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Technical Guide for Drill Pipe Corrosion Protection: From Sulfide-Resistant Steel Grades to Internal Coatings
Author:
WHH
Source:
LONGWAY
Published:
2026-09-18
Corrosion is one of the primary failure modes of drill pipes. Statistical data indicate that, in oil and gas wells containing H₂S and CO₂, corrosion accounts for more than 40% of drill‑pipe failures. Corrosion not only directly thins the pipe wall and reduces its load‑carrying capacity but also interacts with cyclic fatigue loading, thereby accelerating drill‑pipe fracture. This paper systematically reviews the types, mechanisms, influencing factors, and protective strategies of drill‑pipe corrosion, providing technical guidance for material selection, procurement, and field management.
I. Main Types of Drill Pipe Corrosion
| Corrosion Type | Mechanism | Typical environment | Consequences |
| Uniform corrosion | Uniform thinning of the entire surface | Acidic drilling fluid, high salinity | Wall thickness reduction leads to a decrease in strength. |
| Pitting corrosion | Localized deep pits form. | Contains Cl⁻ and dissolved oxygen | Stress concentration, fatigue crack initiation |
| Crevice corrosion | Medium stagnation within the gap | Threaded joints, shoulder surfaces | Seal failure, tripping |
| Galvanic corrosion | Dissimilar metal contact | Drill pipe and drill collar joint | Accelerated corrosion on the anode side |
| Corrosion fatigue | Corrosion + Cyclic Stress | All downhole conditions | Crack propagation is rapid, leading to fracture. |
| Sulfide Stress Cracking (SSC) | H₂S + tensile stress | H₂S-containing wet environment | Brittle fracture suddenly occurring |
| Hydrogen-Induced Cracking (HIC) | Hydrogen atoms permeate into steel. | H₂S-containing environment | Internal cracks, step-like fracturing |
| CO₂ corrosion | Carbonic acid corrosion | CO₂-containing condensate gas well | Local deep pit, wall thickness reduction |
Corrosion fatigue is the most hazardous failure mode in drill pipes: corrosive media induce pitting on the surface, with the pit bottoms serving as stress concentration points; under cyclic loading, fatigue cracks initiate at these sites and propagate rapidly.
II. Key Factors Affecting Drill Pipe Corrosion
1. Corrosive medium
H₂S: It can induce SSC and HIC, with increasing risk at higher concentrations. NACE MR0175/ISO 15156 specifies material suitability under different partial pressures.
CO₂: Dissolves in water to form carbonic acid, lowering the pH and accelerating both uniform corrosion and pitting corrosion.
Cl⁻: Destroys the passive film, initiating pitting and crevice corrosion.
Dissolved oxygen: significantly accelerates corrosion, particularly in drilling fluid circulation systems.
2. Environmental Conditions
| factor | Impact |
| Temperature | Increased temperature accelerates corrosion reactions, but it also affects SSC susceptibility (with a peak around 80°C). |
| pH | Low pH accelerates uniform corrosion; high pH reduces the risk of SSC. |
| Flow rate | High flow velocity exacerbates erosion, but reduces the risk of pitting corrosion. |
| Pressure | It affects gas solubility, thereby indirectly influencing the corrosion rate. |
3. Material Factors
Steel grade: High-strength steel is more susceptible to SSC; S135 > G105 > E75.
Chemical composition: Alloying elements such as Cr, Mo, and Ni enhance corrosion resistance.
Microstructure: Tempered martensitic microstructure exhibits superior SSC resistance compared to the untempered microstructure.
Hardness: The higher the hardness, the greater the susceptibility to SSC (API 5DP specifies that the hardness of SS steel grades shall not exceed HRC 32).
III. Corrosion Protection Strategies for Drill Pipes
1. Material Selection: Sulfur-Resistant Drill Pipe
For environments containing H₂S, the SS series should be selected. Sulfur-resistant drill pipe (SS95/SS105/SS135), designed in compliance with NACE MR0175/ISO 15156 requirements. In 2025, Supplement No. 1 to API 5DP will introduce a new requirement: for SS steel grades, grain size shall be ≥ ASTM Grade 6, and the martensite transformation rate after quenching shall exceed 90%.
Selection Principles:
H₂S partial pressure < 0.3 kPa: Standard steel grade with internal coating may be selected.
H₂S partial pressure of 0.3–10 kPa: Select SS95 or SS105.
H₂S partial pressure > 10 kPa: Select SS135 and strictly limit hardness.
2. Internal Coating Protection
Internal coating (LPC3000P/LPC5000P series) Form an isolation layer on the inner wall of the pipe, effectively preventing corrosive media from coming into contact with the steel. Technical specifications:
| Parameter | LPC3000P | LPC5000P |
| Temperature-resistant | ≤180℃ | ≤204℃ |
| pH range | 2-12.5 | 3-13 |
| H₂S-resistant | <4% | <10% |
| Life extension | 1-2 times | 3-4 times |
Applicable scenarios: condensate gas wells containing CO₂/H₂S, high-salinity water wells, water injection wells, and others.
3. Drilling Fluid Treatment
pH Control: Maintain the pH between 9.5 and 11.5 to reduce the risk of SSC.
Corrosion inhibitor: Add a film-forming or adsorptive corrosion inhibitor.
Deoxygenation: Use a deoxidizer to maintain dissolved oxygen levels below 20 ppb.
Biocides: Control of sulfate-reducing bacteria (SRB)
4. Operation and Maintenance
Before entering the well, inspect the threads and shoulder surfaces to ensure there is no corrosion or damage.
Use the correct thread compound to prevent crevice corrosion.
After pulling out of the hole, promptly clean to remove any residual drilling fluid.
Apply anti-rust grease for long-term storage and install thread protectors.
IV. Corrosion Monitoring and Inspection
| Method | Applicable Scenarios | Test Content |
| Corrosion coupon | Drilling fluid circulation system | Uniform corrosion rate |
| Resistance probe | Online monitoring | Real-time corrosion rate |
| Ultrasonic thickness measurement | Drill pipe body | Wall thickness reduction |
| Magnetic Flux Leakage (MFL) Inspection | Overall tube length | Corrosion pits, pitting corrosion |
| Magnetic Particle Testing (MT) | Thread, shoulder | Surface Cracking (SSC/HIC) |
Recommended inspection intervals: For wells containing H₂S, MT inspections should be performed after each well is pulled out of the hole; for wells containing CO₂, MFL inspections should be conducted every 3 to 5 wells.
V. Procurement and Selection Recommendations
When procuring drill pipes, the following requirements should be clearly specified for corrosive environments:
| Project | Technical Requirements |
| Steel grade | Select SS95, SS105, SS135, or a standard steel grade with an internal coating based on the H₂S/CO₂ partial pressure. |
| Internal coating | LPC3000P/LPC5000P: clearly specified temperature resistance, pH range, and sulfur resistance. |
| Hardness | SS steel grade ≤ HRC 32, standard steel grade ≤ HRC 37 |
| Nondestructive testing | MT+UT+MFL, with a focus on threads and the pipe body. |
| Quality Document | The MTC shall include grain size, martensite transformation fraction, hardness, and SSC/HIC test results. |
| Standard compliance | NACE MR0175/ISO 15156, API 5DP Supplement No. 1, 2025 |
VI. Frequently Asked Questions (FAQ)
Q1: Must all wells containing H₂S use sulfur‑resistant drill pipe?
Not necessarily. An assessment must be conducted in accordance with NACE MR0175/ISO 15156, taking into account parameters such as H₂S partial pressure, pH, and temperature. Under low‑partial‑pressure conditions, a standard steel grade combined with an internal coating and a corrosion inhibitor may be sufficient.
Q2: Can an internal coating completely replace sulfur‑resistant drill pipe?
No. The internal coating primarily protects the inner wall of the pipe, while the threads and shoulder surfaces still rely on the material’s inherent resistance to sulfidation. At higher H₂S partial pressures, an SS steel grade should be selected.
Q3: How can you determine whether a drill pipe has experienced corrosion fatigue?
Corrosion fatigue manifests as cracks that initiate from pitting defects, typically originating at the pipe body surface or at the thread roots. Magnetic particle testing (MT) and ultrasonic testing (UT) can detect cracks, while magnetic flux leakage (MFL) can detect pitting defects.
Q4: Can drill pipes be repaired after corrosion?
Minor corrosion can be removed by grinding, but drill pipes with wall‑thickness reduction exceeding the allowable limit should be downgraded or scrapped. Thread‑corrosion damage typically requires re‑threading for repair, though this is constrained by the amount of material that can be removed.
Q5: How can the service life of drill pipes used in corrosive environments be extended?
Comprehensive measures: select sulfur‑resistant steel grades with internal coatings, control drilling fluid pH and corrosion inhibitors, conduct regular inspections, perform timely repairs, and ensure proper storage.
VII. Summary
| Key points | Core content |
| Major Types of Corrosion | Uniform corrosion, pitting corrosion, SSC, HIC, CO₂ corrosion, corrosion fatigue |
| Key influencing factors | H₂S/CO₂ partial pressure, pH, temperature, Cl⁻, dissolved oxygen |
| Protection Strategy | Sulfur-resistant steel grade + internal coating + drilling fluid treatment + operation and maintenance |
| Detection method | MT for crack detection, MFL for corrosion pit inspection, UT for wall thickness measurement. |
| Procurement Highlights | Material selection shall comply with NACE MR0175/ISO 15156; internal coating parameters must be clearly defined, and a complete MTC is required. |
Corrosion protection for drill pipes is a systems‑level endeavor that requires multidimensional coordination, spanning material selection, coating-based protection, drilling fluid management, and on‑site operational practices. A thorough understanding of corrosion mechanisms and influencing factors, coupled with appropriate material selection and rigorous inspection and maintenance protocols, is essential for extending drill pipe service life and ensuring drilling safety.
Do you need to procure sulfur‑resistant drill pipes or internally coated drill pipes for drilling projects in H₂S/CO₂ environments?
Contact Hebei Longway Petroleum Equipment Co., Ltd.
Obtain professional technical consulting
Hebei Longway offers sulfur‑resistant drill pipes SS95, SS105, and SS135, as well as internal coating services for LPC3000P and LPC5000P, and holds international certifications including API 5DP and API 7‑1.
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