API TR 6AM:1995 pdf download.Technical Report on Material Toughness
2.1 About 1969/70, at the API meeting in Los Angeles, a committee was set up to review the materials listed in API Specification 6A and Specification 6D for low temperature service. This interest was generated by the activities of the Alaska Pipeline Project.
2.2 The directions given by API committees were to re- view the materials listed in API Specification 6A and Speci- fication 6D and to remove those materials which would not meet the standard Charpy V notch requirements of 15 ft-lb average, none less than  perature was selected simply because that was the low end of the temperature range for API products at that time. In re- viewing these materials, it became very apparent to the com- mittee members that most of the materials listed would not meet the standard Charpy requirements at and that some of the materials were even questionable above . With this in mind, a call was put forth to all API members to report and document, if possible, any failures of API equipment which could be attributed to low notch toughness. No such failures were reported even in the Canadian or North Sea sectors. Since no failures were reported, and since it was well known that impact test values are generally considered relative in nature and are not used as a design tool, the com- mittee was put in a quandary as to what action should be taken. There was considerable discussion on how the indus- try would react to removing a material from the API specifi- cations which had been used very successfully for twenty or thirty years with no reported problems. and at the same time, support its existence and continued use in the field.
2.3 The final decision was to leave the need for impact testing at temperatures above up to the users, who could request impact testing at any temperature and stipulate any values they desired. Equipment below Ð20¡F would automatically require im- pact testing.
3.2 The committee was informed that the 15 ft-lb value at- tached to Charpy Impact Testing was the most troublesome item. This value was added to API Specification 6A in 1969 to cull materials destined for Arctic service. The 1969 Task GroupÕs minutes indicate that they chose 15 ft-lb because ASTM A350 and A352 listed this value for the most common forging and casting materials of that time. Furthermore, the 1969 version of A320 Gr L7M bolting required 15 ft-lb. Ap- parently, ASTM acquired the value from the Liberty Ship work of World War II. It was thought that 15 ft-lb indicated the onset of brittle behavior in ferrous metals; that is, less than 15 ft-lb values indicate brittle behavior and greater than 15 ft-lb indicate ductile behavior. The 1969 Task Group did not consider the effects of heat treatment, chemical content or processing. ASTM A370 states that the Charpy test is a Quality Assurance test and that the resulting value has no engineering meaning.