31 replies to this topic

[ogpprocessing]

Dear Experts,

As far as I know, non-slam check valve is a type that minimizes the effects of water hammer and surge pressures. Right?

But I have seen many P&IDs that non-slam check valve is also considered at compressor discharge. So for gas phase how especial is this non-slam check valve? Why non-slam check valve is required at comprssor discharge line?

Edited by ogpprocessing, 06 December 2011 - 08:48 AM.

[ankur2061]

ogpprocessing,

The links below should help you in your understanding:

http://www.adamsvalv...heck_Valves.pdf

http://webwormcpt.bl...heck-valve.html

Regards,
Ankur

[ogpprocessing]

Dear Ankur,

I have read those articles before sending this topic.

By this topic I did how critical is salm concern for compressor handling compressible fluid?

[fallah]

ogpprocessing,

IMO, non-slamming characteristics for check valve in compressor discharge line is being considered in order to prevent reverse flow through compressor during settle out conditions (after SDVs of suction and discharge lines to be closed) and restrict the pressure equalization to anti surge line.

Fallah

[ogpprocessing]

How do you relate non-slam check valve to settle out case? what is the application of non-slam property?

[fallah]

ogpprocessing,

In a compressor, settle out establishment needs pressure equalization of an integrated volume including parts of suction and discharge lines between two closed SDVs and compressor itself. Hence, higher pressure fluid in discharge line tends to flow backward in order to equalize the lower pressure section i.e. suction line and in this way, even though the anti surge line being dedicated and applied as equalization line, it might be passed through the compressor as well.

Now let return to explain about non-slamming check valve and its relation to settle out:

Actually two major parameters make a check valve having non-slamming characteristics i.e. avoiding pressure surge creation, 1) To be closed very rapidly or very slowly in back flow condition, 2) Linearity of valve's disc travel which allows the proportionality of backward flow with disc travel.

As per above explanations, if the non-slamming check valve in discharge line being closed rapidly in the case of the compressor is going to be in settle out condition and while the anti surge valve is in open condition, the pressure equalization would be done via anti surge line and the compressor wouldn't be subjected to pressure surge (may leading to compressor damage) from backflow through discharge line.

Hope above helps you out.

Fallah

[ogpprocessing]

Where is the location of this check valve that you are speaking about? near the compressor discharge nozzle? or just downstream of anti surge line branch from main discharge line?

[fallah]

Near the compressor discharge nozzle!

[ogpprocessing]

What we need is a check valve downstream of anti surge line branch from main discharge line. We do not need any near compressor discharge nozzle.

[fallah]

Means you would allow the settle out condition to be established by back flow through the compressor in addition to anti surge line. Right?

[ogpprocessing]

Check valve at the location that I described can protect compressor itself. Also prevents suction drum over pressurization if compressor is tripped. Then compressor vendor will check if his product is robust enough or not. If not he will make corrective actions.

What you have described is relevant to check valve response and not non-slam property. For definition of slam you can refer to links provided above by Ankur.

[fallah]

In some cases it is needed to consider the check valve not only at the location you described but also after discharge nozzle of the compressor (we have such compressor now is operating), but as far as i had seen most centrifugal compressors are equipped, at least, with a check valve after their discharge nozzles.

Please keep in mind and be informed non-slam characteristics of a check valve directly relates to its response against reverse flow and it should usually be very fast or very slow to create non-slam characteristics.

[ogpprocessing]

In some cases it is needed to consider the check valve not only at the location you described but also after discharge nozzle of the compressor (we have such compressor now is operating), but as far as i had seen most centrifugal compressors are equipped, at least, with a check valve after their discharge nozzles.

Based on Hazop studies check valve near compressor discharge nozzle can get stuck and acts as source of blockage and should be avoided.

Please keep in mind and be informed non-slam characteristics of a check valve directly relates to its response against reverse flow and it should usually be very fast or very slow to create non-slam characteristics.

I think slam refers to water hammer concern and is only applicable for liquid service. Pressure surge (water hammer) is not a concern for gas service.

[fallah]

ogpprocessing,

As far as i know the check valve getting stuck open could be an issue in HAZOP standpoint not getting stuck closed. Although, supposing the check valve stuck closed being possible scenario, even if check valve would be located downstream of the antisurge line take off, as per sec. 4.2.2 API 521 simultaneous stuck closing of antisurge valve and latent failure of the check valve is possible and will result in compressor discharge blockage i.e. your concern.

Then, if slam don't refer to gas service please explain about your observation you mentioned in first post as follow:
...But I have seen many P&IDs that non-slam check valve is also considered at compressor discharge...

Why did they use non-slam check valve in those many P&IDs included compressor discharge line?

Fallah

Edited by fallah, 04 April 2012 - 02:01 AM.

[ogpprocessing]

ogpprocessing,

As far as i know the check valve getting stuck open could be an issue in HAZOP standpoint not getting stuck closed. Although, supposing the check valve stuck closed being possible scenario, even if check valve would be located downstream of the antisurge line take off, as per sec. 4.2.2 API 521 simultaneous stuck closing of antisurge valve and latent failure of the check valve is possible and will result in compressor discharge blockage i.e. your concern.

1. Check valve as a cause of blockage is considered a credible case during Hazop.
2. If check valve is located downstream of anti surge line take-off point (which is my preferred configuration) got stuck then we have high high pressure shutdown and PSV sized for blocked outlet upstream of anti surge line take-off point and can protect the compressor while check valve near compressor discharge nozzle (as advised by you) can not handle this.

Then, if slam don't refer to gas service please explain about your observation you mentioned in first post as follow:
...But I have seen many P&IDs that non-slam check valve is also considered at compressor discharge...

Why did they use non-slam check valve in those many P&IDs included compressor discharge line?

Fallah

This is the reason I made this topic.

[fallah]

ogpprocessing,

1- Please specify valid reference(s) (such as API 521 or same level) refer to check valve as a credible source of line blockage.

2- Even if we suppose check valve blockage is credible scenario in HAZOP standpoint, It is enough to locate the PSV take off point between compressor's discharge nozzle and the check valve near the compressor to avoid overpressure of the compressor.

Attached you will find a page from a valid reference indicates a check valve (if properly selected) could be acceptable in process pressure relieving path, means in most cases it isn't as a potential of line blockage.

Fallah

Attached Files

•  Page from pressure safety design practices for refinery and chemical operations.pdf   77.46KB   196 downloads

Edited by fallah, 08 April 2012 - 03:34 AM.

[ogpprocessing]

Fallah:

The reference document which is shared by you clrealy mention that check valve is not permissible at PSV inlet and outlet ines and also flare lines. The reason is the same as blockage concern that I have mentioned as is considered at Hazop meeeting as a credible case.

[fallah]

<sup>ogpprocessing,

You fail to specify valid reference on the requested matter, also no comment on my second explanation in my previous post.

Anyway, we should seriously avoid confusing in our discussion. The main issue on which we are discussing is using the check valve in compressor discharge line not using it in PSV inlet/outlet lines. If you accurately read the page of document i did attach it refers to the point that using check valve in "process pressure relieving path" could be acceptable, and there is no contradiction with other point in this document mentioned that using check valve in PSV inlet/outlet lines isn't permissible. Obviously the first point addresses to process path and the second one to PSV inlet/outlet and flare lines.</sup>
In fact, in the cases the PSV's are located on process lines (such as compressor discharge line) the PSV inlet/outlet lines are parts of "pressure relieving path" and the remain is "process pressure relieving path".

^Fallah

Edited by fallah, 11 April 2012 - 02:42 AM.

[ogpprocessing]

^Fallah:
1. As I mentioned check valve as a cause of blockage has been considered a credible case at many Hazop meetings. This is a valid and common reference and we can not share confidential documents at this forum. If you have no experience with this you need to study more.

2. Your second comment is against your previous statement "(we have such compressor now is operating), but as far as i had seen most centrifugal compressors are equipped, at least, with a check valve after their discharge nozzles."
For sure you confirm that for above mentioned operating project the PSHH and PSV is located downstream of check valve.

3. Check valve concern on flare lines is another issue and not relevant to this topic. If you are interested to discuss about this matter you can follow up this in another topic.

[fallah]

1. As I mentioned check valve as a cause of blockage has been considered a credible case at many Hazop meetings. This is a valid and common reference

ogpprocessing,

IMO, API 521 is most valid reference in which the credible causes of overpressure have been discussed and for a check valve as a cause of overpressure just addressed as a potential of reverse flow due to its downstream blockage that can overpressure its upstream.
Nevertheless, i did submit a valid reference (in post 16) mentioned a check valve with the conditions specified there isn't a credible cause of the blockage and you hadn't any acceptable comment on it. With your above statement i can suppose you cannot refer to any valid reference on the issue. Obviously, if you were able to introduce a valid reference included this point that: a check valve in any condition is considered as a cause of blockage, i did accept the point without any hesitant.
I have paticipated in many HAZOP meetings within which the check valve isn't considered as a cause of blockage. Then, for your information a HAZOP report couldn't inherently be a general valid reference at all and is prepared based on specific hazards and operating conditions of a plant for which the HAZOP meeting is held, also itself should be based on many valid references. A valid reference: 1) could be found by those need to it, 2) needs not to be submitted itself, 3) it should be such that, at least, could be addressed.

Fallah

Edited by fallah, 12 April 2012 - 12:33 AM.

[breizh]

http://webcache.goog...n&gl=th&strip=1

It might be interesting to read this post .
Breizh

[ogpprocessing]

1. As I mentioned check valve as a cause of blockage has been considered a credible case at many Hazop meetings. This is a valid and common reference

ogpprocessing,

IMO, API 521 is most valid reference in which the credible causes of overpressure have been discussed and for a check valve as a cause of overpressure just addressed as a potential of reverse flow due to its downstream blockage that can overpressure its upstream.
Nevertheless, i did submit a valid reference (in post 16) mentioned a check valve with the conditions specified there isn't a credible cause of the blockage and you hadn't any acceptable comment on it. With your above statement i can suppose you cannot refer to any valid reference on the issue. Obviously, if you were able to introduce a valid reference included this point that: a check valve in any condition is considered as a cause of blockage, i did accept the point without any hesitant.
I have paticipated in many HAZOP meetings within which the check valve isn't considered as a cause of blockage. Then, for your information a HAZOP report couldn't inherently be a general valid reference at all and is prepared based on specific hazards and operating conditions of a plant for which the HAZOP meeting is held, also itself should be based on many valid references. A valid reference: 1) could be found by those need to it, 2) needs not to be submitted itself, 3) it should be such that, at least, could be addressed.

Fallah

Fallah:
This is interesting to read you have participated to many Hazops and they missed to consider check valve blockage case !

Read more about this common case at:
http://www.cheresour...-valve-failure/

[fallah]

ogpprocessing,

Your efforts to find a valid reference is admirable! IMO, if you continue to investigate you will certainly succeed to find!

Fallah

[ogpprocessing]

ogpprocessing,

Your efforts to find a valid reference is admirable! IMO, if you continue to investigate you will certainly succeed to find!

Fallah

Fallah,

After checking the link that I did provide at my previous post (http://www.cheresour...-valve-failure/) I found even at that topic this is explained by some of the very experts of the forum (like Mr.Art Montemayor) to you about blockage due to check valve malfunction. Same concept is again given here. Interesting to see somtimes some people do not want to update themselves even if they are given with many past real experiences !

[fallah]

ogpprocessing,

Art/ Ankur/... viewpoints same as those of other members in this site have been respected and utilized by me in all times and they can involve into current discussion if they need to be involved...
Because you fail to submit a valid reference i have to attach again the previous reference i did attach it in 16th post of this thread.
If you didn't read it till now please read it carefully and then you will see that one should update himself regarding the matter might be yourself!
Actually, IMO, as per attached if we are facing with an unknown check valve in "type" and "internal parts" point of views we might generally consider check valve blockage as a credible scenario. But, as you may know, e.g. in HAZOP meeting we normally discuss on actual plant with known equipment, valves,...in "type" and "specification" point of views, then we can consider in hand information in our judgement to determine if, e.g., a check valve with regard to its type and specification could be a source of blockage.
Bottom line is that if you are facing with a no specific check valve you may consider it as a source of blockage but if even during HAZOP meeting you face with a type of check valve located in relief path and may be a potential of blockage (of course in most cases the type is already selected such that there would be no possibility of blockage), you can change the valve type (by recording in relevant action sheet) toward having no blockage rather than considering facilities against possibility of overpressure due to such blockage!

Fallah

Attached Files

•  Page from pressure safety design practices for refinery and chemical operations.pdf   77.46KB   74 downloads

Edited by fallah, 06 May 2012 - 06:36 AM.