For piping that is not fully restrained, B31.8 will use a B31.3-style evaluation of the expansion stress range. In B31.8, the terms Sc & Sh (those B31.3 terms in setting SA) are based on Su - the ultimate tensile strength; one-third of Su. You do not have Su defined. (There is no Su in our database for A105.)
Enter a value for Su and you will see an allowable expansion stress range for your B31.8 EXP check.