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Central Pipeline Services Ltd was established in 1991, based on 25 years experience in the oil, gas and water pipeline industries.

The company has been involved in both UK and overseas operations, including the supply of fittings, equipment and running training courses for clients in Underpressure techniques.

We have available Underpressure drilling machines including all ancillary equipment for site works. We have also developed a range of special Underpressure machines for carrying out Underpressure works on GRP (Glass Reinforced Plastic) Pipelines.

Underpressure Techniques
-Method

1. Pipeline is cleaned and calipered to confirm the outside diameter. Circumference measurement also taken to check outside diameter.

2. Underpressure tee is brought to site, and fixed to pipeline at agreed location. Outlet is positioned to suit requirements.

3. Test plate is fixed to Underpressure tee outlet. A portable pressure test pump is used to pressure test the seal in the tee, to a minimum of 1.5 times the normal operating pressure, for a set period.

4. The full bore valve is fitted to the Underpressure tee outlet. The valve is fully opened and supported to ground.

5. The Underpressure drilling machine is fixed to valve outlet, and the cutter head is manually fed to the pipe wall.

6. The cutter rotation is set in motion, with feed engaged.

7. When cut is complete, the cutter head containing the coupon is withdrawn back through the open valve.

8. The valve is then fully closed, and the machine adaptor head is depressurised.

9. The Underpressure drilling machine can be removed, and the closed valve on the Underpressure tee is now ready to be used.

10. The Underpressure connection has been completed, and the retained coupon in the Underpressure drilling cutter can be removed, and used to give an indication of the internal condition of the pipeline.

Advantages of Underpressure techniques

  • Generally, the amount of space used for an Underpressure connection requires less excavation and reinstatement than a cut out.

  • Ovality can be taken up in the flexibility and design of the Underpressure tee. Having to source special couplings and flange adaptors can cause major problems on a cutout.

  • Problems of having to work within a ‘window’ and having valves which may not fully close can be avoided.

    Three Types of Underpressure situations

    1) Drilling and Tapping:
    This method is carried out by fixing a suitable drilling and tapping machine to the pipeline, and then producing a threaded hole in the pipe wall, Underpressure. A ferrule, located through the machine is screwed into the preformed thread, underpressure. It is made operational by use of a key or extractor, used through a valve. This is the highest risk method of making a small underpressure connection.

          

    2) Underpressure Tees:
    This is normally supplied in two parts with a threaded or flanged outlet, and is fixed to the pipeline for horizontal or vertical use. A pressure test can be carried out before use, normally through a full bore valve. The Underpressure drilling machine can be fixed to the outlet, and the cut is carried out through the pipe wall. When the cut is complete, the cutter is withdrawn, and the valve is closed. The machine is depressurised, and removed.

    3) Welding onto pipeline:
    This method is usually used on steel pipelines. A pre-profiled fitting with a threaded or flanged outlet is welded around it’s base directly onto the pipe wall. The pressure fitting is tested in situ. A full bore valve is fitted to the outlet, and underpressure drilling is made through the pipe wall.

    Types of Underpressure tees available


    -This type is usually used for underpressure probe entry points, using a connection from 10mm to 50mm in diameter.

    Underpressure tapping of GRP (Glass Reinforced Plastic) Pipelines

    Following a long study of the problems normally encountered when attempting Underpressure connections into GRP pipelines, Central Pipeline Services have designed and developed a special Underpressure drilling machine. This allows technically acceptable cuts to be made through the various layers making up the GRP pipe wall.

    This new method prevents the delamination normally encountered using conventional methods. Many Underpressure connections have since been carried out in the UK and overseas on GRP pipelines using this machine and pipeline fittings developed to suit. The largest connection so far made is a 250mm cutout on a 400mm GRP pipeline, for a UK water authority.

       

    Underpressure connections for probe insertion

    This method can be used to make a live installation of flow metering equipment, pressure indicators, sampling devices and temperature gauges. The device can be located into the pipeline and can be positioned at any point across the internal diameter. Generally, Underpressure connections are made between 10mm and 50mm diameter. Access into the pipe is normally made through a gate valve, which allows positioning and removing of the probe device.

    Types of flow probes

    Underpressure Drilling Machines (Auto feed)

    Underpressure Drilling Machines (Manual feed)

    On site Operations


    Drilling and Tapping machines

    Twin spindle without isolation >
    < Single spindle with isolation valve in base

    Live pipe wall samples

    CPS have a machine which allows pipe wall samples of up to 44mm diameter to be withdrawn underpressure for inspection.

    The sample Shows the internal condition of the main, including of debris onto the lining or directly onto the inner wall of the pipe. The sample also shows wear and corrosion affecting the surface of the pipe wall.

    A comparison of actual wall thickness to specified, can be made. Metallurgical analysis can then be carried out on the sample.

    Pipeline fittings

    Training Courses available

  • Classroom training courses
  • Onsite operational training
  • Audio visual materials
  • Training aids and programs
  • Equipment demonstrations




    Contact us today to discover the advantages of CPS, equipment and expertise.

    Simply click on option 5, on the main navigation menu and talk to us directly about the Central Pipeline Services Interactive Demonstration Disc.