Is a 022Cr19NI10 heat exchange tube, i.e., a plain tube, simply a tube that lacks fins and threads?

As the names imply, it should be relatively easy to distinguish between bare tubes and threaded tubes. I hope the following information will be helpful to you----------------------------------------------------------- http://www.sohu.com/a/165737606_99916590 Here you can find information and pictures about finned tubes. Finned tube, also known as finned pipe or ribbed tube. As the name implies, a finned tube is one in which numerous fins are fabricated on the surface of the original tube, whether it is the outer or inner surface, thereby expanding that surface and creating a unique heat transfer element. Excerpt on deformed steel bars from Baidu with illustrations: Deformed tubes, also known as low-ribbed tubes, rely on ribs on the outside of the tube (with a ribbing coefficient of 2-3) to increase the heat transfer area; they are generally used in situations where the heat transfer coefficient inside the tube is more than twice that outside the tube. For external condensation and boiling, surface tension also provides a good enhancement effect. For example, the “imperial” pipe thread with a diameter of 1/2\" corresponds to a “metric” diameter of DN15; in China’s local system it is also referred to as a four-inch pipe. To ensure that the inner diameter of the pipe is 1/2 inch (15 mm in metric units), and taking the wall thickness into account, the outer diameter of a 1/2 inch pipe thread is 20.995; therefore, the outer diameter of the pipe itself should be 21 mm. For example, the “imperial” pipe thread with a size of 3/4” corresponds to a “metric” diameter of DN20; in China’s local system it is also referred to as a six-inch pipe. To ensure that the inner diameter of the pipe is 3/4 inch (20 mm in metric units), and taking the pipe wall thickness into account, the outer diameter of a 1/2 inch pipe thread is 26.441, so the outer diameter of the pipe itself should be 27 mm. For example, an imperial pipe thread with a diameter of 1\" corresponds to a metric diameter of DN25; in China’s domestic system it is also referred to as an 8-inch pipe. To ensure that the inner diameter of the pipe is 1 inch (25 mm in metric units), and taking the wall thickness into account, the outer diameter of a 1-inch pipe thread is 33.249, so the outer diameter of the pipe itself should be 34 mm. “\"British pipe thread\" and \"British thread\" are two different concepts; confusing them will lead to confusion. Sometimes, experienced Chinese craftsmen talk about 4/8-inch pipes or 6/8-inch pipes, but when it comes to 1-inch pipes, they’re not sure whether that refers to an actual inch or a Chinese inch; in fact, 1-inch pipe is equivalent to 8/8-inch pipe. Baidu link: https://baike.baidu.com/item/%E8%9E%BA%E7%BA%B9%E7%AE%A1/1399009?fr=aladdin

A plain heat exchange tube is simply a regular tube without fins or threads

It is indeed the case, and it was specifically noted, which is why I’m confused.