3 replies to this topic

[Steve1977]

Hi All,

I have been assigned a design of a 48 km oil pipeline (onshore and offshore) for a marine terminal. I already finished the hydraulic analysis and found 55 bar as the pressure loss and 102 as the surge pressure when the ESD suddenly shuts the flow off.

My question is: based on 55bar of pressure loss and 102bar of surge pressure (water hammering), what should be the MAOP and the design pressure?

My understanding is that the MAOP should be 102/1.1 as allowed by ASME B31.4 for incidental pressure. Is this correct?

Thanks
Steve

[ankur2061]

Steve,

Clause 403.3.4 of ASME B31.4 states:

Transient overpressures including pressure rise due to surge. Surge pressures in the pipeline are produced by a change in the velocity of the moving fluid that results from shutting down a pump station or pumping unit, closing a valve, or blocakge of the moving fluid.

Surge calculations should be made and adequate controls and protective equipment shall be provided so that the pressure rise due to surges and other variations from normal operations shall not exceed the internal design pressure at any point in the piping system and equipment by more than 10%

Your interpretation is absoutely correct. What you have mentioned in your post can be explained in the form of a statement as follows:

The pipeline MAOP should be selected such that the MAIP or pressure rise due to surge is never more than 1.1 times the MAOP.

Regards,
Ankur.

[TS1979]

IMO, MAWP for the piping can be any number above 60 barg. You can use a ruputure disc or PSV to protect the piping from overpressuring. It depends on the frequency of the transient condition. If the ESD shutdown happens frequently, you may have to design the piping class up to the transient pressure. If the ESD shutdown is just for emergency and the cost for updrading the pipeline to the transient pressure rating is too high, you may consider to design the piping with lower class provided that you provide pressure relief for the piping system

[fallah]

My understanding is that the MAOP should be 102/1.1 as allowed by ASME B31.4 for incidental pressure. Is this correct?

Steve,

As per ASME B31.4, surge pressure as a nonsteady state condition is limited to 10% higher than internal design pressure. Then, it is better the ratio of 102/1.1 be titled "Internal Design Pressure" rather than MAOP beause MAOP is normally same as MAWP. Obviously, maximum steady state operating pressure shall not exceed the internal design pressure.

Fallah

Edited by fallah, 13 June 2012 - 11:39 PM.