I am designing a horizontal pressure vessel to be installed indoors, supported on 2 saddles, and rigidly mounted in a 2B seismic region. This is my first of this type and our customer has not made any indication of requirements for seismic conditions. If the job specification states "Installation by Customer" what exactly is my scope of responsibilty on the project other than providing mounting holes in the equipment?

This is not my area so keep that in mind with my comments.

At least where I work, our civil/structural group does the foundation design which would include the effect of seismic loads. That design work would include checking the connection details from the foundation to your base plant/support plates. I've seen them mark drawings for larger holes over the vendor's original proposed sizes and/or larger members on saddles.

Speckworm, my experience is in S&T exchangers, I would normally proceed this way:

I would consider my scope to be the vessel, supports and anchor bolts. In my class of work the vessels themselves are pretty rugged and are not much of concern. Using my "favorite" seismic standard and treating the vessel as "equipment" rather than "structure" I would design the supports for the longitudinal load, anchor bolts for shear and check for overturning. I would normally consider the seismic load reacted by one of two supports and two of four anchor bolts as S&T exchangers normally have one end floating. It there were unusual features of the design they would be checked as well. If the customer specified a seismic standard it would be used. My scope stops at the baseplate, the foundation belongs to others.

It doesn't sound as though you are obligated to do anything, but you may want to consider the basics anyway.

Regards,

Mike

You have to consider seismic load in your drum. The worst case in many times will be test condition (full of water).
Depending on the span of the supports and the operating temperature, you may have a fixed end saddle and slotted end saddle. The Piping group will determine which end shall be slotted based on pipe stress analysis. It is not your job to determine.
You need to pass the seismic load to Civil group to check the support pier/foundation design. Normally, they only need weight and seismic base shear in two conditions: design and test (full of water).
If the pier is exisitng, check if the anchor bolt can take the seismic shear and overturning moment.
If no one can check the pier/foudation, don't put drum on it unless it is replaced in kind or has less weight than existing drum. If you have big nozzle, that will also have impact on the foundation due to piping load. Look at the big picture, it can be more complicate than you think.
Piping/Vessel/Structural groups all work together even it is a simple drum. Keep this in mind.

jtseng has nailed right, so a small comment only, that your responsibility is to provide as early as practicable the foundation loading forces, including the type, size and number of anchor bolts (in case of Installation by Customer). The foundation design is his responsibility and is completely out of your control. However, if you are paid to design the foundation, you need a qualified civil engineer to do the design.
Cheers,
gr2vessels