Piggable” pipeline requirements are regularly debated among designers of new systems. Due to certain misconceptions about existing pipeline restrictions, operators of older systems may not even consider using “smart” pigs. With technological improvements in the tools, notably more efficient power systems and much smaller computer chips, most tools have shrunk and are more compact, with even better resolution. Other improvements have also increased operator ability to use smart pigs in lines that were not previously considered piggable.

The need for smart pigging for caliper surveys, reliability assessments, internal corrosion inspections, and even geometry surveys required more extensive capabilities to accommodate the pigging hardware. Internal dimensional tolerances, broad sweeping long radius bends, and long barrel traps became important for making sure that a pipeline could be piggable.

The smart pig tools included computers, transmitters, magnetic flux elements, ultrasound detectors, and recorders to store large amounts of collected data. The pig train comprising the tool required suitable power to collect and process data from insertion into the launcher to arrival at the receiver. Long-life battery packs followed long tools in the train connected with umbilical cords. The traps had to be long enough to insert and receive the full tool package.

The geometry of these long tools caused traverse concerns in bends and fittings. Few if any of these early tools could traverse long radius (1.5 x pipe diameter) elbow fittings. Risers on offshore pipelines were normally specified for 5D (5 x pipe diameter) radius bends. These bends became the standard for the tool design to be capable of traversing.

Smart tools for pigging have matured. A recent technical survey requesting recommendations for pipeline and piping design requirements for bend radii and spacing between induction bends or tube turn fittings was issued to the following international contractors:

  • T.D. Williamson
  • GE Energy Pipeline Solutions
  • Rosen Inspection
  • Varco Tuboscope
  • BJ Pipeline Services.

The following report highlights the findings following responses from each of the above pigging specialty firms.

With regard to 5D versus 3D induction bends or fittings:

  • It is accepted that 3D bends are standard for all inspection tools.
  • All tools will traverse a 3D radius fitting or bend.
  • Most tools will also traverse a 1.5D X 90 degree elbow.
  • Magnetic and ultrasonic tools will provide a higher resolution on heavy wall pipe in a 5D bend. If the bend is on a platform, the higher resolution is not as important since an exterior inspection could actually yield even better results.
  • In thick wall pipe of small diameter (6 in. to 10 in.), the tool is inherently limited to lower resolution due to the limits on size of the tool and the internal magnets.
  • A wall thickness over 0.625 in. is hard to full saturate with magnetic tools.
  • The 8.625 X .500 in. wall X-65 pipe may require 6-in. tools for some contractors due to internal diameter and tolerances. If the 6-in. tool is required, they can accommodate 1.5D bends.

With regard to minimum spacing between bends:

  • There was no mention by any of the contractors about a full pig-length distance between bends.
  • The most severe minimum distance mentioned for the 8-in. line was from BJ Services who recommended 3-5 X pipe diameter (24-in. to 40-in.). Rosen Inspection can accommodate 1.5D/3D bends in opposite directions, back-to-back with a minimum of 36-in. in between.
  • The response from the remaining contractors indicated that the bends could be fitting to fitting with no separation.
  • The contractors install cups on the tool while considering internal diameter with geometry of the tool compared to the curve of the bend. Sizing the cups and placement along the tool assures sealing for full pressure drive when traversing ovality, buckles or dents.
  • The reason for spacing between bends is to limit surging of the tool through the bend. This impacts positioning of the detected anomaly in the pipeline and resolution of readings in the bend. If the bend is at the terminal end of the pipeline next to the receiver, this is not an issue at all. Such is the case on the wellhead platform.

The following were among the report’s conclusions and recommendations:

  • Technically, 3D bends should be accepted as the minimum specification for 6-in. and 8-in. NPS diameter high pressure gas pipelines.
  • The minimum distance between bends should probably be limited to 5 X diameter (40-in. for 8-in. NPS lines). On a case by case basis, this could be reduced to 3 x diameter minimum (24-in. for 8-in. NPS lines). In extreme cases where piping layout is critical, this could be relaxed to fitting to fitting make-up with no minimum spacing.

If you are considering whether the pipeline you own or must build is “piggable” with “intelligent tools,” get “smart” and ask. Just be careful what the old pipeline guy down the hall tells you.