chapter  5
Safety Classes
Pages 2

The classification of containments should be based on the specific risks to structural safety and on the potential economic risks. It could be structured in three safety classes in the same way as they are provided in the EUROCODE. Different levels of reliability are defined for the ultimate limit states and the serviceability limit states. Tab. 2 presents the classes in terms of the safety index (5 as well as the failure probability Pf. Higher classes mean higher safety or higher reliability. Table 2. Safety classes

1 2 3

ULS 4.2 4.7 5.2

SLS 2.5 3 3.5

reference 1 year

The arrangement of the different types of containments into the three classes should be based on the risk-criterion. Some qualitative aspects are given in the following:

Risks to structural safety: - loss of strength, overall equilibrium and buckling collapse:

—> risk according to type of containment and filling material - local wall buckling: -> no risk - cyclic plastification and fatigue causing collapse:

—> high risk if no inspection is provided —> low risk if regular inspection is guaranteed

- cyclic plastification and fatigue causing leakage: —> high risk with mineral oil, toxic liquid, highly corrosive contents —» low risk with water or granular material

Economic risks: - local wall buckling (if not tolerable because of appearance):

if elastic buckling: —> low risk, because easy to repair if plastic buckling: —> higher risk with mineral oil due to expensive repair

(high costs for cleaning) - overall deformation (ovalisation etc.):

—» high risk with floating roof tanks —> high risk with attached piping

- leakage: -» low risk with harmless filling, like water etc. —> high risk with oil etc.