This paper discusses the plastic limit pressure of elbows without defects and with local thinned area in the extrados. Finite element analysis (FEA) and experiments have been used. The results of FEA show that the limit load of elbows under internal pressure increases with increasing wall thickness and bend radius of the elbow. The results are consistent with the calculated results by the Goodall formula, the maximum error is 6.58%. By data fitting of FEA, an empirical formula for the limit load of elbows with local thinned area in the extrados has been proposed, which is validated by experiments.

This paper discusses the plastic limit load of elbows under combined internal pressure and in-plane closing bending moment. Finite element analysis (FEA) and experiments have been carried out. The results of FEA show that when the ratio of pressure to the limit pressure (P/PL) is smaller than 0.469, the limit moment of elbows increases with the increasing of the pressure; when the ratio (P/PL) is bigger than 0.469, the limit moment of elbow decreases with the increasing of the pressure. The results of FEA are verified by experiments. By fitting the results of FEA, the safety assessment figure for elbow under combined internal pressure and in-plane closing bending moment is drawn. The safety assessment method using the figure is simple and is applicable for the engineering.

对在内压作用下弯管的极限载荷进行研究。研究采用了有限元分析法、公式计算法和试验测定法。有限元分析结果表明，弯管的极限载荷随着弯管壁厚和弯曲半径的增加而增加，并与Goodall公式计算结果一致，最大误差为6.58％。这些结果得到了试验测试的证明。

Welded joint between different Cr-Mo steels are used in furnace tubes in petrochemical plants. A carbon migration from low Cr side to high Cr side in joint is often observed, which leads to the formation of decarburized zone and affects the performance and aervice time of the welded joint. Inthis paper the carbon migration between 9Cr1Mo and 15CrMo steels was studied. Accelerating experiments were performed. The relation between decarburized zone width and temperature and time of service was proposed to describe the influence of carbon migration on structural performance.