Newbie question - About design of subsea valves 1

[Albator]

Hi all.

My question will certainly look like evident for some people.

I'm currently beginning design of subsea valves.
I read several standards, but there is something I can't fix about the class pressure.

What I retained is that the design has to follow a pressure class as any other valve design, and that "valves shall be designed for loads other than internal pressure and temperature if specified by the purchaser" (from API 6DSS).

So let's say I have process conditions giving a 600# class (150 bars), but that my valve is to be placed by -3000 meters (300 bars of external pressure).

How should I design it?
Like any other 600# valve, but adding thickness to resist to 300 bars of external pressure, modifying the seals, etc.?
Or like an API 5000 valve for example (345 bars internal)?

I really can't make the difference between those 2 options regarding the standards.
There is obviously something I didn't understand.

Please don't laugh of me ;-)

 

[BigInch]

Both, in the worst combination possible.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[Albator]

Thanks BigInch.

But then what concerning the seals, trunnions bearing (these are ball valves),...
Which class should they follow?

 

[BigInch]

I'd think you'd want to have the typical internal pressure classes as a basis, then perhaps adding several maximum depth classes too, ie. to 2000 m, to 3000 m, to 4000 m, making those actual depth limits to correspond with various material or dimensional limitations. For example, if a material can be used with a particular design model valve down to 2650 m, make a line of models that can be installed down to say 2500 m depth, change materials and make the next line of models work down to the next depth limit encountered, whatever that might be. Likewise model design might be based on those material limits too, or commonly available material thicknesses, for example also changing body wall thickness at the same 2500 m depth material limit to something that will get you to 3500 or 4000 m with a new wall thickness and a new material. You'll have to look at all possible limiting points of dimensional design and material design and see what depth ranges overlap then optimize the dimensional design with the material selection to produce the products you think are marketable.


"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[Albator]

Many thanks, this is an approach I didn't think of!!!

 

[BigInch]

I don't really know anything about designing a valve; I just use them, but that's how I'd approach designing a line of valve products, or a line of any kind of product for that matter. Hope it works out.

"I'm all in favor of keeping dangerous weapons out of the hands of fools. Let's start with typewriters."
- Frank Lloyd Wright (1868-1959)

 

[gerhardl]

.. Interesting approach from BigInch! Another point is of course demand, and for this particular product: future demand and development.

It would always of course be of interest to a designer to talk to end-users and gather some thoughts about sensible price and possible competition, and perhaps lacks in competitive products..

Good luck, Albator!

 

[Albator]

@ gerhardl:

That is exactly what I began with ;-)
But even with this, I was hurting myself to the same thing again and again.

And thanks for the luck