21 replies to this topic

[ogpprocessing]

Dear Process Experts,

I have seen some different configurations for closed drain valving such as:

1. Double block isolation valve and bleed.

2. Single block isolation valve and one globe valve

3. Single block isolation valve, one globe valve and one check valve.

Which configuration should be used?

Edited by ogpprocessing, 12 October 2011 - 01:41 PM.

[ankur2061]

ogpprocessing,

You could have several options for choosing the type of valving for a closed drain system. I had made a standard for a middle east O&G company sometime back.& I am attaching a sketch for the closed drain piping from the vessel to the closed drain drum.

Regards,
Ankur.

Attached Files

•  closed_drain_system_valving.pdf   18.45KB   375 downloads

[S.AHMAD]

Agree with Ankur.

It is a good practice to install a chekvalve in between the two valves. This is to eliminate possibility of back flow due to operational error or inadvertent opening/closing of valves.

[fallah]

Hi,

Some comments on Ankur's sketch as follows:

-Spectacle blinds to be needed just in high pressure applications.

- As AHMAD mentioned, a check valve to be considered between two valves to avoid any back flow due to a high pressure in downstream sump drum. If spectacle blind is considered it should be installed upstream of the check valve.
- First valve (FB ball valve) should be specified as Car Seal Closed.
- Normally bleed line (and valve) not to be needed, but if one would want to consider such line it could be routed to downstream of the globe valve.

Fallah

[ogpprocessing]

Agree with Ankur. It is a good practice to install a chekvalve in between the two valves. This is to eliminate possibility of back flow due to operational error or inadvertent opening/closing of valves.

This case is considered a remote and rare case keeping in mind that drain connection involves isolation valves and spectacle blind. Also the closed drain sub headers invlove isolation valves. So back flow from other sources is unlikely. This is also compatible with common Hazop procedures.

[ogpprocessing]

ogpprocessing, You could have several options for choosing the type of valving for a closed drain system. I had made a standard for a middle east O&G company sometime back.& I am attaching a sketch for the closed drain piping from the vessel to the closed drain drum. Regards, Ankur.

Dear Ankur,
1. Which of the 2 configurations at your manual should be used?
2. What do you mean by draining of pressurized vessels at your manual? as far as I know before the drainage the equipment should be depressurized.

[ankur2061]

ogpprocessing,

1. I prefer the option with the spectacle blind because it precludes the possibility of accidental draining by operator error or due to internal leakage (passing) from the valves.

2. You are partially right when you say that the equipment needs to be depressurized prior to draining, however there may be circumstances where an emergency draining of the equipment may be required while the equipment still under pressure or is undergoing depressurization. This would be only applicable if there is a provision of automatic remotely operated drain valves and with no spectacle blind. Another scenario where draining maybe under pressure is when you want to drain very viscous liquids (e.g. oil-water emulsions from separators) which would find it difficult to flow by gravity and would require some inert gas pressure to be introduced in the vessel to increase flowability and ensure complete drainage of the vessel.

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 13 October 2011 - 06:49 AM.

[kkala]

Attached "drain.doc" contains vessel drain practice for local refineries, along with few comments. It has similarities to Ankur's option with spectacle blind. Hope it is helpful.

Attached Files

•  drain.doc   28KB   220 downloads

[ogpprocessing]

2. You are partially right when you say that the equipment needs to be depressurized prior to draining, however there may be circumstances where an emergency draining of the equipment may be required while the equipment still under pressure or is undergoing depressurization. This would be only applicable if there is a provision of automatic remotely operated drain valves and with no spectacle blind.

Could you please make a real example for this case?

Another scenario where draining maybe under pressure is when you want to drain very viscous liquids (e.g. oil-water emulsions from separators) which would find it difficult to flow by gravity and would require some inert gas pressure to be introduced in the vessel to increase flowability and ensure complete drainage of the vessel.

I do not think this inert gas used is very high pressure because this is originated from utility station and there is pressure regulator valve at outlet of inert gas generator package. What do you think?

[ogpprocessing]

Attached "drain.doc" contains vessel drain practice for local refineries, along with few comments. It has similarities to Ankur's option with spectacle blind. Hope it is helpful.

Dear Sir,

1. Could you please clarify this sentence within your manual:
" It is understood that valves may change from gate to globe or ball, depending on requirements of the specific case, even though this is not specifically explained in the practice."
What do you mean by "specific case"

2. You also confirm my previous idea that check valve is not needed as part of closed drain valving?

[ankur2061]

ogprocessing,

Some of the oil-gas separators that I know are provided a cold start-up inert gas (fuel gas) line which is just a line connecting from the main fuel gas header without any pressure reduction and with manual valves and spectacle blind. This line serves two purposes:

1. Purging the system to remove air (oxygen) prior to cold start-up

2. Providing enough gas pressure to drain viscous residual material from the vessel which would normally be difficult to drain by gravity or at low inert gas pressures.

Emergency draining is routinely applied in most hydrocarbon installations for any emergencies such as fire, accidental leakage (spill containment) etc. I don't have any case histories for emergency draining, if that is what you mean by providing a real case.

Regards,
Ankur.

[ogpprocessing]

Emergency draining is routinely applied in most hydrocarbon installations for any emergencies such as fire, accidental leakage (spill containment) etc. I don't have any case histories for emergency draining, if that is what you mean by providing a real case.

For fire case we prefer to keep the liquid inside of the equipment such that absorb the heat by liquid and prevent accumulation of heat at equipment wall. So maybe for this emergency case we do not need any drainage.

[kkala]

1. Could you please clarify this sentence within your manual:
" It is understood that valves may change from gate to globe or ball, depending on requirements of the specific case, even though this is not specifically explained in the practice."
What do you mean by "specific case"
2. You also confirm my previous idea that check valve is not needed as part of closed drain valving?

1. The sentence was actually my comment on the practice, showing gate valves everywhere without further explanation. Globe or ball valves have been observed here in drain service. So my interpretation is that some of indicated gate valves can be substituted with ball (better tightness) or gate (better manual flow control) valves, as required. This depends on service, as wellas designer's judgment.
For instance, a diesel atmospheric tank draining through a dedicated line into an underground level drum would need nothing more than gate valves. An LPG pressure vessel would generally need ball valves nowadays to avoid leakages into pipe or air (though old LPG installations still have gate valves). Nevertheless the last valve to flare (far right on the scheme) has to be globe due to downstream low pressure. Flow should be manually controlled to a value not causing freezing of external humidity, which could block the valve. In my opinion the small (3/4") valve to atmosphere should be globe for same reason. (And another remote operated -or "self" operated- valve would be placed at the connection of LPG vessel to suction line, for isolation during fire; this does not concern drain, anyway).
2. Local practice does not generally install check valves on drain lines, there is no check valve on the drain scheme. However there are exceptions. Four LPG drum drain lines were connected after some distance to a common line directed to a (soda?) drum. Check valves were installed on all four drain lines. I understand that LPG drums could have different pressures (due to different composition) and some drains could operate simultaneously. So back flow to the lowest pressure LPG drum was possible, check valves tried to avoid it.
Besides liquid draining under pressure cannot be excluded in exceptional cases, under the responsibility of the Operator. Check valves could be hardly useful in such cases, seeing that drain lines of rest tanks are blinded. On the other hand a single check valve has a risk of non operating "on demand".
I had once "tasted" acidified potable water in the factory, due to a leaking valve or check valve. Probably a good way for closed drain safety is "keep network as simple as possible". No permanent connections from other systems (e.g. water), no complex piping, just collect drained liquids in atmospheric drums under the ground and transfer them to proper tanks by pumping. Moreover drain facilities are worthy of laborious engineering and any special issue about needed valves or check valves (etc) should be touched in the Hazop study, or earlier by experienced operators.

Edited by kkala, 15 October 2011 - 04:32 PM.

[ankur2061]

The scheme proposed in the sketch I have attached is typically followed in upstream oil and gas installations. Per my understanding, 'ogpprocessing' was looking for drain arrangements in upstream oil and gas installations. In critical services well established engineering practices are what that counts and not individual opinion.

I would tread with caution on design issues because type of draining arrangement in a particular establishment may not be applicable to another, specially in todays context and considering that modern day engineering and operating practices give the highest priority to safe and reliable operations.

Regards,
Ankur.

[kkala]

... In critical services well established engineering practices are what that counts and not individual opinion.
I would tread with caution on design issues because type of draining arrangement in a particular establishment may not be applicable to another, specially in todays context and considering that modern day engineering and operating practices give the highest priority to safe and reliable operations".

I would say that the designer in charge has to carefully consider established engineering practices on the matter, try to understand "philosophy" of practices already applied in the plant, use judgment to distinguish between applicable and non applicable arrangements on the specific case, then express opinion as a proposal. This does not contradict above statement by Ankur, understood to be against an individual opinion superficially expressed, i.e. neglecting mentioned steps.
Approved engineering practices (of the company you work for) represent the "philosophy" to be followed in the design. Nevertheless they are often generic, leaving much margin for personal judgment, as attachment (post 14 Oct 2011) "drain.doc" and subsequent discussion indicates. These practices are usually (revised and) written for any new project as "Engineering design data" (title can be different) before basic engineering, while subsequent Hazop studies complete them, also solving (or at least pointing out) specific issues. These documents (design criteria & Hazop studies) could clarify some queries, if found. Criteria on drainage and its arrangement for refinery projects are remembered to be reported.
Engineering practices not approved (by the company you work for) need more care in their application, since they may be based on an operating mentality different to this followed by plant operators. Practices on same subject may differ worldwide (even though they are now getting more and more similar) and usually there are more than one ways for same issue, based on different mentalities. A real example (~20 years ago) concerned water injection into suction line for cleaning purposes, resulting in pressures higher than pump casing design pressure if pumps were operating. Designer explained this was an acceptable practice in their plants, where a procedure (we would say administrative measures) prevented pumps from operation during cleaning. Plants of another country, having experienced pump casing burst, considered mentioned practice unacceptable (*). Difference between two practices (or between their risk) concerning drainage may not be so clear as in the example, so critical judgment is often needed to compose the practically best option for the specific case in your plant. Mentality often determines acceptable "administrative measures", especially for a matter like drainage (see last posts of http://www.cheresour...h__1#entry51491).
There are two extreme attitudes, among others, towards engineering practice documents. The former insists on applying some (relevant or irrelevant) practices, not really understood but selected for the plant long ago. The latter generally disrespects practices, as "inferior" to experience gained in the plant. Both attitudes represent an easy road to avoid comparison and judgment, yet cannot offer to safety what it deserves.

(*) We finally proposed water injection at the beginning of pump discharge to solve the problem.

Edited by kkala, 16 October 2011 - 09:47 AM.

[ankur2061]

Most engineering practices which are provided in company or international standards are a judicious mixture of practical observation and application and the desired operational objective. None of the company or interanational standards that I know are stagnant from the time they were first published. All of them have undergone one or more revisions to adopt modern practices of engineering, operability and safety.

I have worked in plant operations and I recall that during those days I was extremely reluctant for any change to be implemented in the plant. I had a tunnel vision of what was right and wrong. If any existing system is working fine at the time I am observing it there was no need to change it. Most operations people are uncomfortable with change and most of them have little idea of the implications of any change because they are thinking only in the present time and do not have a long term perspective of the change.

When you are looking at it from the design perspective factors other than just operability come into picture such as safety, reliability, cost and maintenance.

Engineering practices, standards etc. are meant to guide and give young engineers an early initiation into how systems need to be designed and built and their usage would be far more pertinent than individual opinions and perceptions on any engineering subject.

Regards,
Ankur.

[kkala]

.... the designer in charge has to carefully consider established engineering practices on the matter, try to understand "philosophy" of practices already applied in the plant, use judgment to distinguish between applicable and non applicable arrangements on the specific case, then express opinion as a proposal...
There are two extreme attitudes, among others, towards engineering practice documents. The former insists on applying some (relevant or irrelevant) practices, not really understood but selected for the plant long ago. The latter generally disrespects practices, as "inferior" to experience gained in the plant. Both attitudes represent an easy road to avoid comparison and judgment, yet cannot offer to safety what it deserves.

Engineering practices, standards etc. are meant to guide and give young engineers an early initiation into how systems need to be designed and built and their usage would be far more pertinent than individual opinions and perceptions on any engineering subject.

However the responsible opinion is a result of critical looking into relevant practices / standards (to locate the applicable, any gaps, way to implement) in combination with knowledge of plant specific operation and conditions. Project leaders decide on the above through opinions, more or less justified.
This is my opinion, having seen people blindly godiffying standards in detriment of engineering judgment; or advanced modern practices not to be actually the best for a specific plant, due to difference in operating "philosophy" (rare case though).
Judgment is valuable for engineers, and should be improved by studying standards / practices in a critical way, sometimes expressed through queries in the forum (e.g. suction line design pressure, rationale for API 2000).

Edited by kkala, 22 October 2011 - 01:10 PM.

[ankur2061]

Most engineering practices which are provided in company or international standards are a judicious mixture of practical observation and application and the desired operational objective. None of the company or interanational standards that I know are stagnant from the time they were first published. All of them have undergone one or more revisions to adopt modern practices of engineering, operability and safety.

From what is stated above I reiterate that individual opinion rarely counts in engineering design. The established practices and standards developed over a period of time and carefully evaluated by experienced engineers that count. Note that I have used the plural term engineers and not an engineer. And I definitely do think that anyone who has worked in an engineering background (engineering consulting) would understand this but I also would be sympathetic to the person's ignorance if he or she has never worked in an engineering background.

Ankur.

[kkala]

From what is stated above I reiterate that individual opinion rarely counts in engineering design. The established practices and standards developed over a period of time and carefully evaluated by experienced engineers that count. Note that I have used the plural term engineers and not an engineer. And I definitely do think that anyone who has worked in an engineering background (engineering consulting) would understand this but I also would be sympathetic to the person's ignorance if he or she has never worked in an engineering background.

Thanks for leniency! But let us think who chooses practices, and whether a healthy practice can be effective in the hands of an unworthy person. Laws are necessary but always give way to initiation, they cannot cover all cases. It is people who decide the practices (in contractual, engineering, supervision phase, of course withing the "legal" range), stricter or looser than normal. Basics are chosen at the beginning of the project, details later.
I have seen in Greece a tendency to stick to "formalities" without much thinking, hence my concern for judgment. Hence my personal opinion "do not blindly lean on standards", we should critically study them.
Apart from phrases, actual difference in opinion may be quite small. Argumentation from my part stops here, to prevent "fire".

Edited by ankur2061, 21 October 2012 - 09:59 AM.

[kkala]

Attached "drain.doc" contains vessel drain practice for local refineries, along with few comments. It has similarities to Ankur's option with spectacle blind. Hope it is helpful.

Attachment is almost blank in the referred post, the second example recently seen. I am certain that originally there was a simple drawing (probably made by MS-office drawing symbols). If other readers see no sketch on opening the word file, I suppose some error might have occurred during file manipulation. Can this be possible and how can the original file be restored?

Edited by kkala, 26 August 2012 - 02:34 PM.

[kkala]

I have been informed that "drain.doc" can be viewed from some other PCs (not mine). In the improbable case of problem you can view attached "drain.gif".

Attached Files

•  drain.gif   13.73KB   26 downloads

[kkala]

An editing note was added today to post No 19 (by kkala), concerning engineer's opinion.