一种改进的CRLP最大许用操作压力设计方法

与传统管线钢管相比,复合材料增强管线钢管(CompositeReinforcedLinePipe,CRLP)具有承压能力高和质量轻等优势,但对其压力设计的研究尚不充分。CSAZ662-2015《油气管道系统》和GB/T35185—2017《石油天然气工业用复合材料增强管线钢管》中最大许用操作压力的设计思路不同,且设计结果差别较大。针对此问题,基于组合薄壁圆筒模型对承压CRLP进行分析,对最大许用操作压力下材料的名义许用应力和真实许用应力进行了区分,进而导出真实许用应力的显式表达形式,并以此作为设计安全裕度的评价指标。分析表明:现有规范和标准中的设计公式均无法保证管线钢和复合材料的真实许用应力为常量,对应两种设计方法,各组分材料的真实许用应力均随CRLP规格差异而发生变化,并且随着试压/预应力处理的历程而改变。基于上述分析和CRLP极限状态下的承载特征,提出一种改进的压力设计方法。新方法优先保证复合材料的真实许用应力为常量,并可由设计系数直接确定;在最大许用操作压力的计算中,考虑了加载历程的影响,物理意义明确。算例表明,其设计安全裕度较现有方法更为合理,对于CRLP压力设计的改进有参考价值。

An improved design method for CRLP maximum allowable operating pressure

Compared to the traditional line pipe,the composite reinforced line pipes(CRLP)have the advantages of high pressure bearing capacity and light weight.However,researches on pressure design of CRLP are still insufficient.The design ideas of maximum allowable operating pressure in CSA Z662-2015 Oil and gas pipelines systems and GB/T 35185-2017 Composite reinforced line pipe for the petroleum and natural gas industry are different and the design results vary greatly.For this problem,analysis of CRLP under pressure was carried out based on the combined thin-wall cylinder model,the nominal and the true allowable stress of the material under the maximum allowable operating pressure was distinguished,and the explicit expression of the true allowable stress was derived and taken as the evaluation indicator of the design safety margin.The analysis results show that design formulas in the existing code and standard cannot ensure the true allowable stress of the line pipe and composite material is a constant.In both of the two design methods,the true allowable stress of various constituent materials varies with CRLP of different specification in the process of pressure test and pre-stressing.Based on the above analysis and the bearing capacity of CRLP under the ultimate state,an improved pressure design method was put forward,which preferably guarantees the true allowable stress of the composite material as a constant and it can be determined directly by the design factor.In the calculation of the maximum allowable operating pressure,the effect of the loading process was considered.This new method has a clear physical meaning,and the design examples show that the new method has a more reasonable safety margin compared to existed standard methods,providing useful references for CRLP design.