·Table of Contents
·Reliability and Validation
Magnetic PIG's Evaluation by Means of Automatic Ultrasonic DeviceRicardo de Oliveira Carneval Sérgio Damasceno Soares
Brazilian Oil Company Research & Development Center - PETROBRAS/CENPES
Cidade Universitária, Quadra 7
21949-900, Rio de Janeiro, RJ, Brasil
Fax. (005521) 598-6790, e-Mail :firstname.lastname@example.org
The majority of inspection has been made with magnetic pigs. These devices are quite good to localize corrosion points but not so far to measure the wall thinning precisely. This way the local ultrasonic wall thickness measuring is very interesting.
In this paper the evaluation of corroded areas in oil pipelines is shown These areas are pointed out by magnetic pigs mainly by ultrasonic automatic and semi-automatic corrosion mapping system.
The differences between both techniques (pig and automatic ultrasonic devices), advantages and drawback of each one are commented.
In the work described in this paper we have used automatic and semi-automatic ultrasonic systems to evaluate regions indicated by pig inspection.
Table I presents in a resumed way characteristics of the pig inspected pipe.
|Pipeline||Extension(km)||f (in)||t (mm)||Transported Product||PigType||No. of Points Evaluated|
|3||400||17||9,53 e 6,35||LCO||UT***||2|
|6||8||16||11.13 e 6.35||Oil||HRM**||6|
|Table 1: Inspected Pipelines|
2.2.1 Pig Inspection
The inspections on the cited pipelines were carried out by means of tools known as intelligent or instrumented pigs. These devices could be of different types but their feature is measuring and recording wall thickness along pipe length. These data stored will be used to analyze pipe integrity. In this paper three types of pigs belonging to four companies were used: conventional magnetic (CMA, CMB, CMC, CMD), high-resolution magnetic (higher number of sensors, HRM) and ultrasonic (UT).
|Photo 1: Semi-automatic ultrasonic inspection system NB-2000 by AIS.|
2.2.2.Localized Ultrasonic Inspection
In semi-automatic inspection we applied the system NB-2000 from AIS-Automated Inspection System Inc., using MSEB5 Krautkramer probe, 8mm diameter, 5MHz (photo 1). In automatic inspection we applied digital ultrasonic devices models USD-10 and USD-15 from Krautkramer, Epoch II and III from Panametrics; and MSEB4 Krautkramer probe, 14mm diameter, 4MHz. The automatic system, developed by this paper authors basically is a software (USAquis) that runs in IBM PC compatible under Windows 98 environment, and a automatic probe holder scanner, photo 2.
|Photo 2 : Automatic ultrasonic inspection system by CENPES/PETROBRAS.|
Normally the results of pipeline PIG inspection present the point (location) of pipe extension where damages are located. These longitudinal positions are linked to pipe accidents (valves, deviations, etc) or pig inspection marks (reference magnets). Other flaw characteristics are given like position on pipe perimeter; extent (length); width and; mainly depth (wall loss).
|Table II- Wall loss range(Color Scale)|
To illustrate automatic ultrasonic result presentation some data collected from ultrasonic inspection along pipelines cited in 2.1. are shown. These results are graphically presented and known as corrosion mapping (C-Scan presentations), on those, corrosion depths are correlated to a color scale. The color scaled use in this paper is presented in table II.
|Fig 1: Automatic ultrasonic inspection. (pipeline 1, point 2, and scan 8)||Fig 2: Automatic ultrasonic inspection. (Pipeline 2, point 4, and scan 1)|
Figures 1 and 2 present for illustration purposes automatic ultrasonic results along pipeline points assigned by pig inspection. In these pictures, C-Scan (corrosion mapping) and; B, D and A-Scan (minimum wall thickness point) presentations are shown.
Table III, shows data comparing Intelligent pig and Automatic Ultrasonic inspection results. We consider the maximum wall loss from each point in order to compare both techniques because this parameter is the most relevant to pipeline integrity.
To easy results comparisons dates from Table III are presented in a graphic (figure 3).
|Fig 3: Instrumented Pig "versus" Automatic US|
Table III and figure 3 analysis arrives at the following conclusions:
|PIPE||Inspected Point||PigType||Maximum Wall Loss Pig (%)||Maximum Wall Loss UT (%)||PIG-US Difference (%)|
|Table 3: Maximum Wall Losses|
Instrumented Pig "versus" Automatic Ultrasonic
Instrumented pigs for sure represents a powerful resource to oil pipeline evaluation related to safety aspects. They enable pipeline integrity condition to be assess in a short time and at a reasonable cost, compared with another localized (focused) ndt techniques. However use of them should be made with some care because we have also seen that complex tools (high resolution magnetic and ultrasonic) have some drawbacks when compared with more focused techniques.
We consider localized ultrasonic technique mainly when applied in an automatic or semi-automatic way, as in this paper, to be more precise to discontinuities dimensioning than an intelligent pig. However localized ultrasonic is not practical to be applied along the complete pipeline. So, we recommend use of automatic ultrasonic only to verify and/or certify locals pointed by pig inspection.
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