IBP1294_09 ASSESSING THE EFFICIENCY OF AUTOMATICALLY CONTROLLED VALVES (ACV) FOR PIPELINE SECTIONING Leandro S. da Veiga1, Marcos J. M. da Silva2, João Paulo de B. Leite3, Renata N. R. dos Santos4, Rodrigo B. O. Jardim5, Thiago C. do Quinto6 Copyright 2009, Brazilian Petroleum, Gas and Biofuels Institute - IBP This Technical Paper was prepared for presentation at the Rio Pipeline Conference and Exposition 2009, held between September, 22-24, 2009, in Rio de Janeiro. This Technical Paper was selected for presentation by the Technical Committee of the event according to the information contained in the abstract submitted by the author(s). The contents of the Technical Paper, as presented, were not reviewed by IBP. The organizers are not supposed to translate or correct the submitted papers. The material as it is presented, does not necessarily represent Brazilian Petroleum, Gas and Biofuels Institute’ opinion, or that of its Members or Representatives. Authors consent to the publication of this Technical Paper in the Rio Pipeline Conference Proceedings. Abstract In order to mitigate the effects caused by the rupture of a gas pipeline and following ASME B 31.8 recommendations, block valves are installed in these structures. However, many transportation companies also install devices capable of infer the occurrence of an accident in a gas pipeline. The most common devices are the ones that actuate when pressure in gas pipeline reaches a low value early established (PSL) and those which close valves due to high rate of pressure drop (line-break). Line-break has the function of identifying as fast as possible the occurrence of a rupture in a gas pipeline by high rate of pressure drop in that line. Although PSL presents a later actuation when compared to the line- break, it represents redundance to the line-break system, since it is able to isolate the segment where the accident happened even if other devices or the operator had not done it before. The growing of gas pipelines transport capacity has been generated transients capable of causing an erroneous shut down of the shut down valves (SDV). The aim of this paper, therefore, is to present how the operational limits of SDV can be overcome with remote operation using SCADA System. 1. Introduction Pipelines are generally the most economical solution to transport large quantities of natural gas over land, and consequently, the most employed worldwide. The oldest long-distance interstate gas lines date to the late 1920s. Particularly, the advances in welding technology join steel pipes in the 1920s made it possible to construct leakproof, high-pressure, large-diameter pipelines (Kiefner, J. F, et al). Manufacturers began to form pipe with electric resistance- welded or flash-welded processes, a significant advance in the reliability of the longitudinal seam, and the electric arc girth weld was developed, a significant improvement over acetylene girth welds in use previously. Simultaneously, the industry began to develop material-quality standards and consensus standards for the safe design, construction, operation, and maintenance of pipelines (CASTANEDA, C. J, et al). Yet, the production of natural gas in Brazil only started around the early 60´s, in the northeast of the country, boosting the development of major industry projects of the region. Hence, in 1974 the first interstate gas pipeline was constructed, with 235 km connecting the states of Bahia and Sergipe. The Brazilian gas pipeline network started then to develop but restricted to the northeast coast. Later, between 1980 and 1995, with the discovery of reserves in the Campos Basin, the consumption of natural gas increased significantly, to about 2.7% of the domestic energy matrix, promoting the fast development of the southeast gas pipeline network. In 1999, with the conclusion of a 2539 km gas pipeline connecting Brazil to Bolivia, with capacity for transporting 30 million cubic meters per day, there was a sharp increase in the domestic supply of natural gas, raising its participation in the domestic energy matrix to nearly 10%. In addition, the discovery of new reserves over the last few years has opened new perspectives for rising domestic ______________________________ 1 Control and Automation Engineer – TRANSPETRO 2 Master, Mechanical Engineer – TRANSPETRO 3 PhD, Civil Engineer – TRANSPETRO 4 Master, Civil Engineer – TRANSPETRO 5 Civil Engineer – TRANSPETRO 6 Chemical Engineer – TRANSPETRO Rio Pipeline Conference and Exposition 2009 consumption. The country’s gas pipeline network reached currently nearly 7000 km and has some other 1000 km under construction, mainly to connect the northeast to southeast gas pipeline network. The design of the Brazilian gas pipelines has followed ASME B31.8 standard and complying with Brazilian NBR 12712 standard, being the latter strongly based on the American standard. Both standards encompass, in addition to gas pipeline construction aspects, others related to operation and maintenance. In particular, criteria for the spacing of blocking valves to enable pipeline sectioning. This allows, for instance, the isolation of certain portion of a pipeline ensuring that maintenance can be safely carried out and also limiting inventory losses in case of maintenance or accidents. The code recommendations are restricted to the spacing of such valves and not making any allusion to its specific type and operation features. These are usually shutoff valves manually operated. However, in order to add local intelligence units capable of providing more safety to the gas pipelines and further limiting the inventory losses, concepts of emergency shutdown systems (ESD) were embodied in the sectionalizing block valves of gas pipelines. A particular type of valve was designed to allow the quick full closure activated by preset pressure triggers. These automatically controlled valves (ACV) were mainly intended to replace the manually operated valves in strategic places, as for example, areas of difficult access and also to isolate an upstream or downstream gaseous inventory. Later, with technological advances in instrumentation, data gathering units and communication systems the operation and control of pipelines were gradually shifted to highly equipped remote operation control centers (OCC) and also the sectionalizing block valves were designed to operate remotely, known as remotely controlled valves (RCV). All the three types used for pipeline sectioning have their technical and/or operational up and down sides, so that the choice has been left to the judgment of the operators. Petrobras, the Brazilian pipeline operator in the 1970s, aware of its little experience and limited resources for monitoring the gas pipelines, decided to adopt mainly automatically controlled valves for gas pipeline sectioning. Initially, on/off valves with low pressure triggers, but currently about 97% of gas pipelines contain shutdown valves featuring actuators with double triggers: low pressure and sharp pressure drop. While the Brazilian gas pipelines network was operating with low and steady flows, substantially under its capacity, the ACVs rendered an elusive impression of safety, which served particularly to ease the worries of environmental regulators. However, the gas consumption is growing quickly and operation complexity is very different from that of the 1970s. The gas pipeline network has become an essential part of the Power system of the country. Since the Brazilian production is mainly offshore, the pipeline network is consisted mainly of trunk lines along the coast line, with no redundancy or storage facilities for contingency situations. As a consequence of such changes in operation scenario, apart from few particular cases, the ACVs are no longer suitable for pipeline sectioning, resulting in many undesired and spurious valve closure and supply failure. The arbitrary use of ACVs has become a threat to energy supply system and must be reviewed. In fact, it was observed that in the few incidents that the ACVs should close, they fail to actuate. Natural gas consumption has grown steeply in Brazil, encouraged by federal government programs, reaching the mark of 60 million m³/day in 2008, with a forecast for 2012 of 130 million m³/day. In order to meet this demand, besides investing in new forms of natural gas transportation such as LNG and CNG, Brazil has continuously invested in new gas pipelines as well as in retrofitting those already in place to the enhance transportation capacity. There are, currently, more efficient ways to ensure safety and prevent supply failures, and the local operators are moving towards shifts in operational policies to accommodate the higher demands in the pipeline network complexity. The new National Operations Control Center, provided with some of latest technologies for simulations and remote monitoring, is capable of more precise diagnosis and actions, allowing it to remotely oversee and operate gas pipelines and also compression stations as a unique system in a safety manner. 2. Pipeline Sectionalizing Block Valves As mentioned before, the shutoff valves employed for pipeline sectioning may be classified in three types according to the way they are controlled and/or operated: manually operated valves, automatically controlled valves (ACV) and remotely controlled valves (RCV). 2.1. Manually Operated Valves The manually operated valves generally represent lower costs and are the most employed for intermediate sectioning valves. In the case of large diameters or buried underground