19 replies to this topic

[ogpprocessing]

Dears,

I have been told that "bypass pressurizing line" (sometimes called start-up line) is provided as a cost effective design in applications which involves high differential pressure across ESDV.

I want to know if this is the main function of this pressurizing valve? If so, why the pressurizing line is only provided for ESDV at inlet of the plant (and in few cases for plant outlet ESDV at battery limit)? We usually consider plant sectionalization concept using these ESDV valves at different points of the plant. Why this pressurizing line is not provided for all of the ESD valves?

Any other application for this line?

[tarafdar]

I don't know about bypass pressurising line regarding ESDVs.But large gate valves with big disc surface area must have bypass line to equalize pressure on both surface of the disc.Otherwise pressure on upstream face is so high it is almost impossible to open the valve.

[fallah]

Dears,

I have been told that "bypass pressurizing line" (sometimes called start-up line) is provided as a cost effective design in applications which involves high differential pressure across ESDV.

I want to know if this is the main function of this pressurizing valve? If so, why the pressurizing line is only provided for ESDV at inlet of the plant (and in few cases for plant outlet ESDV at battery limit)? We usually consider plant sectionalization concept using these ESDV valves at different points of the plant. Why this pressurizing line is not provided for all of the ESD valves?
Any other application for this line?

Ogpprocessing,

Yes, it is provided as a cost effective design in such applications.

We may see mentioned bypass around SDVs inside the plant and usually isn't applied around ESDVs (for safety issues).

During startup SDVs are in closed position.The bypass is provided for SDVs which thier downstream should be highly pressurized result in high differential pressure across them (necessity of large actuator).

Fallah

Edited by fallah, 29 August 2011 - 02:06 AM.

[ogpprocessing]

I don't know about bypass pressurising line regarding ESDVs.But large gate valves with big disc surface area must have bypass line to equalize pressure on both surface of the disc.Otherwise pressure on upstream face is so high it is almost impossible to open the valve.

What do you mean by "large"? I mean "large" is just a general qualitative criteria but we need quantitative criteria.

Edited by ogpprocessing, 03 September 2011 - 06:53 AM.

[ogpprocessing]

Dears,

I have been told that "bypass pressurizing line" (sometimes called start-up line) is provided as a cost effective design in applications which involves high differential pressure across ESDV.

I want to know if this is the main function of this pressurizing valve? If so, why the pressurizing line is only provided for ESDV at inlet of the plant (and in few cases for plant outlet ESDV at battery limit)? We usually consider plant sectionalization concept using these ESDV valves at different points of the plant. Why this pressurizing line is not provided for all of the ESD valves?
Any other application for this line?

Ogpprocessing,

Yes, it is provided as a cost effective design in such applications.

We may see mentioned bypass around SDVs inside the plant and usually isn't applied around ESDVs (for safety issues).

During startup SDVs are in closed position.The bypass is provided for SDVs which thier downstream should be highly pressurized result in high differential pressure across them (necessity of large actuator).

Fallah

So, if this is cost effective design, why this by-pass line is not provided around all of the shutdown valves of the plant?

[fallah]

So, if this is cost effective design, why this by-pass line is not provided around all of the shutdown valves of the plant?

ogpprocessing,

Please read my previous response carefully!

As i mentioned when downstream should be pressurized, during start up with SDV itself you have to use larger actuator and a by pass line would help you out to decrease actuator size.Obviously, this by pass line may not be applicable for the systems with low/moderate pressure.

Indeed, for ESDV applying the by pass line isn't usually authorized due to safety issues.

Fallah

[ogpprocessing]

So, if this is cost effective design, why this by-pass line is not provided around all of the shutdown valves of the plant?

ogpprocessing,

Please read my previous response carefully!

As i mentioned when downstream should be pressurized, during start up with SDV itself you have to use larger actuator and a by pass line would help you out to decrease actuator size.Obviously, this by pass line may not be applicable for the systems with low/moderate pressure.

Indeed, for ESDV applying the by pass line isn't usually authorized due to safety issues.

Fallah

Why designers only consider this by-pass line for battery limits of a plant?

[fallah]

Why designers only consider this by-pass line for battery limits of a plant?

ogpprocessing,

Not essentially to be considered as you mentioned above in all cases.Can you introduce any reference in this regard?

Fallah

Edited by fallah, 07 September 2011 - 12:41 AM.

[ogpprocessing]

Fallah:

Can you introduce one plant that for all of the SDVs this by-pass line (as cost effetive option) is provided?

[fallah]

Fallah:

Can you introduce one plant that for all of the SDVs this by-pass line (as cost effetive option) is provided?

ogpprocessing,

No. Please clarify what you are following to know. If i were you, at first i would try to understand the whole concept and then to find the samples in real world for concept verification.

Fallah

[ogpprocessing]

Fallah:

Can you introduce one plant that for all of the SDVs this by-pass line (as cost effetive option) is provided?

ogpprocessing,

No. Please clarify what you are following to know. If i were you, at first i would try to understand the whole concept and then to find the samples in real world for concept verification.

Fallah

What I am looking for is the answer to this simple question:

If by-pass line is a cost effective design for SDV actuator sizing, why is not considered for all of the SDVs of the plant?

[fallah]

What I am looking for is the answer to this simple question:

If by-pass line is a cost effective design for SDV actuator sizing, why is not considered for all of the SDVs of the plant?

ogpprocessing,

The answer to your question is included in my previous posts, but i repeat it as follow:

During start-up all SDVs are in closed position. If downstream of a SDV should be highly pressurized (means by opening the SDV for its downstream pressurization it would be subjected to high delta P leading to larger actuator) considering by pass line for start-up would be cost effective design, otherwise (downstream of another SDV in same plant wouldn't be highly pressurized, let say, in low pressure part of the system and SDV isn't subjected to considerable delta P) there is no need to consider by pass line and in this case it isn't a cost effective design.

Fallah

[S.AHMAD]

Dear fellows

The word "BYPASS" confuses the issue. During start up, the process system is pressurized using the "START-UP" line. We do not use ESDV for pressurizing the system that is the reason for the installation of start-up/bypass line. That is why the other SDVs do not require the so called "BYPASS LINE". I believe the start-up line (better word than bypass) has a globe valve for better flow control during pressurization. SDVs normally are gate valves.

Hope the above explanation clears the confusing issue.

Edited by S.AHMAD, 08 September 2011 - 02:25 AM.

[fallah]

Dear fellows

The word "BYPASS" confuses the issue. During start up, the process system is pressurized using the "START-UP" line. We do not use ESDV for pressurizing the system that is the reason for the installation of start-up/bypass line. That is why the other SDVs do not require the so called "BYPASS LINE". I believe the start-up line (better word than bypass) has a globe valve for better flow control during pressurization. SDVs normally are gate valves.

Hope the above explanation clears the confusing issue.

S.AHMAD,

One of the applications of by pass line around control valves or SDVs is start up performing while the main valve is closed. The other applications of by pass line are maintenance and better flow control.
Contrary to your thinking, some SDVs where may subject to high delta P during start up need by pass line for downstream pressurisation (not for exactly flow control as you mentioned but for control of downstream pressurization via by passing SDV). Again, contrary to your above mentioned statement, SDVs normally are on-off ball valves with TSO characteristics.

Fallah

Edited by fallah, 08 September 2011 - 02:18 PM.

[S.AHMAD]

Dear Fallah,

Thank you very much for the sharing of knowledge and experience.

[mm217]

Dear All,

According to your comments, as safety issue, it's not recommended to use bypass line around ESDV, but in our project which is compressor station, ESDV's are used both as XV's and ESDV's so they have bypass lines!. but only on inlet line; it has ESDV on by pass line too. i mean two ESDV's in parallel. (at the ESD of END of station it's only double block and bleed to back pressurization of equipment at start-up) . Is there any strong standard that i use to reject this configuration of valves, or you may help me to better understand it.
Thanks a lot.

[Butterfly]

I have seen a PID where a SDV (1) is located upstream od a compressor scrubber. This SDV has a bypass, and another SDV (2) is located in the bypass line.
Operation philosophy states that the bypass is used to equalize pressure around SDV-2, and allow then to open it manually.

My question is: don't I have the same problem when I want to open SDV-2? Because when I am about to open it, I have no pressure downstream, so I am in the same situation as when I am to open SDV-1

Thanks

[Butterfly]

^{I looked again at the PID diagram and see that downstream of SDV-2 there is a plate orifice. Does it have to do anything with all this?}

[mm217]

^{I looked again at the PID diagram and see that downstream of SDV-2 there is a plate orifice. Does it have to do anything with all this?}

Butterfly;
As i know the size of the bypass line is smaller than the main line, so the opening of the valve is much easier . There is always the pressure reduction device to prevent sound velocity and tension in second pipe tail.

[Butterfly]

You are right. Thank you