Cryogenic Valves

Cryogenic Valves:

• What & why of Cryogenics
• Expectation from Cryogenic Valves
• Cryogenic Valve Engineering
• Test Process & Setup Requirements

What is Cryogenic in broad-spectrum?

In general definition of Cryogenics in physics, is the construction and behaviour of materials or any item at very low temperatures.

Hence we should know about the specific low temperature, which calls for cryogenic temperature. Scientists define Cryogenic temperature as “temperature below which point on the temperature scale refrigeration ends and cryogenics begins.” This starts below −150 °C (123K; −238 °F ), as a reasonable allocating line, since the normal boiling point of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen and normal air) lie below −150 °C while the Freon refrigerants, hydrogen sulphide and other common refrigerants have boiling points above −150 °C.

Cryogenics in Oil & Gas

For the application of valves in the process application, applications with operating temperature below -45 °C are considered as cryogenic, and generally goes to -196 °C. Temperatures upto -45 °C are classified as Low Temperature.

Common Cryogenic Applications

• Natural Gas Liquefaction & Regasification
• LNG Transportation
• Air Separation Units
• Cryogenic Storage and Tankages
• Petrochemical (Ethylene, Ethane, Propane etc.)
• Liquefied Natural Gas Supply Chain

Production and Liquefaction of Natural Gas

Regasification of Natural Gas

Air Separation Units

Tankages

Key Expectations from Cryogenic Valves

• Suitability of all materials for applicable cryogenic temperature
• Suitability with the media
• Integrity of valve performance by means of consistent performance of all components even with wide temperature variations
• No deterioration in sealing performance with temperature change
• Integrity of valve sealing to atmosphere
• Sound operating mechanisms in place for valve operation
• In line maintenance features in case of valves welded in lines

Cryogenic Valves testing process

• Ambient Valve Testing with Cryo test media
• System proving
• Valve Cavity Purging
• Cooling of the Valve
• Low & High Pressure tests, Valve Operation
• Warm Up and Post Cryo Testing & Examination

Equipment selection

• Insulated tank with capability to take volume and mass
• All connections & fittings suitable for Extreme Temperatures and Pneumatic Pressures
• All test flanges, lifting arrangements suitable for cryo temperature
• Computation & availability of Liquid or Vapour Nitrogen / Dry Ice requirement
• Test media – Helium requirement
• Test setup insulation arrangements
• PPOE for testing manpower

Applicable standards for Low temperature Applications

• BS 6364:1984 Specification for valves for cryogenic service
• ISO 28921-1 Industrial valves – Isolating valves for low temperature applications – Part 2: Type testing
• Shell SPE 77/306 – Production Testing Of Valves In Low Temperature Services

Cryogenic Valves test setup

Ref: ISO 28921-1:2013

Test Process –Cooling Down Cycle

• Valve cooling is done at controlled cooling rates
• Important to give sufficient time for uniformity of temperature across valve external body and internal components
• Helium purge at low pressure is maintained throughout

Test Process –Soaking at target test temperature

• Once the desired temperature is achieved, another 30 minutes is given for complete uniformity.
• This is called soaking of the valve at test temperature
• Helium purge is maintained at all times

Test Process –Leakage testing

• Testing is carried out at incremental pressures with Helium

• Leakage measurement through
  • Inline Flowmeters
  • Measuring Cylinders using displacement method
• Valve Cycling

Test Process –Remove valve for Liquid N2

• Remove top insulation cover
• Valve to be removed from Insulated tank
• Natural Warming up cycle to restore ambient temperature

Test Process –Warming up

Ref. Courtesy:  Advance Valves