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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operating temperatures increased the solubility product (K sp ), reducing scale deposition, while high chloride levels degraded the protective nature of the remaining scale.

Figure 8: Iron carbonate scaling temperatures, local temperatures, and scale dissolution tendencies vs pipe length for the last 30 days of the well’s production

Table 4: Summary of pitting corrosion rate and interim results at lowest pH points in tubing.

Summary period

Results Lowest pH

Type of wettability Water-wet Water-wet

Flow rate (m³/day)

Wall shear stress (kPa)

Maximum pitting corrosion rate (mpy)

First 30 days Last 30 days

3.6 3.9

16.8

183.7

1.35 0.85

2.2

2.8

The failure analysis of the "short" sample attributed localized loss of scale protection and deep pitting to three main factors: low CO₂ partial pressure near the wellhead, relatively low temperatures (even within operating limits), and high fluid velociti es (gas: 34.3×10³ m³/day; water: 4.0 m³/day), all of which compromised FeCO₃ scale formation and adhesion [36]. Figure 10 illustrates the resulting Mises equivalent stress surface under varying internal pressures and axial loads, reflecting the mechanical response of the corroded tubing. Figure 11 shows the critical failure curve at equivalent stress equal to the flow strength, revealing that corrosion significantly reduced structural integrity. Using API 5CT's hydrostatic failure pressure formula, with J55 pipe parameters ( σᵧ = 379 MPa, ID = 60.32 mm, WT = 4.23 mm), a conservative upper bound pressure of 32.0 MPa was calculated. Yet, actual failure was observed at approximately 15 MPa, indicating that corrosion-induced thinning led to a ductile overload condition. Though simplifications in stress modeling were made, such as excluding residual tensile, bending, and dynamic stresses, these unaccounted factors likely exacerbated longitudinal stress, contributing further to failure. Ultimately, the combination of chemical degradation and mechanical overstress culminated in tubing failure due to insufficient resistance to progressive wall loss under corrosive CO₂ service conditions.