Are there any inspection parameters for instrument air?
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What are the specific requirements for compressed air used in instrument systems? For example: moisture content, oil content, temperature, etc. – how much of an impact do these have on the instrumentation system?
The main considerations are the requirements related to instruments that use pneumatic power, as well as the sensitivity and accuracy of these instruments; relevant standards are established based on the actual usage of instruments within the plant. Our factory has low requirements for instrument air; compressed air can be used as a substitute for a short period of time
Based on practical experience, the main concerns regarding instrument air are freezing and clogging; as for the issue of oil, we lack relevant experience. Our factory uses oil-free lubrication air compressors. It is said that the pressure-reducing filter in front of the control valve also needs to be lubricated. 1. Instrument air has a dew point parameter; high moisture content is a concern mainly because it can cause the instrument air pipelines to freeze up (become blocked) ； 2. Additionally, instrument air has a dust content parameter, which is also used to prevent dust accumulation from blocking the air supply pipelines. Refer to the \"Design Specifications for Instrument Air Supply\" HG/T 20510-2000: 2.0.1 The dew point of the air source in the instrument air supply system under operating (online) pressure should be at least 10°C lower than the local annual (seasonal) extreme minimum temperature in the working environment or in historical records. 2.0.2 The location of the inlet for the instrument air source should be chosen in such a way as to prevent the intake of flammable, explosive, toxic, or corrosive gases (or vapors). Inhalation of industrial dust and atmospheric dust should also be avoided. 2.0.3 The air source used for instrument gas supply must be purified. Through the purification unit, at the filter outlet, it is required that the dust particles in the instrument air have a size of no more than 3 μm. The dust content should be less than 1 mg/m3. 2.0.4 In the design of instrument air supply systems, oil-free lubricated air compressors should be preferred. The oil content in the instrument air supplied by the air supply unit should be less than 10 mg/m3 (8 ppm (W)). 2.0.5 When an oil-lubricated air compressor is used or when process compressed air is directly employed as the instrument air source, a high-efficiency oil remover must be installed to keep the oil content in the compressed air below specified levels; in addition, appropriate filtering and drying devices as well as spare storage tanks are required.
Generally, the dew point requirement is what is tested
There is a standard for gauge pressure; what’s important is mainly the dew point
Refer to Compressed Air, Part 1: Pollution Control Levels
The requirements for instrument air in petrochemical plants are very high and strict. In simple terms, the instrument air used in factories is required to be free of water, dust, and oil, but specific requirements may vary depending on the region (mainly latitude). The dew point of instrument air is a very strict parameter; generally, it is required that the dew point of instrument air be at least 20 degrees lower than the local minimum temperature. The requirements regarding dust and oil are relatively more lenient, as these can be purified again using pressure reduction filters before use.