Christmas Tree Rating 1

[Johnrem]

Hi Every sepecialist;
I have some questions dealing with Wellhead facilities and I need someone to help me.

1) Very often in API 6A Christmas tree literature, we heard about "up rating" or "rectifying" API 5000 psi Xmass tree to 6650 psi class. I looked through API 6A standard and I didn't find this class rating.

My concern is the mating piping flange with an uprated class to 6650 psi. What shall be the mating flange with an API 6A Cl 6650 class?
For your information:
If the Xmass tress is 5000 psi rating, the mating piping flange can be ASME B16.5 Cl 1500.

2) In many projects I have seen Gas injection piping systems (class 2500) connected to API 6A christmas tree rated to 5000 psi. At the battery limit between API 6A and B31.3 (sometime B31.8) design codes we have an API 6A Cl 5000 flange and a CL 2500 ASME B16.5 flange (A694 Gr F60 or F65 are the material generaly used).
Given that CL 5000 psi= 348 bar, and Classe 2500= 425 bars (for example material group 1.1. ) bigger than 5000 psi.
My question is as follows: How can an API 6A cl 5000 psi sutain a classe 2500 pressure? How can be these two different rating systems connected together? How it is working without failure?

Many thanks in advance.

 

[terje61]

1)
Upgrading/uprating is not a standardised work method. The API 6A has clearly identified several classes and if you would work in line with the API 6A you would have to go from API 5000 to API 10000.
But that does not mean that you cannot do it. Sometimes materials do not allow to go to 690 bar (API 10000), but can be used for 460 bar ('API 6650'). Even when using API 5000 dimensions. If the user, buyer, local regulatory offices and manufacturer all agree that this is a solution for their situation, why not make it?
You can however never call this an API 6A valve. Since it does not comply.

2)
Using your example. Suppose that your system design pressure is 300 barg. First you have your process equipment certified to ASME standards, where you have to use the next higher rating: Class 2500. Then you have your wellhead equipment and you also use the next higher rating: API 5000.
As long as it is clear that the system design pressure is 300 bar it will work without failure.

Regards,
Terje

 

[Johnrem]

Terje61;

Thanks a lot.

1) You said in your answer: "Sometimes materials do not allow to go to 690 bar (API 10000), but can be used for 460 bar ('API 6650')".
What do you mean exactely and can you give example of such material?

2) In your example (design pressure=300bar)you supposed a situation that is covered by both API5000 and ASME CL 2500.
Generally in gas injection the design pressure is bigger than 380 bar. We know that ANSI CL 2500 covers the 380 bars but not the API 5000 class.
How an API 5000 can sustain 380 bars (or more in some cases)?

Best Regards

 

[terje61]

Hi Johnrem,

1)
A valve manufacturer could for example design a valve that is suitable for ASME 2500. They could use normal carbon steel material e.g. ASTM A352 Gr. LCC for a casting. The wall thickness is quite thick, because this is a low strength material.
If they would select an API carbon steel material with the same valve design, which is somewhat stronger, like ASTM A487 Gr. 1C, this would probably boost the valve design pressure up to 460 bar. This needs to be checked with design calculations of course.
The materials in the example are unlikely to be able to boost the design pressure to 690 bar.

2)
Ah, new information. And I thought I had a clever answer ;-). When the system design pressure is 380 bar and you do not have an injection choke valve that brings the pressure below 345 bar, I can inform you that nobody (= national regulating bodies/local regulating bodies/insurance companies) will allow an API 5000 X-mas tree to operate.

Regards,
Terje

 

[Johnrem]

Terje61;

Many thanks for your answers. It is getting more clear for me.
Just one more question:
1) If I want to use ASTM A487 Gr. 1C for valve body, how can I calculate the design pressure that a classe 2500 can sustain? Which code or formulae to use?
I looked through B16.34 code to get the design pressure for that material but it seems that this material is an unlisted one.

 

[terje61]

Hi Johnrem,

Since the valve you are looking for is not an ASME valve and not an API valve, it is difficult to use these standards. Note that the standards are there to make your life easy, so you have clear rules and if you follow them the valve should be good for purpose. Now you have to work as if there is no standard. YOU must define the rules. The conclusion is that by 'cutting corners' and using 'uprated' valves instead of higher class valves you take on a big responsibility. This does not mean that you can/should not do this, but you must be sure of what you are doing.

To start with: you probably want/need to have your valves certified in some way. In Europe you would therefore typically speak to a PED-certification body and ask them what they would accept.

For your situation I think you will get far when using the API6A as a guideline, but with an alternative design pressure. In any case you have to do strength calculations to show that the valve is strong enough for the design pressure.

Good luck,
Terje

 

[Johnrem]

Strength calculation is exactely what I want to do but I don't have idea how to proceed.

Many thanks