Hydrogen is a colorless and odorless gas with a density of 0.09 g/L (the lightest gas) and is difficult to dissolve in water under standard conditions. At - 252 ℃, it becomes colorless liquid, and at - 259 ℃, it becomes snowflake solid.
Under the condition of high temperature and high pressure, hydrogen molecules are relatively active, and hydrogen molecules are small, penetrating, and there will be hydrogen corrosion, often referred to as "hydrogen permeation";
Hydrogen itself has active chemical properties but is not corrosive. Because the size of hydrogen atom is far smaller than that of metal atom, hydrogen can be dissociated into hydrogen atom and penetrate into the lattice gap of metal material under high temperature and high pressure. At this time, when the pressure disappears, hydrogen will escape from the diaphragm of the transmitter again. After repeated time, The diaphragm of the pressure transmitter becomes porous and fragile as if it were corroded. If there is hydrogen molecule escaping through the diaphragm and entering into the silicone oil, the capillary where the silicone oil is located is totally closed because it needs to conduct pressure. At this time, the extra hydrogen will also cause the deformation of the diaphragm of the pressure transmitter, resulting in inaccurate measurement of the pressure transmitter.
Because the thickness of the measuring diaphragm is less than 0.1mm, the conventional pressure transmitter is prone to hydrogen embrittlement and is affected, resulting in the degradation of the measuring diaphragm toughness and loss of elasticity, and cavity bulge or crack. With the passage of time, hydrogen molecules can even penetrate the measuring diaphragm and enter into the isolated silicone oil conductive fluid. The presence of bubbles increases the loss in the process of pressure transmission, and also directly interferes with the measuring effect of the pressure transmitter, resulting in the zero drift of the pressure transmitter, unstable output, and the occurrence of measurement errors that make the pressure measurement parameters fluctuate. In more serious cases, even damage to the instrument may cause accidents. Pressure transmitter is a device integrating measurement and signal transmission. It can convert pressure signal into standard electric signal for control and real-time data remote transmission. Its core components are sensor core and measuring capsule. In the process of brittleness, if the pressure transmitter is a flange remote transmission type, its body will not be damaged. However, due to the destruction of the pressure transmission pressure at the front end, the data measured by the pressure transmitter itself will also be completely distorted and cannot operate normally. If the pressure transmitter and flange are directly connected, the pressure transmitter itself will be damaged when the silicone oil is filled with hydrogen molecules or the corrugated diaphragm is directly in contact with hydrogen.
The corresponding solution is:
(1) The sensor shall be plated with gold or filled with fluorinated oil (fluorinated oil).
(2) "O" ring seal shall not be used, but all-welded structure.
(3) Increase the thickness of steel parts.
(4) Adopt other types of sensor core, such as glass micro-melting.
Reasonable selection of pressure instruments is an important means to ensure production safety.