Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2002-03-21
2004-11-09
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S602000
Reexamination Certificate
active
06813949
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a pipeline safety program, namely a system of addressing pipeline anomalies prior to failure of pipeline integrity, and particularly to a pipeline inspection system integrating a novel serviceability acceptance criteria for pipeline anomalies, specifically wrinkles, with an improved method of correlating ultrasonic test data to actual anomaly characteristics.
2 Description of Related Art
Typically, a pipeline company will have a thorough pipeline safety program that will include a routine for the identification of pipeline defects and review of pipeline integrity. Such a plan should include, but should not be limited to: i) a review of previous internal inspection n report logs by a third party with demonstrated expertise in interpreting inspection report data; ii) excavation of sites identified by this review of the internal inspection report logs for visual examination of anomalies; iii) repairs as necessary; and iv) the use of internal inspection tool surveys and remedial action to the extent needed to address factors in the failure and verify the integrity of the pipeline.
A pipeline safety program can be only as effective as the interpretation of internal inspection reports. If the data recorded by an inspection pig is improperly classified, anomalies that would otherwise require repair may never be identified as serious enough to dig up and inspect. Nearly as problematic, on the other hand, is the great time and energy that may be spent digging up the pipeline searching for anomalies that do not, in fact, warrant inspection.
Proper classification of data recorded by the pig thus is essential for pipeline safety. For example, in one specific case as discussed more fully herein, a 1997 internal inspection of a length of pipeline using sophisticated Ultrasonic Testing (UT) technology identified an anomaly that was misclassified as a pipeline fitting, rather than the true defect—a wrinkle, which wrinkle later led to catastrophic failure of the pipeline. The vast majority of the deformation features examined in the field in this specific case were “ripples” or “wrinkles” that were evident in cold field bends and located on the intradose of the bend. These types of features are characterized by a “sinusoidal” surface waveform with both an inside and outside displacement component. This particular event, and other recent pipeline construction experience (from the late 1980's), has demonstrated that it is often difficult to produce field bends that have smooth contours without the presence of small discontinuities within the bend intrados. Such discontinuities have been referred to generally as “buckles”, “ripples”, and “wrinkles”. Industry research into the structural integrity aspects of wrinkles or buckles in pipelines has been conducted for the past 25 years with the majority conducted since about 1990.
Since the late 1980's, it has become increasing evident that the commonly used field bending “rule-of-thumb”—that pipe could typically tolerate a maximum bend angle of 1.5 degrees per pipe diameter—can no longer be applied universally. It has been found that wrinkles in fact could be formed at smaller bend angles, for example, on the order of 0.75 to 1.0 degree per pipe diameter, and sometimes less.
Bending problems could often be traced to poor field bending practices including the improper setup of bending machines. However, other factors impacted the “bendability” of line pipe, including among others higher yield strengths, increased diameter/thickness ratios, and pipe steel properties, particularly the stress-strain behavior. It also had been found that the heat cycle associated with the application of fusion bonded epoxy coatings also promoted rippling at low bend angles due to alteration of the stress-strain behavior. In some cases, pipe produced to identical specification by different pipe manufacturers could not be bent to the same radius without wrinkling. Even pipe produced by the same manufacturer has exhibited bendability variations during pipeline construction.
Such pipe bending flaws were encountered worldwide, and led to industry research aimed at establishing engineering limits of acceptability for ripples in pipe bends. Thus, not only were there no serviceability acceptance criteria for pipeline wrinkles, but neither was there pipeline inspection data that could be used to develop such an acceptance criterion for wrinkles in pipe bends. Even while pipeline inspection tools became more and more sophisticated, there was no adequate method of correlating that data to represent the true characteristics of the anomaly, which type and severity of anomaly would be found upon repair digs.
Current US Code Requirements for Gas and Liquid Pipelines
For gas pipelines, 49 CFR Part 192 contains requirements for bends in Subpart G titled “General Construction Requirements for Transmission Lines and Mains”. With respect to bend contours, Paragraph 192.313 mandates that “a bend must not impair the serviceability of the pipe” and that each bend must have a smooth contour without evidence of buckling, cracks, or other mechanical damage. Also, with some exceptions, longitudinal welds must be near as practical to the neutral axis of the bend. Paragraph 192.315 relates specifically to wrinkle bends in steel pipe. Wrinkle bends are not allowed in pipelines operating at 30% SMYS or higher, and below that, wrinkles must not contain “any sharp kinks”. Wrinkles must be separated by at least one pipe diameter and can't have a deflection of more than 1.5 degrees each. The requirements in Chapter 4 of ANSI/ASME B31.8-1999, “Gas Transmission and Distribution Piping Systems” w are similar to those in 49 CFR 192. Paragraph 841.231 provides that bends “shall be free from bucking, cracks, or other evidence of mechanical damage. Like 49 CFR 192, wrinkle bends only are permitted for operation at less than 30% SMYS and must not contain “sharp kinks”.
With respect to liquids pipelines, 49 CFR Part 195 contains requirements for pipe bending in Subpart D, “Construction”. Bending criteria provided in Paragraph 195.212 prohibit wrinkle bends while “each bend must have a smooth contour and be free from buckling, cracks or any other mechanical damage.” Requirements in ANSI/ASME B31.4-1999, “Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids” mandate that bends shall be free from buckling, cracks, and mechanical damage. (Paragraphs 404.2, 406.2, and 434.7).
The relevant US code sections therefore do not allow wrinkle bends in pipelines operating at more than 30% SMYS, and prohibit wrinkles anywhere in new pipeline construction.
Wrinkle Acceptance Criteria In Foreign Codes
Several foreign jurisdictions have extensively studied wrinkle problems, including the countries of Australia and Canada that have established acceptance criteria for anomalies like wrinkles. The first acceptance criteria for buckles in Australia was contained in a 1990 amendment to Australian Standard AS 2885-1987, wherein “a buckle shall be deemed to be a defect where it does not blend smoothly with adjoining surfaces or its height is greater than 25% of the nominal thickness and the width of its base is less than eight times its height”. Pipeline field bending problems in Australia led to the research that resulted in changes reflected in the current revision of Australian Standard AS 2885.1-1997, “Pipelines-Gas and Liquid Petroleum Part 1: Design and Construction”. In this code, a buckle has been defined as “an unacceptable irregularity in the surface of a pipe caused by a compressive stress”. The present code also differentiates between “ripples or buckles” formed during cold field bending, and those that may be formed as a result of other factors. In the latter case, the buckle height cannot be greater than 50% of the wall thickness, must blend smoothly with the adjacent pipe, and cannot reduce the internal diameter to less than the approved minimum value.
Section 6.6 of AS 2885.1 covers cold fiel
Broussard John
Christoffersen Stephen
Johnston Dennis
Kiefner John
Masaniello Richard
Lava Group Law by Smith & Frohwein, LLC
Mirant Corporation
Saint-Surin Jacques M.
Smith Gregory Scott
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