ASTM A106 is a material specification of carbon steel pipes for high temperature service and of seamless manufacture. A106 yield strength is in the range of 25-30 KSI.
On the other hand API 5L defines grades that are comparable to A106 (Gr A & B) while 5L encompasses much more higher strength grades mainly used outside plant piping for transmission pipelines of liquid and gas hydrocarbons.
Moreover, 5L covers methods of manufacture and conditions of delivery in a wider perspective. Rework and toughness are more elaborated on.