Thermo Scientific ISQ 7000, Руководство по оборудованию

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Preface
Hydrogen Safety Precautions
xxii ISQ 7000 Hardware Manual Thermo Scientific
Stainless steel is usually recommended because it is a safe, cost-effective material. Piping
of
black iron or copper must not be used, as the pipe can become brittle with age.
Elastomeric/plastic tubing of various plastics and polymers should not be used, unless the
tubing is approved for use with hydrogen. If elastomeric/plastic tubing is used for
hydrogen gas delivery, the tubing should be tested for hydrogen permeability to minimize
leakage.
The hydrogen piping system must be flexible enough to endure routine thermal
expansion and contraction. The system should also include considerations for the most
severe condition of temperature and pressure expected during service. Piping and
supports must be able to withstand static loading introduced by such things as ice and
snow; and dynamic loading from high wind and earthquake.
Caution should be used if burying hydrogen piping. Proper controls should be used to
protect against damage and corrosion, and also to prevent Hydrogen from entering a
building if there is any leakage.
• Fittings— All fittings must be of the proper type approved or designed for use with
hydrogen gas. Use as few fittings as possible to minimize the potential for leaks. After
installation, ensure that leak testing is carried out prior to system use, and on a regular
basis.
There must be no PTFE tape or other things like plumber's putty used to enhance a seal, as
this actually is a detriment to a good seal. Ideally the best installation would use stainless
steel tubing with appropriate gas-tight fittings.
Welding is usually preferred for joints in hydrogen piping systems since welding provides
a better connection and reduces the potential for leaks compared to mechanical fittings.
Soft solder joints are not permitted for hydrogen systems (due to the low melting point of
soft solder and its potential for brittle failure at cryogenic temperatures). Brazed joints are
permitted, but such joints should be protected against the possibility of external fire.
Tubing connections should be clamped to barbed or press-fit type connections. Hose
clamps or
jubilee clamps must not be used.
• Valves— All valves must be suitable for hydrogen service and for the specific operating
conditions. Valves, including regulators, must not be used for hydrogen, unless they are
designed and identified for such a use. Ball valves are often chosen because of their
superior leak tightness through the valve seat. Pneumatic operators are usually chosen for
remotely operated valves so that potential ignition sources (electricity) are remote from
the valve.
Manual shutoff valves should be provided near each point of use, within immediate reach.
If a hydrogen cylinder or hydrogen generation system is located within immediate reach,
a separate point-of-use shutoff valve is usually not necessary.
Line regulators that have their source away from the point of use should have a manual
shutoff valve near the point of use.