CodeCalc supports the following flaw assessments for cylindrical shells, simple cones, and formed heads:
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Section 4, General Metal Loss.
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Section 5, Local Metal Loss.
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Section 6, Pitting Corrosion.
There are three levels of assessments available for each flaw type.
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Level 1 - Typically involves a simplified method using charts, simple formulae, and conservative assumptions.
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Level 2 - Generally requires a more detailed evaluation and produce more accurate results
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Level 3 - Allows flaw assessments using a more sophisticated method such as FEA.
CodeCalc provides only Level 1 and Level 2 assessments. In each assessment level, the respective remaining life or the de-rate value of MAWP is calculated depending on passing or failing acceptance criteria.
Section 4 covers flaw assessment procedures for components subject to general metal loss resulting from corrosion and/or erosion. Meanwhile Section 5 covers the analysis of local metal loss or Local Thin Areas (LTAs), which include groove-like flaws or gouges. In general, flaw assessments using Section 4 criteria produce more conservative results.
The differences between Section 4 and 5 when applied to LTAs are as follows:
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Section 4 - Rules for all Level 1 and 2 assessments are based on the Average Thickness Averaging approach, which is combined with the ASME Code rules to determine the acceptability for continued operation.
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Section 5 - Rules for all Level 1 and Level 2 assessments are based on establishing a Remaining Strength Factor (RSF), which is used to determine the acceptability for continued operation.
The Assessment of General Metal Loss described in Section 4 can be performed using either point thickness (random type readings) or profile thickness (grid type readings) measurement data. API RP 579 requires a minimum of 15 data measurement points be used for the analysis.
The localized metal loss assessment (described in Section 5), can only be performed using profile thickness data according to a grid setup as shown in Figure 10.3. Two data entry types are provided in the Profile Type selection list; Grid and Critical Thickness Profile (CTP). The number of rows and columns are set by entering the number of points in both the circumferential and longitudinal directions.
The total number of data inputs provided are 256 for both point and profile thickness data measurements.
For most evaluations, it is recommended to first perform the assessment using Section 4, then perform Section 5 if necessary. The rules in Section 4 have been structured to provide consistent results with Section 5. However, it is the responsibility of the user to review the Assessment Applicability and Limitation whenever the assessment changes.
API 579 Section 4 limitations for Level 1 and Level 2 assessments are as follows:
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The original design is in accordance with a recognized code or standard.
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The component is not operating in the creep range.
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The region of metal loss has relatively smooth contours without notches.
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The component is not in cyclic service (less than 150 total cycles).
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The component under evaluation does not contain crack-like flaws.
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The component under evaluation has a design equation, which specifically relates pressure and/or other loads, as applicable, to a required wall thickness.
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With some exception, the following specific components do not have equations relating pressure and/or other loads to a required wall thickness may be evaluated using Level 2 assessments:
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Pressure vessel nozzles and piping branch connections.
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Cylinder to flat head junctions.
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Integral tubesheet connections
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Flanges
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Piping systems.
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Currently, CodeCalc does not support API 579 analysis on nozzle, flange, tubesheet,
flathead, and piping system components.
The following limitations on applied loads are satisfied
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Level 1 assessment - Components are subject to internal and/or external pressure (negligible supplemental loads).
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Level 2 assessment - Components are subject to internal and/or external pressure and/or supplemental loads such as weight, wind and earthquake.
Limitations for API 579 Section 5 Level 1 and Level 2 assessments are similar to the limitations for Section 4 with the following additions:
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The components cannot be subjected to external pressure, or if the flaw is located in the knuckle region of elliptical head (outside of the 0.8D region), torispherical/toriconical head, or conical transition.
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The material component is considered to have sufficient material toughness.
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Special provisions are provided for groove-like flaws such as:
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Groove (no mechanical cold work).
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Gouge (mechanical cold work).
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For more details, refer to Section 4 and Section 5 in the API Recommended Practice 579.
Section 6 covers flaw assessment procedures for components that are subjected to pitting damages as described below:
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Widespread Pitting.
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Localized Pitting.
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Region of Local Metal Loss Located in an Area of Widespread Pitting.
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Pitting Confined within a Region of Localized Metal Loss.
Pitting damage can occur on the inside, outside, or both sides of the component surfaces. For components with pittings on both surfaces, be sure to indicate the location of each pit-couple in the data entry table. Pitting damage is described using pit-couples, each is composed of two pits that are separated by a solid ligament. The procedure for determining pit-couples is described in the API 579 paragraph 6.3.3.3. A representative number of pit couples measurements in the damage area should be used. If the pit flaw is uniform then a minimum of 10 pit-couple measurements should be used. For non-uniform pit flaw, additional pit-couple measurements are required. CodeCalc can analyze up to 36 pit-couples measurements.
The limitations for API 579 Section 6 Level 1 and Level 2 assessments are similar to the limitations for Section 5 Level 1 and Level 2 assessments. For more details, refer to API RP 579 Section 6.