left(substring(docid,charindex('~',docid)+1,len(docid)),7)

declare @vt_t table (docid varchar(50))

insert into @vt_t
select '99~B007340~9822151~LR5~250' union all
select '99~B007599~9417974~LC0~240'

select substring(docid,charindex('~',docid)+1,7)FirstString,
	    substring(docid,CharIndex('~', docid, charindex('~',docid)+1 + 1) + 1, 7) SecondString
from @vt_t

-- Use this if the format for all records are the same
select substring(docid, 4, 7) FirstString,
	   substring(docid, 12,7) SecondString
from @vt_t