Natural Gas Utility Supply 4

[Boghi1990]

Hello,

Could ypu please explain to me what a Letdown Station is and does it function?This is in regards with a natural gas utility supply.

Kindly Regards,

One Point

 

[Zapster]

Try to Google a answer. Key words would be:
natural gas "pressure reducing station"

 

[BigInch]

Its a pressure reducing station, usually used between a main transmission line and a takeoff to a lower pressure pipeline. These can usually be found at a connection to a local distribution company at a "Town Border Station". A big pressure regulator station, often with several pressure reduction valves. A town border station could also have motorized block valves, sales meters, mercaptan oderization equipment and data transmission equipment.

 

[katmar]

It is more economical to transport NG over long distances at high pressure, but for safety reasons it is used in domestic or industrial appliances at low pressure. The Letdown Station simply controls the pressure reduction from the high pressure in the transmission pipeline to the low pressure at which it will be used.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[davefitz]

The letdown station can also be a scope break between the utility and the local consumer, and this may affect the requried design code used for designing the downstream piping system, engineering scope of responsiblility , code inspector responsibiliy, insurance coverage, etc.

 

[BigInch]

Sorry Dave, beg to differ. A letdown station is a point where pressure is "let down". Its been that way for the last 30 years and doesn't matter where it is, who owns what, or what color its painted.

 

[vzeos]

Davefitz is correct. Especially in "farm taps" or M&R stations where custody is transferred from the transmission company to the customer. For example, a transmission company delivering gas to a power plant has a jurisdictional change at the M&R station. The transmission line is regulated by the DOT code and the power plant is constructed under ASME code.

 

[BigInch]

Ya, well maybe there's a code change and maybe there aint.

Come on! Code changes, insurance requirements, transmission or LDC, DOT, ASME, meter station, custody transfer points, has nothing to do with the term "letdown". We have pleanty of letdowns where we let the pressure down into our own facilities and there's no code change, its all B31.8, or Title 49 Part 142, if you prefer, for gas or B31.4, etc. for liquid, both on the pipeline and inside the stations. How do you explain that? You mean I should believe that ya'll say, "I think this is where I'll make a code "letdown". :-(
Don't try to sell it here.

Google It! the first 3 references that come up are,

1. "Automatic pressure letdown,"

2. "Flashtubes for pressure letdown"

3. "clean power from pressure letdown "

4. "Slurry-Phase High-Pressure Let-Down"

5. "Dynamic Slurry Pressure Let Down Device"

6. "Yarway, Control Valves
It combines the functions of a check valve, flow sensing device, minimum flow control and pressure letdown into a single valve. ..."

7. " fabrication methods, system plugging, pressure letdown, "

8. "eg, during pressure letdown or during"

9. "pressure letdown lines in the CVCS. ..."

10. "[PDF] Natural Gas Liquefaction
File Format: PDF/Adobe Acrobat - View as HTML
Pressure let-down liquefier– (Sacramento Plant) Utilizes pressure drop between. transmission lines and distribution lines to liquefy 10% of gas flow ..."

11. "ProSciTech: Page K3: K3: Critical Point Dryers & Freeze Dryers
Fine Control Needle Valve Pressure Letdown (Flow Gauge Monitor OPTION.) Illuminated Chamber with Side Viewing Port and Protective ‘Lexan’ Shield. ..."

12. "[PDF] Flow Control Before installation these instructions must be fully ...
File Format: PDF/Adobe Acrobat
flow and provide pressure letdown. Operation. Flow through the check valve overcomes. the spring force to open the main check. valve element. ...

http://www.tycoflowcontrol-na.com/getlit.asp?lit=ld/972562 (9200 2 to 4 Inch).pdf

- Similar pages"

13. "PDF] ExxonMobil High-Pressure Process Technology for LDPE
File Format: PDF/Adobe Acrobat
"the low-pressure letdown valve and fed to the low-pressure. separator. At this point, most of the remaining entrained ethyl- ..."


Strange not one mentioned a code change, farm taps, DOT, ASME or ...anything else you said.

If that's what Google and ExxonMobil says it is, its good enough for me. Sorry, I'm sticking with my definition.

 

[davefitz]

Well, I was careful enough in my wording to state" can also be ", which it remains a true statement.

It is also trivially true that a pressure breakdown station is a pressure breakdown station, but that does not preclude that it can also be a scope break or a code break etc.

Most of the design codes I have seen that apply to fuel gas piping systems make a distinction between high pressure distribution ( above about 60 psig) and low pressure consumer piping ( below about 60 psig), and the types of safety systems, inspections, etc vary considerably between these 2 different pressure classes.

 

[BigInch]

Still more comments. I'm having a hard time following this thread now and I'm not sure why its continuing. I think 13 example definitions should be sufficient to call a halt to it, but just to offer some direction as to how IMO all of us should proceed when defining a word...

I think the idea of trying to define a particular term should be more something like actually getting closer to an exact definition in each suquential post, rather than writing a more inclusive, broader and broader definition that gets so far away from the original meaning and winds up so large in scope that finally it includes every place you can point to on a pipeline or in a power station such that it is no longer relavent to original question asked, is not what we should be trying to do here. I mean like, following your logic where I think you say you are technically correct because, a letdown might or "can also be" or include something else, just doesn't make sense. To give you an example: your letdown can also be ... an airplane, as we can probably presume there is a pressure letdown somewhere in a 747's hydraulic system. A little bit over the top, would you not agree? Can we leave it?

 

[itsmoked]

Certainly IMO as opposed to IMHO.

I think it's great to point out to someone who doesn't even know what a "Letdown STATION" is that it could mean precisely that or more than that.

And all the googling in the world be damned.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com