1 Rule Application for Fatigue Requirements

1.1 Scope

1.1.1 General

This chapter provides requirements applicable to ships having rule length L between 150 m and 500 m to evaluate fatigue strength of the ship’s structural details considering an operation time in North Atlantic environment equal to the design fatigue life, T_DF.

1.1.2 Assessed area

Fatigue assessment is performed for structural details located in the ship’s cargo hold region in order to prevent the following types of fatigue failure:

Fatigue cracks initiating from the toe of the weld and propagating into the plate.
Fatigue cracks initiating from free edge of non-welded details.

1.1.3 Structural details to be assessed

The structural details required for fatigue assessment are given in Ch 9, Sec 2:

Structural details to be checked are listed in:
- Ch 9, Sec 2, [1] for simplified stress analysis according to Ch 9, Sec 4, or
- Ch 9, Sec 2, [2] for finite element stress analysis according to Ch 9, Sec 5.
Structural details to be checked by screening fatigue assessment are listed in Ch 9, Sec 2, Table 2.

Additional specific details may be requested to be checked on a case-by-case basis by the Society.

1.1.4 Detail design standard

Detail design standard given in Ch 9, Sec 6 provides welding requirement at critical structural details in order to prevent the following types of fatigue failure:

Fatigue cracks initiating from the weld toe into the base material.
Fatigue cracks initiating from the weld root and propagating into the plate section under the weld.
Fatigue cracks initiating from the weld root and propagating through the weld throat.
Fatigue cracks initiating from surface irregularity or notch at the free edge into the base material.

1.1.5 Material

The fatigue assessment is applicable for steel material with specified minimum yield stress less than or equal to 390 N/mm². For steel with specified minimum yield stress value higher than 390 N/mm² and for steels with improved fatigue performance, the S-N curves to be used are considered by the Society on a case-by-case basis.

1.1.6 Wave loads

Fatigue assessment is based on quasi-static wave loads.

1.1.7 Loads other than wave loads

Fatigue induced by low cycle loads such as cargo variations or impact loads such as sloshing in partially filled tanks which may induce fatigue damage is disregarded in this chapter.