Test Points

In general NYY-O cable is used with a minimum copper cross-section of 2 X 2.5 mm. The cable is connected to the pipeline by a suitable process [5-7], and the connections carefully coated. The cable is usually connected to aboveground test points and covered with hoods, tiles or a cable ribbon. 

In order to be able to recognize the type and function of the test point even without an inscription, it is recommended that the design of the test point conform to factory standards. Aboveground test points are usually installed in marker posts with a closable flap. The measuring cable is attached to a plastic plate with terminals (see Fig. 10-7). 

The plastic plates and terminals are fitted into cast housings inside concrete columns or in built-up areas, in cable junction boxes installed at walls. Belowground test points should be installed in built-up areas only in exceptional circumstances. In this case watertight, flush-mounted test stations are installed under a street-level covering and can be kept dry only by the most careful construction. 

---

For each independent variable, form the average value at which it was run in the complex. Draw a line from the coordinates of the worst cake through the average point—called the centroid—and continue on that line a distance that is twice that between these two points. This point will be the next test point. First decide if it is feasible. If so, bake the cake and discover if it leads to a cake that is better than the worst cake from the last set of cakes. If it is not feasible or it is not better, then return half the distance toward the average values from the last... 

The pipe/soil potential is conventionally measured at a test point with a reference electrode Bn. 

Fig, 10-7 Aboveground test points, potential measuring points (2) and (3), pipe current measuring point (1/2). 

Cathodic protection with magnesium anodes can be just as economical as impressed current anode assemblies for pipelines only a few kilometers in length and with protection current densities below 10 xA m" e.g., in isolated stretches of new pipeline in old networks and steel distribution or service pipes. In this case, several anodes would be connected to the pipeline in a group at test points. The distance from the pipeline is about 1 to 3 m. The measurement of the off potential... 

Fig. 10-8 Pipe/soil potentials and protection currents for a pipeline. Drainage test x-x after 1 year o-o. P = potential test point R = pipe current test point LA = cathodic protection station / = insulating joint SP = pipe casing potential test point.

Determination of tank/soil potentials is only possible at the outer edge of the tank. For monitoring the local cathodic protection, the distance between test points should not exceed 2 m [3]. The measurement of the tank/soil potential by the current... 

For adjustment and for monitoring the cathodic protection, test points are necessary along the cable (see Section 10.3.2). It is convenient to install these test points at the cable sleeves. This gives distances between test points of about 0.5 km. The installation of test points to measure conduit current is also convenient for locating accidental contacts. 

Fig. 19-7 Potential variation with time at five test points after switching off the protection current.

Reference electrodes at the test points may only be needed part of the time, depending on the mode of operation of the protective systems (e.g., for monitoring or for permanent control of potential-controlled protection current equipment). Potentiostatic control is always preferred to galvanostatic systems where operational parameters are changing. 

Pipeline connection with reference electrode and pipe current test point, including material and earthworks DM 4500... 

---