ASME B31G-2012 pdf download

ASME B31G-2012 pdf download.Manual for Determining the Remaining Strength of Corroded Pipelines.
(g) Some operating conditions, such as low- tempera ture service, or long-term exposure to sour environments or to very high temperatures, could adversely affect the ductility and fracture toughness properties of some materials. It is the user’s responsibility to consider such conditions where necessary before applying methods described herein.
1.8 EvaLuation Procedure
Evaluations shall be carried out in accordance with the procedures described in section 2. In addition, the following considerations apply:
(a) Units may be in any self-consistent system. It is the responsibility of the user to determine unitary conversion factors as may be required.
(b) This document makes no recommendation as to which evaluation level and evaluation method to select. All methods described herein have been demonstrated to provide reliable and conservative results when they are applied correctly and within stated limitations. Not all methods give identical numerical results or consistent degrees of conservatism. It is the pipeline operator’s responsibility to select an evaluation method, based on experience and judgment, that is consistent with its operating procedures.
(c) Original source reference documents for each methodology are cited. Further references may be found in other documents available in the public domain. While each method can be applied as presented, source documents may provide additional information to the user. The user should consider referring to applicable sources as necessary in order to best implement a given method.
(d) Other evaluation methods may evolve or come into use which were not contemplated by this document. It is not the intention of this document to prohibit their use, but the user of such methods shall be able to demonstrate that the objective of a safe and reliable assessment of metal loss can be achieved.
1.9 Safety Factors and the Meaning of Acceptance
A flaw or anomaly is considered acceptable where the computed failure stress is equal to or greater than the hoop stress at the operating pressure multiplied by a suitable safety factor. There is no single safety factor that is suitable for all types of pipeline construction, for all modes of pipeline operation, or for all types of flaws or anomalies.
Metal-loss corrosion anomalies indicated by inline inspection may be evaluated by a Level I or Level 2 evaluation method. The user is cautioned against overstating the precision of evaluations applied with flaw dimensions indicated by inline inspection without adequate calibration or verification of actual flaw sizes by investigations carried out in the field.
1.12 Flaw Interaction
The methods described herein arc suitable for evaluating isolated areas of metal loss. Corrosion may occur such that multiple areas of metal loss are closely spaced longitudinally or transversely. If spaced sufficiently closely, the metal loss areas may interact so as to result in failure at a lower pressure than would be expected based on an analysis of the separate flaws. The following guideline is suggested with reference to Fig. 1.12-1, based on limited testing and analysis:
(a) Flaws are considered interacting if they are spaced longitudinally or circumferentially from each other within a distance of 3 times the wall thickness (3t). Interacting flaws should be evaluated as a single flaw combined from all interacting flaws.
(b) Flaws are considered noninteracting if spaced outside of the above dimensions. Noninteracting flaws should be evaluated as separate flaws.
Care should he exercised when grouping or clustering anomalies indicated by inline inspection for purposes of evaluating interaction during the prioritization process. Consideration should be given to minimum thresholds of metal loss for reliable detection and sizing, minimum thresholds for reporting, and the expected mode of coating failure (e.g., localized failure versus disbondment over large areas). Methods employed for clustering of inline inspection anomalies should be validated by field verification of actual flaw dimensions and spacing.
1.13 Flaw Orientation
Corrosion caused by disbondnient of continuous wrapped coatings may exhibit a helical pattern. If the helical pattern lies at an angle less than 45 deg to the pipe axis, the overall length of the corroded area indicated as L1 in Fig. 1.13-1 shall be considered in the evaluation. If the helical pattern lies at an angle of 45 deg or greater to the pipe axis, it is sufficient to consider the most severe longitudinal section through the corroded area having a length L2 in Fig. 1.13-1.
Corrosion may occur with a circumferential orientation, e.g., adjacent to a girth weld.