operation, should be steam traced.
(d) Piping should preferably be free draining.
(e) Pockets where condensate accumulates, which may have adverse effects on the
indications of instruments (such as PG, and lead pipes of PT), should be steam
traced.
(f) Lines, which are likely to have adverse effects on continuous operation due to the
condensing of the fluid, should be hot insulated.
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Air and Nitrogen Piping
Special attention should be paid to the following.
Instrument air and nitrogen contain little moisture. Instrument air and nitrogen
piping, therefore, are not required to be hot insulated; such piping should be
constructed of materials for low-temperature services considering the lowest
ambient temperature.
When plant air is dry, plant air piping may be bare. When it is not dry, they should be
steam traced and insulated.
Steam Piping
Attention should be paid, in particular, to the following items.
Winterization of Equipment
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(a) Of towers, vessels and heat exchangers, those handling fluids that may freeze
should be provided with a drain valve at a position allowing the fluids to be drained
completely during the suspension of plant operation.
(b) Parts of vessels (boots, etc.) that come into contact with water, nozzles, valves,
and piping should be heat traced and hot insulated.
(c) No winterization is required for the equipment which can be heated by internal or
external heating coils or similar facilities, even if the equipment contains liquid
during plant shutdown.
Heat tracing should not be done during seasons in which the lowest temperature is above
0°C.
Experience shows that when the temperature falls to about −5°C, water freezes and bare
piping, therefore, breaks at pockets.
The heat tracing of the equipment and piping handling process fluids with 10°C or lower
pour point may be suspended during seasons in which the lowest temperature exceeds
15°C. Seasons may be divided into two groups, for example, summer season and winter
season, in view of the complexity of operation.
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