Some structural steel fabrication drawings have material specifications that are probably incorrect. For example, many architects and engineers mistakenly detail their drawings calling for the use of pipe with an A53 vs. A500 grade specification in their bill of material.
A500 pipe is normally used in structural applications and general construction. It should be used for curved columns, curved tube trusses, and curved steel frames in buildings. A53 is the specification for pipe that normally is used in mechanical and pressure applications such as steam, water and air lines. The main advantage of using A53 pipe is that it requires hydrostatic testing and has a sealant that coats the pipe. Hydrostatic testing (i.e. pressure testing) is not needed in curved structural application and only adds unnecessary cost.
But the lacquer coating that usually comes on A53 grade pipe makes the pipe harder to fabricate and paint.
A500 pipe is normally better for the majority of your structural steel construction projects because it has a higher yield strength than the A53 type pipe specification. This means that the strength-to-weight ratio is better than A53 grade pipe. A500 is not only stronger but also has better quality when used in curved structural steel applications.
A500 pipe has straightness tolerances of 1/4 inch every 10 feet. There is no specification used to measure how straight the pipe has to be for A53. A500 has a closer outside diameter wall tolerance. Having better tolerances means less twisting when curving and a more level curved product that will sit flat on the ground.
A majority of steel service centers carry pipe in A500 grade C but do not generally stock A53 grade material. The reason for this: A53 pipe is only available in single random lengths of 21ft or double random lengths of 42ft, while A500 pipe can be produced in lengths ranging from 20ft to 75ft. This makes it harder and more costly to find the length needed in A53 grade.
As far as the bending of pipes is concerned, both pipe grades curve equally well. The only difference is that the A53 pipe grade is more expensive and not as readily available as A500 pipe. The picture below shows A53 piping with a lacquer finish on the outside which is fine for liquid and gas flow but not desirable in most structural applications because, again, it will need to be cleaned before painting.