Hard Spot : An area in the pipe with a hardness level considerably higher than that of the surrounding metal, usually due to localized quenching. (Bul 5T1).
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}