38" ID Flange for Subsea Application (external pressure)

[mathias28]

I'm trying to choose a flange for a subsea vessel but I'm having some problems to make the best choise.

a) In subsea equipments I always go for a API 6A/17D flange, but it goes up to 30" size, so 38 inches is way to big for API flanges. And API don't address what to do for bigger flanges.

b) I thought about ASME flange with ring type joint, but ring gasket according to ASME 16.47 is suitable up to NPS 36 (35 ID).

c) I couldn't find any note at ASME code regarding external pressures. I'm talking about REAL EXTERNAL PRESSURE (1500 psi), not just vacuum pressure.

d) ASME class 900 is 100 psi lower than my need of 2300psi internal pressure. And no bigger pressure class is available. Extrapolation on ASME tables is not allowed either.

I have 1500psi external pressure (3000 feet water depth)and 2300psi internal pressure.

Thanks in advance,
Mathias

 

[gr2vessels]

Check out the link below, also google for offshore compact flanges;-

http://www.ltsusa.com/L005 COMPACT FLANGE.htm

Cheers,
gr2vessels

 

[BigInch]

I'm not a vessel engineer, as this question will suggest, but why isn't the design pressure = 800 psi? Will it be pressurized to 2300 at the surface, then lowered? Pipeline codes allow the design pressure as the maximum difference between internal and external pressure. Could it be the same for vessels?



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[gr2vessels]

Jim,
when the vessel is pressurizet at 2300psi internal pressure, that is a design point;- when is de-pressurized at the bottom of the ocean, the external pressure will be 1500psi, the second design point (minus the atm pressure). The 800 differential pressure is a no-no, because it will explode at 2300 psi or implode at 1500 psi. The question however is the use of suitable interconnecting flange, when the B16.5 and B16.47 limits are exceeded. The Norsok type of compact flanges have been specifically developed for this particular application, along with several other interconnecting jointing solutions for deep sea piping/pressurized equipment.
Cheers,
gr2vessels

 

[BigInch]

gr2, thanks for that apparent correction, although I don't follow the logic how, if it is actually pressurized at and remains at that depth, it could ever see 2300 psi net differential and explode as you suggest. I can obviously and easily agree with the 1500 psi external load under those same conditions, so no problem there. I would appreciate some explanation even though as I said, I'm not a vessels engr, I would at least like to understand the logic, or perhaps shall we say, the method to the madness(?).

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[gr2vessels]

Sorry, I didn't intended as a lecture, just to follow the original poster who stated the internal pressure of 2300 psi and external 1500 psi. In pressure vessel design, these are the minimum design conditions for which you have to calculate the minimum wall thickness plus allowances. This is assuming that the pressurized vessel might break free from the anchors and raise to the surface, whilst the internal pressure is still 2300 psi. Conversely, while anchored at the bottom, a 'valve' malfunction could depressurize the vessel until say atmospheric pressure, via an interconnecting pipe raised to the surface, exposing the vessel to 1500 psi external pressure.
If the minimum shell thickness was selected to resist only 800 psi, the vessel will explode when internal pressure will be 2300 psi and normal atmospheric external pressure. Or will be crushed under external 1500 psi and atmospheric internal pressure, at the bottom of the sea.
Again, all this is my assumption only, it was never said the vessel will always be safeguarded against full internal pressure or full external pressure. It was my deduction when mathias28 said that "ASME class 900 is 100 psi lower than my need of 2300psi internal pressure. And no bigger pressure class is available. Extrapolation on ASME tables is not allowed either." Perhaps his last sentence is a bit ambiguous, that both pressures might not exist simultaneously or the other way around? Sh..ugar, now I am going around...
Cheers again,
gr2vesels

 

[BigInch]

No. No problem. I for sure wasn't thinking about the vessel breaking off and floating up. If that is possible, it is a valid concern. Go for it.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

Although it might present a better overall manageable scenario if it exploded at 800 foot, or something depth, rather than drifting around on the surface to Lord knows where or into what with 2300 psi in it. Just thinking the Navy wouldn't lift old explosives to the surface to detonate, right? Oh now, my hat is getting holes in it thinking about this.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[mathias28]

Thank you all for the answers. Just to be clear about the pressure issue.

When i said that class 900 is 100 psi lower than what I have, is that, according to ASME, selcting my material and my temperature, the allowable pressure was 2200psi.

About the differential pressure: I always have to design my vessel disregarding the "compensations" that may occurs.
Let me explain:We need to test it before install, so as the tests are made at the factory it will be atmospheric outside. And when installed it's all empty and sealed so it will keep atmospheric pressure inside until I open the valves for the wellhead. That's why we must consider both situations separatedly.

Regards,
Mathias

 

[mathias28]

gr2vessels,

You suggest me to go for compact flanges. I didn't mention before to not address the answers to that solutions, but I've heard about this with another company, Vector flanges

http://vectorint.edge.be/index.cfm?PageID=18601

This flanges as I could see is based on FEA analisys and the geometry must be developed by myself and then Qualified. on API flanges, for example, the standard provides us all the dimensioning and it's all proven, so no qualification is required.

Do you know something more about this LTS Energy you sent me the link?? and about this issues I said about compact flanges?

Mathias

 

[gr2vessels]

Size for size (and rating) you can carve the standard ASME / API flange and fit inside the equivalent compact flange. The Norsok L005 has standardized the compact flanges, based on the original design developed by the Vector in UK (you can download free the L005 from Norsok website). Today, there are many fabricators following the same standard, in Europe, US and for sure a cheap version made in China. LTS is one of these fabricators. You will have to shop around.
Also, I'm sure there is a misunderstanding, you cannot develop the compact flange profile, that is part of the standard and is supplied to you by the fabricator (like Vector for eg.) to your specification (NB, rating, material if you want) with full guarantees. That's what you are paying for, so you don't need to design the flange.
For the nice finish, nobody is using anymore the ASME / API flanges for sub-sea applications.
Cheers,
gr2vessels

 

[mathias28]

Why you say that nobody is using anymore API flanges for sub-sea applications? As far as I know, API flanges are being used widely for subsea equipments up to 21". Is suitable for external pressure as no other standard flange.
I completely agree with you about ASME flanges.

For the aplication I need, 1000 meters water depth (up to 2500 meters for other), Vector flanges said that their flange are not suitable for high external pressure and offered a flange with a HX sealring (NORSOK shows only IX sealring). See what they say about external pressure:

"The IX sealring has external pressure capacity however we would recommend the use of HX sealrings for subsea use."

http://www.group-vector.com/index.cfm?PageID=18633

This makes me think that I can't use Compact Flanges as shown at the L005, since Vector do not trust on that for high external pressure.

I'm able to follow a standard and design a flange myself, FEA analyse and qualify, but the HX sealring is not mentioned at the NORSOK standard.

Do you think I have to buy from Vector this not standard special flange or delevop a new connection based of our on experience on hub-and-clamp flanges?? (we've already design a 28" clamped flange using a mettalic seal)

Cheers,
Mathias

 

[gr2vessels]

mathias,
I would gladly take over from you the selection of the most appropriate flange for your application;- my fees are standard consulting fees and I can provide the support of my business for your project. The other option for you is to put together a specification for what you need, start searching on the internet (type in the google 'sub-sea compact flanges') and select 10-20 suppliers you consider able to provide a suitable product. The Norsok website can provide you a very credible standard for the selection of suitable supplier. Send your specification to the selected suppliers and start reviewing carefully their submission. Select the best one (technically and commercially) and call him in for further negotiations and technical clarifications. You could also contact a number of sub-sea operators, they gladly will advise who was their best selection/supplier of flanged or clamped connections and what was the outcome of their similar construction. It's really not that complicated.
Cheers,
gr2vessels

 

[mathias28]

Thanks gr2vessel.

I'l do that for sure. I've already started some conversations with Vector as I told you, but now I see that I can go deeper on my researsh and ask other companies and operators as well.

Thank you very much for your time and help.

Cheers,
Mathias28