UFC 3 -430-11
14 February 2001
CHAPTER 3
GENERAL REQUIREMENTS
3-1
GENERAL. Provide control systems in accordance with applicable codes.
Refer to paragraph 3 -15 for applicable codes. Design control systems so that the loss
of the control medium (e.g. air, electricity, or other) will leave the controls in a fail-safe
position.
3-2
CONTROL LOCATION. Locate instrument control in the control room as
much as practical. Provide local control panels where they are required for equipment
start-up and where constant attendance is not required.
3-3
TURNDOWN. Instruments have to cover normal operating as well as upset
conditions. Several instruments might have to be provided to cover all of the ranges. It
is important that all instruments be reviewed for covering all operating as well as upset
conditions during the plant design stage.
3-4
INSTRUMENT RANGES. Size flow instruments based on a normal operating
flow of approximately 70 percent of full scale. For all other instruments set the normal
operating point at 50 percent of full scale. Use the following scales:
Flow -- Direct reading
Pressure -- Direct reading
Temperature -- Direct reading
Level -- 0-100% linear
Analyzers -- Direct reading
Suppressed ranges for temperature a nd pressure may be used as long as
they cover startup and upset conditions.
3-5
ALARMS AND SHUTDOWNS. Design the plant controls to avoid nuisance
shutdowns. These can be caused by unnecessary items being interlocked into the
shutdowns, bad design, or la ck of provisions in the case of power or instrument air
failure. Also design for easy restart in the case of shutdown, especially when caused by
non-process type failures such as interruption of power or instrument air.
3-5.1
Design Criteria. Use contac ts that open on abnormal conditions to alarm or
shut down. For all shutdowns provide a pre-alarm that precedes the shutdown. Provide
separate devices for alarms and shutdowns. Do not use the same device for an alarm
or shutdown as used for control. An e lectrical power or instrument air failure must shut
off all fuel and require operating personnel attention for a restart.
3-5.2
Testing and Servicing. Include provisions for the testing and servicing of
the shutdown device and related alarms without inte rfering with plant operation.
3-1
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