Aquashield to Mitigate Water Ingress of Gas Pipes

Transcription

1 IGEM Young Persons Paper Competition 2017 Aquashield to Mitigate Water Ingress of Gas Pipes Assistant Engineer Technical Development Section, Distribution Operation Department The Hong Kong and China Gas Company Limited 1 P a g e

2 Abstract Water ingress in gas pipe can cause interruption of gas supply to a considerable amount of customers. Due to congested underground condition, extraction of water from gas pipe could be very difficult and sluggish. For conventional practice, water ingress incident is not notified until customer reports gas supply interruption to the utility. There is a lapse of time between start of water ingress and first report of supply interruption and subsequent isolation by operatives. The longer the lapse time, the greater the extent of gas network is affected by water ingress. It is time consuming to locate the water ingress point and hence difficult to confine the affected area to minimal. In such situation it is crucial to compete with time to avoid water spread out in the gas network and to save the resources for subsequent de-watering and gas resumption. To address the above concern, an automatic shut off device Aquashield is designed to safeguard the gas network by confining the water ingress, if happened, automatically. This paper introduces the design features, working principle, functional verifications and the application in Hong Kong of Aquashield which ensures a more reliable gas supply to the society. 2 P a g e

3 1. Introduction 1.1 Causes of Water Ingress in Hong Kong Hong Kong is a busy and densely populated city. Apart from the road surface where buildings and traffic are congested, the underground is also suffocated with utility pipework. Fig. 1 Small clearance of water pipe and other utilities Due to the congested condition in underground, every utility will try their best to squeeze out any possible space available to accommodate their pipes. Gas mains and water mains are always neighbor to each other as their buried depths are similar. To avoid water ingression to gas mains, there is a requirement of at least 300mm clearance between the two types of pipe, but in reality, sometimes the pipes have less clearance due to space limitation. The close proximity of pipes and vigorous excavation activities becomes one of the main reasons why gas pipe may suffer from water ingress due to leaking water pipe. When there is water pipe burst near gas main, the high pressure from water jet (usually 6-8bars) together with sand and rock create grinding effect which will damage the nearby gas pipe over time. The water jet will then entered the eroded gas pipe and cause gas supply interruption to considerable amount of customers. 3 P a g e

4 Gas Pipe Water Pipe Fig. 2 Photo of gas pipe damaged by water jet from adjacent leaking water 1.2 Current Challenges of Handling Water Ingress of Gas Pipe in Hong Kong Time Lapse Between Gas Interruption Report Time and Actual Water Ingress Actual time of water ingress is usually unpredictable. Water ingress usually is noticed until customer reported gas interruption and it shows that water ingress to gas pipe already affect certain amount of customers before any action taken. The longer the lapse time, the greater the extent of gas network is affected by water ingress. Minimizing the lapse time between the actual water ingress and the incident report time on gas interruption is very crucial to contain the incident, as well as arrange resources for de-watering and gas resumption Action to Contain the Affected Area Due to the quick spread out of water ingress to gas network, for current practice, huge amount of work force and time are required to locate the exact water ingress point. Immediately upon arrival on site, the emergency team has to determine the extent of the affected area by checking the syhons, saddles, risers and governor along the affected area. The team will check site environment as well as the time and location of customer report as hints. Once the situation is uncontrollable, gas valves and risers will be closed to confine the affected area which may cause gas interruption to customer Locating Water Ingress Point and Follow-up Actions 4 P a g e

5 The possible location of water ingress has to be identified through checking the nearby governors and syphons, if any. Besides, the ground conditions and speed of ingress water may provide hints for identifying the water ingress nature and location. It usually takes time to identify the exact location of water ingress if the water leak is too small to be detected. Once identify the ingress point, dewatering and repairing of gas pipe and subsequence gas resumption also require huge amount of resources and time which depends on the pipe material and area affected. 5 P a g e

6 2.Aquashield 1 st Generation (Metal Iron Body) 2 nd Generation (PE Body) PE Cross Fitting Counter Rods Metal Seat (Magnetized Steel) Shut-off Plate Cantilever Guide Rod (Stainless Steel) Buoy Fig. 3 Internal Structure of Aquashield 6 P a g e

7 To mitigate the effect of water ingress to gas pipe and solve the above challenges, Aquashield is designed as an automatic shut-off device which blocks water ingress in gas pipe at the very first place, far earlier than customer report. The main purpose of Aquashield is to block the flow of the water in pipe wherever the water flows from automatically. It can effectively confine the affected area by water ingression before anyone noticed so the interruption brought to customer can be minimized. Moreover, since affected gas network is reduced, the workforce and time for following actions like de-watering and gas resumption can be further reduced. There are two types of Aquashield, the metal one as an earlier version while the PE one is the latest design with a few improvement features. Simpe is the best! The design of Aquashield consists of all mechanical parts housing in a PE cross fitting, which include the counter rods, shut-off plate, cantilever, metal seat, PE adaptor, guide rod and buoy. It creates a self-triggerred water blocking mechanism by buoyancy principle, lever system and magnatic force. 2.1 Working Principle of Aquashield Fig. 4 Aquashield Mechanism Aquashield is designed to be installed in low pressure distribution network. Its PE spigot ends making it able to be fused on the PE pipe directly. At normal circumstance, Aquashield is fully opened to allow gas flow Assuming water ingress from either side of the gas pipe and the water enters the Aquashield, the water blocking mechanism will be triggered automatically by the buoyancy force of ingress water exerting to the buoy. 7 P a g e

8 2.1.3 As water level in Aquashield increases, the buoy keeps rising. The guide rods ensure the buoy moving in a vertical upward displacement. Fig.5 Aquashield Shut-Off Mechanism Once the buoy rises up to certain position, the systems hit on the counter rods and push the shut-off plates laterally to the metal seats in parallel When the shut-off plates are closed to the metal seats, the permanent magnets embedded in the plates will be attracted to the metal seats made of magnetized steel which closes the Aquashield and water flow into the downstream. Fig. 6 Aquashield Re-opened Before reset the Aquashield back to the open position, a suction tube is inserted into the Aquashield to extract water from the Aquashield cavity. Then a rod is inserted to push the buoy down to the original position. The 8 P a g e

9 shut-off plates will be separated from the metal seats and open the pathway for gas resumption. 2.2 Design Considerations Material Selection The self-triggered shut off device is initiated by the buoyancy force exert on the buoy once water accumulate in the Aquashield cavity. Therefore, the components that lifted up by buoyancy force were made of light-weight materials. The floating element itself was good in buoyancy properties, which is made of expanded Polystyrene foam. Apart from the metal seats made of steel due to its magnetized properties, other components are made of light weight plastic materials like POM, PC, as well as Aluminium. Besides, the materials are rigid to be able to withstand water and gas pressure, as well as good in corrosion prevention way Blockage of Water Direction and location of water ingress are unpredictable, hence the Aquashield is designed to block the water flow no matter which direction it comes from. The two shutoff plates in symmetrical design allow the tight shut off against water ingress from both directions Easy to Install and Operate Aquashield can be installed in existing gas network. It should be able to be installed easily without the modification need of existing gas supply. The operation of Aquashield should be simple and reliable. Its internal parts are maintenance free and easy to be reset. 9 P a g e

10 2.3 Special Features of Aquashield PE Cross Fitting embedded with Metal Seats Fig. 7 Aquashield PE Cross Fitting with a pair of metal seats In order to avoid special made fitting and reduce on-site fabrication, a PE cross fitting which is prefabricated with mechanical parts in factory for ready connection to existing PE network simply by electrofusion. A pair of metal seats made of magnetized steel is embedded in the PE cross by interference fit which acts as a valve seat to the shut-off plate. Once the magnets in the plate brought to the metal plates, a strong magnetic force attract both together to block the water flow from either direction Shut-off Plates Fig. 8 Shut off Plate Assembly The plates are made of polycarbonate embedded with 20 permanent magnets evenly distributed at the outer ring of the plate to create a magnetic force to the metal seats. 10 P a g e

11 Polycarbonate is chosen as the material because of its high Impact Strength. By stress analysis simulation with gas and water pressures exert to the plate, the results show that the plate is able to withstand the forces without failure and deformation. Fig. 9 Stress Analysis of Shut-off Plate The permanent magnet is made of Neodymium N35. The adhesive force of each magnet is about 4.6N and the total magnetic force of the plate is around 92N Cantilever System and Counter Rods Counter Rods Fig. 10 Cantilever and Counter rods The back of Shut-off plate is attached to a cantilever system which ensures the plates move in vertical direction. The cantilever is made of Polyoxymethylene (POM) with light weight, high stiffness, low friction, and excellent dimensional stability. The counter rod hits on the cantilever and pushes the plate outward. No matter water ingress from either side of Aquashield, the plate can effectively block the water ingress to the downstream of gas network. 11 P a g e

12 2.3.4 Buoy and Guide Rods The buoy is made of Expanded Polystyrene (EPS) which has strong floating property due to its low density and weight; the buoyancy force is able to lift up the moving mechanical components of Aquashield. The buoy is used to lift up and trigger Aquashield once there is water accumulates in the Aquashield. To ensure it floats up in a vertical direction, a pair of guiding rods is used as the guide. Buoy Fig.11 Buoy and Guide Rod 12 P a g e

13 3.Functional Test Fig. 12 Aquashield Fabrication Aquashield is fabricated and pre-assembled in factory, the mechanism is proofed by inhouse test which simulating water ingress from either side of the network. The test result shows that Aquashield can be triggered immediately when water accumulates and successfully blocks the pathway of water into gas network. Water Ingress in one side of Aquashield The buoy rises gradually and brings the shut-off plates to the metal seats The shut-off plates block the water flowing to the other side effectively Fig. 13 Aquashield In-house Testing 13 P a g e

14 4.Conclusion Maintaining a reliable gas supply to customers is always our mission. We try all possibilities to reduce any chance of gas interruption. The design of Aquashield is an innovative product that can immediate react to water ingress in the first place, hence reduce the impact of gas interruption by blocking ingress water spread out to the gas network and quickly confining the incident area to minimal. Its simple mechanism ensures the reliability throughout its design life. At the moment the new generation Aquashield is undergoing type tests to ensure a 50 years design life. It will be available to the industry soon this year. 14 P a g e

15 Appendix Testing Requirements of Aquashield To ensure the quality of Aquashield, it is tested to conform to EN1555 Part3, as well as the following additional tests would be conducted: External Leak Tightness Operability Shut-off Strength Calculations Force of Gas Pressure exerted on the Shut-off plate: Area of Shut-off Plate x Gas Pressure = 84.8N Total Magnetic Force of Shut-off Plate: Magnetic Force x No. of Magnet = 92.6N Safety Factor = Force of Gas Pressure/ Total Magnetic Force = P a g e

16 Lever Force Required Lever Force for Both Sides (F) = M (L1/L2) (g) (2) = 8.77N Aquashield Moving Mass = 1.45kg Gravity Force = 14.20N Total Lift-up Force = 22.98N 16 P a g e

17 Buoyancy Force Buoy Volume = mm 3 Buoyancy Force (F B ) = 38N Net Buoyancy Force = 15.02N Safety Factor = 1.65 Volume % = Cavity Volume/ Bouy Volume = 2.91% Push Force when Full Water = 15.02N Push Force = (L2/ L3) (Net Buoyancy Force/ 2) = 4.04N -END- 17 P a g e