| The petroleum pipeline is the lifeline in the development and utilize of oil gas resources. Whether its security or not is influencing the development of petroleum industry, living beings and environment directly. While installation, transport and other industrial accidents of the petroleum pipeline, it is unavoidable to encounter various damage and defect, such as surface flaw, crack, etc. The damage and defect will reduce the bearing capacity of the petroleum pipeline greatly, shorten the service life of the pipeline and threaten the security of the petroleum pipeline and biotic environment. For the security of the petroleum pipeline and its transport, avoiding the great economic losses and destruction of ecological environment, it's very important to make a reliability assessment to the flawed pipelines. It offers the rational and scientific decision basis for the repair of pipelines and the excavation of its potential bearing capacity. Then it will improve the comprehensive economic benefits of the petroleum pipeline greatly.Because the submarine pipeline suffers dynamic load, the safe little flaw under dead load will extend slowly under repeatedly act, then cause the rupture of the pipeline. But it is unavoidable that the pipeline contains the flaws. So EGA (Engineering Critical Assessment) is introduced into the assessment. In fact, EGA is the assessment of the structure, which can't satisfy the standard. It is the assessment method, which uses international admissive experience to assess the structures and units. It can guarantee the structures and units safety in specific time and the specific environment. It is usually conservative in the quality control standard in a .certain aspect. But this quality standard plays a very important role in quality control and safeguard. If the defect is within the range of quality control, it is ok. If the defect is not within the range of quality control, it might not be abandoned. Fit for service is the key to make the choice. Through the corresponding assessment, it can lengthen the service life of the" unqualified" structure and bring certain economic benefits. It is the important function of the EGA The EGA can replace the standard and participate in design and assessment to a certain extent. It can offer a set of substitution where the standard is strict. This kind of substitution standard is very economical and reasonable in specific time and the specific environment.The failure assessment diagram (FAD) method is very effective to the EGA of the pipelines. This method was put forward at first by CEGB. BSI PD6493 standard has adopted this method and establishes the guide on methods for assessing the acceptability of flaws in metallic structures. A further revision has been carried out in the new version BS7910: 1999. It has almost covered all mode of the pipelines' failure. 'Although its initialpurpose is directed against the flawed welded structure, in fact it is suitable for the unwelded structure too. While assessing, we can plot the failure assessment point (FAP) on the FAD. The location of this point is the function of the condition of loading, the flaw size and material property, etc. If the assessment point lies in the area bounded by the axes and the assessment line, the flaw is acceptable; if it lies on or outside the area, the flaw is not acceptable. The point of intersects of the two lines; the assessment points' locus and failure assessment locus indicate the limit flaw size of the structure.In this paper, the application of the failure assessment diagram (FAD) technology, the fracture safety assessment of three grades and the fatigue assessment included in the BS7910: 1999 standard are introduced in detail. Through the fracture assessment method, we can make a fracture assessment to the flawed pipeline under stress, and achieve the maximum length of the flaw in pipeline. Through the fatigue assessment method, we can make a fatigue assessment to the flawed pipeline under dynamic stress, and achieve the fatigue life of the pipel...
|
PDF Full Text Request