Physically there are no differences; however, the use and way of manufacturing makes them different.

304 steel is the most common form of stainless steel used in the world, containing 16-18% chromium and 8-10% nickel. It is resistant to corrosion from oxidizing acids, is economical and practical for most environments.

316 steel has all the components of 304; however, it has 2 to 3% of an additional ingredient called molybdenum, this makes it resistant to chloride which allows it to be used in extreme environments and is even used for the manufacture of medical equipment and pharmaceuticals due to its resistance to oxidizing chemicals.

The welded pipe is physically different because the weld line joining the bent steel plate can be seen internally, while the seamless pipe is made by a mold which does not require the welding process.

On the other hand, the seamless pipe is used for machinery and conduct gases and liquids with higher pressure while the welded pipe supports fluids and gases with lower pressure.

It is a parameter that indicates the thickness of the pipe wall, the greater the thickness, the more pressure the pipe can withstand.