Surge vessel failure

What exactly do you mean by "failure"? Did the tank rupture, did it run dry, did somebody close the fill/drain line?

Dear Tom:

there is a request to study the follwing criteria for possible surge scenarios;
The minimum and maximum surge pressure shall be calculated reflecting the most critical unscheduled events as listed below:
 Power failure of pumping station (trip of all pumps)
 Unscheduled closure of control valves
 Unscheduled closure of isolation valves
In addition, operational load cases as listed below shall be investigated to allow definition of the sequences for flow increase / decrease, etc.:
 Startup of the system
 Shut down of the system
 Surge vessel failure

it is not defined what is the surge failure?

OK, so you are not looking at failure of a surge tank but controlling the effects of failures using a surge tank. It is not something we can quickly cover in a forum but there are many sources to help you.

Start with the in-product help in HAMMER.

Then work through the Quick Start lessons that come with HAMMER.

We also have a lot of wikis that address specific issue in transient analysis. For you problem, you may want to start with

communities.bentley.com/.../24920.initial-surge-or-transient-event-after-adding-a-surge-tank-to-a-model

You may also want to check out this webinar.

www.bentley.com/.../mitigating-risks-of-transients-using-water-hammer-analysis

These will teach you the basics of running a transient analysis. To become really competent, you should take our training classes

learn.bentley.com/.../ViewLearningPathDetails

There is also a chapter on transient analysis in our book Advanced Water Distribution Modeling and Management

store.bentley.com/.../9781934493014--Advanced-Water-Distribution-Modeling-and-Management

With these sources, you should become an expert in transient analysis.

Best wishes

Surge vessel" could refer to either the surge tank node element which is open to the atmosphere, or the hydropneumatic tank element which uses pressurized gas to attain a hydraulic grade much higher than the physical top of the tank. You can read a lot more about the latter in this article:

Modeling Reference - Hydropneumatic Tanks

If by "surge vessel failure" you mean that you need to simulate what happens if something breaks in the tank, then you'll need to consider exactly what will physical happen and think about the hydraulic impact. As with your other post, I would suggest checking with whomever made the requirement for clarification. The requirement may be to check what happens if the tank is essentially not functioning at all, which would mean setting up a scenario in HAMMER with the surge tank inactive (is active = false) or a valve next to it fixed in the closed position.