Область тут следует читать как диапазон, наверное. Как-то так:

Estimated operational life of boiler components operating under pressure before violating design high-temperature limitations for creep range, hrs, lo less than

Существует "safe creep range", начальная стадия ползучести (сreep deformation), при которой какое-то время элементы котла остаются работоспособными


https://www.nationalboard.org/Index.aspx?pageID=181

However, regardless of the cause, the failure will exhibit the characteristics of a creep or stress rupture. ***Indeed, the ASME Boiler and Pressure Vessel Code recognizes creep and creep deformation as high-temperature design limitations and provides allowable stresses for all alloys used in the creep range.*** One of the criteria used in the determination of these allowable stresses is 1% creep expansion, or deformation, in 100,000 hours of service. Thus, the code recognizes that over the operating life, some creep deformation is likely. And creep failures do display some deformation or tube swelling in the immediate region of the rupture.