Hi All, currently I doing a project which required to perform dynamics analysis for the surge pressure in LNG piping. I had read the Caesar II guide and confirm that water hammer/slug flow analysis is suitable in my case.
According to my research, I knew that surge pressure is similar with the water hammer case. As such I calculated the thrust force base the operating pressure give and input in the software and get the result. However, I had done the analysis but my client was rejected it as they claimed that Caesar II is not suitable to use to analyze the surge pressure.


Can anybody or Mr Dave advise me whether I am using a correct software to perform the surge pressure analysis?? Your soonest reply is highly appreciated.

Aaron,

By using CAESAR-II we take care of surge forces by providing sufficient supports. meaning proper support design we are doing.

with equations the force value is very very high, To get actual surge force/ pressure, there are some software's available like PIPENET, KYPIPE, SAP2R etc.,

But overall system is safe or not you have to perform SURGE ANALYIS by using above software's only meaning

1. find out the pressure ( if surge pressure is greater than design pressure) - and design the thickness based on this pressure.

2.check any -ve pressure. Any water column separation is happening or not. If happens then slug also comes in picture to avoid that what are the precautions to be take care.

these things we cannot do in C-II, I think what CLIENT saying is this.

Hi Durga,

Thanks for your info, however I had checked the User Guide and Caesar II can also taking care the slug flow by calculating the thrust force at the elbow. Those formula has also mentioned in the user guide as I found it quite common. My client is not because of the slug come into the picture but they totally mentioned that Surge pressure is totally not similar with Water Hammer/slug flow scenario.

Please correct me if I mentioned anything wrong.


HI Dave pls advise me on this.

Hi All

first of all, I would Ned any expert advice me, is Caesar II not suitable to check the joint failure due to surge pressure by applying the Water Hammer/slug flow matter?

CAESAR II calculates and evaluates piping system response to a variety of loads. Many of these loads are developed by the program - thermal strain, weight, wind and seismic shock spectra. These loads are collected from a wide variety of engineering standards. The magnitude and timing of a transient hydraulic load has not been "standardized". This is where Durga's comments come in - while you can approximate the transient event, a "proper" set of numbers would come from a simulation of the system hydraulics. There are several commercial packages made for this. Is you client requesting this sort of look? If so, then the client is correct, CAESAR II does not do this. But CAESAR II is well equipped to calculate and evaluate the structural response of the system to pressure imbalances over time.
(CAESAR II does NOT investigate the increased hoop stress associated with the surge - we are focused on beam bending.)
You might want to take a look at Jim Wilcox's CAESAR II webinar last month where he uses a commercial transient hydraulics program to create loads and timing and then feeds that data to CAESAR II for evaluation (http://icas.intergraph.com/cii2017).
I think part of the problem here is definition of terms. You and your client should have a conversation.

Dear Dave & Durga,

i had added a file which show calculated the forces which use for water hammer/ slug flow analysis. It seem to me is quite logic. However i would like to share and get your advise on the formula that i used.

Many Thanks.

Hi Aaron,

I think you are confuse with the term of Surge Pressure and Water Hammer. Surge Pressure/Force is one of the Transient event in piping system and can be caused of pump start-up, valve close in a very rapid time, column separation, wrong ARV sizing and so on. Water Hammer/Slug Flow analysis is normally used when you are analyzing 2 phase flow liquid. However Water Hammer can also caused by same Transient event as mentioned above. You can only confirm this by running a Transient analysis by using another software like what Durga mentioned.

You need to talk to your Client and ask them what they really want from your analysis.

Dear Noorsyam,

Yes, if to find out the Surge pressure i required to use other software as mentioned by Dave and Durga. However, currently according to the discussion with client. They required me to confirm that our liquefied natural gas piping system is fine if the inlet emergency shut down valve is suddenly shut due to over pressure.

That the reason, i calculate the forces according to their given pressure as shown in my attached file and input into the water hammer/Slug flow spectra analysis. This formula has also shown in Caesar II user guide under slug flow section.

Is my way of analyze this scenario wrong? Please advise if any. Many thanks.

Dear Noorsyam,

Client need to know is that any failure in our new LNG piping system due the surge pressure given by them.

Is the surge pressure given by your Client exceeding Design Pressure? There are 2 impacts on piping system during Transient event. Surge pressure which may increase pipe hoop stress and surge force which act on your fitting and support. For surge pressure, you input this pressure into you analysis and check against OCC allowable loads. For surge force, you can check them in 2 ways; static and dynamic. Base on your calculation, static analysis is sufficient because your force load is not really high.

Btw your 1330kPa is surge pressure or design pressure?

Dear Noorsyam,

The surge pressure given is 1330 kpa, which my Piping design pressure is 1770kpa. So it is save during this surge pressure. However, for the force acting on the fitting n joint i had calculated and also put in the dynamic analysis to study within 10 second. Result was perfect and problem.

I believe the static way to analyze is to input this forces under "force/moment " to those elbow or fitting node under static analysis right? Run And see is there any failure on those fittings node correct? Pls advice.