Decimal Type Join Columns in Modeling

The problem we are having in our case is, our key columns are drive keys, means it is a combinition of multiple columns, when we are derive these drive keys, their size is more than the normal whole number(bigint in sql server), to accomadate the same, we coverted all these drive key columns types to decimal number(not fixed decimal), which is equal to decimal(38,0) in sql server. We want to know the problems, we may face when we do like this.