Why does the heat transfer coefficient of stainless steel heat exchange tubes change?

Material standard requirements for stainless steel heat exchange tubes!

ASME B366 Inconel 601 Butt Weld Reducer-Elbow-Tee-Cross

ASME B366 Inconel 601 Butt Weld Reducer-Elbow-Tee-Cross

ASME B366 Inconel 601 Butt Weld Reducer-Elbow-Tee-Cross

ANSI-ASME B16.9 Butt Weld Eccentric Reducer

ANSI-ASME B16.9 Butt Weld Eccentric Reducer

ANSI-ASME B16.9 Butt Weld Eccentric Reducer

ASME B366 Inconel 600 Butt Weld Reducer-Elbow