Frank Zou (asker) Dec 5, 2021:

According to the document (DNV-RP-J202-2010), Onshore vent stations may either be permanent or temporary.
Temporary vent stations may be portable for the purpose of depressurising sections of the pipeline for inspection, mainte-nance or repair.
As a minimum requirement, one permanent vent station shall be included that has access for depressurization of the entire pipeline.

Tomasso Dec 5, 2021:

picture block H formation w/ service vent A person can see in the picture on the right hand side..
https://www.google.com/search?q=h stack petroleum line vent ...

this is not something that you go and leave, it is used only occasionaly so the pipeline can be worked on, ant the VENT is to Temporarily releive the pressufe.

Frank Zou (asker) Dec 5, 2021:

vent station is used to release (compressed) gas inside the pipeline to reduce the pressure, so it is not for ventilation.

Tomasso Dec 5, 2021:

输油管道 picture of Block and H shaped lines and valves.h形的图片..https://www.youtube.com/watch?v=pGCa2ZnUips quote.. When a gas pipeline is installed, it is divided up using block valve stations. This enables various sections to be isolated for inspection and maintenance. The block valve is typically a full bore, soft seated ball valve to allow for scraping. However, this valve cannot be opened against full differential pressure without damage to the valve seats. Therefore a bypass is installed around the block valve and used to balance the pipeline pressure prior to opening. Plug valves should be used in the bypass as they are capable of opening and throttling against full differential pressure without damage. h形通风口 ???