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Pipeliners focus on automated class location studies for safety.

Natural gas transmission companies are re-evaluating and strengthening their safety precaution methodologies in the aftermath of recent pipeline safety incidents. Compliance measures, particularly class location studies, are being scrutinized thoroughly as the Department of Transportation's Office of Pipeline Safety (DOT/OPS) prepares to impose more stringent safety requirements on these companies.

Importance of Class Location Studies

Class location studies are mandated in the Code of Federal Regulations (CFR) Part 192.5 which states "...the class location unit is an area that extends 220 yards on either side of the centerline of any continuous one mile length of pipeline...the class location is determined by the buildings in the class location unit." Classes 1 through 4 are assigned according to number and types of buildings per mile. This is known as the "sliding mile" method. A method of limiting the extent of each class location is permitted. Buildings between and including the extents are referred to as "clusters."

A major difficulty for the pipeline companies is that while the regulations spell out a desired result, they do not, however, detail how this result is to be obtained. This has led to a plethora of ways for implementing the sliding mile method, and even more for clustering approaches. In light of this, certain practices have become acceptable and were adequate when class location determinations were performed manually. Emphasis now is shifting to automated studies for better accuracy and cost effectiveness.

An inaccurate class location assessment can be quite costly to a large transmission company. First, the company may be fined by the government for non-compliance if an error is made in determining the class location of a line section. Second, the pipeline company could spend millions of dollars needlessly by replacing good line pipe and equipment. Finally, resources that could be used to meet other objectives are committed to an unnecessarily lengthy class location project.

Advantage: Automation

Several methods can be used to automate class location assessments: (1) purely tabular computations, (2) Computer Aided Drafting (CAD) assisted methodologies, and (3) integration with Automated Mapping/Facilities Management (AM/FM) and Geographic Information Systems (GIS). Each offers dependable, accurate, and economical advantages to its user.

Computerized Tabular Computations

Computerizing tabular computations essentially is the most basic method for automating class location studies. It speeds up tedious manual tasks of tabulating buildings and assigning classes. Typically, a pipeline is divided into 1/8 mile segments and the number of buildings is tallied for each segment. The sliding mile is calculated by summing eight consecutive 1/8 mile segment tallies, and assigning the class accordingly. Then the sliding mile is moved down by one segment and the process is repeated until the entire has been evaluated and classes assigned. Thus, for any given increment, a sliding mile is processed eight times since a sliding mile passes over the segment in question 1/8 mile at a time and eight classes are assigned. Highest class assigned becomes the final class for that portion.

This means that a 1,000 mile pipeline will have class locations calculated 64,000 times. Clearly, this is a tedious, repetitious process which can consume considerable time and resources. However, it can be greatly enhanced and speeded up by using any structured programming language such as C, or with a database language such as those which are supplied with most xBase systems. Greater accuracy of class locations is possible since calculations can be done on a building-by-building basis rather than 1/8 mile segments.

CAD Offers Graphical Interface

CAD assisted methodologies can greatly improve tabular computations. They can provide a graphical interface for entering building locations, and a graphical output for depicting resulting class locations. Completeness of building count can be substantially improved by digitizing pipeline alignment and building location data from aerial photographs. Generating a graphical output relative to these aerial photographs provides an ideal format for analyzing results of class location determinations. Aerial photography also can be updated periodically, usually every five years in areas of average development.

AM/FM/GIS Maximizes Accuracy

Automated Mapping/Facilities Management (AM/FM) and Geographic Information Systems (GIS) offer rapid, accurate access to large amounts of other data which pipeline companies gather and maintain. These data may include pipe specifications, land ownerships, and strength test results, and are supported by digital mapping which shows both pipeline facilities and non-pipeline features such as roads and water courses.

AM/FM/GIS also supports new imaging technologies for displaying digital aerial photography. Digital aerial photographs can be produced by scanning film-based photographs or using a digital aerial camera. Digital photography can be inexpensive to gather, and therefore can be updated more frequently. Also, a digital aerial photograph can be used as a background for a digital map or alignment sheet. Significant detail, particularly buildings, can be shown in the photographs.

AM/FM/GIS can be used to digitize building locations from aerial photography in the same manner as CAD systems use photographic prints. Computing class locations with an integrated package provides data which can be analyzed along with other information provided by AM/FM/GIS. For example, if pipe data for an area in which the class location has changed is analyzed with this method, the Maximum Allowable Operating Pressure (MAOP) can be calculated automatically and relayed to the database for output as a printed report.

Also, "what if?" scenarios can be proposed to focus on possible changes. For example, if building is underway along a section of line pipe, a pipeline company can determine how many more buildings can be built before the class changes for that segment and when that will likely occur.

The technology to perform automated class location studies is available to gas transmission companies is available today. Class locations can be automatically maintained in relational database tables for analysis with other data such as types of line pipe, maximum operating pressures, and strength test records. Automatic generation of maps is possible within minutes after completing class location computations.

The use of automation methods for these class location studies will continue to increase as safety guidelines are tightened and compliances require more accuracy. Gas transmission companies will seek the most economical solutions for complying with future mandates. The question is not whether they can afford to automate class location studies, but rather can they afford not to utilize a more accurate, reliable means? Once that question is resolved, it must be determined if it is economically feasible to invest resources in developing in-house software or to purchase computer-ready software which is ready to be implemented.
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Author:White, R. Michael; Hughes, R. Harvey
Publication:Pipeline & Gas Journal
Date:Sep 1, 1994
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