By Stephen J. Gliebe, P.E.
The first and second installments of this series of newsletters focused on Level 1 and Level 2 general metal loss in what API 579-1 / ASME FFS-1 2007 defines as Type A Components. These are components that have a design equation that specifically relate pressure or liquid fill height, and other loads, to a required wall thickness (e.g., pressure vessel cylindrical and conical shell sections).
In this (third) installment, we will take a look at general metal loss (GML) in nozzles. In API 579-1, nozzles are considered Type B Components. These are components that do not have a design equation that specifically relate pressure or liquid fill height, and other loads, to a required wall thickness. These components have a code design procedure to determine an acceptable configuration. These rules typically result in one component with a thickness that is dependent upon another component. Other examples of Type B Components include the reinforcement zone of conical transitions, branch connections, and flanges.
Assessment of GML in Type B Components must start at Level 2. Below are some guidelines for performing a Level 2 assessment for a reinforced nozzle connection in a shell such as that shown below. Nomenclature can be found in API 579-1 Part 4 and Annex A.
GML Level 2 assessments are permitted only if certain conditions are satisfied. The complete list of limitations in Parts 2 and 4 of API 579-1 should be reviewed before proceeding with a GML Level 2 FFS assessment. Some of the limitations for nozzle assessments are:
Guidance on performing a nozzle GML assessment is provided in API 579-1 Part 4, and Annex A Para. A.3.11. The procedure is based on the one used for the design of nozzles in the ASME Code Section VIII, Division 1. It may be used on nozzles with or without a reinforcing pad.
Article 4 in this series will cover API 579-1 Level 1 pitting assessments.