QUICK DEFINITION: 13CR PIPE (API 5CT L80-13CR)13Cr is a martensitic stainless steel OCTG designed for wet CO₂ (sweet) service to eliminate weight-loss corrosion, restricted strictly to environments with negligible H₂S (<1.5 psi) and temperatures below 300°F (150°C).
For upstream engineers, 13Cr (API 5CT Grade L80 Type 13Cr) represents the baseline Corrosion Resistant Alloy (CRA). It bridges the gap between carbon steel—which requires continuous chemical inhibition in wet CO₂ environments—and the significantly more expensive Super 13Cr or Duplex stainless steels. However, its lack of Nickel and Molybdenum makes it operationally fragile; it possesses almost no resistance to sulfide stress cracking (SSC) or oxygen-induced pitting.
COMMON FIELD QUESTIONS ABOUT 13CR PIPE
Why is my "stainless" 13Cr pipe rusting in the pipe yard?
13Cr is not weatherproof. Unlike austenitic stainless steel (e.g., 304/316), 13Cr has low chromium (12-14%) and almost no nickel. It relies on a passive film that is unstable in humid, chloride-rich air. It must be stored with ID/OD protective coatings or in climate-controlled environments to prevent storage pitting.
Can we run standard acid jobs (15% HCl) through 13Cr tubing?
Not without specific high-temperature corrosion inhibitors designed for metallurgies. 13Cr is highly sensitive to acid corrosion once the passive film is stripped. Spent acid must be flowed back immediately; extended static exposure to spent acid will cause severe mass loss and pitting.
Does 13Cr require special torque/turn values compared to L80-1?
Yes. Martensitic stainless steels are prone to severe galling (cold welding). You must use Premium connections or API connections with specialized non-metallic dope, reduce makeup speeds to <10 RPM to minimize friction heat, and often utilize couplings with anti-galling surface treatments (e.g., copper plating).
Chemical Composition and Mechanical Properties
13Cr derives its corrosion resistance almost exclusively from Chromium. It lacks the alloying elements required for passivity in reducing (sour) environments.
Element / Property
API 5CT / ISO 11960 Limit
Operational Consequence
Chromium (Cr)
12.0% – 14.0%
Provides CO₂ resistance. <12% fails to maintain passivity.
Carbon (C)
0.15% – 0.22%
High carbon content renders 13Cr effectively non-weldable.
Nickel (Ni)
≤ 0.50%
Lack of Ni results in poor toughness and low SSC resistance compared to Super 13Cr.
Yield Strength
80 – 95 ksi (552–655 MPa)
Upper yield is capped to limit susceptibility to cracking.
Hardness (API)
Max 23 HRC
Standard manufacturing limit.
Hardness (NACE)
Max 22 HRC
Strict limit for any sour service exposure.
Table Takeaway: The absence of Molybdenum and Nickel distinguishes 13Cr from Super 13Cr; this chemistry dictates that 13Cr should never be used where pH < 3.5 or H₂S > 1.5 psi.
Why is the NACE hardness limit lower than the API limit?
API 5CT allows L80-13Cr up to 23 HRC for general manufacturing consistency. However, NACE MR0175 / ISO 15156 imposes a stricter 22 HRC limit because empirical data shows susceptibility to Sulfide Stress Cracking (SSC) increases sharply above 22 HRC in trace H₂S environments.
Operational Limits: When to Use 13Cr
What is the Maximum H₂S Partial Pressure for 13Cr?
According to NACE MR0175 / ISO 15156, standard 13Cr is acceptable only if the partial pressure of H₂S (pH₂S) is below 1.5 psi (0.1 bar) and the in-situ pH is ≥ 3.5. Exceeding this limit creates an immediate risk of catastrophic brittle failure via Sulfide Stress Cracking (SSC). Note that many operators apply an internal safety factor, limiting 13Cr to < 1.0 psi H₂S.
What are the Temperature Limits?
13Cr is generally suitable up to 300°F (150°C). Above this threshold, localized pitting corrosion becomes a primary failure mode, particularly in high-chloride brines. While CO₂ corrosion rates remain low at higher temperatures, the risk of Stress Corrosion Cracking (SCC) limits its utility. Super 13Cr (S13Cr) is typically required for temperatures between 300°F and 350°F.
Can 13Cr be used in water injection wells?
Only if the water is strictly de-aerated. 13Cr is extremely sensitive to dissolved oxygen. If oxygen levels exceed 10 ppb, the passive film breaks down, leading to rapid, deep pitting. If oxygen ingress cannot be guaranteed (e.g., poor scavenger maintenance), lined pipe or GRE is preferred.
When 13Cr Pipe Is the Wrong Choice
Engineers often misapply 13Cr by assuming it is a "better" version of carbon steel for all environments. It is not. Avoid 13Cr if:
H₂S is Present (>1.5 psi): The material will crack. Upgrade to Super 13Cr (safe up to ~3.0 psi depending on pH) or Duplex.
Oxygen is Present: Aerated surface water or shallow aquifer water used for workovers will destroy 13Cr tubing.
Acidizing is Frequent: If the well requires regular acid stimulation, the cumulative corrosion loss on 13Cr may outweigh the benefits of CO₂ resistance, unless strict inhibition protocols are followed.
Workover Costs are Low: If a well is shallow and accessible, inhibited carbon steel (L80-1) is often more economic than 13Cr, provided the corrosion rate is manageable (< 3-5 years tubing life).
Frequently Asked Questions (Decision Logic)
Can I use 13Cr for gas wells with high CO₂?
Yes, provided the gas is "wet" (contains produced water). In dry gas streams, carbon steel is sufficient because CO₂ corrosion requires water phases to occur. However, if water breakthrough is expected later in the well life, 13Cr is the standard preventative selection for high CO₂ partial pressures.
Will 13Cr fail if the pH drops below 3.5?
Yes. At pH levels below 3.5, the passive chromium oxide layer becomes unstable. This leads to generalized corrosion rates similar to carbon steel, but often with localized pitting. If formation water is naturally acidic or high CO₂ pressure drives the pH down, Super 13Cr (which contains Molybdenum) is the mandatory upgrade.
What are the alternatives if 13Cr is insufficient?
The immediate upgrade is Super 13Cr (S13Cr), which adds 4-6% Nickel and 1-2% Molybdenum, raising the H₂S limit to ~3.0 psi and temperature limit to ~350°F. If H₂S is higher (e.g., >3 psi) or chlorides are extreme, the selection moves to 22Cr Duplex or 25Cr Super Duplex. For extreme sour service, Nickel Alloys (Alloy 28, Alloy 825) are required.
