ON THE ISSUE OF USING CONTROL ELECTRODES FOR THE MARINE VESSEL PROTECTORS TECHNICAL DIAGNOSTICS
Abstract and keywords
Abstract (English):
The world statistics of fleet accidents indicate that the most dangerous type of damage to engineering structures are fragile destructions that occur suddenly and spread at high speed. The causes of brittle fractures are defects such as corrosion-fatigue cracks, which often occur due to active corrosion processes. Seawater contains a large number of microorganisms that contribute to the acceleration of corrosion and fouling of metal structures in contact with water. The main method of corrosion protection of systems and mechanisms of marine fishing vessels is tread protection. To increase the effectiveness of tread protection, it is necessary to improve the methods of technical diagnostics of treads in order to use new methods at ship repair plants and marine vessels. It is proposed to use control electrodes made of stainless steel for technical diagnostics of marine vessel protectors. Laboratory tests of a stainless steel electrode and a standard silver chloride reference electrode were performed. The experiment took place at the installation for technical diagnostics of marine protectors, which was specially developed at the Department of “Power Plants and Electrical Equipment of Ships” of the Kamchatka State Technical University. Control measurements of the potential of the working protector were performed for five days, while 50 single control measurements of the working potential of the protector were performed daily using each electrode. The accuracy of the measurement results was evaluated using a mathematical and statistical method. The results of diagnosing the potential of the tread, obtained using an electrode made of stainless steel, comply with regulatory requirements. The proposed type of electrode can be used by ship crews for technical diagnostics of marine vessel protectors.

Keywords:
protection of ships, tread protection against corrosion, protectors working potential, protectors technical diagnostics, measuring the working potential of a protector, standard reference electrode, non-standard reference electrode
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Introduction

The corrosion studies carried out by the authors [1, 2] on Kamchatkaꞌs sea-going vessels, have brought to light many cases of using low-quality protectors at these vessels. For this reason, the workers of small ship-repair enterprises of the Kamchatka Region applied to Kamchatka State Technical University with a request to develop a simple method for technical diagnostics of ship protectors in order to check their working capacity.

According to the standard requirements [3], when technically diagnosing ship protectors it is necessary to measure their operating potential and current output. These tread characteristics are assessed using an expensive set of devices [3]. It should be noted that standard methods [1, 4-10] of protector quality control are not intended for continuous non-destructive testing of individual marine protectors. It is also necessary to take into account the experience of using silver-chloride reference electrodes (CRE) on Kamchatkaꞌs sea-going vessels to measure the operating potential of protectors. No shipꞌs crew of Kamchatka fleet uses CRE in their practical work [11]. This is because of the high cost of CRE and the complexity of its storage. For this reason, it is necessary to stop using CRE when organizing incoming quality control of marine protectors and replace it with a non-standard control electrode intended for use at small ship repair enterprises and sea-going vessels.

The papers [12-17] present the results of tests of non-standard control electrodes (of aluminum, copper; electrodes made of shipꞌs hull steel, etc.) used to control the tread protection systems of sea-going vessels’ hulls. This paper presents the results of technical diagnostics of protectors using a control electrode made of stainless steel.

The purpose of the article is to exchange experience in the quality control of marine protectors.

 

Еxperimental part

For five days (from 11.14.2022 to 11.18.2022), the operating potential of a P-SSA-4 type protector made of AP-1 aluminum alloy was measured in the laboratory conditions. The measurements were performed using a UNI-T UT39E+ multimeter and two electrodes:

– CRE;

– a control electrode made of CR (chrome) 17 stainless steel in accordance with the recommendations of the regulatory document [3].

Fifty single measurements of the tread potential were carried out daily using each control electrode. The total time for carrying out daily measurements is approximately 10 minutes. A diagram of the installation for technical diagnostics of sea-going vessel protectors is shown in Fig. 1. This installation was developed at the department “Power Plants and Electrical Equipment of Ships” of the Federal State Budgetary Educational Institution of Higher Education “Kamchatka State Technical University”. The installation contains a steel container 1 filled with sea water 6. In the center of the steel container, there is a dielectric perforated container 3, which is attached to the steel container 1 using an adhesive connection 2. At the bottom of the perforated container 3, there is an elastic dielectric lining 4 made from foam-rubber. The perforated dielectric container 3 contains a replaceable controlled protector 5 fixed in the vertical position with the help of a float 12 made of dielectric material. A measuring cable 8 is connected to the steel armature 15 of the controlled protector through a spring-loaded self-clamping contact (of crocodile type) 13. A cable tip 7 is soldered to the free end of the measuring cable 8. A measuring cable 9 is soldered to the control electrode 10, besides the soldering point is protected with VK-9 glue. A cable tip 11 is soldered to the free end of the measuring cable 9 of the control electrode 10. The control electrode 10 is attached to the perforated container with the help of a rubber clamping ring 14.

 

 

Fig. 1. The design of an installation for technical
diagnostics of marine vessel protectors

 

The experiment has been performed the following way:

– the steel container was filled with sea water to the specified level;

– the controlled protector was placed in the perforated dielectric container in the vertical position which was fixed with the help of a dielectric float;

– the measuring cable equipped with a cable tip was connected to the steel armature of the protector with the help of a self-clamping contact;

– the electrode was placed in seawater, and attached to a perforated container with the help of a rubber clamping ring;

 5 minutes after placing the controlled protector in sea water, the potential difference (ΔU) between the protector and the reference electrode was measured, 50 control measurements being performed with a pause of about 5 seconds between measurements, according to the recommendations [18-22];

 the obtained measurement results were entered into special forms, the experimental data were digitized, and initial mathematical processing of the measurement results was carried out with the help of the Microsoft Office Excel 365 software product;

 after processing the measurement results, electrode No. 1 was removed from the electrical measuring circuit, and electrode No. 2 was attached;

 then the measurement cycle was repeated with the help of control electrode No. 2, according to the recommendations proposed in papers [18-22].

It is worth noting that in order to connect the electrode test wire to an electrical measuring instrument (multimeter), one can use a bolted connection, a built-up connection, or a simple cable tip. The UNI-T UT39E+ multimeter was used in the experiment, but other electrical measuring instruments can also be used.

 

Results of the experiment and discussion

The results of the experiment and assessment of their metrological characteristics with the help of mathematical and statistical methods [23], obtained on the above installation by means of two control electrodes, are given in the Table (Uav – simple average, mV; R – variation range; d – average linear deviation; D – dispersion; σ – average quadratic deviation; Kd – linear variation coefficient, %; Kr – oscillation coefficient, %; V – variation coefficient, %) and in Fig. 2, 3.

Results of monitoring the working potential of P-KOA-4 protector from 11/14/2022 to 11/18/2022

 

No.

 

Results of measurements of the potential difference between the protector
and control electrodes U=, mV, obtained with the help of electrodes per day

Electrode No. 1 CRE

Electrode No. 2 made from stainless steel

14/11/2022

15/11/2022

16/11/2022

17/11/2022

18/11/2022

14/11/2022

15/11/2022

16/11/2022

17/11/2022

18/11/2022

1

939

945

941

933

947

393

390

383

375

388

2

939

946

942

933

948

393

390

383

374

388

3

939

945

942

933

948

393

390

383

375

388

4

939

946

941

932

948

393

390

382

374

388

5

939

945

942

932

947

393

390

383

375

388

6

939

946

941

932

948

393

390

382

374

387

7

939

945

942

932

948

393

390

382

375

387

8

939

946

942

932

947

393

390

383

374

387

9

939

946

942

932

948

393

390

383

375

388

10

939

946

942

932

948

394

390

383

374

388

11

939

946

942

932

947

394

390

383

375

388

12

939

946

942

932

948

394

390

383

374

388

13

939

946

942

932

948

394

390

383

375

388

14

939

946

942

932

948

394

390

383

374

388

15

939

946

942

932

948

394

390

383

375

387

16

940

946

942

932

948

394

390

383

374

387

17

939

946

942

932

948

394

390

383

375

387

18

940

946

942

932

948

394

390

383

374

388

19

939

946

942

932

948

394

390

383

375

388

20

939

946

942

932

948

394

390

383

374

388

21

940

946

942

932

948

394

391

383

375

388

22

939

946

942

932

948

394

391

383

374

388

23

939

946

942

932

948

394

391

383

375

388

24

940

946

942

932

948

394

391

383

374

388

25

939

946

942

932

948

394

391

383

375

388

26

939

946

942

932

948

394

391

383

374

388

27

939

946

942

932

948

394

391

383

375

388

28

940

946

942

932

948

394

391

383

374

388

29

939

946

942

932

948

394

391

383

375

388

30

940

946

943

932

948

394

391

383

375

388

31

940

946

942

932

948

394

391

383

374

388

32

939

946

942

932

948

394

391

383

375

388

33

940

946

942

932

948

394

391

383

374

388

34

939

946

942

932

948

394

391

383

375

388

35

940

946

942

932

948

394

391

383

374

388

36

939

946

942

932

948

394

391

383

375

388

37

940

946

942

932

948

394

391

383

374

388

38

939

946

942

932

948

394

391

383

375

388

39

940

946

942

932

948

394

391

383

374

388

40

939

946

942

932

948

394

391

383

375

388

41

940

946

942

932

948

394

391

383

374

388

42

939

946

942

932

948

394

391

383

375

388

43

940

946

942

932

948

394

391

383

374

388

44

939

946

942

932

948

394

391

383

375

388

45

940

946

942

932

948

394

391

383

374

388

46

939

946

942

932

948

394

391

383

375

388

47

940

946

942

932

948

394

391

383

374

388

48

940

946

942

932

948

394

391

383

375

388

49

940

946

942

932

948

394

391

383

374

388

50

939

946

942

932

948

394

391

383

375

388

 

Uav, mV

939.34

945.92

941.96

932.06

947.92

393.82

390.60

382.94

374.52

387.88

R

1.00

1.00

2.00

1.00

1.00

1.00

1.00

1.00

1.00

1.00

d

0.45

0.15

0.12

0.11

0.15

0.30

0.48

0.11

0.50

0.21

D

0.22

0.07

0.08

0.06

0.07

0.15

0.24

0.06

0.25

0.11

 

σ

0.48

0.27

0.28

0.24

0.27

0.39

0.49

0.24

0.50

0.33

Kd, %

0.05

0.02

0.01

0.01

0.02

0.07

0.12

0.03

0.13

0.05

Kr, %

0.11

0.11

0.21

0.11

0.11

0.25

0.26

0.26

0.27

0.26

V, %

0.05

0.03

0.03

0.03

0.03

0.10

0.13

0.06

0.13

0.08

 

 

Fig. 2. Dynamics of the results of the potential difference measuring in the period
from November 14, 2022 to November 18, 2022, obtained with the help of electrode No. 1 (CRE)

 

 

Fig. 3. Dynamics of the results of the potential difference measuring in the period
from November 14, 2022 to November 18, 2022, obtained with the help of electrode No. 2 made of stainless steel

 

The results of the experiment given in the Table show that each group of measurements is homogeneous, the degree of dispersion of the measurement results is insignificant, since V < 1%. The dynamics of changes in the results of the potentialꞌs measurements over the period of the experiment is illustrated in Fig. 2, 3.

The results of the experiment given in Fig. 2, 3, show the following:

– repeatability (convergence) of the control measurement results corresponds to the accuracy category of “precise measurements”, since the variation coefficient V, %, has proved to be less than 1% [23];

– intra-laboratory precisionness [24] of measurement results meets the requirement: |XmaxXmin| = |948 – 932| =  16 ≤ 20 mV [10].

The results of measuring the protectorꞌs working potential, obtained with the help of the control electrode made of stainless steel, have shown the following:

– repeatability (convergence) of the control measurement results, according to [23], corresponds to the accuracy category of “precise measurements”, since the variation coefficient V, %, has proved to be less than 1%;

– intra-laboratory precisionness [24] of measurement results complies with the condition: |Xmax Xmin| =  |394 – 374| = 20 ≤ 20 mV [10].

 

Conclusion

1. The results of monitoring the protectorꞌs potential obtained with the help of an electrode made of stainless steel, comply with standard requirements.

2. The results of the research can be used in training operators for technical diagnostics of sea-going vessels and shipsꞌ protectors.

References

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