PCM Technology
Known as the Pipe Current Mapper, the PCM technique makes use of an electric current of extremely low frequency (4 Hz), whose behavior is very close to the direct current from the lines cathodic protection system, being such current applied in metallic pipings aiming at the complementation of the protection provided by the external coating.
The method consists of introducing a signal in the piping to be inspected and to catch such signal along the same piping, making use of a portable receiver calibrated in the same frequency. This receiver shall indicate the planimetric position of the line, as well as its depth.
The signal mapping is performed with readings in regular pauses, which allows obtaining the current distribution along the piping, identifying in this way the current loss points. These loss points can be associated to the existence of fissures in the piping external coating and / or contact with other structures. Subsequently, the fissures are detected and measured with considerable precision by means of the complementary technique “A-frame”.
Services Executed
ESTEIO S.A. performed the localization, geopositioning, mapping and inspection of the coating in more than 2.000 km of lines in several regions of the country.
The services were carried out aiming at the obtaining of the real position of the lines (As-Built) in the strips and at the inspection of the condition of the lines coating, being the very first service of such magnificence to be carried out in Brazil.
Service Region
The existing lines localization, geopositioning and mapping actions were carried out in the strips that interconnect Barra do Furado to Taubaté. In this segment, the following sections outstand:
|
SECTION |
EXTENSION |
LINES (DIAMETER) |
|
Barra do Furado – Cabiúnas |
70 km |
OCAB (38"), GASCAB I (38"), GASCAB II (20") |
|
Campos Elíseos – Estação de Japeri |
40 km |
GASVOL (18"), OSVOL (12") |
|
Estação de Japeri – Serra das Araras |
20 km |
GASVOL (18"), OSVOL (12") |
|
Serra das Araras – Volta Redonda |
40 km |
GASVOL (18"), OSRIO (16") e OSVOL (10") |
|
Volta Redonda – REVAP (São José dos Campos) |
250 km |
GASPAL (22") e OSRIO (16") |
Methodology
The surveys are based in the Pipeline Current Mapper (PCM) method, making use of manufacture equipment from Radiodetection Inc. to locate and inspect the coating conditions.
The lines were located in the strip making use of this electromagnetic technique, being delimited with markers representing a point each 20 m of topographic profiling. The UTM coordinates of each delimited point were surveyed with GPS making use of the stop-and-go technology with base points situated 5 to 10 km from each other.
PC System State Reports
Prior to the localization process, some inspections are performed along the Cathodic Protection System such as:
The results of these inspections were presented in the specific report called RL nº 2. With this report, Petrobras came to know the condition of part of the Cathodic protection system and arranged the due repairs for the carrying out of the localization service.
After the conclusion of the positioning services, a second report was elaborated containing the low insulation points of the line, the identification of the regions with significant current loss, its gradation in three levels (at least), depth of the points measured in meters, N and E coordinates of the current measurement points and terrain portion. This report is called RL nº 1.
GPR Usage (Ground Profiling Radar)
In the place which the PCM met interferences, the service was carried out with GPR equipment. These places are areas with the presence of radio frequency, high tension towers, railways, telephony, microwaves and others.
Besides that, an additional reading was performed each 10 km with the GPR, intended to confirm the PCM results, and each 20 km of strip, a manual drilling (pit) was performed, in order to confirm the readings performed and / or adjust the equipment.
Coating Inspection
The coating inspection was carried out in its qualitative and quantitative mode, using the “Attenuation Current” technique.
The Qualitative Inspection consists of the Current Mapping carried out as a whole with the localization, grading the regions with fissures in the anti-corrosive coating of the line. The current readings shall be done at the localization markings of the line, at each 50 meters.
The Quantitative Inspection consists of the localization and delimiting, in the field, of the coating fissures, using the A-Frame technique, and the positioning of numbered marks, (reddish) placed in the ground in the epicenter of the fissures.
The areas to be surveyed by means of the A-Frame accessory are defined after the analysis of the current loss points, considering the processing of the PCM data and the indications from RL nº 1.
Final Plans
The drawings of plan and profile (Digital Orthophoto Maps) of the lines strips with the respective lines positioned in the strip were delivered in digital means, georeferenced and ready for insertion in SIG.
Result
The final result of this service seeks to assist PETROBRAS regarding the real positioning of the lines in the strips and the condition of their coating, such knowledge which shall allow the implantation of new lines, replacement of problematic sections, improvements in the effectiveness of the cathodic protection system, besides a higher level safety in any building, repair or maintenance activity along the strip.