Dent Assessment Research Articles

A verification study of fatigue-based methods in API RP 1183 for estimating fatigue life of pipeline dents

Pipeline dents are mechanical damage caused by a third party in buried pipelines during construction or maintenance repair. Dents are recognized as a leading cause of pipeline failures for both liquid and gas transmission lines, and their assessment and management are critical to pipeline integrity. To meet the industry need, American Institute of Petroleum (API) in 2020 published a recommended practice (RP) 1183 – Assessment and Management of Pipeline Dents. This API code provides the pipeline industry “standard methods” for evaluating severity and fatigue life of pipeline dents with a single peak.This paper performed an initial verification study of fatigue-based methods prescribed in API RP 1183 for estimating fatigue life of pipeline dents. A brief review was first given to the dent fatigue-based methods, including three dent screening methods for estimating dent fatigue life in Sections 7.4.1, 7.4.2, and 7.4.3 of API 1183 and one dent assessment method for predicting fatigue life in Section 8.3.4. In order to verify these fatigue life prediction methods, a set of “standard examples” of dents provided in Annexes A.1 to A.5 of API RP 1183 were utilized in this study to calculate fatigue life, to determine restraint condition, and to evaluate both screening and assessment methods for single-peak dents. Through detailed calculations and comparisons, this study confirmed some specifications of API RP 1183, but also found some self-inconsistences and errors existing in this new API code. This includes the self-inconsistences between three screening methods and the self-inconsistence between the screening and assessment methods. On this basis, recommendations were made on how the operators should use API RP 1183, and what actions API should take to improve this code.

Standards and methods for dent assessment and failure prediction of pipelines: A critical review

Dent, a common mechanical damage on pipelines, is associated with a significant local plastic deformation. Dents can cause pipeline failures, especially when they are combined with other types of defects such as gouges, fatigue, corrosion, and cracks. In this work, a systematic review of various assessment methods and standards for pipeline dents, including the combination of a dent with other defects, is conducted. Generally, the methods available today are not sufficiently accurate and reliable to assess pipeline dents, especially the dent-defect combinations. For plain dents on pipelines, both the depth-based criterion and the strain-based criterion are commonly used in engineering. Their main problems include inaccuracy and conservatism. For a dent combined with other defects, the existing assessment techniques are not mature enough to give reliable results. Both experimental testing and numerical modeling through finite element (FE) analysis are capable of investigating the influence of dents and dent-defect combinations on burst failure pressure of the pipelines, although an approximation to the reality is still the main difficulty existing in the experimental testing and FE analysis. Nowadays, relevant studies on assessment techniques for plain dents, a dent with fatigue and a dent with a single gouge have been common in literature. The combinations of a dent with corrosion or cracks have been rarely assessed due to complicated mechanisms involving a multi-physics coupling effect. Development of novel assessment methods by integrating mechanical stress and strain, electrochemical reactions and steel metallurgy will be a key topic to accurately assess the dent-defect combinations for improved pipeline integrity.

A new criterion based on strain determination for dent assessment of pipelines

Dents are one of the most common defects on pipelines and compromise the structural integrity. To date, relevant studies on failure assessment of dented pipelines have been limited, and the existing standard, mainly American Society of Mechanical Engineering (ASME) B31.8, contains major problems, making assessment results not sufficiently accurate and reliable. In this work, a new method based on ductile damage failure indictor (DFDI) criterion combined with improved strain determination by a finite element (FE) model was developed for pipeline dent assessment. Dents with different depths were created by applying a spherical indenter of 100 mm in diameter on a pipe segment of 720 mm in outer diameter and 8.1 mm in pipe wall thickness. The DFDI formula considers the influence of spring-back upon removal of indenter, and the difference between the equivalent strain at dent apex and the maximum equivalent strain at the whole dent area. When the indenter displacement is smaller than 8% of pipe outer diameter, the maximum DFDI can be determined from the equivalent strain at the dent apex. When the initial displacement exceeds 8% of the pipe outer diameter, the maximum equivalent strain at the dent area, which deviates from the dent apex, should be determined by the FE model. Moreover, the limitations of ASME B31.8 in dent assessment were explained.

Mechanical behavior investigation on the formation of the plain dent of an API 5L L245 pipeline subjected to concentrated lateral load

As the main geometric defect in pipeline maintenance, dent has been paid more attention by pipeline managers because of its strong stress concentration. To investigate the formation mechanism of a pipeline dent, an indentation test of a pipe subjected to concentrated lateral load was carried out in the laboratory to simulate the formation process of the dent, and a 3D numerical model corresponding to the test was established to verify the results between the experiment and simulation. Subsequently, the stress and strain response of the dented pipeline was analyzed in detail in various stages of dent formation process. Deformation analysis revealed that the residual stresses state formed in the dented area after unloading is related to the depth of the dent, which may be in tension or in compression. During the formation of the dent, the pipeline presents “∽”-type wave-like bending state in the axial direction. These dent formation mechanisms may provide a guidance for dent assessment studies.

An alternative to traditional GPA for evaluating student performance

In response to the growing problem of grade ination in Amer- ican undergraduate institutions, alternatives to GPA and GPA-based stu- dent assessment are discussed. One alternative summary, based on a Bayesian latent trait formulation, eliminates many of the inequities as- sociated with GPA-based measures and has been proposed as a replace- ment for GPA-based class ranks at Duke University. 1. BACKGROUND Grade point average, or GPA, is the most widely used summary of undergraduate student perfor- mance in our educational system. Unfortunately, combining student grades through simple averag- ing schemes to obtain GPA's results in systematic biases against students enrolled in more rigorous curricula and has important consequences in stu- dent course selection. It creates perverse incentives for faculty to inate grades and lower standards, and it rewards students for selecting less chal- lenging courses and majors (Larkey and Caulkin, 1992).

Motivation: vehicle for public health nursing interventions?

AbstractClients' motivation to engage in health promotion, health maintenance, and risk‐reduction activities has been of long‐standing concern to public health nurses. While health practices are often attributed to motivation, no measurement of this construct has existed to assist us in either assessing or developing interventions relative to this characteristic. This study reports additional psychometric data on a new multidimensional measurement of motivation and examines selected predictors of the measurement The test‐retest correlation over a two‐week period for the total instrument was 0.86. Age, sex, and educational level accounted for 18 percent of variance in the total construct Age, sex, educational level, and income differentially explained 15,15,9, and 11 percent of the respective ante in the construct's four separate dimensions‐judgment, behavior, competency, and intemaYextemal cue responsiveness. The results provided evidence of the stability of the health selfdeterminism index (HSDI) and supported the significant contributions of four sododemographic tmiables in predicting total and subscale scores. The HSDI may prove to be useful to public health nurses in dent assessment and as a guide for developing specific intewentions at both the individual and aggregate levels.