Query about vent line provided. 1

[tranvietnga1905]

Hi Gentlemen,
In piping system design, I normally provide drains and vents wherever there are loops. But i don't know the case that piping system transfer fluid, the vent line also is provided, so fluid is inside. Could you help to explain that this vent line to be operated/ or used and its functions.

Thanks

 

[BigInch]

Its usually convenient to provide drains and vents using plugs for construction-commissioning purposes, or with valves, if the line must be drained or vented for routine operating necessities.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[pennpiper]

tranvietnga1905

What kind of plant are you talking about?
What are the commodities in this plant?
What are the Design Pressures for these commodities?
What are the Design Temperatures for these commodities?
What Code is to be used to design this plant?


High Point Vents and Low point Drains. What are they? Why do we have them? These are both very good questions. So let’s us take a look at some answers to these questions.
First you might ask if there are there other types of vents. Yes, there are other types of vents. And by association there are also other types of drains besides the Low Point Drain. There are the Process vents and there are the Process drains. The process vent and process drain is provided for multiple usages during the proper active operation for which the plant was designed.
Every plant that is built with piping systems must insure that the piping systems are properly fabricated, installed and safe. Some of these systems may have very hot or very cold or hazardous or toxic chemicals in them. These types of commodities can kill, maim or seriously injure the operators working in one of these plants or the people living around these plants.
In order to insure that a piping system is secure, the system must be tested and properly prepared prior to start-up. The method used for this testing is to fill the system with water and then apply pressure. This is called “Hydro-testing.” Hydro-testing can be done with other types of fluids but water is the normal choice. The water, under pressure will seek and find weak points in the piping system and then squirt out. Water under pressure is not as dangerous as a normal commodity such as high pressure steam or sulfuric acid. Some systems only need to be tested for tightness. Others must be tested then because the water is not compatible with the process, it must be flushed with a solvent or other cleaning agent to remove the water. For this Hydro-test to be done and be affective the system must be absolutely and completely full of water (or other fluid).
In order to completely fill a piping system you must be able to get all the air out of the pipes. The air will naturally accumulate in the high points of the system. Thus we install “high point vents” to be able to get rid of the air. Once the test is completed we must be able to get rid of or drain out all the water. The water naturally gravitates down to the low points of the system. So we install “low point drains.”
Hydro-test vents and drains are normally ¾” or 1” in size. Most of these vents and drains are only used when the plant is first built or when a system is modified and must be retested. These vents and drains do not always require valves. Some plants only install temporary valves for use during the testing process. After the test the valve is removed and a plug is installed. Other plants may use some selected hydro-test vents or drains as process start-up vents or drains so the valves installed in these are retained. Still other plants require that all hydro-test valves be permanently installed and plugged.
In conclusion, high point vents and low point drains are a small but important and necessary detail of the piping system in a process plant.

 

[dcasto]

in this day and age I have re-thought the whole vent/drain point ideas. Now I install about 75% fewer because of VOC monitoring requirements.

Back in days of old, the more the merrier was the norm when it came to taps or drains on a system.

Today with excellent hot tapping systems and better ways of purging lines, the needs are lower. Even if in a country tyat doesn't have all the VOC regulations, you might think again about the number and locations.

 

[tranvietnga1905]

Hi there,
Thank you very much, at very right detailed explaination from pennpiper would provide me with precious knowledge in the field. Regarding your questions, i am checking some lines those will be conveying fluid gas in a Gas Seperation Plant, design conditiions are mostly at the ATM DP and 70 celsius degrees DT, ASME B31.3 codes are used. Also thank to some additional information from dcasto and BigInch.

 

[BigInch]

There's not much else you can say.

If the line is to flow gas, and it can accumulate liquid that cannot be handled by the process, you should install drains to remove the liquid. If the line is to flow liquid, you should have gas that cannot be handled by the process, install vents to remove it. If its a frequent problem for operations, use a valve. If it is usually not going to be necessary, a plug may suffice.

For filling and draining testing meduim (water for hydrotest), you may find it is convenient to install both vents and drains in areas of the piping that will not be easy, or will not otherwise vent or drain without installation of vent or drain plugs.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla