Ronaldo D. Vieira

The Critical Path Method for Assessment of Pipelines With Metal Loss Defects

The Critical Path (CP) Method (CPM proposes a set of rules allowing the drawing of failure lines that represent adjacent areas positioned along selected circumferential and longitudinal directions of pipelines that contain colonies of corrosion defects. Failure pressures are calculated for each of those lines to determine the most critical one. This selected line is considered as the most probable path of rupture, and it corresponds to the minimum calculated internal pressure to take the pipeline to fracture. The proposed method was checked against twelve burst pressure tests performed on pipeline tubular specimens. Three specimens were labeled as control specimens — one was a pipe without defect and the other two had single small base defects of different depths. Nine of the specimens contained interacting corrosion defects, which were composed of the combinations of two or more base defects. Comparisons were made of the measured burst pressures with those predicted by the CPM, by one recently proposed method called MTI, version 1, or MTI V1, and by four other Level-1 or Level-2 assessment methods, namely the American Society of Mechanical Engineers (ASME) B31G method, the Det Norske Veritas (DNV) RP-F101 for single and for complex and interacting defects, and the RSTRENG Effective Area method. The CPM and MTI V1 methods predicted the failure pressures closest to the actual test failure pressures, with the CPM presenting suitable small mean error of evaluation as well as very low standard deviation error for its predictions.Copyright

Use of FBG Strain Gages on a Pipeline Specimen Repaired With a CFRE Composite

Laboratory tests were conducted to understand and describe how the reinforcement layers of a carbon fiber epoxy composite material can enable a steel line pipe specimen with a metal loss defect to withstand pressure loading, and to compare the test results with those predicted by mechanics of materials and by finite element numerical solutions developed previously. Hydrostatic burst tests were performed on three pipe (API 5L X65 ERW) specimens: one with metal loss defect, one without metal loss defect, and one with metal loss defect but repaired with a carbon-fiber-reinforced epoxy composite system. Fiber Bragg grating strain gages were used during the tests of the repaired specimen. The strain gages were bonded either directly on the surface of the defect, or were inserted in between some of the composite layers in order to show the reinforcement’s effective contribution to the strength of the repaired pipes. The analytical and numerical results agreed very satisfactorily with experimentally determined burst pressures and pressure–strain curves, showing that the behavior of composite reinforced pipelines can be well predicted by using simple mechanics of materials or sophisticated finite element solutions.

Measurement of Stresses in Pipelines Using Hole Drilling Rosettes

On-shore buried pipelines are loaded by internal pressure, by longitudinal displacement restrictions caused by support or soil interaction, and by temperature differential. If a referential initial state of stress can be established by some means, conventional strain gage techniques can be used to determine the existing loads relative to the reference state. If a reference cannot be established, residual stress measurement techniques are strong candidates for use in the measurements because they measure the absolute state of stress present at the assessed point of the pipeline. This paper aims to provide laboratory test results to show how uncertain measurements using conventional strain gage or residual stress techniques can be when used in determining existing loads. The tests utilized a special device designed and built for applying combined states of stress. The device had a U-shaped format. The horizontal part of the U-shaped device consisted of the specimen to be tested: a segment of an API 5L X60 steel pipe with length, diameter and thickness equal to 910mm, 323.3mm and 9.7mm, respectively. The pipe segment was capped at both ends by welding two reinforced plates that formed the two vertical legs or arms of the U-shaped device. A pressurized water inlet was introduced into one of the caps to provide for the internal pressure loading of the test specimen. Besides capping the pipe, the vertical leg-plates were connected by two threaded spindles. The spindles and the long plate arms made it possible to apply axial forces and intrinsically coupled bending moments to the pipe segment. The spindles were instrumented with four electrical resistance strain gages in a full bridge arrangement to measure the applied forces. The resulting applied stress states in the pipe walls caused by normal force, bending moment and internal pressure were measured using several rosettes of electrical resistance strain gages that were appropriate for applying the blind-holedrilling technique. Three sets of data points were collected during the tests. The first set consisted of measurements of strains caused by applying simple or complex load combinations. The second set consisted of strain measurements made after the blind holes were drilled in order to determine the residual stresses caused in the fabrication of the steel pipe. The third set of data consisted of measurements of strain variations caused by unloading the device. All the data of the experiment were analyzed and compared with strains calculated by means of analytic (Strength of Materials) and numeric (Finite Elements) methods. These comparisons helped to reach the conclusion that the use of a residual stress measurement technique such as the blind-hole drilling method to determine pressure induced and soil movement loading in operating pipeline will furnish inaccurate results even if a reasonable number of measurement points are used to describe the stress states of points along the analyzed cross sections. The reason for this is the possibility of a large variation in the residual fabrication stresses not only along the outer perimeter of one cross section of the pipe, but also the large variation in the distributions that occur along neighboring sections of a short pipe segment. For the case of predicting strains generated by the complex loading applied to the pipe test specimen, the comparison of experimentally and analytically determined strains allowed for the evaluation of an overall strain prediction uncertainty of 50µe. Furthermore, an uncertainty value of 26µe for the hole drilling method was also determined by comparing the initially imposed combined strain states with those measured after drilling the blind holes and unloading the test specimen.

Measuring the Remaining Strength Factor of a Steel-Adhesive-Repair System

A new repair-reinforcement system to be utilized on pipeline showing external metal loss was developed and tested by employing scaled models in order to verify the system’s effectiveness in reestablishing pipeline structural integrity. The repair system is composed of pre-curved thin layers of steel lamina, which are set in place on the external metal loss defect area of a pipe and cemented in place with epoxy resin. Hydrostatic burst tests were performed on three types of pipe specimens: with metal loss defects, without metal loss defects and with metal loss defects but repaired with the new system. Strain gages were used to monitor elastic and plastic strains during the tests. Test results, burst pressures and pressure-strain curves were compared using simple analytical equations that were developed to determine the number of thin steel layers to be used in the system and to model the behavior of each tested specimen. The investigation reached the conclusion that the simple analytic equation is effective for determining the required repair thickness and its number of layers, that the repair system reconstructs pipe integrity and that it should be further investigated as to applying it while the pipeline is still in operation.© 2006 ASME

DIC Strain Analysis of Pipeline Test Specimens Containing Metal Loss

The elastic and plastic strain data of two tubular specimens, with longitudinal and circumferential metal loss at areas on their external surface, tested under internal pressure are presented and analyzed. The specimens were cut from two longitudinally welded tubes made of low carbon steel with nominal outside diameters of 76.7 and 102 mm and nominal wall thicknesses of 2.04 and 3.2 mm respectively. Each of the tested specimens had milled metal loss areas simulating external longitudinal and circumferential corrosion defects. Digital Image Correlation was employed to determine elastic and plastic strains at the metal loss defects and their results were verified and compared with data collected with electrical resistance strain gages and results obtained with a finite element numerical solution.

Strain Measurements Using DIC, Strain Gages and Reflection Photoelasticity

This investigation applied, simultaneously, two or three experimental strain measurement techniques to different structural models in order to highlight their specific advantages and fields of application. The applied techniques were the digital image correlation method (DIC), the electrical resistance strain gage method (SG), and the reflection photoelasticity method (RP). The DIC, SG and RP results for strains measured at the same points or at similar points of the tested models proved to be satisfactorily close.

Use of Fiber Bragg Grating Strain Gages on a Pipeline Specimen Repaired with a CFRE Composite System

Re-establishing the maximum operating pressure of a segment of pipeline with metal loss defects, such as erosion or corrosion defects, can be accomplished either by replacing the damaged segment altogether, or by applying a localized repair system. The present paper deals with laboratory tests conducted: (1) to understand and describe how the reinforcement layers of a carbon fiber epoxy composite material can enable a steel line pipe specimen with a metal loss defect to withstand pressure loading; (2) to compare the test results with those predicted by Mechanics of Materials and by Finite Element numerical solutions developed previously. Hydrostatic burst tests were performed on three pipe (API 5L X65 ERW) specimens: one with metal loss defect, one without metal loss defect, and one with metal loss defect but repaired with a carbon fiber reinforced epoxy composite system CFRE. Fiber Bragg grating FBG strain gages were used to monitor elastic and plastic strains during the tests of the repaired specimen. The strain gages were bonded either directly on the surface of the defect, or were inserted in between some of the composite layers in order to show the reinforcement’s effective contribution to the strength of the repaired pipes. The analytical and numerical results agreed very satisfactorily with experimentally determined burst pressures and pressure-strain curves, showing that the behavior of composite reinforced pipelines can be well predicted by using simple Mechanics of Materials or sophisticated Finite Element solutions.

Burst Strength of Pipeline Test Specimens Containing Longitudinal or Circumferential Corrosion Defects

The elastic and plastic strain data of tubular specimens undergoing rupture under internal pressure tests are presented and analyzed. Six tubular specimens were tested. The specimens were cut from longitudinally welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). Each of the six specimens had one external longitudinal or circumferential corrosion defect that had been machined using spark erosion. Tensile specimens and impact test specimens were tested to determine material properties. Post-yielding electrical resistance strain gages were used to measure the elastic and plastic strains. The failure pressures measured in the laboratory tests were compared with those predicted by four assessment methods: the B31G method, the RSTRENG 085dL method, the DNV RPF101 method for single defects and by the Kastner equation. The paper also discusses the strength of the pipe segments used in the tests under the assumptions of following the Tresca and von Mises rupture criteria.

Strain Analysis of Pipeline Test Specimens Containing Longitudinal and Circumferential Corrosion Defects

The elastic and plastic strain data of tubular specimens undergoing rupture under internal pressure tests are presented and analyzed. Six tubular specimens were tested. The specimens were cut from longitudinally welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2mm (18in) and a nominal wall thickness of 7.93mm (0.312in). Each of the six specimens had one external longitudinal or circumferential corrosion defect that had been machined using spark erosion. Tensile specimens and impact test specimens were tested to determine material properties. Post-yielding electrical resistance strain gages were used to measure the elastic and plastic strains. The failure pressures measured in the laboratory tests were compared with those predicted by the DNV RP-F101 method for single defects and by the Kastner equation. The paper also discusses the strength of the pipe segments used in the tests under the assumptions of following the Tresca rupture criterion.