InfoPath Dev

I search the forums and did not see an identical post, but this must be a typical request.

I need to replace all occurances of WordA with WordB inside a field.

I tried this:

concat(substring-before(field, "WordA"), "WordB", substring-after(field, "WordA"))

The problem I having is "WordA" may not exist in the string, so it returns empty.

Is there a chance that WordA can occur in the string multiple times?  If not, I think this would work:

concat(substring(field, 1, 1000 * not(contains(field, "WordA"))), substring(concat(substring-before(field, "WordA"), "WordB", substring-after(field, "WordA")), 1, 1000 * contains(field, "WordA")))