New and renewal SRMs are continually being prepared. Renewal SRMs are intended to be completed before the supply of an existing SRM is exhausted. However, this is not always possible and a SRM may be out of stock for a time. When this occurs, those ordering the material are so notified and possible substitute SRMs are suggested. When a renewal is issued, customers who have ordered the previous lot are promptly notified of the price and availability of the renewal. If little demand exists or if an alternate source of supply becomes available, production of a SRM may be discontinued permanently.
Renewal SRMs may not be identical to the preceding lot; however, they meet the same specifications and can be used for the same purpose. For example, the first 0.1% carbon Bessemer steel was prepared in 1909 (Standard Sample No. 8). Since then a number of renewals, 8a, 8b, 8c, etc., have been prepared. The current SRM 8j 0.1C, represents the eleventh issue of the material. Each issue differs somewhat in detailed analysis; thus the use of the specific certificate for SRM 8j is essential.