Unit shut down for maintenance

In accordance with the purging principle, it is not allowed for steam to flow directly through the flow meter and control valve at the beginning; only a small amount of steam can be allowed to flow through them later on, in order to prevent damage to the instrument components during purging

Don’t all normal control valves use a bypass line?

It is necessary to perform a short-duration purging or maintain a low opening for purging; otherwise, what will happen if the instrument technician stops work and finds a pool of oil? If there is oil, it won’t meet safety standards either. Of course, it’s mainly done by blowing across the lines.

Focus on crossing wires, use instruments as a supplement, and take into account instruments while scanning wires.

If the instrument has a bypass, the bypass valve should be fully open and the control valve slightly open. If no bypass is designed, open the control valve to 100%. Blowing and purging must cover every corner to ensure safe maintenance.

Please pay attention to the terminology used; the process of shutdown for maintenance that you mentioned should not be called “purging”; it should be referred to as “replacement”. For example, gas pipelines need to have the gas inside them removed before they are handed over for maintenance. Generally, nitrogen or steam is used to displace the gas; afterward, depending on the maintenance requirements, if it is necessary to enter the area, air must be used for displacement again. . Before use, it should also be purged with steam or nitrogen to remove oxygen from the system. The purging of pipeline systems is the process of removing physical impurities from within the pipes. It requires an airflow with a certain flow rate to purge the pipeline. This requires the removal of the relevant orifice plates and instrument probes, in order to prevent physical impurities from damaging the instruments due to high-speed airflow, or from hindering the gas flow and thus preventing the removal of such impurities.

The flow meter cannot be backblown; use steam to gently push it. As long as the steam purging of the control valve doesn’t take too long, there should be no major problems.

According to the scanning principle, precision instruments such as control valves and flow meters should, in principle, use the bypass line; it is sufficient for them to pass through the main line briefly

Generally, nitrogen is used for material discharge; during steam purging, it should be the bypass flow meter