1. SCOPE ……………………………………………………………………………………
2. REFERENCES ……………………………………………………….
3. SITE CONDITIONS ……………………………………………………….
4. LEVEL INSTRUMENTS ……………………………………………………….
4.1 General ……………………………………………………….
4.2 Differential Pressure Type Level Instruments …………………………..
4.3 Bubble or Dip Tubes Type Level Instruments …………………………..
4.4 Displacer Type Level Instruments …………………………..
4.5 Capacitance Type Level Instruments …………………………..
4.6 Nuclear Source Type Level Instruments …………………………..
4.7 Radar and Ultrasonic Type Level Instruments …………………………..
4.8 Magnetorestrictive Type Level Instruments …………………………..
4.9 Level Switches ……………………………………………………….
4.10 Level Gauges ……………………………………………………….
5. INSPECTION AND TESTING ……………………………………………………….
6. REVISION HISTORY ……………………………………………………….
1. Scope
This standard establishes the minimum requirements for material, design, codes and standards
to be followed for engineering and design of the level instrumentation.
2. References
Reference is made in this standard to the following documents. The latest issues, amendments,
and supplements to these documents shall apply unless otherwise indicated.
SABIC Engineering Standards (SES)
D02-D02 Engineering Tools and Data Structure
R01-E01 Field Instrumentation Design Criteria
R10-S01 Instrument, Tubing Material Specification
R11-C01 General Instrument Installation Criteria
R11-C02 Standard Installation Drawings – Instrumentation
American Society of Mechanical Engineers (ASME)
B31.3 Petroleum Refinery Piping Code for Pressure Piping
BPVC Boiler and Pressure Vessel Code
Process Industry Practices (PIP)
PCCLI001 Level Measurement Criteria
PCELI001 Level Measurement Guideline
3. Site Conditions
Refer to Basic Engineering Data Document (BEDD) for details and descriptions.
4. Level Instruments
4.1 General
4.1.1 General requirements established in PIP PCCLI001 shall be followed.
4.1.2 For general design, guidelines and specification refer to SES-R01-E01.
4.1.3 Dimensional sketches and level calculation sheet shall be prepared for each level
instrument
4.1.4 On boilers level instruments shall be in accordance with the requirements of the ASME
Boiler and Pressure Vessel Code, section I, part. PG-60.
4.1.5 The design of all level instruments shall include an associated local gauge to allow range
checking and visual level verification over the calibrated range of the instrument. SABIC
approval shall be required to eliminate the local gauge.
4.1.6 Flange ratings for level instruments shall be in accordance with the equipment
specifications.
4.1.7 In general, a differential pressure transmitter should be selected for level measurement.
4.1.8 Where process conditions dictate, other types of level instruments, capacitance, nuclear,
radar, ultrasonic, or magnetic float type shall be considered.
4.1.9 Level instrument installation shall be in accordance with SES-R11-C01 and SES-R11-C02.
4.1.10 Level transmitter electronic shall have a self diagnostics feature, and shall comply with the
requirements of SES-R01-E01.
4.2 Differential Pressure Type Level Instruments
Liquid level is measured by differential pressure transmitters by measuring hydrostatic head
pressure. This pressure is equal to the liquid height above the tap multiplied by the specific
gravity of the liquid. The measurement is independent of volume or shape of the vessel.
4.2.1 Differential pressure type instruments shall have an adjustable range and a suppression or
elevation mechanism.
4.2.2 Wetted parts material shall be 316 stainless steel, as a minimum, unless process conditions
require different material.
4.2.3 For vessel containing slurries or waxy oils, the diaphragm seal shall be extended diaphragm
type, i.e. diaphragm flushed with the inside wall of the vessel.
4.2.4 Differences in specific gravity between the vessel contents and sealing fluids shall be taken
into consideration for calibration of the level instrument.
4.2.5 Diaphragm seals used in vacuum service application shall be specifically designed for
vacuum service by the manufacturer.
4.2.6 The diaphragm seal fluid, seal leg fluid, or purge fluid shall be compatible with the ambient
and process temperature extremes.
4.2.7 Capillary tubes shall be adequately protected and supported to avoid mechanical damage
and sagging.
4.2.8 Capillary tubes length shall be specified taking into consideration the routing requirements.
Unnecessary long capillary tubes lengths shall not be specified.
4.2.9 Welded capillary connections or remote sensor electronic technology shall be specified for
vacuum applications.
4.2.10 Remote sensor electronic can be considered in accordance with service application, to
avoid undesirable lengths of impulse piping or capillary tubing, heat tracing, etc.
4.3 Bubble or Dip Tubes Type Level Instruments
A bubbler system using a top mounted transmitter can be used for vessel level measurement.
This system consists of an air or inert gas supply, a pressure regulator, purge flow meter, a
pressure transmitter, and a bubble tube extending down into the vessel. Air or inert gas is
bubbled through the dip tube at a constant flow rate. The pressure required to maintain the flow is
determined by the vertical height of the liquid above the tube opening times specific gravity.
4.3.1 Bubbler type level measurement is not a preferred choice and shall require SABIC approval.
4.3.2 The purge gas flow rate shall be sufficient to keep the system bubbling during level or
pressure rise inside the vessel.
4.3.3 Excessive flow will result in unacceptable pressure drop in impulse lines that will develop
errors in pressure or level measurements and waste gas. In vacuum systems, all the gas
has to be removed to maintain the vacuum.
4.3.4 The flow rate is usually adjusted with a flow restricting needle valve. For vessels operating
at or above atmospheric pressure, the needle valve is located downstream of the meter and
the meter operates at the regulated pressure. For vacuum systems, the needle valve is
usually upstream of the meter and the meter operates at the lower vessel pressure.
4.3.5 The regulated supply pressure should be at least twice, in absolute pressure units, the
vessel pressure to develop a critical pressure drop across the restricting needle valve. This
results in constant purge gas flow despite vessel pressure changes. Where this is not
convenient, and supply pressure varies, a constant differential regulator across the needle
valve may be used to stabilize flow.
4.3.6 Backflow of process fluid into the purged system shall be prevented by using check valves
at the outlet of the purge flow meters.
4.3.7 The pressure sensor should be located above the process vessel to permit condensation to
drain back to the vessel.
4.3.8 Wetted parts material shall be 316 stainless steel, as a minimum, unless process conditions
require different material.
4.4 Displacer Type Level Instruments
Displacement transmitters operate on the principal that a body immersed in a liquid is buoyed
upward by a force equal to the weight of the liquid displaced. If the cross-sectional area of the
displacer is constant over the working length, then the buoyant force is proportional to liquid level.
The force is transmitted to the transmitter via a force-bar or torque tube producing a proportional
level signal. Displacer level instruments may also used for liquid-liquid interface level
measurement service.
Distinction shall be made between displacement and float devices. Displacer elements are
heavier than the liquid being measured, and remain stationary. The measurement signal is
derived from the buoyancy effect due to immersion in a liquid level and the measurement signal
is derived from the float motion or position.
4.4.1 Rotatable head construction is required for external displacers.
4.4.2 External displacer type instruments shall not be used in service where the fluid in chamber
will boil.
4.4.3 Displacer level transmitters shall be used up to 1200 mm (48 inch) in length. For liquid-liquid
interface measurement, displacer level transmitter shall be used up to 1500 mm (60 inch).
4.4.4 Radiation fins and extended bonnet shall be fitted to instruments in service where the
temperature is below -18 deg C or above 204 deg C.
4.4.5 Vent plugs and drain valves shall be provided on external displacer type level instruments.
4.4.6 Displacement devices shall not be used for the following applications.
a. Extremely viscous materials
b. Services that require purging to prevent plugging or sticking
c. Service with excessive condensation or vaporization of fluids in the chamber caused by
vessel-chamber temperature differences
d. Liquids that coat or build up deposits on the displacer and rod
4.4.7 Internal displacer shall have stilling well where agitation is present in a tank or long length is
required.
4.4.8 Changes in the specific gravity of the liquid can cause errors in the level measurement and
shall be considered in design.
4.4.9 Wetted parts shall be suitable for process conditions.
4.5 Capacitance Type Level Instruments
Capacitance type level transmitter consists of a probe extending to the length of the level span to
be measured. For fluid with good conductivity, the probe is a metal rod covered with an insulator.
As the liquid rises around the insulated electrode, it forms the second electrode of a capacitor,
and the capacitance increases accordingly. If the liquid is a dielectric, the probe is a metal rod,
surrounded by a metal tube with a predetermined space between the two. As the liquid level rises
between the electrodes, the capacitance increases proportionately.
4.5.1 Capacitance probes shall not be used in liquids that contain entrained gas.
4.5.2 A capacitance level transmitter special probe with separate electrode for signal return shall
be used on lined or non metallic vessels.
4.5.3 Capacitance type level instrument shall not be used if there is excessive change in the
process fluid conductivity or dielectric constant.
4.5.4 Automatic temperature compensation shall be provided in the level measurement
calculation for liquid in which the dielectric constant changes as a function of temperature.
4.5.5 Side mounting instruments shall be considered only for point level applications. Capacitance
level measurement probes shall be top mounted.
4.5.6 The capacitance type transmitter operates at radio frequencies, so care shall be taken to
avoid RF pickup by the device. RF Interference can be minimized by installing the system in
a metal vessel only. RF filters and electrostatic protectors may be specified where high RFI
is expected.
4.5.7 Information about the dielectric properties of the material and the construction of the vessel
should be transmitted to the vendor to minimize failures.
4.5.8 Wetted parts shall be suitable for process conditions.
4.6 Nuclear Source Type Level Instruments
Radiation type gauging systems measure the amount of gamma rays that are absorbed by the
liquid in the tank. In this system, the source of gamma radiation, such as cobalt 60, is placed in a
vertical column on the outside of the vessel. The measuring cell or detection is located
diametrically opposite the source on the other side. The intensity of gamma rays received by the
detector is inversely proportional to the height of liquid in the tank.
4.6.1 SABIC approval is required for use of nuclear source type level instruments.
4.6.2 Nuclear level instruments shall only be used in applications where there is no alternative
level instrument. Nuclear level instrument shall be used for the following difficult
applications:
a. Viscous or dirty materials that cannot be measured by other methods
b. Liquids subject to polymer build up
c. Cryogenic service
d. Foaming service
e. Highly corrosive service
f. Toxic service
g. Solid or liquid systems
h. Molten liquids
4.6.3 Compliance to all regulatory and safety standards is mandatory prior to procurement and
installation of the nuclear level devices.
4.6.4 A proper procedure for the disposal of the source after instrument is removed from service
shall be in place before installation of the nuclear level device.
4.7 Radar and Ultrasonic Type Level Instruments
An ultrasonic sound generator is placed at the top of the tank and transmits ultrasonic pulses
towards the fluid surface. The reflected sound wave is received by a pick-up transducer, and the
control unit computes the distance based on time span for the waves to reflect from the fluid
surface.
Radar level instrument beams microwave from an antenna located on top of the vessel. The
antenna receives back a portion of the energy that is reflected off the surface of the measured
medium. Travel time for the signal is used to calculate level.
Guided wave radar is an invasive method that uses a rod or cable to guide the microwaves as it
passes down from the sensor into the material being measured. The sensor transmits a
microwave pulse along the surface of a stainless steel cable. When the pulse reaches the
measured material, the pulse is reflected back up the cable to the sensor. The pulse transmit time
is measured and used to measure the distance to the product surface.
4.7.1 Installation and design shall meet manufacturer’s criteria for the probe and system used to
avoid errors that are due to process conditions, pipe diameter, connection sizes, branch
connections, internal vessel obstructions, etc.
4.7.2 Guided wave radar probes used on high pressure and high temperature, i.e. greater than
150 deg C and 40 bar respectively, should have minimum double seal protection.
4.7.3 Guided wave radar transmitter shall have advanced diagnostics capability to monitor coating
or build up over the probe.
4.7.4 Open path radar shall not be used in high density vapor spaces that have high hydrocarbon
content, dusty fines, or droplets forming a heavy fog.
4.7.5 Applications with foam or froth shall be reviewed with the manufacturer for applicability of
radar measurement.
4.7.6 Installation location of the radar element, i.e. horn, wave guide, shall meet manufacturer’s
criteria for distances from side wall and internal obstructions.
4.7.7 Applications for condensing products that result in heavy deposits, e.g. fuel oils, the antenna
design shall be such that minor deposits or condensation will not disrupt level measurement
accuracy.
4.7.8 Guided wave radar can be considered for interface level measurement.
4.7.9 Radar type instruments offer top down, direct measurement and are suitable for process
fluid where density, dielectric, and conductivity is changing.
4.7.10 Ultrasonic transmitters shall be temperature compensated. Ultrasonic transmitters shall not
be used in high density vapor spaces that have high hydrocarbon content, dusty fines, or
droplets forming a heavy fog.
4.7.11 Applications with foam or froth shall be reviewed with manufacturer for applicability of
ultrasonic measurement.
4.7.12 Ultrasonic transmitters shall not be used in vacuum service.
4.7.13 Wetted parts shall be suitable for process conditions.
4.8 Magnetorestrictive Type Level Instruments
The device consists of a Magnetorestrictive wire in the stem and a permanent magnet inside the
float. The float is the only moving part that travels vertically on the stem. Once a pulse current is
induced from the end of the Magnetorestrictive wire, a tubular magnetic field emanates as the
float travels, torsional vibration is launched by the interaction between the float magnetic field and
the Magnetorestrictive wire. The float position is determined by measuring the lapse of time from
the launching of the torsional vibration to the return of the signal.
4.8.1 Magnetorestrictive type level instrument is not suitable for low specific gravity and fluid
services where specific gravity is changing.
4.8.2 External Magnetorestrictive type transmitter can be considered coupled to the magnetic
level gauge.
4.8.3 Wetted parts material shall be 316 stainless steel, as a minimum, unless process conditions
require different material.
4.9 Level Switches
4.9.1 Level switches shall not be used without SABIC approval.
4.9.2 Electrical switch contacts shall be minimum single-pole double-throw (SPDT) type and
hermetically sealed. The contact rating shall be suitable for the specified service.
4.9.3 Level switches that contain mercury shall not be permitted.
4.9.4 Provision for in place testing of the level switch shall be provided.
4.9.5 Level switches shall not be used for safety systems. Level transmitter installation shall be
considered for better diagnostics and reliability.
4.9.6 Wetted parts shall be suitable for process conditions.
4.10 Level Gauges
4.10.1 Level gauges shall be of sufficient length to provide complete coverage of the range of the
associated level instruments.
4.10.2 Block, vent, and drain valves shall be provided on level gauges. Some process may prohibit
the use of block, vent, and drain valves. The elimination of block, vent, or drain valves shall
require SABIC approval.
4.10.3 The level gauge units shall be made of material suitable for the process conditions.
4.10.4 Level gauge shall undergo hydrostatic test to 1.5 times of the maximum operating pressure.
4.10.5 Level gauge glasses shall be armoured transparent type and used for the following services:
a. Distillates below 25 deg API gravity and all crude residuals
b. Propane and lighter fluids
c. Liquids containing solid material which may coat the flutes of a reflex glass
d. When there is an interface between liquids
4.10.6 Level gauge glasses shall be armoured reflex type for all other services.
4.10.7 Tubular level gauge can be used only in water or non-critical service applications with
SABIC approval.
4.10.8 Reflex type gauge glass columns shall have the minimum pressure rating of 69 bar (1000
psi) at 315 deg C (600 deg F).
4.10.9 Transparent armored gauges shall have the minimum pressure rating of 41.4 bar (600 psi)
at 315 deg C (600 deg F).
4.10.10 If opted, tubular level gauge shall be used when the pressure is below 3.50 bar (50 psi) and
the temperature is below 95 deg C (203 deg F).
4.10.11 Gauge glasses shall be limited to a maximum visible length of 1500 mm (60 inch). When
two or more columns are required to cover a longer range, the visible portion of the gauge
glasses shall overlap at least 25 mm (1 inch).
4.10.12 Above 205 deg C (400 deg F) of fluid operating temperature, a single gauge glass column
shall not exceed 1200 mm (48 inch).
4.10.13 Gauges shall have plastic frost shields for applications in which the process fluid has a
temperature below 0 deg C (32 deg F).
4.10.14 Refer to PIP PCELI001 for protective films requirements.
4.10.15 For hot services, and where is necessary to prevent the fluid from congealing, a gauge
glass with steam jacket shall be used.
4.10.16 Illuminators shall be provided as required.
4.10.17 Integral gauge glasses are allowed only on equipment that can be taken out of service
without impacting unit operations.
4.10.18 When a gauge glass column has to be installed in a three-fluid system, the preferred
method is to use dual two-fluid installations. If a single gauge glass is used for the three-fluid
system, balance line(s) are required. A balance line shall be located where it is always
covered with the middle fluid. More than one balance line shall be used if necessary to meet
this condition.
4.10.19 Gauge cocks with ball checks shall not be allowed in vacuum applications.
4.10.20 If used, gauge cocks and ball checks shall be purchased as assemblies as part of the level
gauge.
4.10.21 In steam service over 41.4 bar (600 psi) and in caustic services, mica shields shall be used.
4.10.22 Magnetic gauges should be considered as an alternative to glass for flammable, corrosive,
toxic, high-pressure, high-temperature, or long-visible length service.
4.10.23 Magnetic level gauges shall be in accordance with PIP PCCLI001 and PIP PCELI001.
5. Inspection and Testing
Vendor shall submit the following test certificates and test reports of level instruments for
purchaser’s review:
a. Material certificate
b. Dimensional drawings
c. Hydrostatic test report, if applicable
d. Calibration report