open the graph processing tool 
to create a work flow like this
This can be saved as an xml file: graph-file.xml (4.9 KB)
You can then open the batch processing tool 
to apply this file to as many files as you want.
You can also do this from the command line with the follwing expression:
gpt graph-file.xml -S=infile -T=outfile
Further information:
SNAP Graph Builder
Exercise: Graph Processing Tool (GPT)
STEP forum: Graph Builder
Radiometric & Geometric Correction Workflow