Can anyone share philosophy of Automatic Block Valve and emergency block valve?
What are considerations in view of piping design.?
Back in the day (before I retired) we used to call these "ESV" (Emergency Shut-Down Valves).
These were normally the standard line class block valve fitted with a rapid action motor or pneumatic operator.
The valve, the operator and the control cables were covered with fireproof insulation.
In an emergency these valves would either close or open (as required) automatically and the plant would be shut-down.
Automatic block valve can act as your first layer of protection and once
the alarm condition is reached (e.g. high level), the valve is shut by
means of a software interlock.
The emergency block valve would
act as your final layer of protection and the valve should be shut by
means of a separate hard-wired interlock.
You can have the same
valve performing both applications. e.g. A high level from a level
transmitter will shut the valve. If this instrument fails, a separate
high high level switch will shut the valve.
I have also seen an
application where the above 2 functions are performed by the same valve
by having 2 different solenoids each receiving a different signal.
Many plants use gate valves for isolating units at the battery limits
etc. Large gate valves require many turns of the handwheel to
open. Automated valves may use electric actuators to permit remote
operation. An operator may also push buttons to open or close such
valves. Usually a manual hand wheel is also provided as an override
when power is lost. Such a valve would fall into the automated
isolation valve description. Some quarter turn pneumatic valves are
also operated using a vane actuator (perhaps gas over oil with stored
energy) or double acting pneumatic actuator (perhaps with an air storage
cylinder and double check valves on the supply). Lacking a spring
these automated valves would not be suitable as emergency shutdown
valves.
A pneumatic actuator on a quarter turn ball or butterfly
valve is more common for an emergency shutdown valve. The emergency
shutdown valve should be able to close with no power or air supply.
From the originalgatevalve
.
2010年12月22日星期三
PN Designated Valves - Pressure Temperature Ratings
I am trying to determine in which standard the p/T ratings of PN
designated valves is given. Or in other words, when a valve is stated to
be PN16 Rated - to which standard is is rated as such?
I am
aware of BS EN standards that cover the face to face dimensions etc. but
I cannot seem to find anything that allows you to look up the material,
class, temperature and the corresponding pressure rating for any given
PN designation. (Like one does with the tables in ASME B16.5).
I
am aware that EN1092-1 covers the p/T ratings of the flanges. Do these
extend automatically to the valve as the valve body and components are
assumed to be always stronger than the flanges?
Or is there some other theory behind the determination of a PN designated valves p/T rating?
You don't say where you are from, but from the nomenclature, it appears
you are talking about European (CE)specs? The CE Pressure Equipment
Directive is 97/23/EN (google on those terms, you should be able to find
a copy of this from the CE servers, in the language of your
choice). The PED has tables that specify the pressure and temperature
limits for a part to fall within a particular classification. Moreover,
the manufacturer is supposed to maintain the certification, which
should include the details of the calculations done to show
certification, as well as the temperature and pressure limits defined
for the part, in order to comply with the PED.
Hope that helps. Though, being from the wrong side of the pond, it probably doesn't.
I am working out of the UK - I am currently writing up valve and piping specifications.
Using
the ASME system in this regard is A LOT simpler in that one can simply
state - Class 150# as per ASME B16.5 Table 2..... etc. when specifying a
valve. Proof of compliance with this is then up to the manufacturer.
Also ensuring that you are specifying something that meets both the
pressure and temperature conditions you require is then taken care of.
Most
of the components that I am specifying fall into Class 0 of the PED
with a limited number falling into Class I. In other words they only
require sound engineering practice in terms of their design - with those
in Class I not requiring a CE marking as far as I understand.
So if I understand you correctly what you are saying is:
Ensuring
p/T compliance using the EN 'method' would then require specification
of a nominal rating of PN16 (for example) and going out, finding
products that comply with this spec. Then requesting p/T curves for the
product/s and ensuring that the product meets the worst case scenario
(WCS) for p/T that you are trying to cater for. Alternatively you could
state what your WCS is then go out on enquiry with that p/T information -
which means that you may end up getting a valve with a nominal pressure
rating of PN40 in order to meet the pressure requirements at elevated
temperature.
Either method requires the PN rating to be updated on
the datasheet based on the limitations of the final chosen product -
unless you get it right first time; with the first requiring
considerably more work in terms of picking the final chosen product.
Now
- before I look like one of the guys on these forums trying to get a
quick and easy solution - I am not trying to get out of doing the work
by any means - my basic problem is trying to figure out the industry
standard way of specifying the pressure rating of valves to EN
specifications so that I can ensure I get the same thing every time with
minimal trawling through the limitless number of valves available out
there.
From the originalgatevalve
.
designated valves is given. Or in other words, when a valve is stated to
be PN16 Rated - to which standard is is rated as such?
I am
aware of BS EN standards that cover the face to face dimensions etc. but
I cannot seem to find anything that allows you to look up the material,
class, temperature and the corresponding pressure rating for any given
PN designation. (Like one does with the tables in ASME B16.5).
I
am aware that EN1092-1 covers the p/T ratings of the flanges. Do these
extend automatically to the valve as the valve body and components are
assumed to be always stronger than the flanges?
Or is there some other theory behind the determination of a PN designated valves p/T rating?
You don't say where you are from, but from the nomenclature, it appears
you are talking about European (CE)specs? The CE Pressure Equipment
Directive is 97/23/EN (google on those terms, you should be able to find
a copy of this from the CE servers, in the language of your
choice). The PED has tables that specify the pressure and temperature
limits for a part to fall within a particular classification. Moreover,
the manufacturer is supposed to maintain the certification, which
should include the details of the calculations done to show
certification, as well as the temperature and pressure limits defined
for the part, in order to comply with the PED.
Hope that helps. Though, being from the wrong side of the pond, it probably doesn't.
I am working out of the UK - I am currently writing up valve and piping specifications.
Using
the ASME system in this regard is A LOT simpler in that one can simply
state - Class 150# as per ASME B16.5 Table 2..... etc. when specifying a
valve. Proof of compliance with this is then up to the manufacturer.
Also ensuring that you are specifying something that meets both the
pressure and temperature conditions you require is then taken care of.
Most
of the components that I am specifying fall into Class 0 of the PED
with a limited number falling into Class I. In other words they only
require sound engineering practice in terms of their design - with those
in Class I not requiring a CE marking as far as I understand.
So if I understand you correctly what you are saying is:
Ensuring
p/T compliance using the EN 'method' would then require specification
of a nominal rating of PN16 (for example) and going out, finding
products that comply with this spec. Then requesting p/T curves for the
product/s and ensuring that the product meets the worst case scenario
(WCS) for p/T that you are trying to cater for. Alternatively you could
state what your WCS is then go out on enquiry with that p/T information -
which means that you may end up getting a valve with a nominal pressure
rating of PN40 in order to meet the pressure requirements at elevated
temperature.
Either method requires the PN rating to be updated on
the datasheet based on the limitations of the final chosen product -
unless you get it right first time; with the first requiring
considerably more work in terms of picking the final chosen product.
Now
- before I look like one of the guys on these forums trying to get a
quick and easy solution - I am not trying to get out of doing the work
by any means - my basic problem is trying to figure out the industry
standard way of specifying the pressure rating of valves to EN
specifications so that I can ensure I get the same thing every time with
minimal trawling through the limitless number of valves available out
there.
From the originalgatevalve
.
SPCC Containment Stormwater Discharge
I am reviewing the retrofitting of remote electrical transformer
substations for compliance with the SPCC rules and have a couple of
questions. First, containment structures for new transformers are
easily built during the station construction, but for retrofitting – a
complete concrete structure is not practical. I am aware of options
presented in 112.7(c), but what seems to be the precedent in the utility
industry? Concrete curbing?
Secondly, in the regulations “Section
by Section Analysis”, in 112.8(b)(2) – EPA says ”This rule does not
preclude innovative devices..” regarding the use of imbiber beads, or
assumingly chemical check valves, for discharging accumulated stormwater
from containment structures. It is the manufactures opinion that
chemical check-valves can be used to passively discharge accumulated
stormwater from containment structures, but the rules specially state
that “you must inspect and may drain accumulated stormwater” and keep
adequate records of that event, which is not feasible using these
passive drainage devises. Bottom line, it seems that EPA is saying that
you can install the innovative devise, but you must operate it like a
manual open/close valve. The valve manufactures say they are selling
the valves for SPCC compliance but that seems contrary to what the regs
allow, unless, the users are proposing this under the exception portion
of the rule. Any thoughts?
/////////////////////////////////////////
Both for new installations and for retrofitting we attach a liner to the
transformer pad. The liners drain to gravity oil separation tanks.
The
requirement for manual valves is waived if water is directed to a
wastewater treatment facility. But what other treatment is needed for
oil contaminated water other than oil removal. I guess I would suggest
that the chemical check valve itself constitutes the treatment facility.
Anyone buying?
From the originalgatevalve
.
substations for compliance with the SPCC rules and have a couple of
questions. First, containment structures for new transformers are
easily built during the station construction, but for retrofitting – a
complete concrete structure is not practical. I am aware of options
presented in 112.7(c), but what seems to be the precedent in the utility
industry? Concrete curbing?
Secondly, in the regulations “Section
by Section Analysis”, in 112.8(b)(2) – EPA says ”This rule does not
preclude innovative devices..” regarding the use of imbiber beads, or
assumingly chemical check valves, for discharging accumulated stormwater
from containment structures. It is the manufactures opinion that
chemical check-valves can be used to passively discharge accumulated
stormwater from containment structures, but the rules specially state
that “you must inspect and may drain accumulated stormwater” and keep
adequate records of that event, which is not feasible using these
passive drainage devises. Bottom line, it seems that EPA is saying that
you can install the innovative devise, but you must operate it like a
manual open/close valve. The valve manufactures say they are selling
the valves for SPCC compliance but that seems contrary to what the regs
allow, unless, the users are proposing this under the exception portion
of the rule. Any thoughts?
/////////////////////////////////////////
Both for new installations and for retrofitting we attach a liner to the
transformer pad. The liners drain to gravity oil separation tanks.
The
requirement for manual valves is waived if water is directed to a
wastewater treatment facility. But what other treatment is needed for
oil contaminated water other than oil removal. I guess I would suggest
that the chemical check valve itself constitutes the treatment facility.
Anyone buying?
From the originalgatevalve
.
Is there a Difference?
I’m an engineer at a power plant 1 hour north of Baltimore. I was visiting your site and had a pump question. My plant has 2 single stage liquid ring pumps. They are rated for 30 scfm (we remove 6 - 8 scfm) and they have a hogging capacity of 700 scfm. We have had our vacuum pumps fails 3 times in ten years. Twice the impellors have broken. Once the impellor ripped through the pump casing; fortunately know one was injury. A bad weld job was identified was the cause of one failure and cavitations was the other cause. Currently, because of the water temperature, we are forced to run with both vacuum pumps. We are looking to possibly purchasing another pump; however we need to identify the right pump for our plant. Our vacuum pumps are more or less meant to be hogging pumps (I think). We believe that our pumps are sized correctly, however one theory we have is that hogging vacuum pumps are not normally designed for continuous use; therefore our pumps have a short life span and that we should switch to two stage pumps. Is there any truth to this?
It sounds like your pumps could be oversized, which is not a good thing
for a liquid ring pump. If it cannot suck enough gas the pressure will
go down and you can get cavitation. Your high water temperatures would
make the situation worse. I have also seen impellers come apart under
these circumstances.
It would be helpful if you could describe
the control system as this is another area where it is easy to go wrong.
I have found the technical reps from the suppliers to be very helpful
and knowledgeable and you should get their advice.
What is hogging? Peak load? If so, how can a 30scfm pump take 700scfm?
30scfm
pumps are very small and generally there shouldn't be any problem.
However, you can have a look into the following things, if it is a water
ring pump.
1. Casing should be totally drained before starting
the pump and you should let in water as soon as the pump starts. These
things can be accomplished by a automatic casing drain valve (just like a
check valve) and an automatic valve in the sealing liquid line.
2. Check for casing clearances.
3. Check the teflon balls of the discharge and suction valves. They might have got struck to their seats.
4.
Finally, check your maintenance records. If you hadn't touched them
except when they broke down, 3 times in 10 years is not unusual.
From the originalgatevalve
.
It sounds like your pumps could be oversized, which is not a good thing
for a liquid ring pump. If it cannot suck enough gas the pressure will
go down and you can get cavitation. Your high water temperatures would
make the situation worse. I have also seen impellers come apart under
these circumstances.
It would be helpful if you could describe
the control system as this is another area where it is easy to go wrong.
I have found the technical reps from the suppliers to be very helpful
and knowledgeable and you should get their advice.
What is hogging? Peak load? If so, how can a 30scfm pump take 700scfm?
30scfm
pumps are very small and generally there shouldn't be any problem.
However, you can have a look into the following things, if it is a water
ring pump.
1. Casing should be totally drained before starting
the pump and you should let in water as soon as the pump starts. These
things can be accomplished by a automatic casing drain valve (just like a
check valve) and an automatic valve in the sealing liquid line.
2. Check for casing clearances.
3. Check the teflon balls of the discharge and suction valves. They might have got struck to their seats.
4.
Finally, check your maintenance records. If you hadn't touched them
except when they broke down, 3 times in 10 years is not unusual.
From the originalgatevalve
.
Universal Piping Flanges
Could anyone provide information or a source for "universal pipe flanges"?
There are called Socket-Weld and Slip-On flanges. Pipe schedule is immaterial, and makes the flanges "universal".
I think, if you check the exact bolt hole dimensions on ANSI and DIN
flanges, you will find that they can be bolted together face to face,
with the exception of some 2" flanges where bolt clearence becomes
tight, but I think that even though tight, the bolts can still be
inserted. Check the exact dimensions of the specific case you have
before making any special spools.
Gator, It's probably going to be a situation where the flanges are at a unit or plant
limit that also comes with a code break at the same place, which is
common when connecting between European and American companies in
various parts of the world where there is no national requirement and
one code is thought to be just as good as the next. As long as you used
A code, it was legal. I've
even had requirements for DIN on the pump stations and ANSI on the
pipelines when connecting between defense ministry and national oil
company facilities.
6" and 8" are about the only sizes where you might be able to bolt a
150# flange to a PN10/PN16 flange with a full sized bolt (and a
mallet). You may be able to get some of the smaller flanges together
using undersized bolts, but that would be a sure code violation. At 3" a
150# flange has 4 bolt holes while the DIN PN10 flange has 8.
Apart
from the problem of bolting the flanges together, there is the problem
of wafer type fittings like butterfly valves and disk check valves
trying to fit inside differing bolt circles. Mixed standards are by no
means rare here in South Africa, and it can be a nightmare if it is not
very carefully managed.
My advice - forget about universal flanges and just do it properly.
From the originalgatevalve
.
There are called Socket-Weld and Slip-On flanges. Pipe schedule is immaterial, and makes the flanges "universal".
I think, if you check the exact bolt hole dimensions on ANSI and DIN
flanges, you will find that they can be bolted together face to face,
with the exception of some 2" flanges where bolt clearence becomes
tight, but I think that even though tight, the bolts can still be
inserted. Check the exact dimensions of the specific case you have
before making any special spools.
Gator, It's probably going to be a situation where the flanges are at a unit or plant
limit that also comes with a code break at the same place, which is
common when connecting between European and American companies in
various parts of the world where there is no national requirement and
one code is thought to be just as good as the next. As long as you used
A code, it was legal. I've
even had requirements for DIN on the pump stations and ANSI on the
pipelines when connecting between defense ministry and national oil
company facilities.
6" and 8" are about the only sizes where you might be able to bolt a
150# flange to a PN10/PN16 flange with a full sized bolt (and a
mallet). You may be able to get some of the smaller flanges together
using undersized bolts, but that would be a sure code violation. At 3" a
150# flange has 4 bolt holes while the DIN PN10 flange has 8.
Apart
from the problem of bolting the flanges together, there is the problem
of wafer type fittings like butterfly valves and disk check valves
trying to fit inside differing bolt circles. Mixed standards are by no
means rare here in South Africa, and it can be a nightmare if it is not
very carefully managed.
My advice - forget about universal flanges and just do it properly.
From the originalgatevalve
.
Depressuring Valves to avoid BLEVE during a Fire
What should be the air fail action for depressuring valves installed, or
nominated, to avoid a BLEVE when fire surrounds a pressure vessel?
If air fail closed, and if fire also causes damage to air system then depressuring will not happen and BLEVE possible.
If
air fail open, then vessel depressurizes when there is no fire and at a
far higher frequency than fire, leading to undesired/ unacceptable
release of organics.
As a rider to the general problem above, we
have, in the past, nominated certain PCVs to also serve as depressuring
valves. These PCVs tend to have air fail closed actions. Are there any
comments on this state of affairs?
///////////////////////////////////////////////
This is a very common problme/ question. I used to work on the
design of a NGL plant and there we had the same discussions again and
both arguments are true. But I guess that one would certainly want to
have the Blow down valves be opened during a fire event. So I tend to
make them Air FAil open. But I will then make sure that I have a
relibale source of Air that doesn't fail every now and then.
Other thing is to look for a similar design that your company has with other systems.
I don't think that there is any one answer that is correct for all
situations. As the others have indicated I think the typical action
would be depressuring valves fail open and shutdown valves fail closed
but that does not have to be so in every case.
I believe what you
are doing is the correct way to approach the problem and you need to
evaluate the advantages and disadvantages of your options. Pick the
fail position that makes the most sense for your system but expand your
evaluation to more than just the fail action of the depressuring valve.
I
can't offer any thorough reference for depressuring systems but API
RP-521 does have a little information that you may want to
review. Basically, the key points they make include...
"The valves should remain operable for the duration of the emergency or should fail in a full open position."
I
would put the emphasis on the "or" and don't necessarily interpret that
to mean that all depressuring systems should fail open.
API 521 goes on to say...
"Fireproofing of the power supply and valve actuator may be required in a fire zone."
So there are other factors that should be part of your design that should affect your decision.
For
example, I have seen emergency air supplies (small pressurized
containers) sufficient to actuate an air operated valve located close
connected with valve(API Cast Steel Valves). Maybe you could locate your depressuring valve
outside the fire zone or maybe install redundant valves. A fusible link
sounds interesting, some relief systems on compressed gas cylinders
include a combination rupture disc and fusible plug to ensure release
only during a fire event. What about depressuring your system to some
type of disposal system (flare or scrubber).
I happened to find
this article on the Instrument Society's website that talks about using a
Safety Integrity Level (SIL) selection method relating to depressuring
of a hydrocracker reactor. You might want to consider using an approach
like this to help decide which fail action is best for your system.
From the originalgatevalve
.
nominated, to avoid a BLEVE when fire surrounds a pressure vessel?
If air fail closed, and if fire also causes damage to air system then depressuring will not happen and BLEVE possible.
If
air fail open, then vessel depressurizes when there is no fire and at a
far higher frequency than fire, leading to undesired/ unacceptable
release of organics.
As a rider to the general problem above, we
have, in the past, nominated certain PCVs to also serve as depressuring
valves. These PCVs tend to have air fail closed actions. Are there any
comments on this state of affairs?
///////////////////////////////////////////////
This is a very common problme/ question. I used to work on the
design of a NGL plant and there we had the same discussions again and
both arguments are true. But I guess that one would certainly want to
have the Blow down valves be opened during a fire event. So I tend to
make them Air FAil open. But I will then make sure that I have a
relibale source of Air that doesn't fail every now and then.
Other thing is to look for a similar design that your company has with other systems.
I don't think that there is any one answer that is correct for all
situations. As the others have indicated I think the typical action
would be depressuring valves fail open and shutdown valves fail closed
but that does not have to be so in every case.
I believe what you
are doing is the correct way to approach the problem and you need to
evaluate the advantages and disadvantages of your options. Pick the
fail position that makes the most sense for your system but expand your
evaluation to more than just the fail action of the depressuring valve.
I
can't offer any thorough reference for depressuring systems but API
RP-521 does have a little information that you may want to
review. Basically, the key points they make include...
"The valves should remain operable for the duration of the emergency or should fail in a full open position."
I
would put the emphasis on the "or" and don't necessarily interpret that
to mean that all depressuring systems should fail open.
API 521 goes on to say...
"Fireproofing of the power supply and valve actuator may be required in a fire zone."
So there are other factors that should be part of your design that should affect your decision.
For
example, I have seen emergency air supplies (small pressurized
containers) sufficient to actuate an air operated valve located close
connected with valve(API Cast Steel Valves). Maybe you could locate your depressuring valve
outside the fire zone or maybe install redundant valves. A fusible link
sounds interesting, some relief systems on compressed gas cylinders
include a combination rupture disc and fusible plug to ensure release
only during a fire event. What about depressuring your system to some
type of disposal system (flare or scrubber).
I happened to find
this article on the Instrument Society's website that talks about using a
Safety Integrity Level (SIL) selection method relating to depressuring
of a hydrocracker reactor. You might want to consider using an approach
like this to help decide which fail action is best for your system.
From the originalgatevalve
.
2010年12月14日星期二
Replacing gate valve with proper seacock
On the left is a shot of the original thru-hull for my shower sump. It has a bronze thru hull with a gate valve. It is situated above the waterline unless you’re on a port tack then it’s well underwater. I don’t think it’s not up to code, but it made me squeamish so I am replacing it with a marelon thru hull and ball valve seacock.
There’s a great video on YouTube from Forespar about how to mount Marelon seacocks which I posted previously. I am basically following those exact steps.
1. I removed the old hose from the barb, the valve from the thru hull and the thru hull from the boat.
2. I then prepped the inside of the hull by sanding it down to clean fiberglass with a 4” Ryobi angle grinder.
3. I prepared a 1/2” marine grade plywood backing plate by cutting the wood and coating it with West Systems epoxy. This will be an upgrade over the original installation which has no backing plate.
4. Next I dry fit everything to make sure it would all fit together and be able to be tightened adequately.
From the originalGate Valve
.
There’s a great video on YouTube from Forespar about how to mount Marelon seacocks which I posted previously. I am basically following those exact steps.
1. I removed the old hose from the barb, the valve from the thru hull and the thru hull from the boat.
2. I then prepped the inside of the hull by sanding it down to clean fiberglass with a 4” Ryobi angle grinder.
3. I prepared a 1/2” marine grade plywood backing plate by cutting the wood and coating it with West Systems epoxy. This will be an upgrade over the original installation which has no backing plate.
4. Next I dry fit everything to make sure it would all fit together and be able to be tightened adequately.
From the originalGate Valve
.
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