Since you asked for sed / grep, here it is:

> cat file
igflex01; igflexdev01; igdbstg01;
igldapint01; igjetdev01; igsql01;
igesxstg01; igdbint01; igdmstg01;
igdsdev01; igdmmmo01; igmsgint02;

> sed -nr 's/\s*;\s*/\n/gp' file | grep int
igldapint01
igdbint01
igmsgint02

I'm going to get it also with only single sed call...

Since you asked for sed / grep, here it is:

> cat file
igflex01; igflexdev01; igdbstg01;
igldapint01; igjetdev01; igsql01;
igesxstg01; igdbint01; igdmstg01;
igdsdev01; igdmmmo01; igmsgint02;

> sed -nr 's/\s*;\s*/\n/gp' file | grep int
igldapint01
igdbint01
igmsgint02

Or get it with only a single sed call...

> sed -nr -e 's/\s*;\s*/\n/g;/int/P' file
igldapint01
igdbint01
igmsgint02