main line block valves 2

[sveeta]

For main line block valves above 12" it is clear that virtually no one in the industry locates these above grade. This makes sense intuitively but is there any discussion in the industry as to why?

 

[pennpiper]

Sveeta,
Your statement ("main line block valves above 12" it is clear that virtually no one in the industry locates these above grade.") and your question ("is there any discussion in the industry as to why? ") is not clear.

I will try to give you some insight based on my experience.


A. A "Block Valve" is not a type of valve. It is a Function. Block valves can be any of the following: Ball Valves, Butterfly Valves, Diaphram Valves, Gate Valves, Needle Valve, Pinch Valve, Plug Valves, etc.. Valve Function and Valve type might influence Valve placement but does not dictate the placement.

B. Some "Block Valves" are located below grade (in a Valve Box*), some are located above but near grade (as on Sleeper Pipe Racks) some are located above grade as in an elevated Pipe Racks at Battery Limit isolation points fitted with Platforms for access and others may be in other locations depending on the function of the valve and the function of the line.

C. All Block Valves should (I prefer "shall") have the ability for operation provided. This may be Operator access (at grade or by platform) for walk-up operation. Others may be fitted with Chain Operators or Motor Operators when special conditions exist. An "ESD" (Emergency Shut Down) Valve is an example of a Motor Operated Valve.

D. The type of facility (Pipeline, Refinery, Chemical Plant, Power Plant, etc.) may also influence the placement or restrictions for valve locations, "Main Line Block Valves or any other function.

E. The key issues for Valve location include: Safety, Function, Operation, Maintenance, Initial Installation (Construction) and Cost.

Does any of this help you answer your real question?

(*) The only valves that should be allowed to be direct buried are Cast Iron Fire Water loop isolation valves and or Fire Hydrant Shut-off valves.

 

[sveeta]

I am referring to cross country pipelines and the main line block valves utilized in this application only. I am strictly concerned with placement, i.e., above ground versus below ground. No major pipeline company in the country places these valves above ground (except at stations) and I was curious as to whether there were reasons other than the obvious, e.g., maintenance, vandalism, etc.

 

[zdas04]

My work is all upstream of plants, so my comments my be irrelevant to you, but I'll provide them anyway. I have never, and will never place a big-inch valve below grade. Valves bigger than 12-inch often have actuators and putting an actuater in a valve can is very high risk.

I live in the San Juan Basin of Northern New Mexico and approximately 6 BCF/day leaves here towards California. Every day. The valves that signify the beginning of the pipline connecting these two points are all big-inch, actuated ball valves located outside of any plant fence and are above ground. I've never followed these pipelines west to see if the periodic block valves are buried or not so I can't commment on your "No major pipeline company in the country places these valves above gound (except at stations)" statement except that it doesn't feel right to me.

I've seen river crossings with above grade big-inch block valves on either side of the river. I can't comment on whether this is normal or not.

David

 

[DLite30]

Typically, that is exactly what we do on main lines, bury the valve body.

Valves can be ordered with stem extensions that put the manual handwhell or actuator a few feet above grade. Depending on space available, size of the line and the design of the facility, some mainline pig launch/receiver valves are placed above grade.

There's no particular technical reason why they're buried or raised above grade.

Mainly it's due to installation cost & schedule, and maintenance to a lesser extent.

Placing a valve above grade will require concrete sleepers, clamps, access platforms (depending on the size of the valve), additional bend fittings, etc, that are not required for a buried valve. Yes, you still need sleepers, but they're not as challenging to install. Tack on to that, additional surveying, engineering, drawings, etc.

A normal straight-through mainline valve assemly including blow-offs, can be shop-built (which is considerably less expensive that field fabrication), and dropped right in, with minimal field work.

Any above grade piping you minimize, also minimizes amount of maintenance (namely painting).

Imagine placing a 42" mainline block valve assembly above grade (and do that every 20 miles or so).

Plus an above ground assembly would be much more of an eye-sore to landowners, than just an actuator stem and couple of blow of lines sticking out.

 

[BigInch]

Lease block valves, yes, but I've never put a single MLV above ground on any of 5 continents, for all of DeLite's reasons, plus it makes target practice much more difficult too. Bad enough that the power tanks are exposed, but no product leaks if they get taken out.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[waterpipe]

For main cross country pipelines, I would like to add the following:

- Security and accessibility
Above ground installations are visible and can be accessed more easily. This could be a security concern.

- Protection & maintenance
Every exposed structure needs to be fenced and maintained.

- Freezing
For water pipelines, it's a concern.

- Avoiding obstacles
In a cross country line, it might be difficult to own the land (ROW) and make a visible obstacle. Imagine of valve chambers on the ground when the pipeline comes near cities.

- Easier installation
Corss country pipelines are normally Biginch and pressurize. Making bends to come above ground then leveling for valve installation and then going down for getting what benefit? Make a box around the large diameter pipe and putting the valve seems to be easier and cheaper.

And is there any discussion why it should come above the ground?

 

[zdas04]

The picture that BigInch posted above kind of says it all.

In my world, the choice is between above-grade valve set and a valve can. Valve cans are: (1) confined space; (2) prone to collect vermin (rodents and snakes to prey on them); (3) not much help against freezing; and (4) attractive for people to hide stuff in (we've found drugs, weapons, and evidence of kids playing fort in valve cans). Consequently, valve cans are just about the last thing I'll put on a gathering system.

On the other hand, the extended bonnet valves like BigInch shows in the picture are the best of all worlds. They are not a confined space, no place for vermin, good freeze protection, and no place to hide. Further, you can actuate them without elaborate space venting requirements. These valves have been around for quite a while, but I've never seen one in the wild until earlier this year (not sure why not, just luck of the draw I guess) but the more I see about them the better I like them.

David

 

[waterpipe]

Thank you David & BigInch. Issues to think of and I could see the benefits. However, haven't seen them in water pipelines myself.

 

[BigInch]

In water pipelines you have more options on where you can put them. In gas, oil and product pipelines, the law has requirements as to how far apart they can be on main lines. In water pipelines you don't have the same safety concerns in case of a break. It makes little difference if you lose 10 miles of water or the whole pipeline's volume. If a hydrocarbon pipeline breaks, you're not going to want to have the whole pipeline as a potential fuel source. Block valves come in pretty handy.

Some clients require that the whole installation be buried, in which case it's usually in a concrete celler, but I don't see a need to go to those extremes. In hot humid climates, the celler humidity level build up can play hell with the temperature, pressure and other instrument connections, they flood easily .. well, just plain messy, not to mention costly.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso