深井阳极地床施工方法探讨(张波)

-249-深井阳极地床施工方法探讨张波丁继峰孙超田俊杰张成钢（钢铁研究总院青岛海洋腐蚀研究所266071）摘要：管道采用外加电流阴极保护，具有可靠性高、寿命长、输出电压电流可调及维护保养简便等特点。外加电流系统的重要组成部分-阳极地床，分为浅埋型和深井型。目前深井阳极施工都是照图施工，设计上一般是参考当地的土壤电阻率，先设定阳极地床的接地电阻值，再设计一定深度，多采用的是预组装阳极，安装完阳极后再测量阳极地床的接地电阻，与设计比对。这种做法有一定的局限性，本文对深井阳极地床现场施工提出了新的方法。关键词：井阳极地床MMO阳极接地电阻测试仪电阻平衡1前言管道采用外加电流阴极保护，具有可靠性高、寿命长、输出电压电流可调及维护保养简便等特点[1]。外加电流系统的重要组成部分-阳极地床，分为浅埋型和深井型[2]。浅埋型地床又分为水平式和立式两种，其具有施工简单，维护方便，造价低等优点，但受地表土壤电阻率影响大，征地困难，对邻近埋地金属构筑物有干扰等缺点。深井型地床一般将阳极埋设在地表15m以下，其接地电阻稳定，不易遭到破坏，占地面积小，对邻近金属构筑物干扰较小，但造价高，不便维护。目前深井阳极施工都是照图施工，设计上一般是参考当地的土壤电阻率，先设定阳极地床的接地电阻值，再设计一定深度，多采用的是预组装阳极，安装完阳极后再测量阳极地床的接地电阻，与设计比对。这种做法有几个局限性，一是设计所取的土壤电阻率并不能反映实际深度土壤的电阻率情况；二是预组装阳极一般直径都较大，有些地区在阳极井的目标深度上会碰到岩层，打直径这么大的井既增加成本又拖延工期还存在风险；三是由于土壤电阻率取的不准，阳极又采用的是预组装形式的，必然设计时算得的阳极地床接地电阻会与实际不符。上述三点会给深井阳极地床现场施工及后续系统运行带来不必要的麻烦。本文对深井阳极地床现场施工提出了新的方法。2深井阳极地床施工2.1前期现场勘测对目标阳极地床区域先用四极法测量该地区不同深度的土壤电阻率[3]，并用WinSev软件模拟地层分布情况。南方某天然气管线某站场用四极法测得的不同深度的土壤电阻率数据如下表：表1土壤电阻率测试表间隔（m）电阻（Ω）土壤电阻率（Ω·m）0.525.1378.90820.717.4676.75416110.1863.93041.55.7153.788224.151.49633.7470.461651.9561.2371.7677.3696-250-101.4289.176150.328.26200.6986.664300.4381.012400.3587.92500.1753.38600.1971.592700.1670.336800.1680.384900.19107.3881000.0850.24利用WinSev软件将上述数据模拟之后，地层分布情况见下图：.1110100100010000a[m]110100100010000[ohm·m]根据软件拟合的情况来看，0～1.5m平均土壤电阻率为78.9Ω·m，1.5～2.4m平均土壤电阻率为53.8Ω·m，2.4-6.9m平均土壤电阻率为70.5Ω·m，6.9～10m平均土壤电阻率为77.4Ω·m，10～48m平均土壤电阻率为86.7Ω·m。该区域土壤电阻率都不大，可以考虑做深井阳极地床，土壤分层情况有待成井后测试验证。2.2钻井作业由于该阳极井受用地限制，距离工艺管线较近，因此阳极活性区位置应较深。该阳极地床预计安装MMO阳极6支，井口直径127mm，深度预计50m。现场以长度0.3m，直径0.04m的铁棒作为测试棒，每钻进十米用FLUKE1625接地电阻测试仪以三极法来测试铁棒在井内不同深度的接地电阻，进而由式4ln12lRldρπ⎛⎞=−⎜⎟⎝⎠反推出该层的土壤电阻率。图1土壤分层拟合图-251-表2成井后土壤电阻率测试表深度（m）接地电阻（Ω）土壤电阻率（Ω·m）深度（m）接地电阻（Ω）土壤电阻率（Ω·m）深度（m）接地电阻（Ω）土壤电阻率（Ω·m）59.6254.7199.839798145.2125.298.2329906730.88667.4763354559.3226.6177.792297844.9108.585.1300278630.580.363.004066759220.8173.241568244.696.175.4008818230.289.370.0655436758.7196.5154.175580444.391.271.5562999229.994.273.9101255758.4190.4149.38946824492.472.4978301829.692.872.811673658.1161.2126.478898543.793.173.0470561629.396.175.4008818257.8188.7148.055633743.488.769.594778542910683.1685064857.5199.9156.843249543.19977.6762466228.711791.7992005557.2248.2194.739842542.8111.487.4053926628.485.867.3194137456.9206.7162.178587642.5119.593.7607219328.194.874.380890756.6183.3143.818747542.2112.988.5823054927.8115.290.3869051656.3219.2171.986194541.997.176.1854903727.5134.1105.216006856215168.690838641.6109.685.9930972727.288.469.3593959755.7211.4165.866247841.3121.595.3299390326.966.552.1764686955.4208.1163.277039641121.595.3299390326.678.661.6702321655.1142111.414414340.7122.996.4283910126.389.169.9086219654.8115.590.6222877240.4143.7112.748248926109.385.757714754.5162.6127.577350540.1100.879.0885420125.7119.793.9176436454.2177.1138.954174539.895.574.9301166925.4115.890.8576702953.9137.7108.040597639.5111.787.6407752325.1133.1104.431398253.679.562.3763798639.2114.189.5238357524.8146.9115.258996253.398.777.4408640538.9141.9111.335953524.5129.4101.528346653139.1109.139049538.6122.496.0360867324.288.169.1240134152.7189.8148.918703138.389.269.9870828123.96550.9995558652.4208.7163.74780473894.774.3024298523.670.455.2364420452.1208.5163.59088337.7100.779.0100811623.371.656.177972351.8226.5177.71383737.4107.384.18849762374.758.6102588151.5243.3190.895260637.1100.979.1670028722.779.862.6117624351.2233.9183.519940236.870.255.0795203322.488.469.3593959750.9122.696.1930084436.580.763.3179101222.189.670.3009262350.6117.592.1915048336.285.266.8486486121.890.971.3209173550.3139.4109.374432135.999.578.068550921.596.775.8716469550130.8102.626798635.676.660.1010150621.286.768.0255614349.7125.998.7822166635.310380.8146808320.987.268.4178657149.4131.3103.019102835109.585.9146364120.699.878.30393346图2三极法测土壤电阻率示意图-252-49.1144.7113.532857434.7100.378.6962377420.389.169.9086219648.8176.3138.326487734.496.275.479342672088.769.5947785448.5226177.321532734.196.175.4008818219.794.173.8316647248.2160.4125.851211733.8111.687.5623143719.495.174.6162732747.9132.2103.725250533.5117.191.8776614119.199.578.068550947.6145.3114.003622633.2114.890.0730617418.89675.3224209647.3181.3142.249530432.9109.685.9930972718.589.169.9086219647217.4170.573899132.689.269.9870828118.267.352.8041555346.7142.8112.042101232.366.251.9410861217.969.454.4518334946.480.763.317910123283.665.5932749217.68062.7686841446.174.758.6102588131.789.870.4578479417.383.565.5148140745.888.169.1240134131.489.269.987082811789.269.9870828145.59776.1070295231.186.267.6332571616.793.273.125517022.3阳极安装及测试表2成井后土壤电阻率测试表详细记录了该地层的土壤电阻率分布情况。由数据可以看出有几个土壤电阻率较低的层适合于安放阳极。由于该阳极地床距离管道较近，因此阳极活性区的位置应尽量深一些，阳极密集安装会产生相互干扰，增大阳极地床的接地电阻，综合上述两个因素，6支阳极分别安装在表2中突出显示的位置。阳极安装完成，井内回填焦炭后，用三极法分别对每支阳极的接地电阻进行测量，再对6支阳极并联后的总电阻测量。表3阳极安装完成后接地电阻测量表阳极深度（m）接地电阻（Ω）总接地电阻（Ω）54.118.445.41437.312.731.611.927.436.62223.24.2阳极地床投用后，MMO阳极得到充分极化，由恒电位仪上的输出电压、输出电流读数，可得系统回路总电阻为2.8Ω，为保证每支阳极输出电流相同，对6支阳极做电阻平衡处理，电阻平衡后由设备读数得系统总回路电阻为3.6Ω。结果与讨论（1）将图1土壤分层拟合图和表2成井后土壤电阻率测试表比较，拟合图中由于受到地表测量数据的限制，只显示0～48m的土壤分层情况，土壤电阻率一般在七、八十欧姆米；从表2数据中可以得出16.7～47.9m之间的平均土壤电阻率为78.9Ω。说明用WinSev软件模拟出的土壤电阻率分布情况是具有一定可信度的，对阳极地床的安