Special Piping generally has no specific specifications, other than the need for the material to be extremely straight and round. In some areas A.S.T.M. specifications may be required by project engineers. The specification most commonly called for is A.S.T.M. 139 Grade B. This specification gives parameters for minimum yield and tensile strength of the steel pipe being used for casing, and tolerances of straightness and concentricity. Special Piping is often specified as ASTM A-252 which is a structural grade material that does not require hydrostatic testing and the inspection requirements are not stringent and it usually costs less than other grades such as A-53, A-139 or API 5L. Used natural gas line pipe is also used as casing on many projects because it is often reclaimed in very good condition and can offer a significant cost savings when compared to new steel pipe. Used pipe is most likely to not have any testing data associated with it and is generally used when the only required specification is a given diameter and wall thickness of Special Piping.