Pipeline Integrity Valve Spacing Engineering Assessment (CDN) Grande Prairie Mainline Loop 2 (Progress Section) NPS 36

Transcription

1 APPROVALS Library: EDMS General Page 1 of 10

2 TABLE OF CONTENTS APPROVALS 1 1. PURPOSE BACKGROUND VALVE SPACING ASSESSMENT APPROACH OPERATIONS AND MAINTENANCE CONSIDERATIONS... 6 a. The nature and amount of fluid released due to a blowdown or a failure... 6 b. The time to blowdown the isolated section... 7 c. The effects on the inhabitants of the area from gas release... 7 d. Continuity of service... 7 e. Operating and maintenance flexibility... 7 f. Future development within the valve spacing section... 7 g. Significant conditions that could adversely affect the operation and security of the pipeline... 8 Proposed Actions EFFECT ON THE PUBLIC SAFETY... 8 Proposed Actions CONCLUSIONS RESPONSE PLAN REFERENCES Regulations, Codes and Standards TransCanada Procedures and References Industry Papers and Publications Library: EDMS General Page 2 of 10

3 1. PURPOSE TransCanada PipeLines Limited (TransCanada) on behalf of NOVA Gas Transmission Ltd. (NGTL) provides the Engineering Assessment (EA) for the valve spacing on the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36. A Class 2 site located between the two mainline block valves NW10-0-1SV2- GPM (NW10) and GPM143-2-BV (GPM143) requires the valve spacing to be a maximum of 25 km with an adjustment factor of 25%, as per Canadian Standards Association (CSA) Z Clause in absence of an EA. In accordance with CSA Z Clause 4.4.4, this EA demonstrates that the existing mainline block valve spacing, of approximately 31.7 km, is adequately safe with the recommendations made in this EA. 2. BACKGROUND A class location change site was identified on the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36 between mainline block valves NW10 and GPM143, as outlined in Table 2.1, below. Due to the class location change, the requirement for valve spacing has also changed, according to CSA Z Clause and Table 4.7. The existing spacing between mainline block valves NW10 and GPM143 is approximately 31.7 km, while the required valve spacing for a Class 2 location is 25 km in absence of an EA. Figure 2.1 shows the valve section under consideration, with the mainline block, side, and crossover valves and the Class 2 location section of the pipeline labeled. The relevant crossover and side valves within the valve section are described along with the mainline block valves in Table 2.2 below. Figure 2.2 and Figure 2.3 shows a schematic of the side valve and crossover valve, respectively. Table 2.1: Pipeline Section with Change in Class Location Designation and Valve Section Details Line Name Grande Prairie Mainline Loop 2 (Progress Section) NPS 36 Outer Diameter (NPS) MOP (kpa) Valve Section NW10 to GPM143 Class Location Change Section 6734 m to 8170 m Class Location Change Section Length (m) 1436 Change in Class Location Designation Class 1 to Class 2 Existing Valve Spacing (km) 31.7 Table 2.2: Mainline block, Crossover, and Side Valves in the Valve Section Valve Name Valve Function Valve Type Valve Mechanism Emergency Shutdown Mechanism Available NW10 Mainline block Ball Automatic Yes GPM143 Mainline block Ball Automatic Yes POG10-0-1SV2-GPM (POG10) Side Ball Manual No GPM143-1-U2 Crossover Ball Automatic Yes Library: EDMS General Page 3 of 10

4 Figure 2.1: Location of Valves and the Class 2 Location Site on the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36 Library: EDMS General Page 4 of 10

5 Figure 2.2: Schematic of the Side Valve POG10-0-1SV2-GPM Figure 2.3: Schematic of the Crossover Valve GPM143-1-U2 Library: EDMS General Page 5 of 10

6 3. VALVE SPACING ASSESSMENT APPROACH CSA Z Clause 4.4 describes the requirements for valve location and spacing. This valve spacing EA for the pipeline will be carried out in accordance with CSA Z Clause 4.4.4, which outlines the following factors to be considered to determine the proper valve spacing: a. The nature and amount of fluid released due to a blowdown or a failure; b. The time to blowdown the isolated section; c. The effects on the inhabitants of the area from gas release; d. Continuity of service; e. Operating and maintenance flexibility; f. Future development within the valve spacing section; g. Significant conditions that could adversely affect the operation and security of the pipeline. In addition to these operations and maintenance considerations, it is also necessary to consider the effect of increased valve spacing on public safety. The two risk measures used by TransCanada to evaluate public safety are Individual Risk (IR) and Societal Risk (SR). IR is the annual probability of a fatality to an individual located on top of the pipeline. It is a risk assessment performed for every pipeline. SR is the annual risk to a group of structures, or a settlement, due to its proximity to the pipeline. Combined, IR and SR will capture the acceptability of risk from a safety perspective for both sparsely and densely populated areas. Both of these risk measures are then compared to the industry accepted risk criteria to determine the acceptability of risk. In the following sections, the above-mentioned considerations will be addressed for the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36 between mainline block valves NW10 and GPM OPERATIONS AND MAINTENANCE CONSIDERATIONS a. The nature and amount of fluid released due to a blowdown or a failure The service fluid in the pipeline is sweet natural gas. If a blowdown is required for planned maintenance activities, a transfer compressor will be utilized to draw the valve section down to 1000 kpa. The remaining gas would then be vented to the atmosphere. At this pressure, the volume of gas vented would be as follows for the existing valve spacing and the CSA Z required valve spacing: 31.7 km valve spacing: m km valve spacing: m 3 In the event of an emergency blowdown, such as an emergency repair, the volume of the gas released from the line would be dependent on the pressure in the line. At maximum operating pressure (MOP), the volume of gas vented for the two compared valve spacing distances, assuming that the mainline block valves have closed, would be: 31.7 km valve spacing: m km valve spacing: m 3 Library: EDMS General Page 6 of 10

7 b. The time to blowdown the isolated section For both the existing valve spacing of approximately 31.7 km and the required Class 2 location valve spacing of 25 km, the blowdown times would be less than 8 hours. It should be noted that this applies to both blowdowns with and without silencers. The implication of the blowdown time being less than 8 hours is that the blowdown could be performed during the normal working hours. c. The effects on the inhabitants of the area from gas release According to the TransCanada Operating Procedure (TOP) Pipeline Operations (Gas Handling), local landowners and relevant government agencies will be advised at least 48 hours prior to any planned blowdown operation. A silencer would be installed (if planned maintenance is to occur) at NW10 or GPM143 if there were residents within 750 m of either valve site. There are no residents located within 750 m of either NW10 or GPM143. d. Continuity of service In the case of either planned or unplanned maintenance activities between NW10 and GPM143, the valve section would need to be taken out of service temporarily. Since this pipeline has parallel pipelines, flow is able to be diverted around the valve section and service would not be interrupted for the temporary period. Furthermore, any changes to the valve spacing would not have any impact on the continuity of service for this pipeline. e. Operating and maintenance flexibility Current system design has two receipt meter stations tied to the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36. However, both receipt meter stations have tie-ins to other pipelines. Therefore, the existing valve spacing has no impact on the operating or maintenance flexibility of this pipeline. f. Future development within the valve spacing section The existing valve spacing of approximately 31.7 km for the Grande Prairie Mainline Loop 2 (Progress Section) NPS 36 is not in accordance with CSA Z Clause and Table 4.7. This EA was performed to evaluate the safety impact of the existing valve spacing, as per CSA Z Clause The Class 2 location site driver is the presence of a hazardous industrial installation. It is not anticipated that any section of pipe in this valve section will undergo further class location upgrades, as there is no anticipated residential development of over 46 dwelling units in the area. It is not anticipated that further development in the area will have additional impacts on this valve section. Library: EDMS General Page 7 of 10

8 g. Significant conditions that could adversely affect the operation and security of the pipeline Conditions that may affect pipeline operation are addressed above in sections d. and e. In addition, the valves operating incorrectly would pose another significant condition that could adversely affect the operation of the pipeline for this valve section. It is thus proposed to ensure that all valves within the valve section are winterized annually according to TransCanada s valve stem winterizing procedure before the winter season each year. Proposed Actions Starting in 2017, ensure that the mainline block valves, NW10 and GPM143, the side valve POG10, and the crossover valve, GPM143-1-U2, are winterized annually according to TransCanada s valve stem winterizing procedure before the winter season each year. The proposed action is to ensure the reliability of the valves and to maintain good working condition of the existing valves. 5. EFFECT ON PUBLIC SAFETY The effects of changing the valve spacing on public safety are minimal if the valve spacing is more than 10 km, as shown in the Pipeline Research Council International (PRCI) report Valve Spacing Basis for Gas Transmission Pipelines. This is because the greatest consequence of a pipeline rupture occurs within the first 30 seconds after the failure and the subsequent ignition. This initial stage following the failure will be independent of the valve spacing, therefore making the effects on the population independent of valve spacing. The following three arguments are made by the PRCI report as to why the impact of valve spacing is minimal on the population: 1. The primary consequence of a natural gas pipeline failure is related to the effects of thermal radiation exposure of the fire ball following ignition. The hazard zone is largest immediately following ignition. Reduction of valve spacing does not diminish the size of the hazard zone immediately following ignition. 2. The jet fire that follows the initial release phase after ignition has a smaller hazard zone. This jet fire could hinder emergency personnel from entering the site so it is important to reduce the duration of a fire. A key factor in reducing jet fire duration is cutting off fuel supply by quickly closing proximate valves. Automatic shutoff valves (ASVs) and remotely controlled valves close more quickly than manual valves. The mainline block valves, NW10 and GPM143, and the crossover valve, GPM U2, are ASVs. The side valve, POG10, is a manual valve. Thus, it is recommended to install an ASV at POG10 by the end of 2017 to ensure quicker valve closure in the event of an emergency. 3. According to the PRCI study: as the valve closure time increases beyond 7.5 minutes (10 minutes is the practical minimum valve closure time), the risk level is independent of valve spacing and thus valve spacing does not affect the risk to the public. Changing the valve spacing, therefore, will not affect the risk in this case. In the IR and SR calculation, the consequence of pipeline failure is determined based on the hazard zone, which is independent of valve spacing as demonstrated above. Therefore, the reduction of valve spacing will not have any impact on IR and SR. Library: EDMS General Page 8 of 10

9 Proposed Actions An ASV should be installed at side valve POG10 by the end of 2017 to ensure quicker valve closure in the event of an emergency. Since there is no risk reduction with a decrease in valve spacing, it is proposed that the mainline block valve spacing is maintained at the existing spacing of approximately 31.7 km. 6. CONCLUSIONS A valve spacing EA was performed for the section of pipeline between mainline block valves NW10 and GPM143 of the Grande Prairie Mainline Loop 2 (Progress Section). A section of pipe within this valve section has changed from a Class 1 location to a Class 2 location, requiring a valve spacing of 25 km with an adjustment factor of 25%, as per CSA Z Clause and Table 4.7. However, CSA Z Clause allows for the completion of an EA to demonstrate that the existing valve spacing of approximately 31.7 km is safe for the surrounding population and to ensure it will not adversely affect the operation and maintenance activities on this pipeline. This EA demonstrated that: There is no increase of risk to the population due to the existing valve spacing; The reduction of valve spacing will not have any impact on IR and SR; There is no adverse impact to operation and maintenance activities on the pipeline with regard to the existing valve spacing. Recommendations to increase reliability of valves and reduction in valve closure times are recommended to enable emergency response 7. RESPONSE PLAN TransCanada has determined the appropriate approach to maintain safety for the valve section. The following actions will be implemented for the site to achieve adequate levels of safety and reliability: 1. Starting in 2017, ensure the mainline block valves, NW10 and GPM143, the side valve POG10, and the crossover valve, GPM143-1-U2, are winterized annually according to TransCanada s valve stem winterizing procedure before the winter season each year; 2. An automatic shutoff valve will be installed at POG10 by the end of 2017; 3. The valve spacing will remain at approximately 31.7 km. Library: EDMS General Page 9 of 10

10 8. REFERENCES Regulations, Codes and Standards The jurisdictional regulations and legal requirements that apply to this record are: Canadian Standards Association (CSA) Z Oil and Gas Pipeline System, Clause 4.4 TransCanada Procedures and References The TransCanada procedures, guidelines, reports and documents that apply to this report are: CDN-GAS-IMP Canadian Gas Pipeline Integrity Management Program (CDN) (EDMS No ) TED-MECH-VS-GAS Gas Valve Spacing Directive (CDN US MEX) (EDMS No ) TER-RISK-CON Thermal Radiation Consequence Models for Natural Gas Pipelines (CDN US MEX) (EDMS No ) TOP Pipeline Operations (Gas Handling) (CDN US MEX) (EDMS No ) Industry Papers and Publications The papers and publications that apply to this report are: Eiber, R. et al (2000), Valve Spacing Basis for Gas Transmission Pipelines, Pipeline Research Council International, Report no. L51817 Health and Safety Executive (HSE), Reducing Risks, Protecting People, 2001 British Standards Institute (BSI) BSI , Code of practice for pipelines Part 3: Steel pipelines on land Guide to the application of pipeline risk assessment to proposed developments in the vicinity of major accident hazard pipelines containing flammables Supplement to PD , 2009 Library: EDMS General Page 10 of 10