52 Offshore February 2018 •
PIPELINES & FLOWLINES
receiver point at platform top of jacket). Thus,
these values (required pressure for pushing the
pigs and elevation difference) have been added
to the pressure loss value which is calculated
from theoretical equations. For theoretical calculations, the roughness of the pipeline was
calcluated as 0.05 as for minimum of slightly
corroded carbon steel and maximum of new
carbon steel [ 13].
Based on evaluated references and in the
field experiences, the following strategies
can be presented in order to prevent a stuck
• Propelling a poly pig before the start of
any pigging operations is a recommended
strategy in order to both evaluate the
condition of and pre-clean the pipeline.
• Chemical cleaning is a way of cleaning a
pipeline without the need for launching
brush pigs. The chemical mixture needs
to be designed based on possible contents
of pipeline debris to be capable of breaking
and dissolving the sludge within a short
duration of exposure. It is mostly recommended for short length pipelines which
have accumulated wax and debris. For
using in high length pipelines, a chemi-
cal mixture can be inserted as a batch
between two pigs so that it can help the
pigs confront the wax and debris inside
the pipeline. Also, a chemical cleaning
program removes deposits or solids such
as black powder, millscale, or other solid
elements from the inside of the pipe in
order to enhance its cleanliness for in-line
inspection, and improve its efficiency [ 14].
• Modeling and simulation in analytical
environments (such as ANSYS, OLGA,
SIMULINK, MATLAB, etc.) is another
technical way of predicting the conditions
inside the pipeline. Many works have
been performed in this area which can be
referred to for more information such as
O’Donoghue, Gupta et al. and IDAC and
BP Case Pig Analysis Case Study [ 15].
• Regular cleaning of the pipeline usually
leads to gradually remove the debris and
deposits from the pipeline, making each
pigging operation easier to perform. Dur-
ing the life of a line, operational pigging is
a cheap effective way of maintaining flow
and minimizing back pressure [ 5]. The
reason is that once in service, deposits
can begin to settle on the pipe wall. If
cleaning is not performed on a regular
basis during production operations, these
deposits can build up, encouraging cor-
rosion growth and potentially preventing
inhibitors that can protect the system
from being properly applied. In addition,
cleaning at this stage prepares the pipe-
line for further pigging operations [ 16].
On this matter, the ROSEN Group suggests
the following steps to maintain the pipeline,
increase operational performance, and extend
the operational lifecycle of the pipeline [ 16]:
• Post-construction cleaning
• Operational cleaning
• Change of service cleaning
• Cleaning prior to cessation of production
• Decommissioning cleaning.
According to described condition of the opera-
tion, it can be concluded that the main reason for
pigs getting stuck is an accumulated amount of
debris, which can be either loose debris or sticky
debris. By noticing condition of the second re-
ceived pig, it could be observed that not only
the gauge plate had been broken, but also front
disks of the pig had been rubbed and damaged
in the exact same half side of the pig. Nose dam-
age to the pig had occurred such that even the
front nut had been eroded and destroyed up to
its half. This meant that the reason leading the
pig to this condition had been a constant and
resistant factor or object, not an instantaneous
factor. The condition of the third received pig
also approved this scenario because the disks
were not torn, but eroded asymmetrically. This
showed that the object which had caused the
gauge plate to break had not been a sudden
obstruction such as a dent, but a constant object
like debris and sediments. So, it was decided to
rescue the pigs by means of high flowrate which
could push the debris out of the pipeline and
make the pigs move forward.
Furthermore, since the pipeline had been
filled with seawater for two years and had a
history of two repairs, the roughness of pipeline inner wall was a matter of discussion, and
production of corrosion products inside the
pipeline and formation of sediments was therefore likely. •
The authors would like to thank IPEC for permission
to publish this article. The authors also express their
sincere appreciation to the client for cooperation and
full support during operation of this project in South
Pars gas field.
[ 1] Aidan O’Donoghue, “Why Pigs Get Stuck and How
to Avoid it”, Pipeline Research Limited, Pipeline
Pigging Conference, Amsterdam, October 2002.
[ 2] GIRARD Industries, “Dealing with a Stuck Pig,”
[ 3] Abdullah Al-Khaledi, Hamad Al-Zuwayer, Fahad
Al-Ghanem, “Case Study for Releasing Stuck Pig
in Non-Metallic Pipeline,” Kuwait Oil Company,
Proceedings of the 2014 10th International Pipeline Conference, September 29 - October 3, 2014,
Calgary, Alberta, Canada.
[ 4] Aidan O’Donoghue, “Modelling Pig Train Dynamics in Natural Gas Pipelines,” Pipeline Research
Limited, PPSA Conference Aberdeen, November
[ 5] Anand Gupta, Anirbid Sircar, “Introduction to
Pigging & a Case Study on Pigging of an Onshore
Crude Oil Trunkline,” IJLTEMAS Journal, ISSN
2278 – 2540, Volume V, Issue II, February 2016.
[ 6] Pigtek Ltd, “Rescue Pig for Stuck Pig Location and
Removal,” Operations Guideline.
[ 7] A. Tabatabaei, H. Tabassomi and M. Mahmoudi,
“Lessons Learned from Pig Rescue Operations
during Precommissioning of a 290 km Offshore
Pipeline in Persian Gulf,” Offshore Technology
[ 8] G. Marshall, “Cleaning of the Valhall offshore
oil pipeline,” in Offshore Technology Conference,
[ 9] D. Nesbitt, “The Use of Gelly Pig Technology for
Removal of Stuck Mechanical Pigs,” in Offshore
Technology Conference, 1991.
[ 10] G. Fung and W. Backhaus, “To pig or not to pig:
the Marlin experience with stuck pig,” in Offshore
Technology Conference, 2006.
[ 11] D. Combe and D. Hair, “Problems with Operational Pigging In Low Flow Oil Pipelines,” in
Society of Petroleum Engineers, September 2011.
[ 12] R. W. Fox, A. T. McDonald, P. J. Pritchard, “
Introduction to Fluid Mechanics,” Eighth Edition,
Published by Wiley, 2011.
[ 13] R. K. Bansal, “A Text Book of Fluid Mechanics,”
Published by Laxmi Publications, 2005.
[ 14] J. Tiratsoo, “Pipeline Pigging and Integrity Technology,” Fourth Edition, Published by Tiratsoo
Technical and Clarion Technical Publishers,
[ 15] British Petroleum, “Pig Analysis,” Case Study.
[ 16] Rosen Technology, “Pipeline Cleaning Solutions -
The Smart Way to Efficiency,” PPT Report, 2015.
[ 17] IPEC Confidential Documents of Projects Histories, 2014-2017.
Second pig (received condition) [ 17].