To do this, applying new technology or deviate
from traditional solutions, requires highly qualified design
resources. This includes both personnel and design tools. The
‘Regulation relating to design and outfitting of facilities etc. in
the petroleum activities section 8, stipulates the following
requirements concerning qualification and use of new
technology and new methods: ‘Where the petroleum activities
involve use of new technology or new methods, criteria shall be
prepared with regard to developments, testing and use in order
to fulfil the requirements to health, environment and safety. The
criteria shall be representative of the relevant operational
conditions, and the technology or the methods shall be adapted
to already accepted solutions.
Qualifications or testing shall demonstrate that applicable
requirements can be fulfilled by use of the relevant new
technology or new methods.’THE TECHNOLOGICAL CHALLENGE
In a process plant there is a range of different components
such as vessels with different kinds of inventory, different types
of valves, pipes, tubing, pumps, turbines, heat exchangers, etc.
All have their specific safety related aspects when exposed to
fire.
The main safety issue when process equipment is exposed
to fire is to prevent escalation of the accidental situation. Fire in
a process plant usually implies that an accident already has
taken place. The purpose for the remaining process equipment
is then to maintain integrity and moderate the effect of the
accident.
Most materials will loose their strength as the temperature
increases. A logical strategy is then to reduce mechanical load
on the equipment. Depressurization system is a well-known
mean in the process industry and is normally a standard part of
a process plant. The aim of a blowdown system is to reduce the
pressure inside the process equipment faster than the strength
reduction due to heat exposure. As fire is most probably fed
from the process itself the purpose of the blowdown is also to
reduce fuel supply to the fire. The challenge is to design the
equipment and the system to have the required property.
Figure 1 shows an overview of the physical processes that
govern the blowdown process. Assuming a fire, the heat
exposure on the outside is dependent on convective and
radiative heat transfer to the shell. The heat transfer to the
outside is dependent on the flow situation around the shell and
the emissivity and absorptivity properties of the shell material.
The shell surface temperature is influenced by the conductivity
of the shell material and the heat transfer inside the shell
surface. As the inside shell surface is contact with both liquid
and gas in addition to a splash zone, the heat transfer conditions
are quite complex. Some standards reject heat transfer to the
gas zone with the argument that the heat transfer coefficient to
gas is significant less than to liquid.
This is an erroneous
argument for two reasons. At high pressure the heat transfer
coefficient increase significantly. Even if less heat is
transferred, the density of gas is significant less than liquid and
the temperature increase of the gas might be a main contributor
to the pressure increase.
谢绝机器粗翻 谢谢各位