B31G Method Research Articles

Behavior and damage of a pipe in the presence of a corrosion defect depth of 10% of its thickness and highlighting the weaknesses of the ASME / B31G method

The company DRC (pipe repair Department) located within the SONATRACH Company of oil and gas in Algeria, which is responsible for the repair of pipelines for the transport of gas or crude petroleum, will rehabilitate old pipes that have operated on-line for approximately 30 years or come from remaining projects. On the assumption that rehabilitating a pipeline means making it workable under the same conditions as a new structure and reducing the overall cost of the project. The abandonment of these tubes will have an important environmental and financial impact. The rehabilitation, which consists of recovering the maximum of tube, already used, therefore reduces the cost of the project. Inspection and evaluation of corrosion defects are carried out in accordance with ASME/31G method that is applied to low alloyed carbon steels with corrosion defects having soft profiles with low stress concentration. Our research will consist in developing a method using a behavior-damage coupling of the material to highlight the weaknesses of the ASME / B31G method and show for defects whose depth does not exceed 10%, these defects can survive hydrostatic testing but will develop during service when the pressure is variable.

Study of the reliability of corroded pipeline by the ASME B31G method

Study of the reliability of corroded pipeline by the ASME B31G method

PART 5: RUPTURE TESTS OF PIPELINE CONTAINING COMPLEX-SHAPED METAL LOSS DEFECTS

An earlier paper—the third in the present series 1 — discussed data acquired for pipe segments with uniform and long or short metal loss defects that were tested under internal pressure up to rupture. These defects were machined to generate uniform-shaped external or internal metal loss profiles. That paper was followed by the fourth in the series,2 which presented the burst tests of seven tubular specimens loaded with internal pressure and containing internal and irregularly shaped real corrosion defects. The present paper—the fifth in the series—presents results for test specimens containing machined irregular or complexshaped external defects. An upcoming article will address test results for the case of closely located and interacting defects. Burst tests were conducted on two tubular specimens. Each of the two specimens had one external complex-shaped metal loss defect, which was machined using spark erosion. The specimens belonged to test batch 2, as listed in Table 1 of Freire et al. 3 The specimens were cut from longitudinally welded tubes made of American Petroleum Institute (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 postyield strain gage rosettes, one displacement transducer and two pressure transducers. The failure pressures measured in the laboratory tests were compared with those predicted by five assessment methods: the American Society of Mechanical Engineers (ASME) B31G method, 4 the Det Norske Veritas (DNV) RP

PART 4: RUPTURE TESTS OF PIPELINE SEGMENTS CONTAINING LONG REAL CORROSION DEFECTS

shaped internal corrosion defects. Measurements were taken in order to determine the actual dimensions of each of the tubular specimens and their respective metal loss defect profiles. Tensile specimens were tested to determine the actual material properties. The failure pressures measured in the laboratory tests were compared with those predicted by four assessment methods: the ASME B31G method, 4 the DNV RPF101 method for single defects, 5 the RSTRENG effective area method, 7 and the DNV RP-F101 method for complex-shaped defects. 5

Failure probability of corrosion pipeline with varying boundary condition

This paper presents the effect of external corrosion, material properties, operation condition and design thickness in pipeline on failure prediction using a failure probability model. The predicted failure assessment for the simulated corrosion defects discovered in corroded pipeline is compared with that determined by ANSI/ASME B31G code and a modified B31G method. The effects of environmental, operational, and random design variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress and pipe thickness on the failure probability are systematically studied using a failure probability model for the corrosion pipeline.