compressor api 14c 1

[142846]

Hello. I have question about use of bdv for compressors based on API 14c. API rp 14c 2017 says "A blowdown valve should be located on the compressor unit final discharge line(s) for compressors greater than 1000 hp." what is the concept of application of this bdv? Is this sentence applicable for reciprocating compressors that there is not surge for this type of compressors.Normally and usually Applicable of BDV returns to fire and gas but I think concerns of this sentence of api 14c is about compressor protection not event of fire and gas? thanks a lot.

 

[rotw]

Surge for recips ??

If you plan an escape, you must succeed as if you fail, you will be punished for trying. Never say or write down your plan. Heart is the only place where secrecy is granted.

 

[142846]

My question is only what is the meaning and Interpretation of "A blowdown valve should be located on the compressor unit final discharge line(s) for compressors greater than 1000 hp." why we should use bdv for compressors greater than 1000 hp. thanks

 

[pmover]

the blowdown valve is used to evacuate the gas to a safe location in the event of an unsafe operating condition. when the unsafe operating condition occurs, the unit shall shutdown, suction/discharge valves close, bypass/crossover valve opens, and blowdown valve opens. the unsafe condition can be an event such as gas detection &/or flame detection. excessive vibration, high bearing temperatures, etc. are other unsafe conditions.

 

[georgeverghese]

In my experience, all equipment containing flammable hydrocarbons with max operating pressure greater than 100psig should be blown down during plant emergencies and for other operational reasons. Am not sure about the cutoff pressure, it may be as low as 50psig. This lower cutoff limit is subject to plant Owner guidelines. Check with your plant manager / process safety engineer.

 

[142846]

pmover and georgeverghese thanks alot.I understand opening of BDV in the event of an unsafe operating condition such as gas and flame detection. excessive vibration, high bearing temperature, but based on Figure B.2—Example SAFE Chart api 14c,I do not understand that some conditions such as high/low pressure or level of inlet or inter stage scrubbers can open the BDV. Why these conditions should open the BDV?

 

[georgeverghese]

Agreed, from a safety perpective, events such as abnormal levels, PSHH need not trigger the BDV. However, from an operational perspective, some compressor trains have to be depressured partially to allow a pressurised restart. This is because the train settleout pressure (on shutdown) may be higher than PSHH on one or more stages, thus inhibiting train startup. In other cases, a total depressurisation may be required ( especially when a compressor train is kept in the pressurised and shutdown state for more than a given time duration).
Pls note that shaft seal failure for 2stage and 3stage gas seals is also wired to initiate a shutdown and total depressure sequence.

 

[142846]

georgeverghese I appreciate your respond. it guide and clear some subject to me.but there is still one question. As i mentioned above I am very close to API rp 14c and this standard (better say recommended practice)is PURE SAFETY standard and why a safety standard says about OPERATIONAL issue. I think if api 14c says compressor systems shall be have depressuring, api concerns is about safety aspects. summery i think if for example level high high inlet scrubber causes compressor system shutdown and depressuring, depressuring returns to safety aspects not operational. but i do not know answer the question.Question is application of BDV as SAFETY DEVICE for all conditions for example fire, gas, bearing temprature, LIQUID LOW LOW LEVEL IN SUCTION SCRUBER, ...

 

[georgeverghese]

Perhaps the API RP14C does not take credit for the antisurge valve, since the ASV is not a safety device. Hence, to prevent surge on shutdown, it relies on the BDV, which I presume is considered to be an instrumented safety device. Hence the suggested activation of the BDV for all shutdown events.
Ideally, opening the ASV AND activation of the BDV would enable a lower risk of machine damage on shutdown due to surging, but in actual practice, many companies tend to rely on a well tuned antisurge controller and its ASV alone ( and sometimes a HGB also) to keep the machine out of surge during the shutdown. If you have witnessed a large compression train shutdown, you may some times hear the compressor going into surge just for a few seconds before the effect of the full open ASV takes effect, even on a welltuned antisurge controller. Activation of the BDV will help to reduce this further.
But activation of the BDV alone, most likely, does not prevent the compressor going into surge, in most large machines. The full open ASV / or recycle valve is also required.

 

[pmover]

Dararia,

API RP 14C: Recommended Practice for Analysis, Design, Installation, and Testing of Basic Surface Safety Systems for Offshore Production Platforms

clarify/confirm the reference material.

 

[142846]

georgeverghese I appreciate again. I am not expert in operation of compressors but i think that surge is not applicable for positive displacement compressors. API 14c says "A blowdown valve should be located on the compressor unit final discharge line(s) for compressors greater than 1000 hp." That means for ALL TAPE of compressors {just more than 1000 HP} BDV shall be installed.

 

[georgeverghese]

Agreed, surging risk for pd compressors is not applicable, but a BDV is required for depressurisation in case of shaft packing leaks at the piston end and crosshead end, and general F&G events. To prevent transient overpressure on shutdown, capacity recycle valves are used.

 

[1503-44]

Blowdown of all compressors units and compressor stations involved in natural gas transportation is required by ASME B31.8 and CFRs Title 49 Part 192.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

ax1e- question is under which conditions (except fire and gas) BDV should be opened? or under which process conditions bdv opens? thanks a lot.

 

[1503-44]

Basically, and as a minimum, compressor station shutdown, including blocking and blowdown of all gas discharge piping must be initiated by any one or more of the following, not all of which are what you might call "process" related.

Any automatic ESD activation,
Manual ESD activation from any ESD switch located within the plant, or from one of at least two located outside the plant near emergency escape or access gates.
Fire detection in a critical area of the plant.
Gas detection within buildings >= 50% of explosive limit.
Overpressure of piping >= 15%

Except for unmanned, onshore stations of horsepower <= 1000








“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

ax1e thanks alot
appreciate if tell me:
what is the reference of "Overpressure of piping >= 15%"
and api 14c says hp>1000 hp (offshore manned/unmanned)and about onshore is quiet.which standard is applicable for onshore?

 

[1503-44]

CFR Title 49 Part 192 SS 167 Emergency Shutdown
Onshore: No specific ESD pressure set point is given
Offshore or inland navigable waters: ESD setpoint is MAOP+15%

You may want to consider shutdown of the compressors without initiating ESD block & blowdown in following circumstances,

B31.8 843.3.1
Auto shutdown of compressor(no blowdown reqd) on scrubber hi liquid level.

843.3.3
Shutdown compressor on overspeed (no blowdown reqd)

843.3.4
Pressure relief to vent must activate at pressure <= MAOP + 10% (not mentioned in ESD or blowdown context)

843.3.8
GAS DETECTION is 25% lower explosive limit (is ESD -blowdown reqd? It only says "monitor" and "warn". (CFR says 50%))

Others not actually reqd by codes
Safety Relief valve active for X minutes.
Hi vibration
High temp
Low oil level
Low suction pressure
Overspeed
Etc, etc.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

AX1E-THANKS A LOT
BASED ON ATTACHED FILE BLOWDOWN HAS BEEN OPENED EVEN FOR SCRUBBER HIGH LEVEL AND ANY OTHER PROCESS CONDITIONS NOT FIRE AND GAS. IN YOUR OPINION WHY API 14C INSIST AND PERSISTENCE TO OPEN BDV EVEN IN HIGH LEVEL SCRUBBER? BECAUSE I AM AGREE WITH YOU AND I THINK THERE IS NO NECESSARY TO OPEN BDV IN THESE CONDITIONS.

 

[1503-44]

Looking at 14C, I only see that blowdown of the compressor discharge piping is required, although it would certainly not be prohibited to provide blowdown to a seperator if you want to do that.

Where did you get the example safety analysis?

If you could point to where you think 14C is requiring the blowdown of separators, I will be happy to give my opinion. This is the link to the 14C copy I am looking at. I don't see it there.

https://ia800502.us.archive.org/16/items/gov.law.api.14c.2001/api.14c.2001.pdf

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[142846]

ax1e,
your att. is from OLD version 7th ed of api 14c. my att. is from NEW api 14c 2017 8th edition pages from 90-96. that is why you could not see all of the subjects.