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API 579 - Local Metal Loss - Component Types?

API 579 - Local Metal Loss - Component Types?

API 579 - Local Metal Loss - Component Types?


For Local Metal Loss, API579 limits the diameter of horizontal vessels to D ≤ 3.05m (10 ft). Thus pressure vessels with a diameter exceeding this cannot be treated as Type A components.
I would then expect such a vessel to be a Type B or C component but I have some trouble understanding the criteria and are therefore looking for someone who might shed some light on this matter.

In chapter 4.2.5 the following is stated:

1. Type B, Class 1 components have the same geometry and loading conditions as described in a) above but are not classified as Type A components because supplemental loads in combination with pressure may govern the required wall thickness....

The sentence "the same geometry and loading conditions" hints that the same limitation applies to the diameter, that a Type B component also needs to satisfy D ≤ 3.05m (10 ft)? I do not believe this is the intention and thay I might be misinterpreting this statement. Is it simply such that API579 determines that supplemental loads can be neglected for components with D ≤ 3.05m (10 ft) but must be accounted for when D > 3.05m (10 ft)? i.e. that a Type B component may have a diameter exceeding 10 ft?

Kind Regards
Björn Nilsson

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