组合应力作用下含腐蚀缺陷海管安全工作压力评价方法

在较高温度和压力作用下,由于土壤的摩擦阻力,海管会产生很大的轴向压力,以及由侧向屈曲引发的弯矩。因此对含腐蚀缺陷管道安全工作压力的评价,须考虑轴向压应力的影响。对目前工程界的评价方法进行对比分析,在内压和轴向压应力组合作用下,含腐蚀缺陷海管的安全压力评价方法还很不完善,尤其是复杂缺陷,目前的规范还不完全适用。通过对许用应力法安全系数的讨论和分析,基于Von Mises准则和有限元分析,提出了组合应力作用下含腐蚀缺陷海管的安全工作压力评价方法。通过该方法对某运行了近三十年的管道进行了安全工作压力的评估,同时考察了轴向压应力对安全工作压力的影响。此方法对应的轴向压应力限值和安全等级以及安全系数相关,当安全等级低时,其值和DNV-RP-F101规范值基本一致,当安全等级高时,其值比DNV-RP-F101规范值大。

Assessment Method of Safe Working Pressure of Corroded Subsea Pipeline under Combined Stress

Under high temperature and high pressure,the subsea pipeline is subjected to extensive compressive axial force due to soil friction resistance and could also be under bending moment due to lateral buckling.Therefore,the assessment of safe working pressure should take into account the effect of longitudinal compressive stress.In this paper,the available assessment approaches have been reviewed,which reveals that there is lack of engineering methods in this regard,especially for complex corrosion defects.The application of allowable stress method requires rational selection of relevant safety factors(usage factors),which has been evaluated from the perspectives of hoop stress,longitudinal stress and Von Mises equivalent stress.Based on the Von Mises equivalent stress and finite element analysis,an assessment method of safe working pressure has been proposed herein to account for the effect of longitudinal compressive stress.It has been applied to assess the safe working pressure of a corroded pipe of over 30-year operation.Meanwhile,the influence of longitudinal compressive stress has been evaluated and discussed.The compressive stress lower limit in the proposed method is associated with safety class and hence safety factor.Under low safety class,the compressive stress lower limit agrees with that value determined by DNV-RP-F101,however,under high safety class,it is rather higher.