Introduction

The offshore industry has been using the method of pigging for cleaning the walls of rigid pipelines for many years. Pigs come in a variety of designs and offer a number of solutions in the pipeline industry. The pigs are generally the same diameter or larger than the internal diameter of the pipe. When placed in a pipeline the pig is fired down cleaning any deposits off the pipe wall.

Client Requirements

The question has been asked at Dunlop Oil and Marine as to the suitability of pigging offshore hoses and to recommend a suitable method for removing waxy build up deposited on the lining of a hose after product transfer. The biggest concern when considering pigging offshore hoses has always been the rubber lining construction and, unlike rigid pipelines, the flexibility of the hose. Dunlop were given the task of developing a safe method for cleaning hose bores that would not damage the lining of the hose so rendering it useless for further service as stated by Oil Companies International Marine Forum latest edition 1991 (O.C.I.M.F.).

Project Execution

A project was developed to run a number of trials at Dunlop’s Grimsby site to prove that pigs can travel down flexible hoses without causing damage to the rubber lining and to find a suitable pig capable of removing the waxy build up deposited on the lining of the hose. The trial was run in conjunction with iNPIPE PRODUCTS™, manufacturer of pigs. For the purpose of the trials Conoco kindly gave permission for the use of three of their 24” Dunlop Saflote double carcass hoses.

The trial consisted of three pig varieties, ‘Soft Foam’, ‘Long Run Standard Duty Criss Cross’ and ‘Star Wheel’ pigs, all supplied by iNPIPE PRODUCTS™. A short string was constructed using the three Conoco hoses to simulate the use of the pigs on used linings and to see if the deposit on the hose lining could be removed. To run the trial the pigs required only 0.7 bar to traverse along the string but required a high volume of water to seal the pig against the pipe wall. A pump capable of delivering over 76 litres per second at 0.7 bar was used to propel the pigs through the string and calculated to take around three and a half minutes to complete a run.

The Foam and Long run pigs proved successful at negotiating the hose string and upon inspection had not damaged the lining of the hoses, but they only managed to remove light surface dirt and not the hard waxy deposits seen on the lining.

The Star Wheel pig trial consisted of the string being initially placed in a straight line and the pig was then forced down the hose string 10 times. With the hoses bent through 180°, the pig was pushed through the string a further 10 times. The attached picture illustrates the hose string being bent to 180° and the ‘Star Wheel pig’ exiting the string during the trials.

After the completion of the trials the hose linings were inspected and found to be clean and free from damage and the Star Wheel pig had successfully removed a significant amount of waxy deposit from the lining of the hose.

Summary

The conclusion of the full scale trials carried out in conjunction with iNPIPE PRODUCTS™ has confirmed the suitability of three pig types, ‘Soft Foam’, ‘Long Run Standard Duty Criss Cross’ and ‘Star Wheel’ for cleaning the bores of offshore hoses manufactured by Dunlop Oil and Marine Ltd. The Star Wheel pig trialled by Dunlop proved itself more than capable of removing hard wax deposits from hose linings.