For pipes with an outside diameter greater than or equal to 2 3/8", isolated slag inclusion (ISI) is unacceptable when the aggregate length of indications exceeds what in any continuous 12" length of weld?

In the context of API 1104, isolated slag inclusions (ISI) refer to defects that occur within a weld due to trapped slag, which can compromise the integrity of the welded joint. For pipelines with an outside diameter of 2 3/8" or greater, the standard outlines acceptable limits for these types of defects to ensure the reliability and safety of the welded structure.

The standard stipulates that for any continuous 12" length of a weld, the aggregate length of indications related to isolated slag inclusions must not exceed 3". This specific limit is established based on the need to maintain sufficient structural integrity and performance of the weld, as excessive slag inclusion can weaken the weldment and lead to potential failures.

This threshold reflects a balance between acceptable production tolerances and the necessity for maintaining high-quality welding standards in pipeline construction and repair. Adhering to this limit helps in ensuring that the welded joints will withstand service conditions without adverse effects on safety or operational efficiency.