safety relief valve reaction force

[pancevo]

Hello,

how to include safety relief valve reaction force in calculation (static calculation)?

I have following load cases:

1 - dead load
2 - normal operating
3 - design minimum
4 - design maximum
5 - pressure test

Thanks,

Regards

[rohr2support]

Hallo

Generally you can add an occasional load case "safety valve blowing".
In this load case you add the safety valve reaction forces.
If your safety valve blows into the open air, you just add it at the valve in the opposite of the blow direction.
If you have a long line from the safety valve onto the roof or into a silencer you may want to consider the dynamic
loads of the pressure wave traveling from the valve to the exhaust.

Here is an example with 2 rupture disks and a safety-valve.

sv_reaction.PNG

Best regards

Rohr2 Support

[pancevo]

Thanks for quick support.

I have further question:

In Rohr2 tasks when I define load case "safety valve blowing" what load case should I use as Associated reference load case?

SRV Blowing.png

Thanks in advance

[rohr2admin]

Hello,

as in this load case only your reaction forces will act, the reference load case only has an influence on the Y-modulus, which will be determined at operating temperature. So the operating load case should be fine.

Best regards,
ROHR2support

[PSch]

Hello,

I have a question regarding the post above, even though it’s nearly 10 years old.

I would like to evaluate the temperature-induced forces as well as the safety valve reaction forces on the outlet side within an occasional load case. In this case, temperature effects on the downside are only considered within the occasional load case itself. I have enabled in "global loads" of the occasional load case both axial thermal expansion and axial expansion due to operating pressure.

Is this the correct approach?

Or should I determine the temperature-related forces separately in another secondary load case - thermal expansion?

Best regards,
PSCH

[rohr2support]

Hallo

The thermal-induced forces are usually considered as an operation case (with the exhaust line hot).
The resulting stresses will then end up in the stress range over all operation cases.
The loads are secondary (limited in displacement) and the check against a S4 equation, checks against ratcheting and cyclic plastic failure based on all secondary load cases (range).

You then apply the loads due to SV blow-off in a separate occasional load case which includes only the forces (not the thermal expansion).
The verification using an S2 equation checks against gross plastic deformation due to the blow off forces.
These (rare) occasional forces are usually not combined with other occasional loads, unless there is a risk of SV opening created by the other occasional effects (e.g. turbine trip -> SV opening).

For seismic loads there is an option in the EN13480-3 that you can include the secondary loads (differential displacement of building) in the S2 equation directly and then ignore the secondary effects in the stress range equation S4.
I am not sure that this approach is also acceptable for safety-valve related thermal expansion.
In most cases you do not want to take this approach anyway as the limits for an S2 equation are much lower than for an S4 equations.

Best regards

ROHR2 Support