The pressure loss and flow rate in two different coiled gas pipes were measured. The length of the pipes was 4 m. Two various diameters were used, 4 and 6 mm, respectively. The coils were treated with adsorbed layers for gas drag reduction purposes. The friction factor and the Reynolds number were calculated from the measured parameters, and finally the friction factor versus the Reynolds number was plotted. The results from the experiments were compared with the corresponding measured values conducting for a blank coil.

In this laboratory test, three chemicals, two inhibitors and fish oil were tested. The identity of the inhibitors is not allowed to be published, so they are called D and E. The adsorbed layer gave a slightly decrease on the friction factor for the 4 mm diameter coil, for the 6 mm coil the chemicals resulted in no reduction. This may be caused by differences in the viscous sublayer thickness in the coils. For a thin sublayer, the long tail ends of the polymers could reduce the turbulent gas streamlines and thus decrease the friction factor. In addition, the inhibitors could also have a too high concentration, so the decreasing effect on the friction factor disappears.

In gas pipelines the high velocity of the gas will give turbulent flow. The inner surface of the gas pipelines is usually rough. In order to reduce the roughness, the inner surface of the gas pipelines is coated. In turbulent flow some of the energy is lost due to eddies and other random motions. This energy loss will increase the pressure drop faster compared to laminar flow. For turbulent flow, the pressure drop is expected to be a function of the wall roughness. Accordingly, it is important to reduce this roughness.

The purpose in this diploma work was to apply corrosion inhibitors and fish oil on the inner surface of the pipe wall, in order to reduce the pipe surface roughness, and to mitigate the gas turbulence along the interface. This was achieved by fixing an adsorbed layer to the surface of the metal inside the pipeline. A lot of work has been published in minimising the hydrodynamic drag in pipelines for the flow of crude oils. However, for the friction reduction in gas pipelines, the published literature is scarce. It is believed that the reduction in friction factor could be induced on a microscopic length scale level. The molecules in the gas drag reducing agents bind strongly to the metal surface and mitigate the gas turbulence along the interface. The gas drag reducing agents used in this study are also filming chemicals that can directly reduce apparent pipe surface roughness, and thus increase the gas throughput.

This work is a continuation of the fourth year project, and the same small-scale lab setup was used to reduce the friction factor in a coiled pipe by using corrosion inhibitors. Compared to the earlier experiments, the old rotameter was replaced by a more effective suitable one for high rates in some of the currently experiments.

The equipment used was originally constructed for measuring the pressure loss for porous core samples, but modified for the present work. Based on the experimental measurements, the friction factors and the Reynolds numbers were calculated. The friction factors obtained by using inhibitors were compared to the corresponding values for blank coils.

This report is organised as follows: In Chapter 2, the theory for the experiment is presented. Chapter 3 discusses the pressure loss reduction in gas pipelines, and Chapter 4 gives a description of the drag reducer agents used in liquid and gas pipelines. In Chapter 5, the behaviour of the corrosion inhibitors is described, and Chapter 6, gives details of the laboratory setup and pipe dimensions in the experiments. Chapter 7 describes the initial study including some preliminary results for these experiments, and Chapter 8 presents the procedure for preparing the adsorbed layer. In Chapter 9, the measured results are presented and discussed, and Chapter 10 gives the conclusions. In Chapter 11 the recommendations for further work are given.

The tested inhibitors D and E, and fish oil were the three chemicals used in this laboratory work.

Experiments have shown that the friction is reduced in the coil with a diameter of 4 mm when an adsorbed layer has been applied on the inner surface of the coil. For the same experiments with the coil with an inner diameter of 6 mm, the friction is not reduced. The chemicals used in these two experiments are of the same type.

To get more relevant results, dedicated equipment should be constructed and adjusted for these kinds of measurements in question.

The viscous sublayer is probably thicker than the long tail ends of the polymers, such that the inhibitor could not reduce the created turbulent eddies and reduce the stream lines between the pipe wall and the fluid, in the 6 mm diameter coil. In addition, the inhibitor concentration may be too high, so the decreasing effect on the friction disappears.

The coiling of the pipe seems to have no influence of the pipe inner diameter. The reason is that both the Blasius formula, Equation (9.1), and the Colebrook formula, Equation (9.3), fits best with the experimental results using the 6.00 diameter in the calculations.