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Sec~9 9 Inspection of Buried Piping 埋地管道的检验


9 Inspection of Buried Piping 埋地管道的检验


9 Inspection of Buried Piping 9.1General 9.2 Types and Methods of Inspection 9.3 Frequency and Extent of Inspection 9.4 Repairs to Buried Piping Systems 9.5 Records


9.1 General 总则 不同于其他工艺管道检验,因为土壤腐蚀性显着影响管道外部腐蚀和埋地也给外 观检验带来困难. 非强制性地下管道检查的参考有  API 574- Inspection Practices for Piping System Components 管道系统部件的检查实践  API 651- Cathodic Protection of Aboveground Petroleum Storage Tanks 地上石油储罐阴极保护


NACE RP0169- Control of External Corrosion on Underground or Submerged Metallic Piping Systems 地下或水下金属管道系统外部腐蚀控制 NACE RP0274- High-voltage Electrical Inspection of Pipeline Coatings Prior to Installation 管道涂层高压电器检测 NACE RP0275- Application of Organic Coatings to the External Surface of Steel Pipe for Underground Service 地下服务钢管外表面有机涂料中的应用.


9.2 Types and Methods of Inspection 类型和检验方法


9.2.1 Above-grade Visual Surveillance 地面目视监控 埋地管道泄漏可能包括地面的表面轮廓的变化, 对土壤变色,沥青软化摊铺,池形 成,陷坑,鼓泡,或有明显的气味:地面目视监控能带来一些有用的信息.


沥青软化摊铺,池形成.


大连输油管道爆炸事故原因尚待调查:海洋污染影响水域100平方公里


9.2.2 Close-interval Potential Survey 密间隔管电位测量 在地面进行的调查埋地管道电位测量能有效的定位管的表面上的腐蚀活 跃点. 由于涂层管表面和腐蚀表面的电位差, 腐蚀位置能被测量出来.


http://www.rogeralexander1938.webspa ce.virginmedia.com/cpn/cips.htm


9.2.3 Pipe Coating Holiday Survey 管涂层漏电调查 管涂层漏电调查能用来检测新建管线涂层质量,也能检测重新挖开的在职管线 表面涂层的质量信息.从调查数据显示,涂料的有效性和涂料恶化率可确定.


9.2.4 Soil Resistivity 土壤电阻率 土壤的腐蚀性是以土壤电阻率来确定, 土壤电阻率越低土壤腐蚀性越大, 特别是地埋管道接触显著不同土壤电阻率的区域. 有三种常用的方法确定电阻率;  温纳四针法(ASTM G57) Wenner Four-pin Soil Resistivity Test  土壤杆 Soil Bar Used for Soil Resistivity Measurements  土箱 Soil Boxes Used for Soil Resistivity Measurements


API574: Figure 30—Wenner Four-pin Soil Resistivity Test


API574: Figure 31—Soil Bar Used for Soil Resistivity Measurements


API574: Figure 32—Two Types of Soil Boxes Used for Soil Resistivity Measurements


9.2.5 Cathodic Protection Monitoring 阴极保护埋地管道应定期监测,以保证足够的保护水平,监测应包括定期 “管/地”(pipe to soil)电位差测量和分析. 参考: NACE RP0169 and Section 11 of API 651适用于埋地管道的阴极 保护系统的检查和维护指导  API 651 Cathodic Protection of Aboveground Petroleum. Storage Tanks.  NACE RP0169- Control of External Corrosion on Underground or Submerged Metallic Piping Systems.

Charlie Chong/ Fion Zhang/ He Jungang / Li Xueliang


9.2.6 Inspection Methods 测定方法 参考 API 574 更加详细描述检验方法 以下是一些检验地埋管到外表与内部检验的方法:    

智能清管器检验方法 摄像机 挖掘 外加筛查技术-LRUT/LRGUT

http://www.ndted.org/EducationResources/CommunityCollege/Ultrasonics/Equipm entTrans/ematlambwave.htm


9.3 Frequency and Extent of Inspection 检查的频率和范围


9.3.1 Above-grade Visual Surveillance 地面目视监控 大约每隔6个月的调查 (看 9.2.1). 9.3.2 Pipe-to-soil Potential Survey 管/地电位差调查 阴极保护线: 密间隔电位测量能有效的确认管道是否全面的保处于护电位.不良管道涂层导致不

均匀的电压差,这些管道应每五年进行测量,探测出的腐蚀热点并开挖检查外表 腐蚀情况. 9.3.3 Pipe Coating Holiday Survey 管涂层漏电调查 管涂层漏电调查通常是基于其他形式的腐蚀控制失效时,用来检测管道涂层的完

整性.


地面目视监控 大约每隔 “6个月”的调查 (看 9.2.1). 管地电位调查 不良涂层, 阴极保护不完善的管道, “5年”的时间间隔进行核查.


9.3.4 Soil Corrosivity 土壤腐蚀性 对于非阴极保护,长度大于100英尺(30米)管道-每五年做土壤腐蚀性/土壤 电阻率测量.


9.3.5 Cathodic Protection 如果管道阴极保护,该系统应监视的时间间隔,在根据第 NACE RP0169 Section 10 或 API 651. NACE RP0169-2002 “Standard Recommended Practice Control of External Corrosion on Underground or Submerged Metallic Piping Systems” 10.3 The effectiveness of the cathodic protection system should be monitored annually. Longer or shorter intervals for monitoring may be appropriate, depending on the variability of cathodic protection factors, safety considerations, and economics of monitoring.”


9.3.6 External and Internal Inspection Intervals 外部和内部检查间隔 没有有效的阴极保护管道,运用内管检测器(pigging)或要定期(表-5)在一个或多个 位置被认为是最易受腐蚀开挖目视检查. (开挖目视部位为6 ft to 8 ft /2.0 m to

2.5 m) .

9.3.4 Soil Corrosivity 土壤腐蚀性 对于非阴极保护,长度大于100英尺(30米)管道-每五年做土壤腐蚀性/土壤电阻率 测量.


9.3.7 Leak Testing Intervals 泄漏测试时间间隔 替代或补充检查是执行泄漏试验,实验压力为110% MAWP. 时间间隔:  非管道阴极保护: Table 5 一半的时间间隔  管道阴极保护: Table 5 时间间隔


泄漏测试应保持 8小时:  前四小时: 初始加压四小时后,检查压力,如果有必要重新加压到原始试验压力,  后四小时: 隔离受压系统观察保压压力变动. 如保压压力降低 5%以上,执行目视外部和/或内部检查, 定位泄漏部位 与评估腐蚀程度


9.4 Repairs to Buried Piping Systems 埋地管道系统的维修


9.4.1 Repairs to Coatings 涂层的维修 涂层修复应符合下列条件: • • • • •

够的粘合力以防止的水分的渗透 足够的延展性抵抗开裂 涂层没有气孔, 漏点等缺陷 足够的强度适用处理和土壤应力 阴极保护合适性

使用高电压漏电检测器测试维修后涂层,电压必须调至合适被检测的涂层厚 度.发现到的漏点进行标记,局部修复.(重新高压漏电检测)


9.4.2 Clamp Repairs 钳修复 钳修复的位置应记录在检查记录,并可进行表面标.所有夹具修复应视为暂时的 应在第一时间(机会)做永久修复.


9.4.3 Welded Repairs 焊接维修 焊接维修应按照8.2.


9.5 Records 地管道的记录系统应按照7.6.档案.


140) Why is the inspector of buried process piping (not regulated by DOT) different from other process piping inspection ? a) The insulating effect of the soil increases the possibility of more internal combustion b) Internal corrosion has to be controlled by cathodic protection c) Significant external deterioration can be caused by corrosive soil conditions d) Internal corrosion must be controlled by internal coatings. 141) Indications of leaks in buried piping may include several indications. Which of the ones listed below is NOT one of the indications ? a) b) c) d)

A change in the surface contour of the ground. Water standing on the pipeline right-of-way Discoloration of the soil Notice odour


142) Corrosion cells can form on both bare and coated pipe where bare steel contacts the soil. How can these cells be detected ? a) Run an acoustic emission test on the piping b) Visually survey the route of buried piping c) The potential at the area of corrosion will be measurable different than other areas and a close-interval potential survey can detect the location of corrosion d) Run an internal survey of the piping using a video camera 143) A pipe coating holiday survey is used to locate coating defects on coated pipes. It can be used on newly constructed pipe systems to ensure that the coating is intact and holiday-free. More often, it is used on buried pipe to: a) Show the measurable differences in electrical potential in corroded areas b) Evaluate coating serviceability for buried piping that has been in-service for a long time. c) Determine the depth of the piping for resistivity testing d) Evaluate the cathodic protection components of the under-ground pipe


144) Cathodically protected buried piping should be monitored __________ to assure adequate levels of protection: a) b) c) d)

Regularly Intermittently Erratically Frequently

145) If an "intelligent pigging" system is used to inspect buried piping, what type of bends are usually required in the piping system ? a) b) c) d)

Five diameter bends 90 degree pipe ells Ten diameter bends Three diameter bends


146) How often should above-grade visual surveillance of a buried pipeline rightof-way be made? a) b) c) d)

Once a month Approximately 6 month intervals Once a year Once every 3 months

147) How often should poorly coated pipes with inconsistent cathodic protection potentials have a pipe-to-soil potential survey made ? a) b) c) d)

Yearly Every 2 years Every 5 years Every 7 years


148)On buried piping, what is the frequency of pipe coating holiday surveys? a) The frequency is governed by the leak test interval of the pipe b) It is usually based on indications that other forms of corrosion control are ineffective. c) Surveys are normally made every 5 years d) Pipe coating holiday surveys are made when the pipe is excavated. 149)For a piping buried in lengths greater than __________ feet and not cathodically protected, evaluation of soil corrosivity should be performed at 5-year intervals. a) b) c) d)

50 75 100 150


150)If buried piping is cathodically protected, the system should be monitored at intervals in accordance with Section 10 of NACE RP0169 or Section 90 of API RP 651. API RP 651 specifies __________ interval. a) b) c) d)

Annual Biannual Biennial Trennial


152) After excavation of buried piping, if inspection reveals damaged coating or corroded piping: a) The condition should be noted in the records and the inspection interval shortened b) The complete piping system must be day-lighted (excavated) for repair or replacement. c) The damaged coating or corroded piping must be repaired or replaced d) Additional piping shall be excavated until the extent of the condition is identified. 151) Buried piping inspected periodically by excavation shall be inspected in lengths of __________ feet at one or more locations judged to be most susceptible to corrosion a) b) c) d)

2 to 4 4 to 6 6 to 8 8 to 10


153)If buried piping is contained inside a casing pipe, the casing should be: a) b) c) d)

Capable of carrying the same pressure as the product pipe Checked to see if its protective coating is intact and serviceable Pressure tested to make sure it is serviceable Inspected to determine if water and / or soil has entered the casing

154)An alternative or supplement to inspection of buried piping is leak testing with liquid at a pressure at least __________ % greater than the maximum operating pressure at intervals ½ the length of those shown in Table 9-1 of API 570 for piping NOT cathodically protected and at the same intervals as shown in Table 9-1 for cathodically protected piping. a) b) c) d)

5 10 25 50


156)The leak test for a 8" diameter buried piping system is 300 psi. After 7 hours, the pressure reacts 273 psi. What should the inspector do? a) Nothing is required. The loss of pressure is negligible and will not affect the test. The loss can be disregarded. b) The system should be re-pressurised to the original leak test pressure and the test should begin again. c) The test charts and the temperature should be reviewed to determine if any change in temperature caused the pressure drop. d) The piping should be visually inspected externally and / or inspected internally to find the leak and assess the extent of corrosion.

155)The leak test for buried piping should be for a period of __________ hours. a) b) c) d)

4 8 12 24


157) A buried piping system that is not cathodically protected has to have an inspection interval set. The soil resistivity is checked and found to be 3400 ohm/cm. As the inspector, what interval would you set? a) b) c) d)

2.5 years 7.5 years 5 years 10 years

158) Buried piping also may be surveyed for integrity by removing the line from service and performing a leak test. This inspection method typically involves pressurising the line with a __________, allowing time for the __________ to diffuse to the surface and surveying the buried line with a gas-specific detector to detect the __________ a) b) c) d)

Tracer gas (such as helium or sulphur hexafluoride) Light hydrocarbon (such as butane) Smoke type material (such as chemical smoke) Water vapour (such as steam)


159) Repairs to coating on buried piping may be tested using a) b) c) d)

A low-voltage holiday detector Light taps with an inspection hammer A flaw indicator fluid A high-voltage holiday detector

160) If buried piping leaks are clamped and reburied: a) No further action is required unless the piping leaks again b) The date of installation shall be marked on the clamp for future identification c) A record of the location and the date of installation shall be maintained d) The clamped line shall be leak tested.


18)An inspector finds a thin area in the body of a NPS 6, 600 lb. gate valve body. The body is made from ASTM A216 WCB material. The system operates at 900 psi and 750 degrees F. Using a corrosion allowance of 0.125", what minimum required thickness must the valve body have to continue to safely operate? (Round to the nearest 3 decimals) a) b) c) d)

0.492” 0.427” 0.510” 0.345”

t = 1.5x [(900x6.625) / 2(14800)] + 0.125


Api570 chapter 9  
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