Pipeline monitoring corrosion

In areas where general corrosion is the expected form, a simple ultrasonic thickness gage can be utilized to determine the extent of corrosion, based on baseline readings made at installation or previous inspections. The entire unit need not be examined. Attention can be focused on those areas most likely to corrode, such as liquid levels, mixing zones, or areas of high turbulence. Corrosion probes, which can be placed in process equipment or pipelines, can monitor corrosion conditions by measuring an actual corrosion current, or other process parameters known to be related to general corrosion rates. These data can be constantly monitored and recorded to predict equipment wear, or as an alert to upset conditions. 

An effective method to monitor corrosion in buried structures is to measure the pipe/soil potential along its span. With horizontal pipelines this is technically feasible however the access to data on the local CP performance in well casings is very limited and can only be obtained using expensive logging tools. 

A large percentage (57%) of mains and services (46%) is metal (steel, cast iron or copper), and corrosion is a major issue. For distribution pipe, external corrosion is of primary importance, although internal corrosion has been noted in some cases. The methods of monitoring corrosion on cathodically protected pipe are similar to those in the transmission pipeline sector, including pipe-to-soil potential and coating surveys. One difference is that in distribution systems, leak detection is an acceptable method of monitoring for these pipelines without CP (nearly 15% of the steel mains). 

General corrosion control, prevention, and monitoring should be planned for from the onset. To detect and monitor corrosion, various methods must be used, while corrosion protection would be done by the addition of inhibition and use of protection coatings [5]. Visual examination, laser methods, the replication microscopy liquid penetration testing method, magnetic particles testing, the eddy current inspection method, acoustic emission technique, thermal methods of inspection, and nondestructive methods are the various methods to be adopted when monitoring pipeline corrosion [5]. 

Cathodic Protection Monitoring for Underground Pipelines, NACE Corrosion Information Compilation Series, Kpeline Corrosion, NACE International, Houston, TX, 1999. 

Procedures for monitoring corrosion of pipelines and related surface facilities using retrievable specimens are described in NACE Standard Practice for Preparation and Installation of Corrosion Coupons and Interpretation of Test Data in Oilfield Operations (RP0775). One of the main concerns in the use of such specimens is the problem of location, since corrosion is generally associated with a separate water phase. In some cases, special dropout pots are used to trap a water phase to provide a severe location for specimens. Electric resistance probes can be used in place of specimens. In locations where there is a continuous water phase and fouUng is not a problem, polarization type probes can be used [74,75]. 

Once the site has been exposed, corrosion monitoring devices (e.g., coupons, electrical resistance probes) can be installed to identify and monitor corrosivity in the pipeline. Inline inspection results may also provide information to assess the downstream conditions of the pipe. Once regions most susceptible to corrosion are free of damage, it is then considered that pipeline integrity to a large extent is assured. 

Electrochemical techniques measure electrochemical potentials and currents that are fundamentally related to the thermodynamics and kinetics of corrosion reactions. They are often used to measure the rates of uniform corrosion, to determine the tendency of localized corrosion, to study a wide range of corrosion-related phenomena such as passivation, galvanic corrosion and sensitization effects. Electrochemical corrosion testing and monitoring can be performed in a diverse range of environments in the laboratory or in the field, in a pipeline or in an autoclave. For instance, they have been successfully employed to monitor corrosion in multiphase oil/water conditions with as little as 1-2% water " ... 

S. Papavinasam, R. W. Revie, M. Attard, A. Demoz and K. Michaelian, Comparison of techniques for monitoring corrosion inhibitors in oil and gas pipelines . Corrosion,... 

Properly installed coupons are excellent for monitoring corrosion. They are not very successful in pipeline programs because they need to be installed in places that are generally not easily accessible. 

Strommen, R. and Roland, A., Corrosion Surveillance of Submarine Pipelines by Electric Field Strength Monitoring , Materials Performance, 20 No. 10, 47 (1981)... 

It should be noted that there are still many deficiencies in the science and technology of corrosion monitoring, mainly in the areas of localised corrosion (pitting) and the inability to monitor at inaccessible sites such as downhole (oil and gas wells) and subsea installations (satellite wells and pipelines). 

The structures used (platforms) require monitoring in addition to sub-sea pipelines, satellite wells and other equipment (e.g. manifolds) on the sea floor. Corrosion inhibitors are widely used in internal-streams (from the reservoir and many of the downstream operations). Corrosion monitoring can provide valuable data for assessing the effectiveness of the inhibitors used and for optimising dosage rates. 

Pipelines Pipelines carrying wet gas and crude oil present a corrosion hazard and are protected accordingly by coatings and/or inhibitors. Limitations of corrosion monitoring arise from sampling, in relation to the sampling and interval, and access problems for subsea pipelines (major trunk lines). 

Corrosion is by far the most serious hazard of pipeline incidents. It is imperative that adequate corrosion monitoring programs be provided for all hydrocarbon pipelines. Order crude oil pipelines operating at elevated temperatures appear more susceptible to corrosion failures than other pipelines. 

For this reason, it is recommended that addition of corrosion inhibitor to previously uninhibited systems be closely monitored. Initial low level addition followed by a gradual increase in the corrosion inhibitor treat rate will help to minimize the removal of pipeline rouge and filter plugging problems. 

Monitoring of the pipelines, (inspections, pigging, corrosion, cathodic protection, helicopter survey, etc.)... 

The task of purging pipelines for maintenance is almost second-nature to well-experienced operators in this unit. Typically, pipeline clearing is routine and is uneventful. This time, however, the utility dry air system was also being utilized as a source for instrument air in the operating area. Hence, this corrosive material was able to backflow throughout the instrument air system into monitoring and control systems. The backflow created expensive instrument damages. 

In addition to drinking water and environmental applications, water purity is critical to many industries. Conductivity detectors are used in semiconductor and chip fabrication plants, to monitor cleanliness of pipelines in the food and beverage industry, to monitor incoming water for boilers to prevent scale buildup and corrosion. Any process stream with ions in it can be analyzed by conductometry. Conductivity detectors are part of commercial laboratory deionized water systems, to indicate the purity of the water produced and to alert the chemist when the ion-exchange cartridges are exhausted. The detector usually reads out in resistivity theoretically, completely pure water has a resistivity of 18 MO cm. 

A large percentage of mains (57%) and services (46%) are metallic systems (steel/cast iron/copper), and corrosion is a major problem. For distribution pipe, external corrosion is the primary problem and internal corrosion has also been observed in some instances. The methods of corrosion monitoring on cathodically protected piping are similar to the methods used in the case of transmission pipelines... 

The effectiveness of cathodic protection can be accomphshed by monitoring the pipeline potential using the close interval potential survey (CIPS) method or by using direct current voltage gradient (DCVG) or IR coupon techniques. Also, physical and electrochemical methods can be used to estimate the corrosion rates of a cathodicaUy protected system. 

The most widely used potential monitoring measurements are based on protection potential criteria. Despite improvements in these methods, they only indicate if the pipeline is protected, underprotected, or overprotected. These methods can only estimate the corrosion rates, but should not be used to predict the life expectancy of the system. A more advantageous solution would be the introduction of kinetic CP criterion that... 

A.A. Ivanov, System for monitoring of corrosion process in pipelines, Zashchita Okruzhayushchei Sredy v Neftegazovom Komplekse Janusz 1 (2000) 25-27. 

Underground pipelines are essential requirement of any developed country. Transportation of crude oil, gas, and many hydrocarbons are carried out through underground CCPs, as they are one of the safest modes of transportation, causing minimum disturbance to mankind. Since the material of construction of pipelines is steel, which is prone to severe corrosion, both from inside and outside, safety of pipelines depends upon a foolproof system of corrosion protection. All three major techniques of corrosion protection, namely, coatings, inhibitors, and cathodic protection, are used to protect pipelines. Protection of pipelines alone is not enough it is also important to monitor... 

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