Dear all,

The 0.3 barg blast load design criteria on the hydrocarbon equipment and piping applies.
How i built the load case for blast load. what are all combination is required.

Blast load case are
1) (OPE) W+T1+P1
2) (SUS) W+P1
3) (OPE) W+T1+P1+U1+WIN1
4) (OPE) W+T1+P1+U1+WIN2
5) (OPE) W+T1+P1+U2+WIN1
6) (OPE) W+T1+P1+U2+WIN1
7) (OPE) W+T1+P1+U1+WIN3
8) (OCC) L8=L3-L1
9) (OCC) L9=L4-L1
10)(OCC) L10=L5-L1
11)(OCC) L11=L6-L1
12)(OCC) L12=L7-L1
13)(OCC) L13=L8+L2
14)(OCC) L14=L9+L2
15)(OCC) L15=L10+L2
16)(OCC) L16=L11+L1
17)(OCC) L17=L12+L2

SHALL I FOLLOW THIS ABOVE CASES FOR BLAST LOAD ANALYSIS. PLEASE GUIDE ME.

Hello Shabeer,

Load cases are correct. But remember combination method for L8 to L12 should be Algebraic and L13 to L17 Scalar.
You can also add 2 load cases for pipe support load check as follow:

(OPE) L18=L1,L2,L13,L14,L15,L16,L17 with combination SignMax
(OPE) L19=L1,L2,L13,L14,L15,L16,L17 with combination SignMin

Please read DNV-RP-D101. There are a lot of things to think about, apart of load cases.

Load cases should be as for wind but all directions (even vertical) but you should consider also things like CD or DLF.
In any case do not conduct these calculations by yourself, it is dangerous.

But you will discover soon what mean 0.3 bar drag load.

Best regards,

Thanks Danb and Farhad Salehi,

i will discuss with my senior for above load cases,he gave some suggestion regarding Load case, the acceleration in U1,U2 and U3.
U1- acceleration In X-dir
U2- acceleration In Y-dir
U3- acceleration In Z-dir
WIN1- wind in X-dir
WIN2- wind in Y-dir
WIN3- wind in z-dir

he re-write the load case below one plz confirm,

1) (OPE) W+T1+P1
2) (SUS) W+P1
3) (OPE) W+T1+P1+U1+WIN1
4) (OPE) W+T1+P1+U1-WIN1
5) (OPE) W+T1+P1+U2+WIN2
6) (OPE) W+T1+P1+U2-WIN2
7) (OPE) W+T1+P1+U3+WIN3
8) (OPE) W+T1+P1+U3-WIN3
9) (OCC) L9=L3-L1
10)(OCC) L10=L4-L1
11)(OCC) L11=L5-L1
12)(OCC) L12=L6-L1
13)(OCC) L13=L7-L1
14)(OCC) L14=L8-L1
13)(OCC) L13=L9+L2
14)(OCC) L14=L10+L2
15)(OCC) L15=L11+L2
16)(OCC) L16=L12+L2
17)(OCC) L17=L13+L2
18)(OCC) L18=L14+L2

Shabeer,

It sounds good.

I don't think that you should include also g's with your drag load.

Regards,

Dear Shabeer,

You should not combine Acceleration and blast case together. Acceleration is a accasional case whereas blast case is an accidental case. You shall make two files. One for design and another is blast case. As allowable stress for blast is much higher compared to accasional case. Blast should be treated as wind loads except it has vertical loads and also Dynamic load factor. Before doing blast calculation, please go through Design of accidental loads (DAL) prepared by techical safety department. It would say direction of blast pressure. In my opinon 0.3 bar of drag pressure is significant.

As one of the participant send, please read DNV-RP-D101 code for pipe stress analysis. this code available on internet for free.

best regards

Rao

Dear Rao,

thanks for your resonance.

In blast load, we considered wind pressure vs elevation. shall i apply 0.3 barg of drag pressure. please confirm where i have to include in drag pressure please guide me.

Yes, in User defined - wind pressure vs elevation. Same as for wind. And in your input file do not forget to specify the "Wind shape factor" as the product of CD and DLF (note that CD is 1....1.2 or even bigger, pending on your project specification and DLF typically 1.5....2).

Always remember that 0.3 barg = 3 tons on square meter. Multiplied by CD and DLF you will obtain a pretty nice load on your piping. Check also your supports as it may be not good for blast load.

Best regards,

Dear Dan,

thanks...

and i have one more doubt. In blast load analysis, did we have to check nozzle allowable load or else we check only stresses are within limit.

which acceleration is to be considered for balst load analysis either extream acceleration or operation acceleration condition.

please confirm.

Shabeer,

The equipment manufacturer will have to give you a set of allowables for blast (ask for them).
The problem is to maintain the integrity of the entire system (equipment included) in order to avoid escalation.

Regarding the accelerations, it is a matter of statistics, blast is not an occasional event is accidental. As Rao said, you don't have to combine the two.

Note that you will have to perform also leakage check.

Best regards,

As Per rao said, not combine Acceleration and blast case together.based on that here re-write the load case below one plz confirm,
How i have to considered Acceleration in X, Y and Z direction in blast condition? can anyone re-built the load case. urgent....
(OPE) W+T1+P1
(SUS) W+P1
(OPE) WIN1
(OPE) WIN2
(OPE) WIN3
(OPE) L6=L1+L3
(OPE) L7=L1-L3
(OPE) L8=L1+L4
(OPE) L9=L1-L4
(OPE) L10=L1+L5
(OPE) L11=L1-L5
(OCC) L12=L2+L3
(OCC) L13=L3-L3
(OCC) L14=L2+L4
(OCC) L15=L2-L4
(OCC) L16=L2+L5
(OCC) L17=L2-L5

Dear rao,

why we should not combine Acceleration and blast case together? i agree Acceleration is a occasional case whereas blast case is an accidental case. but in off shore piping we have acceleration in normal operating cases. That why i combine with above cases'.

Shabeer,

For explosions, the frequency of exceedance is between 10-4 and 10-5 p.a.


You should follow your owner and the third party verificator requirements.

Best regards,

Hai dan,

Whether we have to check for nozzle load in pipe stress analysis for blast condition. Since we did operating cases,transit case and blast case. Nozzle load are allowable in operating cases and transit but exceed in blast case. In previous project,last minute we did blast case, at that time we have considered only stresses are within allowable.Please confirm.

its dependence up on the client. For Statoil ( Norway projects) We check the Nozzle loads against the TR1968 Document.We check the Resultant bending Moments at the Nozzle junction location.

In the blast Case Flange Leakage check also required.

Shabeer,

Remember that the aim of the blast analysis is to make sure that the system maintain the integrity after a explosion event. So if the pipe maintain integrity but the equipment not.........

Plastic deformation is acceptable because nobody expect to continue to operate the plant after an explosion, but mechanical integrity must be maintained (for the selected systems). As previously said, also leakage check (including at the flanges connected to equipments) is also required so in some cases this will be the limiting factor.

Regards,