PSI - Issue 80

G. Mubarak et al. / Procedia Structural Integrity 80 (2026) 157–168 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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trend of Figure 7 [28]. Moving upward along the tubing, the pH decreases to a minimum between approximately 0.5 km and 1 km below the surface, depending on operating parameters, before gradually increasing again toward the wellhead.

Figure 4: Fracture face seen under stereomicroscope showing deep corrosion and pitting from external surface and bevel/shear lip from plastic deformation during ductile overload

Table 2: Chemical composition of the submitted tubing samples

Element

Composition (mass fraction, %)

API 5CT J55 specification

Carbon, C

0.27 1.14

Not specified Not specified

Manganese, Mn Phosphorous, P

0.005 0.003

0.030 max 0.030 max

Sulphur, S Silicon, Si Copper, Cu Nickel, Ni

0.21 0.14 0.05 0.03

Not specified Not specified Not specified Not specified Not specified Not specified Not specified Not specified Not specified

Chromium, Cr

Molybdenum, Mo

< 0.001 < 0.001

Niobium, Nb Titanium, Ti Vanadium, V

0.002 0.002

Boron, B

0.0004