Dear all,

Please advice regarding blast load (DNV-RP-D101-2008)

Blast load, F = 1/2*ρ*v^2*D*C*DLF [Where: 1/2*ρ*v^2 = dynamic drag pressure]


Safety department do simulation and give output overpressure (not dynamic drag pressure or air speed).

Is there any formula to have dynamic drag pressure by using overpressure given by Safety Departement?


We have an example in Table 3-1 of the code.
"Tabulated pressures are based on figure 5.3 in FABIG Technical
Note No 8, Protection of Piping Systems Subjected to Fires
and Explosions. This table is only meant for information and
to show that the relationship between overpressure and drag
pressure is not linear"

So we can't use table 3-1?

In that code said also:
In order to obtain more reliable values for the overpressure and
drag pressure for an offshore installation with steelwork, piping,
firewalls, equipment etc a 3D blast event simulator should
be used. The FLACS (FLame ACceleration Simulator) programme
is a commonly used software tool for such simulations.

Please share and advice if you have any others method..

If Safety dept. has done the simulation they should give you also the drag pressure. After all they have the speed calculated.

Dear danb,
Currently our safety dept use DNV-Phast (not FLACS). They don't have output "dynamic drag pressure or air speed".

I wish if we have air speed output due to blast then it will be easy to anylize the model by using "as wind load"

Sir Richard Ay,
Regarding wind load, Does Caesar II consider wind load in "horizontal axis" of the pipe? i think it is small..IMHO

Ask then what formula their program uses for the overpressure calculation.

It should contain in my opinion something that help you get the gas speed.

Dear danb,

I will take a look on it.

Sir Richard,

Sorry..what I meant : "Regarding wind load, Does Caesar II consider wind load in "local axial axis - x (small) axis" of the pipe? i think it is small..IMHO

No, Ceasar does not consider wind load for elements that have axis parallel with wind direction.

Dear danb,

I have the same idea with you. I believe air speed only have significant effect on local lateral and local vertical axis of pipe (axial neglected).

To apply blast load it will be easier also as "wind load" rather than "uniform load per length (N/mm)" in term of inputting.

I need respond also from Richard..thx Richard..

Wind load is applied to the area of the pipe perpendicular to the wind direction. Therefore, if the wind direction aligns with the axis of the pipe, there is no wind load.

For those users that have addressed the "blast load case", and have subsequently discussed the issue with me, they are all applying the blast as a wind pressure.