Pipeline conductivity methods

Conductivity methods have been successfully used to measure solid concentration in multiphase systems, where the conductivity of continuous phase is greater than zero, for example, sand-water slurries and oil-in-water emulsions (65). These methods have been used to measure bulk and local solids concentration in the slurry pipelines. Nasr-El-Din et al. (27) developed a four-electrode conductivity probe for measuring local solids concentration in slurry pipelines (Figure 20). The probe is... 

Capacitance methods have been used to measure the concentration of dispersed phase in slurry (79) and emulsion (65) pipelines in which the continuous phases have low conductivity, for example, water-in-oil emulsions. The advantage of the capacitance methods over the conductivity methods is that the effect of temperature on the dielectric constant of water is not significant. According to Pal (65), capacitance methods are not effective to measure the concentration of dispersed phase, when the continuous phase has high conductivity. 

To measure local particle velocity in slurry pipelines, Brown et al. (88) modified Beck et al. s (86, 87) conductivity method. They developed a new conductivity probe where four electrodes are mounted on an L-shaped probe. The probe has two field electrodes and two sets of sensor electrodes separated by a known distance (Figure 24). The probe is capable of measuring particle velocity in vertical and horizontal slurry... 

Conducting soil resistivity surveys is a primary step in designing of a cathodic protection system for pipelines. The methods of determination of soil resistivity have been described in an entire section. Pipelines in low resistivity soils would require a greater amount of current for protection than pipelines in a high resistivity soils, because of a higher magnitude of corrosion in the former. Hence, low soil resistivity areas are selected to install the anode ground-bed. 

The other means of transporting large volumes of liquid is via pipelines, a method that offers very significant benefits over road or rail transport. Despite frequent assertions that methanol pipelining would not be practicable, methanol has been very successfully transferred by pipeline in two demonstrations conducted in Canada in 1986. One demonstration involved a crude oil line running from Edmonton, Alberta to Burnaby, British Columbia, a distance of 716 miles the other used a liquefied petroleum pipeline over a distance of 1819 miles. Figure 5 shows analyses of the two shipments, each of which comprised 4000 t. In both cases, the transfer was effected well within the impurity limits dictated by any proposed fuel methanol specification. Such pipelined distribution of methanol must become standard if a significant fraction of the ciurent transportation fuel market is ined by fuel methanol (see Table 5). 

Technical Committee Reports of the National Association of Corrosion Engineers, USA, on pipeline corrosion control, including Statement on Minimum Requirements for Protection of Buried Pipelines , Some Observations on Cathodic Protection Criteria , Criteria for Adequate Cathodic Protection of Coated Buried Submerged Steel Pipelines and Similar Steel , Methods of Measuring Leakage Conductance of Coatings on Buried or Submerged Pipelines , Recommended Practice for Cathodic Protection of Aluminium Pipe Buried in Soil or Immersed in Water ... 

Flow-through conductivity sensors suitable for insertion in pipelines (see Fig. 6.47a) are now available for use at temperatures up to 480 K. and pressures up to 1700 kN/m2(64). As conductivity is temperature sensitive, a thermistor is usually included in the detector circuit as part of a temperature compensator. Screw-in cells (Fig. 6.476) will withstand higher pressures. More recently, electrodeless methods of measuring conductivity have become available. In this case the solution is placed between two energised toroids. The output voltage of the instrument (from the output toroid circuit) is proportional to the conductivity of the solution provided that the input voltage remains constant. This type of conductivity meter can be used under much more severe conditions, e.g. with highly corrosive or dirty systems 43 . 

Buried pipelines are subject to external corrosion from ground water and highly conductive soils. The corrosiveness of soils is often estimated based on soil resistivity measurement. The measurement is made with the Wenner four-pin method, which is used in conjunction with a Vibroground(1 and a Miller U 10-pin conductor set to determine the average electrical resistivities. A general relationship between corrosion and soil resistivity is as follows ... 

Various techniques are available to measure velocity and solids concentration profiles in slurry pipeline. Sample withdrawal using an Li-shaped probe can give a representative sample at isokinetic conditions. Other sample devices will produce significant errors that must be corrected. Conductivity probes can be used to measure local velocity and concentration profiles simultaneously. However, the carrier fluid should be conductive. NMR imaging methods do not disturb the flow with a probe however, they are limited to pipes of small diameter. 

In recent years, continuous zinc ribbon anodes have been used in a variety of underground applications (Kurr, 1973 Peabody, 1976 O Connell, 1977). This type of product has broadened the applications for zinc anodes, for it provides small increments of current continuously along the entire length of a cathode. Its uses are generally considered to lie in specialty applications, where other methods of cathodic protection are either impractical or extremely costly (see later section on induced ac on pipelines). Bagnulo (1973, 1984) has developed a tape with an electrically conducting adhesive as described in the Mechanical Coatings part of Chapter 1. 

For salt aqueous solutions in the absence of any other chemical additives, the hydrate suppression temperature (i.e., dissociation temperature shift) can be determined by measuring the electrical conductivity (Mohammadi, et al, 2007) [16], To characterize liquid mixtures for industrial processes, an acoustic multi-sensor system was developed to measure the concentrations of the chemicals such as MeOH and MEG in the solutions without salts (Henning, et al, 2000) [10]. However, these methods may not be applicable to most hydrocarbon transport pipelines where salts and at least one inhibitor often coexist in the aqueous phase. (Sandengen and Kaasa, 2006) [18] developed an empirical correlation that determined the MEG and NaCl concentrations by measuring the density and electrical conductivity of water samples under examination. However, the critical weakness of this method is that it requires high accuracy of the density measurement, which prevents it from application to real produced water samples that usually contain solid particles (sands and clays) and oil droplets. 

For evaluation of the effect of flow velocity on corrosion in pipelines, NACE Standard Test Method of Conducting Controlled Velocity Laboratory Corrosion Tests (TM0270) can be used to evaluate several steel samples at one time, at velocities up to 8 ft/s (244 cads). 

To conduct a proper study on friction losses, it is a good idea to begin with practical historical cases, as discussed in Chapter 11, as well as test data. The methods for hydraulic friction loss estimation have been covered extensively in Chapters 2 to 5 for closed conduits and in Chapter 6 for open channel flow. A pipeline may consist of both types of flow. For example, slurry may be pumped to a tank situated at a high point, and then be allowed to flow by gravity to the tailings pond. 

Marhavilas et al. (2011) describes that different studies on risk in the natural gas pipeline environment have been conducted using different methods of evaluation which have included qualitative and quantitative approaches. More specifically, given these aspects, this paper presents quantitative analyses, based on the application of a multiple criteria... 

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