Centrifugal compressor vibration fault caused by rotor scaling
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摘要: 针对某天然气增压站离心压缩机转子结垢导致机组振动超标并触发停机的故障，利用状态监测技术结合压缩机输气能力变化、内窥镜检测及拆机检修情况对故障机理进行分析，确定了导致转子不平衡的原因是叶轮结垢。对叶轮和流道垢层进行化验和成因分析，其结果验证了故障诊断技术的实用性与有效性，并且提出了加强过滤排污等防控措施，为天然气长输管道离心压缩机同类故障诊断及处置提供了参考。Abstract: In a certain gas booster station, the vibration of centrifugal compressor exceeds the criterion due to the scaling of its rotor, and consequently the centrifugal compressor is shutdown. In this paper, the failure mechanisms of the centrifugal compressor were analyzed by means of the state monitoring technology, combined with transport capacity change of compressor, endoscope detection, and disassembly maintenance. It is confirmed that the cause of the rotor imbalance is the impeller scaling. Then, tests and cause analysis were carried out on the scaling buildup of impeller and passageway, and the practicality and effectiveness of the fault diagnosis technique were verified. Finally, the prevention and control measures were put forward, e.g. strengthening filtration and drainage. The research results provide the reference for the diagnosis and treatment of similar faults of centrifugal compressors for long-distance natural gas pipelines.
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Keywords:
- natural gas /
- long distance pipeline /
- centrifugal compressor /
- rotor /
- scaling /
- imbalance /
- fault
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国内外直埋供热管道敷设技术已有70多年的历史。工程实践证明, 供热管道直埋敷设与过去采用的地沟敷设方式相比, 一般可以节省约50%左右的投资, 施工周期可以缩短一半左右, 并且施工方法简便〔1〕。对于直管段部分的应力分析, 一直采用材料力学的方法, 忽略管道的截面尺寸, 将直管作为弹性地基梁进行分析。随着管径的增加(目前管径可以达到500~1 000 mm), 工程精度无法满足, 为了得到精确的应力解, 必须考虑管道的截面尺寸效应。
一. 模型的提取和参数的确立
根据工程实际, 将直埋管道直管段作为柱壳来处理。对于柱壳而言, 采用曲线坐标(高斯坐标)比直角坐标更符合需要, 为此建立如图 1所示的平衡方程, 图 1中的r为管径, α、β(取θ=α, x=β)为曲面上的坐标。
直管段(柱壳)属于形状较简单的曲面, 其拉密系数(Lame)和曲率可以利用第一基本形I=A2(dα)2+B2(dβ)2观察得出:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE1.png")
得到的拉密系数和曲率为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE2.png")
二. 管道受力分析
作用于管道上的静力荷载主要有内压、埋土压力、热胀力和土体与管道之间的摩擦力等, 仅在特别需要时, 如地震区和横穿马路的管段, 才需要考虑动力荷载。
(1) 供热管道一般为薄壁管道, 设一直管管径为Dn, 壁厚为δ, 两端封闭, 受内压p作用(见图 2)。根据材料力学, 在管道内壁处, 径向应力σr远小于σz和σθ, 一般忽略不计, 在曲线坐标中, 管道α、β、n向受到的内压力为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE3.png")
(2) 管道与埋土之间存在着变形与力的相互作用, 对于管体与埋土所构成的异性体超静定体系, 必须从两者所组成的整体进行分析。目前, 国内外进行管道应力分析时, 广泛采用的是环压理论。根据环压理论〔2〕, 可以得出曲线坐标中直管段受到的α、β、n向埋土压力为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE4.png")
式中 γ——土壤单位容重;
h0——埋土深度(管顶至地面)。
(3) 直埋供热管道在安装和运行时的温度变化很大, 温度变化将在管内引起较大的温度应力〔3〕。由于温度变化引起管道的轴向应力远远大于径向应力, 因此只需要计算温度变化产生的轴向膨胀力。弯头受到的α、β、n向的膨胀力为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE5.png")
式中 E——管材的弹性模量;
T——管道的升温值;
α——管材的线膨胀系数。
(4) 根据北京市煤气热力设计所试验研究的结果可以得到, 在曲线坐标中, 埋地管道与周围土体之间的摩擦力在α、β、n向的分力分别为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE6.png")
式中 l——管道长度;
f——埋土与管道外壁之间的摩擦系数。
计算中一般认为管道表面单位面积上的摩擦力为均匀常数, 管道受热位移, 但土体未被破坏。由于热管变形使土体形成的空腔是暂时的, 因此可以近似认为管道周围土体是完全弹性的。
(5) 分析弯头过渡段部分受到的内压、埋土压力、热胀力、土体与管道之间的摩擦力等外力, 对弯头所受的α、β、n向的外力归纳如下。
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE7.png")
三. 问题的求解
分析直管段的受力情况可以看出, 其受力基本符合壳体无距理论存在的条件。采用无距壳体理论, 作为柱壳的直管段, 其拉密系数A和B为常数, 有:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-FE8.png")
则平衡方程可以简化为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-E1.png")
(1) 将内力T1、T2和T12代入式(1), 并适当简化〔4〕, 则平衡方程将变为由位移v、w作为基本未知量的方程组:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-E2.png")
(2) 考虑到边界条件β=0时, v=0, w=0, 则直管段β向和n向的位移v和w为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-E3.png")
(3) 根据物理方程, 利用式(3), 得到α和β向的正应力σ1、σ2, 分别为:
![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-E4.png")
(4) ![](/fileYQCY/journal/article/yqcy/2018/8/href="yqcy-22-12-19-E5.png")
(5) 四. 结论
通过对管道受力解析研究, 首次在理论上获得了曲线坐标下直埋供热管道直管段的应力解析解。该解析解相对于国内外直埋供热管道直管段部分的弹性地基梁解更为精确, 可以满足目前大管径工程精度的需求, 具有一定的理论意义和工程价值。如果将该解析解转化为直埋敷设热力管道实用技术的科学论题, 尚需进一步探讨。
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