Corrosion Allowance
2
The corrosion allowance is the diminution of steel allowable due to corrosion measured over a specific dimension of the element. This diminution may occur on internal surfaces or external surfaces. Particular care should be taken to apportion the corrosion allowance in accordance with the design intention, particularly in relation to piping, vessels and tanks. The corrosion allowance may vary according to the location on a particular element (e.g. web and flanges of UB). Metacor uses the minimum corrosion allowance for the whole of that element. Metacor uses an external corrosion allowance within three different processes: i Determination of criticality ii Determination of retiral (loss of fitness for purpose) iii Determination of available maintenance envelope Methodology There are three methods of calculating this external corrosion allowance. 1. Metacor Corrosion Allowance Module Metacor uses member unity (utilisation) and punching ratios for structural members, and maximum allowable pressure for containment elements such as piping.These values are used to calculate a conservative theoretical maximum allowable metal loss before loss of fitness for purpose. This figure is capped to a maximum proportional to the element thickness (defaulted to 0.25) and apportioned between internal and external surfaces as required. 2. Flexible Corrosion Allowance Module Metacor accommodates a user-defined calculation set together with member unity (utilisation) and punching ratios for structural members, and maximum allowable pressure for containment elements such as piping.These values are used to calculate maximum allowable metal loss to client-defined parameters. This figure is capped to a maximum proportional to the element thickness, and apportioned between internal and external surfaces as required. 3. Direct Entered Corrosion Allowances Metacor accommodates directly entered corrosion allowances, from design or assessment criteria, and apportioned between internal and external surfaces as required. corrosion allowances THE NEW STANDARD IN EXTERNAL CORROSION MANAGEMENT
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Allowance of Corrosion
Transcript of Corrosion Allowance
The corrosion allowance is the diminution of steel allowable due to corrosion measured over a specific dimension ofthe element.
This diminution may occur on internal surfaces or external surfaces. Particular care should be taken to apportion the corrosionallowance in accordance with the design intention, particularly in relation to piping, vessels and tanks.
The corrosion allowance may vary according to the location on a particular element (e.g. web and flanges of UB). Metacor usesthe minimum corrosion allowance for the whole of that element.
Metacor uses an external corrosion allowance within three different processes:
i Determination of criticalityii Determination of retiral (loss of fitness for purpose)iii Determination of available maintenance envelope
Methodology
There are three methods of calculating this external corrosion allowance.
1. Metacor Corrosion Allowance Module
Metacor uses member unity (utilisation) and punching ratios for structural members, and maximum allowable pressure forcontainment elements such as piping. These values are used to calculate a conservative theoretical maximum allowable metalloss before loss of fitness for purpose. This figure is capped to a maximum proportional to the element thickness (defaulted to0.25) and apportioned between internal and external surfaces as required.
2. Flexible Corrosion Allowance Module
Metacor accommodates a user-defined calculation set together with member unity (utilisation) and punching ratios forstructural members, and maximum allowable pressure for containment elements such as piping. These values are used tocalculate maximum allowable metal loss to client-defined parameters. This figure is capped to a maximum proportional to theelement thickness, and apportioned between internal and external surfaces as required.
3. Direct Entered Corrosion Allowances
Metacor accommodates directly entered corrosion allowances, from design or assessment criteria, and apportioned betweeninternal and external surfaces as required.
corrosion allowances
THE NEW STANDARD INEXTERNAL CORROSION MANAGEMENT
AberdeenSuites 5/6 • Langstane House • 221-229 Union StreetAberdeen • AB11 6BQ
T: +44 (0) 1224 621915 • F: +44 (0) 1224 621215
E: [email protected] • www.metacor.co.uk
Great YarmouthVentureforth House • South Denes RoadGreat Yarmouth • Norfolk • NR30 3PT
T: +44 (0) 1493 845390
THE NEW STANDARD INEXTERNAL CORROSION MANAGEMENT
Element Internal Corrosion allowance External Corrosion Allowance
Structural (atmospheric, non flooded,closed ends).
0% 100%
Piping (atmospheric, not lined). 80% 20%
Criticality Max. % sacrifice of corrosion allowance allowed
4 25%
3 35%
2 50%
1 70%
0 100%
Apportioning the Corrosion Allowance
The corrosion allowance will be apportioned as default below:
Corrosion Allowance Diminution Allowed (CADA)
The corrosion allowance affords the asset operator a safety margin in case of loss of corrosion protection. However, predicting ratesof corrosion carries with it a degree of uncertainty.We therefore set limitations, relative to criticality, on the maximum amount ofcorrosion allowance that can be sacrificed before the latest timing of corrosion protection reinstatement.
Default values are shown in the Table below, but these may be set according to the client's requirements.
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