A hard spot is an area with a hardness increase compared to the surrounding base metal. Such localized hardness elevation is an active threat that operators are managing in the United States (U.S.). A large portion of the U.S. transmission network contains “vintage” pipe manufactured pre-1970. The existence of hard spots in combination with the relatively poor material properties and quality issues associated with vintage pipes and other active threats is an issue that operators are including in their integrity management plans. With the drive towards a decarbonized economy and the introduction of hydrogen into existing natural gas transmission and distribution networks, the threat from hard spots in the presence of hydrogen has become a critical focus area. Material hardness anomalies on pipelines are detected and characterized using in-line inspection (ILI). Over the past number of years, extensive validation work has been completed to assess and characterize the reported anomalies, leading to the discovery of different types of material hardness anomalies, with variation in peak hardness, location on the outside or inside surface, dimensions, etc. This paper provides a description of the work performed in the U.S. to detect, characterize and size hard spots, and the significant amount of learning available to share with the industry as a platform to manage the threat of hard spots, not only in the U.S. but also in other regions.