The Hydraulic Characteristics of a Heated Heavy Crude Pipeline
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摘要: 与一般热油管道相比，热稠油管道的流动特性主要有两个特点，一是在给定加热温度和管段压降条件下，该管段流量的试算过程可能陷入其特性曲线的不稳定区，该区域内管段的摩阻损失随流量增加而降低；二是稠油在管道中的流动可能位于层流和紊流的过渡区，通常用l临界雷诺数2 000作为层流和紊流的分界点，而分别按层流和紊流公式确定的该点的摩阻系数有较大差别，因此对于某些加热温度和管段压降而言，可能不存在合适的流量与之对应。基于对某热稠油管道在不同加热温度、不同总传热系数和不同流量下的水力计算，得出了其一个站间管段的一组管路特性曲线，即摩阻损失和流量之间的关系曲线，以此可以确定其不稳定区的流量区间。认为从保障流动安全的角度出发，管道应该避免在流量不稳定区间工作。Abstract: The paper addresses the hydraulic characteristics of a heated heavy crude pipeline.It is worth notice that the pipeline does not behave like the usual hot oil pipelines in two ways.Firstly, under given heating temperature and pressure drop, the convergence of the trial—and—error process to solve the flow—rate of the pipeline segment would be likely damaged by an unstable flow-rate interval, in which the friction loss of a pipeline segment decreases with the increase of flow-rate, just contrary to usual oil pipelines.Secondly, the flow of heated heavy crude through the pipeline is probably in the critical regime between laminar flow and turbulent flow.Because of different friction factors of the critical Reynolds number 2000 used as the interface of these two regimes determined respectively from laminar flow and turbulent flow, it is possible that an exact flow—rate can not be found corresponding to the combination of heating temperature and pressure drop of the segment.For the pipe segment, based on its hydraulic calculations at different upstream oil temperatures, different heat transfer conditions between it and its surroundings, and different flow。rates.the curyes of fiction lOSS versus flow-rate are plotted, from which the unstable flow-rate intervals may be determined.From the angle of safe operation, the unstable flow—rate interval should be avoided.
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海底管道在安装期间, 有时候需要将管子吊出海面进行焊接〔1〕。当管道从海底吊出海面进行焊接时, 吊点位算的选择是重要的。一方面, 从安装角度讲, 管子吊出海面之后, 要保证顺利对接, 端口不能倾斜; 另一方面, 从强度上来考虑, 起吊诱发的管中应力不宜超过许用应力。因此, 要求分析管子的受力和变形。
图 1表示管子在海底起吊时的典型状态。管子在海水中的重量为q, 吊点在B点, 它距离管端为a, 需要将管子端口吊起的高度为Δ, 这一高度应高于海面, 需要确定吊点B吊起的高度ΔB及所需要的提升力P。起吊后, 一段长度的管子要离开海底, 设悬于海中的管子长度为l, A点是管子与海床的接触起点, A点和B点的距离为b, 在接触段上, 存在弯矩为零的边界条件。
为方便起见, 分别考虑均布载荷和集中载荷单独作用时的挠度和转角方程〔2〕, 选取如图 1所示的坐标系。
（1）集中载荷单独作用时:
当x=b时的挠度和转角方程分别为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E1.png")
(1) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E2.png")
(2) 当x=l时的挠度和转角方程分别为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E3.png")
(3) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E4.png")
(4) (2) 均布载荷单独作用时:
当x=b时的挠度为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E5.png")
(5) 当x=l时的挠度和转角方程分别为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E6.png")
(6) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E7.png")
(7) 在端口, 应满足的位移条件为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E8.png")
(8) 将式(3)和式(6) 代入, 得:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E9.png")
(9) 在接触段上应满足弯矩为零的边界条件, 因此, 有静力平衡方程:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E10.png")
(10) 将式(10) 代入式(9), 得到确定l的方程:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E11.png")
(11) 有多种方法得到此式的数值解, 一旦求出以后, 可以得到管中的弯矩。
AB段(0 ≤ x ≤ b) :
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E12a.png")
(12a) BC段(b ≤ x ≤ l) :
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E12b.png")
(12b) 最大弯矩为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E13.png")
(13) 相应的应力为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E14.png")
(14) B点应提起的高度为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E15.png")
(15) 管端口C点的转角为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E16.png")
(16) 为了便于安装, 管端口的转角应为零, 以保持管端口竖直和其它管子对接。
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E17.png")
(17) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E18.png")
(18) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E19.png")
(19) 将上式代入式(11)得:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E20.png")
(20) 其余各量得:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E21.png")
(21) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E22.png")
(22) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E23.png")
(23) 管中最大应力、悬空段长度和提升力随管端提升高度的变化曲线示于图 2、图 3和图 4。
为了应用于一般设计计算问题, 图中均采用无量纲参数来表示。取特征长度、特征提升力和特征应力分别为:
![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E24.png")
(24) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E25.png")
(25) ![](/fileYQCY/journal/article/yqcy/2008/6/href="yqcy-15-11-31-E26.png")
(26) 从分析可以看出, 由式(20) 可以确定管子在海水中的悬空段长度l, 最佳吊点位置距管端l/3的地方, 吊点选在此处, 管端的转角将为零。实际施工时, 可在此点的附近配置数个吊点(一般为3个以下)。
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[1] WU Changchun, CUI Hongsheng, ZUO Lili: Some Interesting Plow Characteristic8 of a Heavy Crude Pipeline, Proceedings of IPC 2006, 6th International Pipeline Conference, Canada, 2006.
[2] 严大凡: 输油管道设计与管理, 石油工业出版社(北京), 1986。 [3] 曲慎扬: 原油管道工程, 石油工业出版社(北京), 1991.
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