23 replies to this topic

[ankur2061]

Hi,

I would request some of learned and senior colleagues to give me some background on drain systems in an oil and gas installation, both onshore and offshore.

Follwing are the questions:

a) Can an open drain system be connected to a closed drain system? To my undertsanding this is not permissible in new installations as per several operating company guidelines. However, there may be extreme circumstances where due to equipment/piping layout constraints and process requirements it may be required to do so. Process requirements mean where the hydrocarbons removed from the open drain collection vessel and the closed drain vessel have a common end destination.

If this is permissible, what are the design constraints that need to be considered when connecting open drains to closed drains?

Are there any international standards (API, ISO) which provide guidelines for open and closed drain systems?

c) Is there a classification methodology / heirarchy of drain systems such as open/closed, hazardous/non-hazardous, oil-contaminated/relatively oil free/completely oil free in oil and gas installations. If yes, can the heirarchy be represented as a diagram or sketch?

Would appreciate a lot if some of the learned veterans of this forum could answer my questions or at least direct me to some literature/article/standard which would answer all of the above questions.

Regards,
ankur2061

[Afshin445]

Hi ankur2061

I have same problem as you.I am busy in project as refurbishment of some wellhead platforms.
In those platforms there is no open drain system and also due HSE consideration we installed plate instead of greating for preventationm of release of oil to SEA. In new design all of funnels containing oily water need to directed to closed drain system.
But we have diffuclty regarding Air Ingress form funnels to Closed Drain Drum. I didn't find any safe mechansim
for preventation of Air Ingress yet.I also very appreciate if you or someone can help in this regard.

Thanks,
Afshin

Edited by Afshin, 01 February 2010 - 02:44 AM.

[ankur2061]

Hi ankur2061

I have same problem as you.I am busy in project as refurbishment of some wellhead platforms.
In those platforms there is no open drain system and also due HSE consideration we installed plate instead of greating for preventationm of release of oil to SEA. In new design all of funnels containing oily water need to directed to closed drain system.
But we have diffuclty regarding Air Ingress form funnels to Closed Drain Drum. I didn't find any safe mechansim
for preventation of Air Ingress yet.I also very appreciate if you or someone can help in this regard.

Thanks,
Afshin

Afshin,

This is a very old post (3 yrs old) & I suggest you start a new thread for your query. Over these 3 years a lot has changed in my understanding of drain systems for off-shore installations.

You cannot avoid air ingress from open drains into the closed drain drum. But you can always reduce the risk hazard of the system by extending the inlet header into the closed drain by dipping it below the liquid level at a depth of 1 m. Essentially your open drain header pipe is dipped into the closed drain drum at a level of 1 m below the minimum liquid operating level.
This prevents ingress of hazardous gas into the open drain sytem if you are using a common drain drum for both open (non-hazardous) & closed (hazardous) drains & reduces the risk of an explosion or fire.

Hope this helps.

Regards,
Ankur.

[Afshin445]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

Edited by Afshin, 02 February 2010 - 04:33 AM.

[shan]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

You may consider liquid seal pots to block air ingress.

[Afshin445]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

You may consider liquid seal pots to block air ingress.

Shan,

Could you please give a sketch for your suggestion.

In this regards, please note that Wellhead Platforms are Unmanned
and there is normaly no person present in platform.

Regards,
Afshin

[shan]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

You may consider liquid seal pots to block air ingress.

Shan,

Could you please give a sketch for your suggestion.

In this regards, please note that Wellhead Platforms are Unmanned
and there is normaly no person present in platform.

Regards,
Afshin

Please see the attachment for the seal pot sketch. No personal maintenan  SEAL POT SKETCH.xls   20KB   347 downloadsce needs at all.

[Afshin445]

Shan,

Thank you for your reply.But I think this is very important to maintain the water level in Seal Drum
in constant level. do you have any suggestion about required instrumentaion in Seal Drum?

Regards,
Afshin

Edited by Afshin, 06 February 2010 - 02:00 AM.

[shan]

Shan,

Thank you for your reply.But I think this is very important to maintain the water level in Seal Drum
in constant level. do you have any suggestion about required instrumentaion in Seal Drum?

Regards,
Afshin

There is no instrumentation at all on the seal pot. The liquid level is controlled by the position of outlet piping.

[Afshin445]

Shan,

Thank you for your reply.But I think this is very important to maintain the water level in Seal Drum
in constant level. do you have any suggestion about required instrumentaion in Seal Drum?

Regards,
Afshin

There is no instrumentation at all on the seal pot. The liquid level is controlled by the position of outlet piping.

Shan,

I prepared a prelimanery sketch as attached based on your proposd seal drum. I am gratfule if I have your comments in my sketch.

Regrads,
Afshin

Attached Files

•  Seal Drum_2003.xls   102KB   282 downloads

Edited by Afshin, 09 February 2010 - 08:29 AM.

[shan]

Shan,

Thank you for your reply.But I think this is very important to maintain the water level in Seal Drum
in constant level. do you have any suggestion about required instrumentaion in Seal Drum?

Regards,
Afshin

There is no instrumentation at all on the seal pot. The liquid level is controlled by the position of outlet piping.

Shan,

I prepared a prelimanery sketch as attached based on your proposd seal drum. I am gratfule if I have your comments in my sketch.

Regrads,
Afshin

Please see the following for my assumptions and comments.
Assumptions
A) Open drain fluid is able to flow into the seal pot by gravity.
The seal pot fluid is able to flow into the closed drain drum by gravity.
Comments
1. Seal pot is not a piece of equipment (No equipment number). It is a piping special item.
2. It is not a drum. There is no requirement of the diameter size. No capacity. No resident time.
4. Portable water tank drain should be directed to drain header instead pot vent.
5. There is no process need for the inlet global valve and outlet control valve.
6. LG, LSH, and LSL are unnecessary because liquid level will be at the location of outlet line always.

[AZIZ_MN]

Hi ankur2061

I have same problem as you.I am busy in project as refurbishment of some wellhead platforms.
In those platforms there is no open drain system and also due HSE consideration we installed plate instead of greating for preventationm of release of oil to SEA. In new design all of funnels containing oily water need to directed to closed drain system.
But we have diffuclty regarding Air Ingress form funnels to Closed Drain Drum. I didn't find any safe mechansim
for preventation of Air Ingress yet.I also very appreciate if you or someone can help in this regard.

Thanks,
Afshin

HI AFSHIN,
IN MY PLANT FOR THIS PURPOSE, WE HAVE "SAMPLE COLLECTION DRUM" WHICH IS EQUIPE WITH FUNNEL WITH PIPELINE AS INLET OF THIS DRUM, ONE NITROGEN LINE TO PRESSURISE THIS DRUM, ONE DRAIN LINE TO 'CLOSE WET SLOP DRUM" AND ONE VENT LINE TO DEPRESSURISED THIS DRUM ( SAMPLE COLLECTION DRUM) TO ATMOSPHERE, WE ARE COLLECTING LIQUID HYDROCARBON SAMPLING AND LABORATORY LIQUID WASTE TO BARREL AND THIS BARREL WE ARE POURING TO INLET FUNNEL WITH ALL SAFETY APPLIANCE PERSONAL PROTECTIVE EQUIPMENT TO THIS "SAMPLE COLLECTING DRUM" AFTER THAT PRESSURISING WITH NITROGEN TO 1 BARG AND TRANSFERING TO "WET SLOP DRUM" BY DEFFERENCIAL PRESSURE AND OBSERVING LEVEL GUAGE IN "SAMPLE COLLECTING DRUM", THIS METHOD WILL NOT PREVENT AIR INGRESS BUT IT WILL REDUCE FOR SOME EXTEND,
THANKS AND BEST REGARDS

[ankur2061]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

Afshin,

Please see the attached sketch for off-shore WHT (Well head towers) drain arrangement. The sketch is from a company standard I prepared for a major off-shore O&G company in the middle-east.

Regards,
Ankur.

Attached Files

•  Well_Head_Towers.doc   54.5KB   263 downloads

[shan]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

Afshin,

Please see the attached sketch for off-shore WHT (Well head towers) drain arrangement. The sketch is from a company standard I prepared for a major off-shore O&G company in the middle-east.

Regards,
Ankur.

Hi Ankur,

Execuse me to make a few comments on your company standard design, although nobody invited me to do so.
1. It takes much more volume and weight for holding 1 m seal height liquid in the drain sump tank than in a seal pot. The drain sump tank will be a relative heavy and bulky vessel.
2. The liquid level of drain sump tank depends on the instrumentation control of discharge pump or dump valve because liquid outlet is on the bottom of tank. The liquid level of seal pot will be there always because the outlet line is located in the middle to pot.
3. There is recovered oil outlet but no water outlet on the tank.

Regards

Shan

[Afshin445]

Shan,

Please find below my answers in your comments:
1- Agree
2- Agree
4- This is not Drain Line, it is Water Line for Start-Up of system, when seal drum is empty.
5- If we don't install inlet globe valve then how sysyem will be sealed in long time becase liquid is Seal Pot
may vaporized when system dosen't work in long time, this valve isolate system from upstrem, the same scenario is
applicable for Outlet MOV, when operator forgoten to closed inlet valve or in case of leakage in inlet valve.
6- I am agree for removing LSH & LSL but I think LG is necessary for filling of seal pot by operator by potable water.

Based on our discussion, I prepared new sketch, I hope I have your new comments.

Regards,
Afshin

Attached Files

•  Seal Drum_2003.xls   132KB   177 downloads

Edited by Afshin, 10 February 2010 - 12:12 AM.

[Afshin445]

Ankur

Thanks you for your fast reply. I think your suggestion is usfule for
preventation of ingress of HC from Closed Drain Drum to Funnels Header.
By my problem is vice versa, I must prevent of Air ingress from Funnels Header
to Closed Drain Drum.

In this regards, I am grateful if you will accompany your suggestion with a sketch.

Regards,
Afshin

Afshin,

Please see the attached sketch for off-shore WHT (Well head towers) drain arrangement. The sketch is from a company standard I prepared for a major off-shore O&G company in the middle-east.

Regards,
Ankur.

Ankur,
Thank you for your suggestion, but the problem is Drain Drum is Existing equipment and it's hard to do such a things
on that.

Regards,
Afshin

[shan]

Shan,

Please find below my answers in your comments:
1- Agree
2- Agree
4- This is not Drain Line, it is Water Line for Start-Up of system, when seal drum is empty.
5- If we don't install inlet globe valve then how sysyem will be sealed in long time becase liquid is Seal Pot
may vaporized when system dosen't work in long time, this valve isolate system from upstrem, the same scenario is
applicable for Outlet MOV, when operator forgoten to closed inlet valve or in case of leakage in inlet valve.
6- I am agree for removing LSH & LSL but I think LG is necessary for filling of seal pot by operator by potable water.

Based on our discussion, I prepared new sketch, I hope I have your new comments.

Regards,
Afshin

1. I don’t understand why you have the siphon piping configuration at the outlet. Moreover, why is the siphon broken on the top? I don’t think the siphon works with top hole and if it works, air will intrude from that point.
2. If the start-up is a concern, the pot may be pre-filled with liquid. I expect the filling will be neither continuous nor often. The liquid evaporation will not be a problem because the pot is installed on the offshore platform with 100% humidity environmental.
3. In my opinion, your valves and instruments are luxury items (not necessary for the basic process). If you have enough money, you may also install PI, TI, Sample Port and Cleaning Port. Sometimes, people may just think we are not sophistical enough if we provide a simple, economical, and direct solution for their problem.

[ankur2061]

Hi Ankur,

Execuse me to make a few comments on your company standard design, although nobody invited me to do so.
1. It takes much more volume and weight for holding 1 m seal height liquid in the drain sump tank than in a seal pot. The drain sump tank will be a relative heavy and bulky vessel.
2. The liquid level of drain sump tank depends on the instrumentation control of discharge pump or dump valve because liquid outlet is on the bottom of tank. The liquid level of seal pot will be there always because the outlet line is located in the middle to pot.
3. There is recovered oil outlet but no water outlet on the tank.

Regards

Shan

Shan,

1. The attachment provided is a schematic and not a P&ID & hence without any instrumentation details.

2. When you have several sources (both open & closed drains) draining into the drain sump tank, it is obvious that the vessel would not be a small vessel. Please note that any open drip trays or open drains that are accidentally oil contaminated would be very large sources of oily water due to the possibility of rain water mixing with them.

3. I am not trying to compare the seal-pot with the drain sump tank which is a much larger tank.

4. As mentioned earlier, since the attachment is just a schematic it only gives partial details. There certainly will be a bottom drain connection for removal of water. If you notice carefully the oil removal line extends up into the seal pot as a stand-pipe. The pumping system shown is for removal of oil to either the main oil line or to the service boat, which is the major function of the drain system on the WHT and fulfills the requirements of a schematic.

5. Unfortunately, I am not in a position to provide a P&ID at present otherwise I would have attached it, where you would definitely find the items you have claimed to be missing such as the bottom drain connection & the instrumentation for the pump start/stop on level control of the drain sump tank.

Hope this clarifies my position on the attachment I have provided.

Regards,
Ankur.

[narendrasony]

Shan / Ankur,
Please refer the attached sketch with U-loop seal and indicate if there is a concern.

Ankur, referrring to your scheme, if there is no draining from open drain system, there will be hazardous vapors emission (though vap preesure is very low) from the the dip leg.

Regards
Narendra

Attached Files

•  Open drain sys with loop seal.xls   56KB   272 downloads

[ankur2061]

Shan / Ankur,
Please refer the attached sketch with U-loop seal and indicate if there is a concern.

Ankur, referrring to your scheme, if there is no draining from open drain system, there will be hazardous vapors emission (though vap preesure is very low) from the the dip leg.

Regards
Narendra

Narendra,

I think the concept is still not clear. The schematic I have provided is for a tank which receives drained liquid from both Closed (hazardous) & open (non-hazardous) drains. Open drains are supposed to be non-hazardous & hence they are open. The purpose of the seal leg is to prevent hazardous vapors from the closed drains entering the open drain system thereby creating a hazard in the open drain system & not vice-versa as you are suggesting.

In many instances where space is not a constraint on the WHT, you can have separate tanks for closed & open drains. In such a scheme you would be pumping the contents of the open drain tank to the closed drain tank wih adequate measures to prevent hazardous vapors entering the open drain tank from the closed drain tank. However in the schematic I have attached, space is at a premium & hence the drain vessel is the destination for both closed & open drain sources.

Hope this clarifies the scheme I have presented.

Regards,
Ankur.

[narendrasony]

Ankur,
I'm not denying that hazardous sump vapors will not be exposed to atmosphere via open drain system.

But what will happen during the intermittant periods when there is no flow from open drain system ?
In the seal leg, there will be HC vapors (very less as compared to sump vapors) over the sealing liquid and it will slowly diffuse to atmosphere through open drain system. Though it may be practically insignificant for creating a hazard. Assuming that sump liquid vap. pr. is slightly higher than atm. pr . How do you percieve such scenario?

Regards
Narendra

[ankur2061]

Ankur,
I'm not denying that hazardous sump vapors will not be exposed to atmosphere via open drain system.

But what will happen during the intermittant periods when there is no flow from open drain system ?
In the seal leg, there will be HC vapors (very less as compared to sump vapors) over the sealing liquid and it will slowly diffuse to atmosphere through open drain system. Though it may be practically insignificant for creating a hazard. Assuming that sump liquid vap. pr. is slightly higher than atm. pr . How do you percieve such scenario?

Regards
Narendra

Narendra,

As long as the seal leg is dipped in liquid I do not foresee any vapor migrating into the open drain system. In order for the vapor to migrate into the open drain system, the vapor pressure of the vapor has to overcome the static head of the liquid column equivalent to 1 m in the seal leg, which I cannot foresee. The path of least resistance to any vapor would be the open vent with flame arrester given on top of the drain sump tank.

Hope this clears the matter.

Regards,
Ankur.

[Afshin445]

1. I don’t understand why you have the siphon piping configuration at the outlet. Moreover, why is the siphon broken on the top? I don’t think the siphon works with top hole and if it works, air will intrude from that point.
2. If the start-up is a concern, the pot may be pre-filled with liquid. I expect the filling will be neither continuous nor often. The liquid evaporation will not be a problem because the pot is installed on the offshore platform with 100% humidity environmental.
3. In my opinion, your valves and instruments are luxury items (not necessary for the basic process). If you have enough money, you may also install PI, TI, Sample Port and Cleaning Port. Sometimes, people may just think we are not sophistical enough if we provide a simple, economical, and direct solution for their problem.

Shan,
1. The first U-pipe helps seal pot regarding sealing of path (Double Seal) and the second inverse-U-pipe maintain liquid in seal pot in our desired level.
Regarding different elevation of closed drain drum & Seal pot, when closed drain pump is working seal pot liquid will be siphon to closed drain drum and we need a balance line for avoiding this phenomena.
2. Regardless start-up condition, normally seal pot filled wit crude oil and may be crude oil will be blocked inlet & outlet line. I think it's better we have a water line for washing seal pot after each usage.
3. If we haven't any valve how we can be sure about sealing of system in long time period? They only instrument I suggest is LG, do u think is not necessary too?

In this regards, what is your idea about sketch presented by Narendra?
I am very grateful if you will attached your good comments with a sketch.

Regards,
Afshin

Edited by Afshin, 13 February 2010 - 08:58 AM.

[narendrasony]

Ankur,
I'm not saying that vapors in the sump will migrate to atmosphere from the seal leg. But I'm referring here to the vapors present over the liquid in the seal leg. Though It may be practically insignificant and can be ignored.

What is your opinion about the scheme with the U -loop seal I attached ? I think loss of liquid seal will be a concern there and a level gauge or a low level switch can be provided. Water can be used as seal make up.

Regards
Narendra