Selection of Low-temperature Equipment

High-pressure operations should be performed only in special chambers equipped for this purpose. Laboratory workers should ensure that equipment for operations using pressure vessels is appropriately selected, properly labeled and installed, and protected by pressure-relief and necessary control devices. Vessels must be strong enough to withstand the stresses encountered at the intended operating pressures and temperatures. The vessel material must not corrode when it is in contact with the material(s) it contains. The material should not react with the process being studied, and 

Pressure-containing systems designed for use at elevated temperatures should have a positive temperature controller. Manual control using a simple variable autotransformer, such as a Variac, is not good practice. The use of both a back-up temperature controller capable of recording temperatures and shutting down an unattended system is strongly recommended. 

In some localities, adherence to national codes such as the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code (ASME, 1992) is mandatory. Selection of containers, tubing, fittings, and other process equipment, along with the operational techniques and procedures, must adhere to the constraints necessary for high-pressure service. The proper selection and assembly of components in a pressure system are critical safety factors. Compatibility of materials, tools used for assembly, and the reliability of connections are all key considerations. 

All pressure equipment should be tested or inspected periodically. The interval between tests or inspections is determined by the severity of the usage the equipment has received. Corrosive or otherwise hazardous service requires more frequent tests and inspections. Inspection data should be stamped on or attached to the equipment. Pressure vessels may be subjected to nondestructive inspections such as visual inspection, penetrant inspection, acoustic emissions recording, and radiography. However, hydrostatic proof tests are necessary for final acceptance. These tests should be as infrequent as possible. They should be performed before the vessel is placed in initial service, every 10 years thereafter, after a significant repair or modification, and if the vessel experiences ovrapressure or overtemperature. 

Testing the entire apparatus with soap solution and air or nitrogen pressure to the maximum allowahle working pressure of the weakest section of the assembled apparatus can usually detect leaks at threaded joints, packings, and valves. 

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