I don't know what the official answer is (and there is quite a bit of naming overlap between brands), but I primarily use a welding/chipping hammer (usually one chisel face and one pointed tip, but they can be found in chisel/cross chisel combo too) for knocking slag off of welds. I use the tip that works the best for the situation, but most of the time I am using the pointed tip. The head itself is usually longer in total length and often a bit narrower overall so it can reach into tight areas easily. I have two main weld chipping hammers, both are Atlas Tomahawk brand. One is a point/chisel combo head, and the other is a point/cross chisel combo head.
A scaling hammer usually has two chisel faces, and one is oriented 90 degrees to the other (chisel/cross chisel). The hammer head itself is usually much shorter in total length from one face to the other face, and it is often made thicker overall because it is usually used to hit things that are out in the open and easily accessible. I use a scaling hammer mainly for removing rust scale from larger metal surfaces, for breaking off unwanted dry concrete, and sometimes as a brick hammer to quickly score and break bricks.