J. L. F. Freire

Burst Tests on Pipeline Containing Interacting Corrosion Defects

In this paper the burst tests of seven tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal 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). The specimen IDTS 1 is a defect-free pipe. The specimen IDTS 2 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other five specimens contain groups of interacting defects constituted by the combination of two or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects.Copyright

STRESS ANALYSIS OF PIPELINES WITH COMPOSITE REPAIRS

The repair of corroded pipelines with fiber reinforced composite materials is a well-developed practice in the oil and gas transportation industry. Laboratory hydrostatic burst tests and field practice of several years have shown that these repairs are effective for pipelines with external corrosion defects. This paper deals with laboratory tests carried out to compare the behavior of fiber reinforced composite repairs applied to defects machined in pipeline test specimens. The experimental results were compared to results from Finite Element Analysis (FEA) of the tubes tested. The parameters of FEA were calibrated to this specific problem, beforehand. Some hipotheses were tested during FEA trials to better explain the experimental results. The results indicated that, up to the starting of yielding of the pipe defected region, practically only the elastic pipe stresses equilibrate the pressure loading, due to the steel high Young modulus. After yielding, the composite material starts to work, carrying an important part of the pressure loading increments. Experimental results also showed that the repair systems tested allowed the pipes to achieve the original design pressure before bursting. However, only one of the repair systems was approved in all strength verification tests for both internal and external defects. This system operated for four hours under a hydrostatic pressure test associated to the specified minimum yield strength (SMYS) of the steel and was also able to support ten pressure cycles of the design pressure afterwards, without showing any visual damage.

Burst Tests on Pipeline Containing Closely Spaced Corrosion Defects

In this paper the burst tests of five tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from a longitudinal welded tube 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). The specimen IDTS 8 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other four specimens contain groups of interacting defects constituted by the combination of three or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by five assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method and the RSTRENG Effective Area method.Copyright

Burst Tests on Pipeline Containing Circumferential Corrosion Defects

Circumferential defects are the ones in which the width w is greater than the length L (w > L). In this paper the burst tests of three tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal 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 three specimens had one external circumferential corrosion defect, machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective defect. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the burst tests are compared with those predicted by five assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects (Part B), the RPA method and the Kastner equation.Copyright

Burst Tests on Pipeline Containing Irregular Shaped Corrosion Defects

A corrosion defect can be considered as being of a regular shape if its defect depth profile is relatively smooth and the longitudinal area of metal loss is approximately rectangular. A corrosion defect can be considered as being of an irregular shape if its defect depth profile presents one or more major peaks in depth. In this paper the burst tests of four tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal 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 four specimens had one external irregular shaped corrosion defect, machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective defect. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for complex shaped defects.Copyright

Burst Tests on Pipeline With Nonuniform Depth Corrosion Defects

PETROBRAS is conducting a research project with the purpose of investigating the behavior of pipeline with long nonuniform corrosion defects. In the first phase of this project, burst tests of two tubular specimens were carried out. Each of the two specimens had one external nonuniform depth corrosion defect, machined using spark erosion. The specimens were cut from longitudinal welded tubes made of API 5L X60 steel with an outside diameter of 323.9 mm and a nominal wall thickness of 9.53 mm. Each of the two tubular specimens was instrumented with 17 post-yield strain gages rosettes, one displacement transducer and two pressure transducers. This paper describes the tubular specimens tested and the instrumentation used. The measured burst pressures are compared with those predicted by the ASME B31G and the RSTRENG Effective Area methods. The material properties used were determined by tests of tensile specimens. Photographs of the fractured defects are presented along with comments about their differences in shape. Some values of strain measured during the tests are also presented and commented.Copyright

Fatigue life prediction of repaired welded structures

Abstract This paper discusses the fatigue life prediction of welded structures which had cracked in service and were repaired by welding reinforcing plates over the cracked sections. The maximum working stress histories under actual loading conditions were measured and the fatigue lives of the welded repairs were predicted using international design codes. These damage evaluations were compared with the actual numbers of cycles to failure ontained in industrial operation.

On DIC measurements of DeltaKeff to verify if it is the FCG driving force

Redundant data obtained under quasi-constant {DeltaK, Kmax} loading conditions is used to verify if the effective stress intensity factor (SIF) range DeltaKeff DeltaKmax DeltaKop is indeed the fatigue crack driving force. The crack opening SIF Kop is measured along the entire crack path on DC(T) low carbon steel specimens by a series of strain gages bonded along the crack paths, by a strain gage bonded on their back faces, and by a digital image correlation technique. All such measurements showed a significant Kop decrease as the crack sizes increased, while the fatigue crack growth rates remained essentially constant both in the thin and thick specimens, a behavior that cannot be explained by DeltaKeff arguments.