PSI - Issue 36

Roman Dzhala et al. / Procedia Structural Integrity 36 (2022) 17–23 Roman Dzhala et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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3. Contactless testing of underground pipeline insulation by non-contact current measurements Through non-contact measurements J n-1 and J n of the alternating current component of the cathodic protection installation at the ends of the site of UP (interval) in length l n we define the flux density (leakage) of the current per unit length of UP (Dzhala et al. (2018)). By current distribution (Fig. 2 a ) CCM the state of the insulation cover in different areas of UP are compared, the transient resistance and its components are determined (Dzhala et al. (2019), the places of UP insulation damages are detected. The relative linear current density (relative current consumption per length unit of pipeline) is calculated:

(1)

nc n J J J l ) / ( ) ( 1 − = − , m n n

-1 ,

n dJ l

where is the average value of current in pipeline at n -th interval. The relative linear density of current leakage dJ n ( l ) (Fig. 2 b ) is proportional to the electrical conductivity of insulation coatings and is considered as damage indicator of UP insulation: the maximum value of dJ n indicates the location with the least transient resistance of the protective coatings (Nykyforchyn et al. (2009), Dzhala et al. (2018)). ) 1 2 nc n n J J J − = + (

0,35 0,40 0,45 0,50 0,55 0,60 0,65 0,70

J, A

0

50

100

150

200

250

300

350

L, m

a

-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

dJ n , %/m

0

50

100 150 200 250 300

L, m

b

Fig. 2. ( a ) distribution amperage J ( l ) along the pipeline from the measurements of CCM equipment; ( b ) calculation of the relative consumption of current dJ n ( l ).

Through CCM we obtain differential estimates of the state of insulation at different sites of UP, identify the sites of insulation damages and through additional measurements of constant and alternating voltages we determine the components of the transition resistance (soil, insulation, polarization) (Dzhala et al. (2019).