Jinheng Luo

Impact of improving design factor over 0.72 on the safety and reliability of gas pipelines and feasibility justification

Many years experience of the operation of high stress (>72% specified minimum yield strength, SMYS) gas pipelines and statistical analysis results of pipeline incidents showed that the operating pipelines at stress levels over 72% SMYS have not presented problems in USA and Canada, and design factor does not control incidents or the safety of pipelines. Enhancing pipeline safety management level is most important for decreasing incident rate. The application history of higher design factors in the U.S and Canada was reviewed. And the effect of higher factors to the critical flaw size, puncture resistance, change of reliability with time, risk level and the arrest toughness requirements of pipeline were analyzed here. The comparison of pipeline failure rates and risk levels between two design factors (0.72 and 0.8) has shown that a change in design factor from 0.72 to 0.8 would bring little effect on failure rates and risk levels. On the basis of the analysis result, the application feasibility of design factor of 0.8 in China was discussed and the related suggestions were proposed. When an operator wishes to apply design factor 0.8 to gas pipeline, the following process is recommended: stress level of line pipe hydro test should be up to 100% SMYS, reliability and risk assessment at the design feasibility or conceptual stage should be conducted, Charpy impact energy should meet the need of pipeline crack arrest; and establish and execute risk based integrity management plan. The technology of pipeline steel metallurgy, line pipe fabrication and pipeline construction, and line pipe quality control level in China achieved tremendous progresses, and line pipe product standards and property indexes have come up to international advanced level. Furthermore, pipeline safety management has improved greatly in China. Consequently, the research for the feasibility of application of design factor of 0.8 in China has fundamental basis.

A damage model for assessing pipeline safety in corrosion environments

Considering such practical pipeline service conditions in the petroleum transportation field as corrosion from harmful media (H2S, CO2 etc.) and load from the pressure of flowing petroleum as key factors, the degradation of the mechanical properties of pipeline steels and the corresponding variations in stress states are studied. A damage variable is introduced to reflect the degradation in the mechanical properties of the pipeline due to corrosion. A diluted solution approach is proposed to model the corrosion process of harmful media within the pipeline and the distribution of the damage variable along the radial direction of the pipeline is derived. An approach to the safety evaluation of damaged pipeline is proposed by comparing the instant properties of pipeline steels with servicing conditions.

Research on the Fatigue Character of ERW Pipe Welded Seam and Fatigue Life Assessment Method

The fatigue character of electric resistance weld (ERW) seams in API X65 grade line pipe steel at the stress ratio of 0.1 and 0.6 have been investigated. Repeated loading was applied to compact tension specimen, and the fatigue crack propagation rate and threshold of X65 ERW pipe seam are tested using high-frequency fatigue testing machine. Radiographic inspection has shown that the crack caused by the cold welding is the main weld defect in the ERW pipe. Based on the failure assessment diagram (FAD) recommended in the API 579-2007 and the Miner’s linear cumulative damage model, considering the influence of stress ratio to the fatigue life, the fatigue life assessment method for the ERW pipe containing seam defects is established.Copyright

Research on the Critical Buckling Strain Criterion for Pipelines

The local buckling of pipelines is regarded as a kind of failure. The critical buckling strain is an important parameter in strain-based design of pipelines. According to the grey system theory, the factors affecting the critical buckling strain were analyzed and the correlation between these factors and the critical buckling strain was quantitatively measured based on test data. According to the dimension analysis theory, the factors affecting the critical buckling strain were analyzed and the correlation between the factors and a new critical buckling strain equation was proposed based on test data. And some advice was provided for the improvement of critical buckling strain equations. Comparing the results with data from full scale tests, these as-obtained equations could provide a higher precision.Copyright

Elastic-plastic collapse of 3-D damaged cylindrical shells subjected to uniform external pressure

Hoo Fatt’s model was modified to obtain analytical solutions of plastic collapse for 3-D damaged cylindrical shells. To assess the effective wall thickness of a damaged pipeline, we used ASME B31G and its burst test results with Hauch and Bai’s approach. The effective thickness represents the corroded region of a pipe; it helps to transfer the response of the undamaged area near the damaged area. We propose solutions for the buckling of a damaged shell subjected to uniform external pressure. In these solutions, we extended Timoshenko’s solutions for the elastic-plastic buckle of linear elastic in a perfectly plastic cylindrical shell. The plastic collapse of a damaged shell is based on a modification of the interaction formula of the fully plastic membrane forces and bending moments in the nonuniform cylinder.

Fracture Characteristics of 9%Ni Steel at Low Temperature

The fracture characteristics of several types of tensile specimens of 9%Ni steel at low temperature was studied, and the Notch (Crack) Sensitivity and Notch (Crack) Relative Strength decreased (increased) Ratio of notch (crack) specimen were studied, while the crack preparation method of the crack specimen was discussed. The results indicate that the Notch (Crack) Sensitivity and Notch (Crack) Relative decreased (increased) Ratio can be used to evaluate the low temperature low stress brittle fracture resistance of the material. 9%Ni steel has good brittle fracture resistance at low temperature. The crack preparation principle of the crack tensile specimen was put forward.Copyright

Finite Element Method Analysis on Deformation of a Φ660-mm × 7.1-mm Pipe Buckling

The buckling of buried pipelines under external applied load is influenced by many factors; it may be caused by external pressure, internal pressure or axial force, and is very complicated. This paper studied the non uniform buckling of a Φ660mm×7.1mm pipe by FEM, the lost steady of steel, pipe form under different load and the main cause of deformation were analyzed.

Field testing and evaluation indexes system of composite materials in repairing and reinforcing pipelines

According to the existed problems in the repair and reinforcement technique of composites during engineering application, and referring to the testing methods of composites, the corrosion resistance technique standard and so on, this paper proposes a simple and feasible testing and evaluating system applied in the field application effect of the composite used in repairing and reinforcing of the pipeline. The evaluation results can be used by the manager as the rule to filter current repair and reinforcement materials, and consequently, improving the repair and reinforcement quality and prolonging the service life of the pipeline flaw.

Risk Assessment of Underground Natural Gas Storage Station

With the development of West-East projects construction, China’s natural gas production and consumption is increasing. But it must be to ensure to supply a continuous gas to users despite pipelines were meeting an accident, solve the inconsistency between storing excess gas during the using troughs and complementing insufficient gas during the using peak, and regulate the gas distribution imbalance caused by gas consumption by day and night and seasonal changes. Underground natural gas storage has unique advantages compared with other methods of peak regulation. The station, as its important part, has many complicated facilities, and the assessment will be extremely important. The paper divided the station into three elements, assessed the risk based on API581. The paper also applied the method to assess these facilities on the station of one gas storage. At last, it presented the suggestive measures to control risks.Copyright

Study on Acceptable Risk for Oil and Gas Pipelines in China

Risk assessment is basis to put pipeline integrity management in practice and the acceptable risk level is important criteria to execute risk assessment and constitute maintenance safeguard. So it is very important to establish a rational and practicable acceptable criterion and present a specific acceptable risk level. It is just for this need that the present paper gave a review of all the available research around the acceptable risk level and analyzed various domestic and overseas standards and documentation concerning how to define the acceptable risk criteria. As a result, a criterion suitable for oil and gas pipeline was presented and recommended acceptable risk level was gave.Copyright