This article is about Sight Glass Gauges / Switches Material Selection Criteria & Design For Level Measurement of Instrumentation and Control Systems as per International Codes and standards for Commercial Buildings, Plants and Refinery Projects.
Sight Glass Gauges / Switches Material Selection Criteria & Design
Material Receiving General Checklist for Instrumentation & Control
Purchase Order and Instrument specification sheet criteria shall be confirmed and compared with instrument stainless steel tags / labels and nameplates, and shipment checked for damage, prior to acceptance of the shipment
Verify that all the instruments are from technically acceptable vendors. (Attachment 1)
Sight Level gauge glasses in hydrocarbon service shall be transparent or reflex type heat-resistant glass with chambers machined from solid bar alloy steel and with drop-forged alloy steel covers. Area lighting shall be provided for all gauges installed in poorly lighted areas.
Gauge illumination shall also be provided to all transparent gauges where readings are taken at night or are vital for safe operation of the process.
“The pressure and temperature ratings of the gauge glasses shall be
equal to or higher than the vessel design pressure and temperature.
Minimum rating for the reflex type shall be 14,000 kPa (2,000 psig) at
40°C, and for the transparent type 7,000 kPa (1,000 psig) at 40°C.”
“Gauge glass gaskets shall be graphoil or graphite-impregnated type
material. The gasket material must be asbestos-free and capable of
sealing under the continuous pressure and temperature conditions set
forth in paragraph 5.1.2 (B5)”
“Gauge glasses, in low temperature or low boiling point service, shall be
large chamber reflex type with minimum ¾ inch female NPT top and
bottom connections. Flange connections may be used when required.”
Large chamber reflex gauges shall have a pressure rating of at least 1.25 times the vessel design pressure at the vessel design temperature.
Large chamber gauge glasses shall be supplied to the required single length dimension whenever possible instead of the manufactures’ standard lengths.
Frost gauges shall be specified for low temperature service below -7°C. Lucite frost shields shall be included and shall extend through the gauge glass insulation.
“Gauge glasses shall not be used on refrigerated storage tanks. Refer to
SAES-B-057.”
Gauge glasses shall not be used except where required for calibration of other instrumentation. Where installed, gauge glasses shall be maintained in a closed and drained condition except when such calibration is being performed. [SAES-B-057 Sec. 10.1]
Reflex gauges shall be used on all clean services, except for liquid interface level. Weld pad type reflex gauges shall be used only in ambient temperature and atmospheric pressure applications.
Transparent gauges shall be used for acid, caustic, dirty or dark-colored liquids, liquid interface, high viscosity fluids, high-pressure steam applications above 2100 kPa (300 psig), and for NGL with specific gravities less than 0.55. Suitable shields (e.g., mica) on the inside of the gauge shall be considered for steam, caustic and other fluids that may adversely affect glass.
Tubular gauges shall not be used in hydrocarbon service. They may be used only in water or non-critical service applications, where the pressure is below 350 kPa (50 psig) and the temperature below 95°C. Tubular gauges shall not be used in fire water applications.
“For pressurized storage vessels, gauge glasses shall be installed only if
required for calibration of other instruments. The gauge glass shall be a single 320 mm gauge with ball check gauge cocks, except as limited in paragraph 5.3.3. The gauge glass shall be installed at the elevation
required to calibrate the other instrument. The other instrument may be local or remote indicating.”
“Ball check type gauge cocks shall not be used in dirty services where
waxy or gummy components exist and deposition can lead to potential
blockage of the ball check flow passages. For corrosive service, the
gage cock body and trim shall be made from corrosion resistant alloys which are compatible with the process fluids. The minimum
requirement for corrosive service is stainless steel stem, seat and ball
check.”
An independent high liquid level alarm shall be installed in each tank. The alarm shall be set to allow operating personnel sufficient time to stop incoming flow without overflowing the tank. The use of a high level flow shutoff device shall not nullify the requirement for a high level alarm.
With the exception of relief valve piping, all instrument connections (except thermo wells) smaller than 50 mm (2 in) shall be provided with excess flow check valves or restricting orifices having an orifice size not greater than 3.175 mm ( 1/8 in), or spring return valve with fusible link.
International Codes and Standards for Sight Glass Gauges / Switches
- Flow Nozzle Material Selection Criteria Design & Flow Measurement
- Venturi Tube Material Selection Criteria Design & Flow Measurement
3. SAES-J-002 – Technically acceptable instruments.
4. SAES-J-300 – Level.
5. SAES-B-057 – Safety Requirements: Refrigerated and Pressure Storage Vessels.
1. Attachment 1: Sight Glass Gauges / Switches Technically Acceptable Instruments – SAES-J-002
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