PSI - Issue 16

Ihor Chudyk et al. / Procedia Structural Integrity 16 (2019) 260–264 Ihor Chudyk et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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metal weight during the reference time period). The general rate of corrosion was calculated by the loss of weight of the metal sample during the experiment:          S t m m K t 2 1 6 8.76 10 , (1) where K t is a corrosion rate, mm/year; m 1 is a sample weight to test, g; m 2 is a sample weight after test, g; S is an initial area of the sample, mm 2 ; t is time of exposure of the metal sample, hour; ρ is the material density, g/cm 3 . The rate of pitting corrosion was calculated by the formula: where K p is the rate of pitting corrosion, mm/year; h is a depth of the largest pitting, mm; d is time of exposure of the metal sample, day. 3. Results and discussion A severe general corrosion damaging and localizied corrosion of the inner surface of damaged drill pipes after service was odserved by visual examination. Such a corrosive behavior indicates a high aggressiveness of the studied killing fluids. It can be concluded that in this case corrosion was the main cause of the failure of the drill pipes. d K h p  365  , (2)

Fig. 1. General view (a) and profile (b) of the drill pipe with corrosion damages on the inner surface.

The next stage of the research was the laboratory modeling of operating conditions and the study of corrosion resistance of samples manufactured from the drill pipe. The tests were carried out in the killing fluids KF1 and KF2 at a temperature of 150  С . The research results of weight loss and corrosion rate of the G105 steel in the killing fluids are given in Table 3. There were no signs of pitting corrosion on the metal samples exposed to the KF1 environment. The rate of localized corrosion observed for the samples tested in the killing fluid KF2 (Fig. 2) was 58.9 – 62.5 mm/year (Table 3); such rate of local corrosion greatly reduces the lifetime of the pipes.

Table 3. Weight loss and corrosion rate of the G105 steel in the killing fluids at a temperature of 150 ° C

Initial sample weight ( m 1 ), g

Sample weight after test ( m 2 ), g

Rate of general corrosion, mm/year

Rate of pitting corrosion, mm/year

Environment

KF1

15.2152 14.5219 15.0881 14.8235

15.1860 14.4902 14.8572 14.5982

0.199 0.216

Not observed Not observed

KF1 (reiterative)

KF2

1.58 1.54

62.5 58.9

KF2 (reiterative)