with s as (
select 'p3-0-200321-b002' [a]
union all
select 'p3-01-200321-b006' [a]
union all
select 'p3-04-200321-b005' [a]
)
select PATINDEX('%[0-9][0-9][0-9][0-9][0-9][0-9]%',a),a,SUBSTRING(a,PATINDEX('%[0-9][0-9][0-9][0-9][0-9][0-9]%',a),6) from s