Design a steel frame 1

Because the load is variable, I'd consider it as live load...

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

I have nothing to add to this conversation except that I didn't know what a "water hammer" effect was and it led be down an interesting rabbit hole.

How would the downwards force acting on the beam be calculated? It appears to me (based on my limited reading, just now) that the hammer effect results in forces acting in line with the pipes, within the pipes only? So is the 50 kips the loading caused by the pipe assembly + fluid only, or does the hammer effect actually contribute to it?

The 50 kips is the load caused by the hammer effect alone. The weight of pipe assembly and fluid are not included in the 50 kips. The existing support of the pipe is damaged due to this force and a new design is required.

Would the hammer be expected to occur or could it treated as an accidental load?

Yes, it would be a live load. Since the existing structure has already been damaged by it, I don't think it would be reasonable to treat it like an accidental load. Water hammer occurs for different reasons in different systems, but a lot of steam systems get it every time you start up if there is any condensation in the pipe. It's quite terrifying if you're not expecting it (and the pipe is next to your head!).

Hopefully the mechanical engineers are working on a system design change to reduce/minimize the water hammer. It can cause serious erosion and pitting of the inside wall of the pipes. If it wasn't properly restrained before, some of the energy was making its way out to the structure (hence the damage). Once you properly anchor and reinforce the structure, much of that energy will stay in the pipe and the release could come through serious damage to the piping system and potential release of whatever is in the pipe.

BellaLuna:
Of course, the pipe hammer loading, 50k in line with the pipe axis, and the gravity loads or other lateral loadings would not be shown together (combined as/into one load), they are two distinctly different types of loadings on the system. The typical pipe support consists of one or two columns with a horiz. beam on top which supports the pipes. These Tee structures or frames take the gravity loads and lateral loads like wind and EQ loading. That 50k pipe axial loading, be it from pipe hammer or thermal action may require another substantial frame parallel to the pipe length. I would ask the Mech. pipe guys if they really mean for you to take this special loading with a (at a) typical pipe support frame, or if they expect a separate frame near the cause of the pipe hammer or at another appropriate location in the system.

You will need to be careful about how the load gets out of the pipe and into the structure. If the resisting load is eccentric to the load application, the structure may be fine, but you may break the pipe.