1. Technical Requirements
All materials and equipment furnished shall be new, unused
and free of defects. Materials and
equipment shall be protected from construction damage, particularly damage due
to sandblasting and painting. Each instrument furnished shall be provided with
fully completed data sheets. Data Sheets
shall be numbered and indicate manufacturer and model numbers. Standard ISA
instrument data sheets will be acceptable.
Multiple listing of instruments on one sheet is permitted;
however, they must be arranged in numerical sequence by tag number. Only identical instruments may be listed on
each data sheet i.e. the only difference allowed is tag numbers. An assigned
tag number which is cancelled due to instrument revisions shall not be
re-used.
Where possible, the instrument selection shall represent the
manufacturer's standard.
Standardization of instruments types, manufacturer, and model shall be
considered for the purpose of simplifying design and reducing spare parts. Selection
of instruments and supporting hardware shall be made with consideration of the
process fluid, the operating environment, and the electrical area
classification. Process fluids, steam or water shall not be channeled into
control rooms for direct measurements.
Instrument pneumatic analog signals shall be 3 - 15 psig, unless
otherwise specified or required by the equipment such as valve operators. Instrument pneumatic on-off signals shall
generally be 30 psig. Pneumatic instruments requiring a regulated air supply
shall be furnished with a SS 316 filter regulator and output gauge of SS 316.
The use of transmitters shall be maximized to improve
overall reliability and availability. All transmitters shall be “SMART”
electronic type utilizing ‘dual mode’ output with 2 wire 4 – 20 mA signal with
superimposed ‘HART’ protocol communication signal.
Local electric control switches shall be DPDT, unless otherwise
specified. Discrete (On-off) electric signals shall be 24 VDC unless otherwise
specified. Use of local electronic control switches in lieu of electronic type
transmitters requires Company approval. Separate instruments along with
separate piping and vessel tapping / connections shall be used for shutdown
initiating devices.
Where two (2) pressure or temperature transmitters monitor
the same parameter then local gauge need not be provided. The control
transmitter installation is to include a plugged connection where a gauge can
be added at future time. Instrument stands shall be designed to accommodate the
future gauge. Each field and control panel instrument shall have a permanent
SS 316 nameplate bearing its tag number. Tag numbers shall be stamped and not
engraved.
2. Instrument Accessibility
Each instrument shall be considered as a normal working
location and therefore shall be properly located in order to satisfy workers
safety conditions as well as efficiency. Instrument accessibility being able to
induce heavy consequence on piping or complex layout, this problem shall be
considered as soon as possible during the detailed engineering stage.
It shall be important to distinguish two kinds of working
location:
a.
Permanent working location
b.
Non permanent working location.
A working location shall be considered as permanent when
visit frequency is higher than once a week. Non permanent working location
shall have visit frequency lower than once a week. For permanent type, the
access shall be easy. Access platforms are to be provided where applicable and
movable ladders not permitted. For non-permanent type, movable ladders shall be
allowed if height is less than 3 meters.
The following instruments and accessories shall be
considered as permanent working location:
Control valves, ON / OFF actuated valves, transmitters,
local controllers, local converters, in-line flow meters, level gages, level
switches, pressure switches, temperature elements (indication and control) with
transmitters, analyzer take off point, sampling loop.
The following instruments shall be considered as non
-permanent working location: orifice flanges, pressure taps, thermocouples or
RTD’s, and thermo well. Permanent access at these locations is not required.
3. Instruments Process Connections
When an instrument is connected to the process by means of
flanges, those flanges shall be ANSI 150# RF rated as a minimum. The following
Table-1 gives the main requirements concerning instrument taps/nozzles.
TABLE–1
Note:
1.
To be confirmed with TW stress calculations,
2½" flange is not allowed due to piping class constraint.
Minimum insertion length of thermo
wells shall be that of 4” pipe expander/reducers as indicated on the
P&ID’s.
