USE OF RISK AND ENGINEERING ASSESSMENTS TO IMPROVE SAFETY IN CLASS LOCATION CHANGES - SOUTH AMERICAN CASE STUDY

摘要

In South America, there is not a unique standard that regulates the Design, Operation, Maintenance and Integrity Management of Pipelines. Most of the countries had developed their own regulations and standards based mainly on the ASME Standards. These standards (like ASME B31.8 and ASME B31.8S) are being developed and updated considering the experience of different operators, but the results not always consider the difficulties in terms of social and cultural aspects of construct and operate pipelines in South America. Expansion of existing residential and commercial areas, or the construction of new developments near these pipelines can change a Location Class 1 into a Class 2 or Class 3 location. This development is not always predictable, besides the efforts of the South American Pipelines Operators made to coordinate this expansions with the local authorities, the growth in these countries are not well planned and the Operators are forced to face the situation without anticipation and without a backup of the regulations. Then the operators are unexpectedly left with a pipeline that no longer meets the requirements of its design code. ASME B31.8 establishes alternatives to adequate this changes into the design code: reducing the maximum allowable operating pressure of a pipeline, pipeline replacement increasing the wall thickness or by re-routing it away from the population. Those alternatives have high costs and significant operational difficulties, especially when the social conditions are not favorable. Additionally, some of these options do not even effectively solve the problem. Lowering operating stress levels do not always address the higher risk levels or safety concerns caused by the change in class. Increasing wall thickness, can lower probability of failure for a pipeline but not for all the combinations of threats, which depend on site specific conditions. The Pipeline Integrity Management System shall address all the threats as it is specified in ASME B31.8S, ensuring human safety as its primary objective. Third Party Damage is an important threat which in most of the pipelines around the world has caused the larger number of incidents. To manage this threat, risk assessments have been employed successfully to determine risk based on land use zones, proximity to utilities, alignment markers, one call and dig notification, surveillance intervals, among other variables. Calculating the risk to a specific pipeline near to a population after the mitigation activities are implemented, it may be shown that this pipeline has no more risk than other pipelines operating entirely in accordance with the design codes. Risks must be maintained "as low as reasonably practicable", using cost benefit analysis to achieve these criteria. The reduction of the risk is accomplished by implementing additional mitigation plans, allowing to effectively use maintenance resources in areas where they will have the highest impact on risk. This paper shows how risk and engineering assessments and their consequent mitigation plans may be used to justify the safe operation of a pipeline without changing its original operating pressure following a change of class designation, exemplified with a case study from South America.