Welding Preheat What, Why & How?

What is Welding preheat? Preheating. Preheat vs. interpass vs. post-heating in welding How it is done, Where to preheat? How to measure preheat temperature? Advantages of the preheat in welding. Preheat requirements according to ASME Section VIII Div 1. Preheat requirements according to ASME B31.1 Preheat requirements according to ASME B31.3 Preheat requirements according to AWS D1.1 Preheat calculation using a preheat calculator Preheating - How, when and why- With code references