A53 Grade B

"A53 pipe comes in three types and two grades, A53 Type F, which is longitudinally furnace butt welded or continuous welded (Grade A only), A53 Type E, which is longitudinally electric resistance welded (Grades A and B), and A53 Type S, which is seamless pipe, produced by hot working, and possibly cold finishing, the steel (Grades A and B). ASTM A53, Type S is now currently an outdated specification and has been replaced by ASTM A106 specification for seamless carbon steel pipe."

There is very little difference other than the weld seam on the grade B pipe is heat treated and has a higher tensile and yield strength....The pipe must be labeled one of the following; Continuous Welded, Electric-Resistance-Welded A, Electric-Resistance-Welded B, Seamless A, Seamless B, XS for extra strong, XXS for double extra strong.

http://www.amerpipe.com/products/carbon-pipe/a53/specifications

http://en.wikipedia.org/wiki/ASTM_A53

Grade A also passes a flattening test for close-radius bends, as in forming serpentine pipe coils for refrigeration. It isn't a high-pressure pipe.