WP-33 Help with Low Pressure Leak Detection

In Tubes, Pipes and Vessels

Close up Weld Orbital Purge Plugs

The oil, gas, water, food and drinks, aerospace, power generation, construction and pharmaceutical industries fabricate many thousands of metres of pipes every year and all joints need to be tested for leak tightness before release for use.

The oil, gas, water, food and drinks, aerospace, power generation, construction and pharmaceutical industries fabricate many thousands of metres of pipes every year and all joints need to be tested for leak tightness before release for use.

Hydrostatic testing is the safest and most common method employed for testing pipes and pressure vessels and this is normally undertaken using water.

Pneumatic testing using compressed inert gas or air may be used, but only under carefully controlled conditions.Failure during testing with water releases only nominal energy because water is almost incompressible. Escape of gas during pneumatic procedures can be dangerous because it can result in the sudden release of very large amounts of energy.

In principle, tests are simple operations. The pipe or vessel being examined is sealed and the test medium is introduced and then pressurised. Leaks are detected either by measuring pressure fall or by examination of the surface for visual evidence.

Selecting the optimum sealing technique prior to testing requires a sound knowledge of available products. The operator needs to consider tube, pipe or vessel diameter, test pressure, any requirement for corrosion resistant materials and possible contamination by the sealing medium. There will also be a requirement to identify products offering fast and easy insertion and removal where speed of testing is mandatory.

The range of diameters involved in low pressure testing may be from 20 to 2000 mm (0.8 to 80 inches). Available products for sealing fall generally into two categories; Expandable Plugs and Inflatable Dams.

Expandable Plugs

Figure 1 Pipestoppers Nylon Plugs Figure 2 Pipestoppers Aluminium Plugs


A comprehensive choice of expandable plugs is available from Huntingdon Fusion Techniques Ltd covering the range 12 to 1000 mm diameter (1 - 40 inches). The nylon versions can be manufactured to meet customer colour preferences. Popular 100 mm nylon and aluminium plugs are very widely used during testing of plastic drains. The open plug illustrates how the various components are assembled prior to expansion.

Plugs are Available with Nylon, Steel and Aluminium Bodies

Nylon base 12 to 150 mm (0.5 to 6.4 inches)
Steel base 60 to 2000 mm (2 to 72 inches)
Aluminium base 40 to 1000 mm (1.6 to 36 inches)


Surrounding each body is a flexible seal that can be expanded by applying a radial force through a manually operated wing nut on the shaft. These seals are available in a variety of materials including nitrile, viton, natural rubber, neoprene and silicone to meet different mechanical and corrosion resistant applications.

Figure 3 Pipestoppers Steel Plugs Figure 4 Pipestoppers Aluminium Plugs


The following are typical pressures against which the plugs can maintain a seal. Actual pressure will depend on various factors such as roughness of the pipe and the presence of lubricants.

12 - 50 mm 8 bar (130 psi)
50 - 100 mm 1 bar (15 psi)
100 - 500 mm 0.3 bar (6 psi)
500 - 1000 mm 0.1 bar (2.5 psi)

 

05W-PipestoppersAluminiumPlugs04W-PipestoppersAluminiumPlugs


The primary cause of lack of effective sealing at higher pressures is tilting or sliding of the plugs. This can be counteracted by clamping (left) or by using double disc plugs (right). Both solutions can allow for a considerable increase in the pressure range shown above.

Inflatable Dams

  • Standard dams are available in spherical, cylindrical or rectilinear formats
  • Spherical versions are ideal for insertion through a small hole to seal a large diameter orifice
  • Cylindrical bags resist any tendency to twist radially in use
  • Rectilinear dams are ideal for use in ducting.
 03W-InflatableStoppers01W-InflatableStoppers


The following are typical pressures against which the dams can maintain a seal. Actual pressure will depend on various factors such as roughness of the contact surface and presence of lubricants; the stopper material and alignment of the device can also have an effect on pressure.

50 - 100 mm (2 - 4 inch) 1 bar (15 psi)
100 - 500 mm (4 - 20 inch) 0.3 bar (6 psi)
500 - 1000 mm (20 - 72 inch) 0.1 bar (2.5 psi)

 
The maximum inflation pressure is prominently stamped on the casing. All dams are fitted with a pre-set and tamper-proof relief valve.

Dams can be located and removed from position in their deflated state and this is useful when insertion into the pipe or vessel through small holes is required.

Nominal Maximum and Minimum Dimensions for Inflatable Dams
Inflated Dam Size
Deflated Dam Size
50 - 200 mm (2 - 8 inch) 50 mm 2 inch
200 - 500 mm  (8 - 20 inch) 100 mm  4 inch 
> 500 mm   (20 inch) 150 mm 6 inch


Selection of inflatable dams from Huntingdon Fusion Techniques (HFT®) covering the diameter range from 50 to 500 mm (2 to 20 inches). Huntingdon Fusion Techniques' 2 metre (80 inch) dam.

Available from stock, inflatable dams are made from high-grade latex rubber and covered with a tough, woven polyurethane impregnated nylon. Alternative materials to resist for example, petroleum and acid products, can be supplied on request. The dams are inflated through an integral valve using a standard foot pump or a compressor.

Conformity: BS EN 752, 1610, 295 Low Pressure Testing and Sealing of Pipes.

Application Examples

06W-PipestoppersAluminiumPlugs

 

08W-PipestoppersAluminiumPlugs 

 

19W-PipestoppersNylonPlugs 

36W-PipestoppersNylonPlugs

 

23W-InflatableStoppers 

 

03W-WeldOrbitalPurgePlugs 

Clockwise from top left

Leak testing domestic or commercial construction piping

Testing flexible pipe exhaust in factory heating system

Petrochemical valve undergoing testing

Custom manufactured inflatable stopper for leak testing special shapes

Landfill gas escape leak testing

Aero fuel system component under test

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