Pigging a challenging pipeline system

Scope

Pigtek Ltd were contracted to carry out a dewatering and swabbing operation on 2 x 500m pipelines that were partly filled with water during construction. The client explained that these pipeline section had been installed by a previous contractor and the details on these sections were lacking technical detail from an as-built perspective. The pipeline features were understood to consist of several 90-degree short radius bends and 2 valves with reduced bore creating a 40mm chamfered bore restriction in the line. The planned approach was to use a variety of coated and non-coated foam pigs with an internal cavity to house a transmitter allowing Pigtek to track the pigs. These pigs would be used to clear any existing water from the line and then foam swabs would be utilised to swab the internal pipe wall. These would all be propelled using compressed air and any existing water would be filtered into a tank.

Reduced bore valve

Dewatering operations (1st visit)

Upon arrival at site an inspection was carried out before dewatering operations commenced and it was visible that the valve reductions in the line looked to be 80-100mm opposed to 40mm, as well as being stepped and not chamfered. It also came to Pigtek attention that several equal unbarred tees were present and that each line had 4 reduced bore valves.

During the first few foam pig runs and it was clear the pipeline was > 90% full of water / mud / sediment. The bore reduction in each valve also led to the pigs becoming compressed to the point that the back plate for the transmitter housing was left deformed allowing compressed air into the cavity and damaging the nose of the pigs leaving them unable to be reused. This resulted in using all the allocated pigs on the first pipeline section.

Foam pig with transmitter cavity

Damaged foam pig

Dewatering & swabbing operations (2nd visit)

Based on the findings from the 1st visit to site a revised plan was developed for the next visit which consisted of using variety of brush foam, coated foam and bare foam pigs all with no transmitter cavities.

Pigtek also planned to introduce fresh water ahead and behind the foam brush pigs to wash the internal pipe wall and to aggressively remove the mud and sediment from the pipe section. Using this method a lot more debris was extracted from the line, this was repeated until the water exiting the receiver was clear.

With the foam pigs having a solid core they were now being received undamaged which allowed Pigtek to reuse them so they could be used multiple times. Following this a series of bare foam pigs were used to swab the line until all free water was removed. This procedure was then repeated on the second line to the client’s satisfaction.

Undamaged pig post run (2nd visit)

Lesson learnt

A few lessons were learned from this project:

• Insist on a site visit ahead of operations taking place to evaluate site conditions and pertinent pipeline features, even if the client deems it not necessary. This is particularly important when a client cannot provide sufficient detail on the pipeline system.
• Plan for the worst-case scenario to ensure that the objectives of the pigging operation can be met.

The lessons are above are not new, but it always good to reiterate these points to ensure that successful pigging operations are completed.