Frangibiliy Requirement for Dome Roof Tank

[James Bonding]

Hi Everyone,

Good Day!

I have this tank project (8m Dia x 13.95 Height) Dome Roof Tank. My question is, Client requested to make it frangible connection. Does this applicable to this tank size? Roof to compression bar connection is as as per detail i of Fig F.2. Kindly help me on how to design this as frangible.

Thanks!

 

[dik]

Why would the client want a frangible connection? I cannot even think of a good reason for one.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JStephen]

See the requirements in 5.10.2.6.
The statements in 5.10.2.6(b)(2) and 5.10.2.6(c)(1) also require compliance with 5.10.2.6a.6 and that seems to be a typo, but I've never followed up on that with the oommittee.

 

[dik]

what reference? Does that require frangible connections?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[James Bonding]

They mentioned this:

Tank design calculation shall include verifying the failure pressure on top shell/ roof
connection and Bottom shell / annular connection. And make sure the failure pressure on
top connection is less than the bottom connection. The tank has a 5.6KPa/-0.5 Kpa design pressure.

 

[DSTankee]

Your client is correct in that the intent of a frangible roof is to design a weak joint above the product line in an emergency over-pressurization event, rather than risk the failure occurring lower on the tank resulting in a loss of product. However, if the roof-to-shell joint is arranged per Figure F.2 detail i as you stated, it will not conform to the requirements for a frangible roof per API 650. In this case you may want consider installing emergency venting per API 2000 (see API 650 5.8.5.3).

 

[dik]

Thanks... that's why a frangible connection, and API 650 is the reference.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[James Bonding]

@DSTankee could you elaborate more why detail i is not conformance with frangibility? As per datasheet the tank is equip with 30in emergency vent. In that case, frangibility is not required? Thanks

 

[DSTankee]

Frangibility per API 650 13th Edition is determined by 5.10.2.6. Due to the size of your tank, we should refer to either subparagraph b or c c or d (depending on whether or not the tank is anchored). Regardless each set of requirements will state that the the tank shall satisfy the requirements of 5.10.2.6.a2 through 5.10.2.6.a6 (as JStephen mentioned earlier). 5.10.2.6.a5 specifically state that the roof-to-top angle compression ring is limited to details a through e. Detail i will not satisfy this requirement.

If the tank is equipped with a 30in emergency vent, there is no need for a frangible roof joint. Roof frangibility is only used as a means to satisfy emergency venting requirements (refer to 5.8.5.3). You should perform the API 2000 emergency venting calculations to verify the vent size is adequate. To design for a frangible roof joint and install emergency vent is redundant.

 

[James Bonding]

@DSTankee thanks sir. Appreciate your feedback.

 

[HTURKAK]

Client may request but this tank is not suitable for frangible roof .
Below , my points short answer;

- For frangible roofs, roof plates SHALL be attached to the TOP ANGLE of the tank with continuous fillet weld only on the top side to make sure the weldement at joint can fail with bending and tear. The suitable details (b,c,d.) of Fig F.2
- The frangibility of the roof is not reliable at smaller diameters less than 10-12 m.

- Frangible roof height would be around 30.0m for 8m Dia and with roof slope (1/6)

- Dome roofs are not considered to be frangible .The roof must be a cone roof with a slope not exceeding (1/6)




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[James Bonding]

@DSTankee, Since the diameter is 8m only, it will fall on the sub-category 5.10.2.6 (d) for anchored tanks of any diameter. Still, the requirement of 5.10.2.6a shall meet. Please note that this tank has 10 nos of anchor bolts.

 

[DSTankee]

@James Bonding, you're correct. In my previous reply I had intended to refer to subparagraph c and d based on the diameter of your tank (subparagraph b refers to self-anchored tanks diameters 9m to 15m). My apologizes, I shall edit my post to correct the mistake to avoid any confusion for any one who comes across this thread in the future.

 

[James Bonding]

Hi @DSTankee and JStephen,

I just need your help regarding interpretation of the clause F.4.1. I am just confused when I calculated the P_F4.1 the design pressure is around 33 kPa and then the std is up to 18kPa only. I'm really confused about this pressure. Hope you can give me explanation. Thank you.

 

[JStephen]

The scope of the standard, in Annex F, only extends up to 18 kPa. The maximum pressure equations may show higher numbers in various cases, but pressure is still limited to 18 kPa for an API-650 tank.
If you actually need higher pressures, API-620 or ASME code are available.

 

[DSTankee]

I agree with JStephen. The maximum pressure equation provide a result dependent on the configuration of the roof to shell joint, however Annex F defines a hard ceiling on the limits of the ratings of the tank. This just means your configuration may be slightly over designed, however this may not be terribly uncommon depending of the material selection.