Research Of Stress Magnetic Measurement Techniques On Marine Riser System

With the development of China’s offshore oil&gas industry, a growing numberof offshore oil and gas resources are explored and discovered, and related technicalresearch is extremely urgent. The marine riser is an important infrastructure inoffshore oil field development system long serving in the harsh marine environment,the marine riser is effected by all kinds of complex loadings. With high-temperatureand high-pressure oil and gas flowing through the internal, the connecting upperfloating platform moving, the bottom interacting with the sea-bed, and the externaleffected by marine environment loadings or even shock loads, earthquake loads etc.The working environment of marine reier is very poor, the stress state is extraordinarycomplicated and once damaged it will cause huge losses. So it is very necesssary toconduct the research of the marine riser system security and stability.This paper mainly aimes to study the structure of the marine riser system and itscommon forces. We do the simulation of the stess by the use of ANSYS, establishthe marine riser stress testing model using magnetic anisotropy testing technologybased on inverse magnetostrictive effect, and develope a stress detecting instrumentwhich can currently monitor the situation of riser stress, find unsecurity risks timelyand achieve the goals of providing forecasts and extending the using life of riser. Weachieve the following conclusions:1. This papper has discussed the main reasons leading to the damage of marineriser. As most of the riser’s damages are caused by the stress, the process of riser being well to distorted, wrong until scrapped off, necessarily reflects a change instress. It is just this change in the stress works on the riser directly that results to thedamages of the riser. This paper disscussed the riser radial plane mechanical model,axial shear mechanical model, and the mechanical model under oher complex load.2. Based on the magnetic anisotropy testing technology of inversemagnetostrictive effect, we have developed the instrumentation and software withintellectual property rights. The test apparatus can be applied to risers with differentdiameters. The riser will be partitioned into four regions measured by four probes,which acquire a higher measurement accuracy.3. We design and develope the centralizer which is suitable for the marine riserand the instrumentation. The centralizer can be scalable by adjusting the telescopicarm length to accommodate testing of risers with different diameters, and can beseparately diamantled and maintained to avoid the loss of a single arm leading toreplacement of the whole instrument which is practicaly applicated.4. Using our own equipment, we execute the experimental study of the stresswithholded by riser in three different ways of simulated loading and thecorresponding stress state were simulated by finite element method. After a numberof experiments the results show that magnetic survey method has many advantages,not needing full contact, not much dependent on thickness and curvature, and the highmeasurement accuracy. Using the magnetic measuring instruments to quantitativelyevaluate the stress state of internal riser, we can conduct evaluation and predictionabout the status of the marine riser safety.