The use of wireline measurements in gas storage gathering lines is a new idea which addresses the problem of internal and external corrosion in pipelines. Gathering lines are subjected to the same corrosive agents (H20, C02, H2S, etc.) as gas storage wells. However, unlike storage wells, where wireline surveys are utilized to monitor metal loss, the level of damage in the gathering lines is largely unknown. Most of the other corrosion monitoring methods are not direct measurements of corrosion. While pipeline inspection pigs detect corrosive damage they have limited application due to the gathering lines relatively short lengths and small diameters.
The use of the Pipeline Corrosion Tool and Video Camera introduces a precise means to completely inspect pipelines. Metal loss is detected and then correlated to a video survey. Both tools have been physically designed to traverse the extreme bends found in gathering systems. Pipeline logging is an accurate and economically attractive alternative for detection of internal and external corrosion in pipelines.
Various corrosion monitoring methods are in use at present to evaluate the condition of gas storage gathering lines. Tests involving coupons, water analysis, hydrostatic testing, cathodic surveys and other techniques are used to evaluate these pipelines. However, these methods provide limited information, giving only an indication of possible corrosion. A direct measurement of metal loss is the most accurate means of ensuring a pipeline's integrity. The electronic inspection pig is widely used in the pipeline industry for a direct survey but has omitted application in gathering lines. Many are limited to large diameters and gentle bends. Another disadvantage of this option is the electronic pig's need for launchers and receivers. -he economics of installing these devises on short gathering lines is often prohibitive. With these limited options total replacement of a suspicious line becomes economically feasible even though only a small portion of the One may have corrosive damage. The application of wireline instruments to provide an accurate inspection in gathering lines is a viable alternative. It offers a means to detect corrosion in lines with diameters from 3 1/2 to 12 inches. No modification is needed in existing gathering lines. The evaluation can be accomplished through open ended pipe or with launchers and receivers in place. Metal loss is detected by the Pipeline Corrosion Tool and presented on a log format with a scale from 100 to 0 percent metal loss. This log is then correlated to a video survey: the survey, on standard VCR tape, visually inspects the pipe. This correlation is used to determine whether measured metal loss is internal, external, general or concentrated.