“aquashield” to mitigate water ingress of gas pipes paper - example 3.pdf · “aquashield”...

“Aquashield” to Mitigate Water Ingress of Gas Pipes Chiu Wai Ting, Rita

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IGEM Young Persons Paper Competition 2017

“Aquashield”

to Mitigate Water Ingress

of Gas Pipes

Chiu Wai Ting, Rita

Assistant Engineer

Technical Development Section, Distribution Operation Department

The Hong Kong and China Gas Company Limited


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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.


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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.

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.

Fig. 1 Small clearance of water pipe and other utilities


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1.2 Current Challenges of Handling Water Ingress of Gas Pipe in Hong Kong

1.2.1 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.

1.2.2 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.

1.3.3 Locating Water Ingress Point and Follow-up Actions

Gas Pipe

Water Pipe

Fig. 2 Photo of gas pipe damaged by water jet from adjacent leaking water

pipes


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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.


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2.Aquashield

1st Generation (Metal Iron Body)

2nd

Generation (PE Body)

Counter Rods

Guide Rod (Stainless Steel)

PE Cross Fitting

Metal Seat (Magnetized Steel)

Cantilever

Fig. 3 Internal Structure of Aquashield

Shut-off Plate

Buoy


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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

2.1.1 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.

2.1.2 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.

Fig. 4 Aquashield Mechanism


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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.

2.1.4 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.

2.1.5 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.

2.1.6 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

Fig.5 Aquashield Shut-Off Mechanism

Fig. 6 Aquashield Re-opened


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shut-off plates will be separated from the metal seats and open the pathway

for gas resumption.

2.2 Design Considerations

2.2.1 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.

2.2.2 2-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 shut-

off plates in symmetrical design allow the tight shut –off against water ingress from both

directions.

2.2.3 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.


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2.3 Special Features of Aquashield

2.3.1 PE Cross Fitting embedded with 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.

2.3.2 Shut-off Plates

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.

Fig. 7 Aquashield PE Cross Fitting with a pair of metal seats

Fig. 8 Shut –off Plate Assembly


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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.

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.

2.3.3 Cantilever System 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.

Counter Rods

Fig. 9 Stress Analysis of Shut-off Plate

Fig. 10 Cantilever and Counter rods


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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.

Fig.11 Buoy and Guide Rod

Buoy


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3.Functional Test

Aquashield is fabricated and pre-assembled in factory, the mechanism is proofed by in-

house 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. 12 Aquashield Fabrication

Fig. 13 Aquashield In-house Testing


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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.


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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 = 1.1


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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


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Buoyancy Force

Buoy Volume = 3873249.1 mm3

Buoyancy Force (FB) = 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-

“aquashield” to mitigate water ingress of gas pipes paper - example 3.pdf · “aquashield”...

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