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.

压力管道广泛应用于各工业领域和城市管网，按我国《压力管道安全监察规定》，城市公用管道为GB级管道。本文从我国城市埋地压力管道的现状出发，简要阐述了风险分析技术在城市埋地管道安全分析中的应用，旨在促进风险分析技术应用的推广和提高我国城市埋地压力管道的管理水平。

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.

对平面闭合弯矩作用下弯管的极限载荷进行了分析研究。研究采用有限元分析法、Kitching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系数的增加而增加，该结果与Kitching公式计算结果以及试验结果一致。

为配合“西气东输”工程南京市启动了城市天然气利用工程的建设，本文对W.Kent Muhlbauer 埋地管道风险评价方法加以改进，形成了更符合实际和常规的评价方法，用该方法对南京市城市天然气利用工程中50km 高压管线进行了风险预评价。结果表明，在设计与施工质量优等的情况下，该管道的相对风险系数为1149.05，与最坏状况的相对风险系数的比值仅为0.033，因此该管道的风险较低。