P110 is a high-strength (110 ksi min. yield) OCTG casing and tubing grade governed by API 5CT. It is used in deep, high-pressure wells requiring substantial burst resistance. It fails catastrophically in sour environments (H₂S) or via hydrogen embrittlement if manufacturers maximize yield strength without adequate tempering.
COMMON FIELD QUESTIONS ABOUT P110 PIPE
Can I reject P110 pipe based on high field hardness readings?
No. Under API 5CT, there is no maximum hardness limit for Grade P110. A field reading of 34 HRC or higher is not grounds for rejection unless the customer specification explicitly overrides API standards. Rejection is only valid if hardness variation exceeds 3.0–4.0 HRC, indicating process control failure.
Is P110 resistant to Sulfide Stress Cracking (SSC)?
No. Standard API 5CT P110 is strictly non-compliant with NACE MR0175 / ISO 15156 for Region 3 (Severe Sour) environments. It lacks the necessary alloying and tempering controls to resist hydrogen cracking and will fail rapidly if exposed to H₂S partial pressures above 0.05 psi.
Why does P110 fail in sweet wells during frac jobs?
Failures in sweet wells often result from Hydrogen Embrittlement (HE) caused by acid stimulation or frac fluid breakdown. If the mill produced the pipe with a yield strength near the upper limit (140 ksi) to achieve "High Collapse" properties, the steel acts like Q125 and becomes brittle under stress.
1. The Tempering Temperature Loophole in API 5CT
The most critical metallurgical gray area in purchasing P110 is the lack of a mandatory minimum tempering temperature. Unlike Grades L80 or C90, which mandate tempering above 1150°F (621°C) to ensure ductility, API 5CT permits mills to temper P110 at any temperature necessary to hit the 110 ksi yield target.
How does low-temperature tempering compromise P110?
To use cheaper, lower-alloy chemistries, some manufacturers temper P110 at dangerously low temperatures (e.g., <800°F). While this achieves the required yield strength, it leaves the steel with high internal residual stresses and significantly reduced Charpy V-Notch toughness. This "stressed" microstructure is prone to catastrophic failure under dynamic loads, such as hydraulic fracturing.
How can I force the mill to prove stress relief?
Specify Supplementary Requirement SR 15.1.2 on your Purchase Order. This mandates that the mill record and report the specific tempering temperature, allowing you to reject heats tempered below a proprietary minimum (e.g., 1000°F).
2. Hardness Testing: Disputes and Rejection Criteria
Field inspectors frequently flag P110 for rejection due to "excessive hardness" (e.g., >32 HRC), assuming it behaves like L80. Metallurgically, this assumption is correct regarding risk, but contractually, it is unenforceable under standard API specifications.
What is the Referee Method for hardness disputes?
Field hardness testers (Telebrineller, Equotip) are indicators, not rejection tools. API 5CT explicitly designates Laboratory Rockwell C (HRC) testing (ASTM E18) on a through-wall specimen or quadrant as the Referee Method. If a field test shows high values, a ring must be cut and tested in a lab before any rejection is valid.
When is rejection valid for hardness?
While absolute max hardness is not capped, API 5CT §7.8/7.9 restricts hardness variation. If laboratory testing reveals a variation greater than 3.0 to 4.0 HRC units across a single specimen, the pipe can be rejected for non-uniform heat treatment (Process Control), regardless of the absolute values.
Can we reject P110 if the hardness exceeds 35 HRC?
Not under standard API 5CT. Unless your company's private specification sets a maximum hardness (e.g., "Max 30 HRC"), the mill is compliant even at 35+ HRC.
3. "High Collapse" P110 vs. Cracking Risk
"High Collapse" (HC) P110 is not a distinct API grade; it is a marketing designation for P110 manufactured with tighter ovality tolerances and yield strengths pushed to the upper limits of the specification.
How does high yield strength increase embrittlement risk?
To achieve HC ratings, mills target yield strengths between 130,000 and 140,000 psi. At this strength level, the material's susceptibility to environmentally assisted cracking (EAC) parallels that of Grade Q125. If annular fluid is trapped behind this pipe during cementing, exposure to breakdown products from frac fluids or acid jobs can trigger Hydrogen Embrittlement.
Does High Collapse P110 require special cementing protocols?
Yes. Because the steel is closer to a brittle fracture mode, a flawless cementing program is critical to prevent corrosive fluids from contacting the external pipe wall.
4. Mill Certificate (MTR) Validation Protocols
Compliance officers must audit Mill Test Reports (MTRs) for specific data points that indicate sub-par processing, even if the pipe nominally meets API 5CT.
Data Point
Requirement
Red Flag (Reject Criteria)
Heat Treatment
Q (Quenched & Tempered)
N (Normalized). P110 cannot be normalized. It requires liquid quenching (water/polymer).
Yield Strength
110 – 140 ksi
>135 ksi. Consistently high yield indicates a brittle microstructure similar to Q125.
P & S
Max 0.030%
>0.020%. High-quality "Clean Steel" mills typically run <0.010%.
Chemistry
Reportable
High Boron (B). Used to harden cheap steel; results in unpredictable toughness.
Engineering Note: MTRs showing yield strengths consistently hovering at 138-139 ksi suggest the mill is struggling to control the upper limit, resulting in pipe with minimal ductility.
What signifies a normalized P110 on the MTR?
Look for "N" or "N&T" in the heat treatment code. This is an immediate cause for rejection as P110 mechanical properties cannot be achieved via normalizing.
When P110 pipe Is the Wrong Choice
Sour Service (Region 3): Strictly prohibited. H₂S partial pressure >0.05 psi will cause rapid Sulfide Stress Cracking.
Uncontrolled Acid Stimulation: High-yield P110 (>135 ksi) is prone to hydrogen embrittlement during acid jobs if inhibitors fail.
Low-Temp Service without Impact Testing: Standard P110 does not mandate Charpy V-Notch testing unless SR 16 is specified. Avoid in arctic/permafrost applications without supplemental testing.
Specialized FAQ: Compliance & Validation
How do we resolve a hardness dispute between field NDE and mill data?
Disputes are resolved exclusively via the "Referee Method" outlined in API 5CT. This requires cutting a ring from the disputed joint and performing ASTM E18 Laboratory Rockwell C hardness testing. Field NDE (ultrasonic or rebound) results are inadmissible for final rejection if the lab results fall within the specification.
Can we override API 5CT to set a maximum hardness for P110?
Yes. Operators can and should create a proprietary "P110-Controlled" specification that overlays API 5CT. This specification can mandate a maximum hardness (e.g., 30 HRC) and a minimum tempering temperature (e.g., 1050°F). Mills must accept these terms at the time of order; they cannot be retroactively enforced on standard stock.
What is the testing protocol for validating proprietary "P110-SS"?
Since "P110-SS" (Sour Service) is not an API grade, validation requires reviewing the NACE TM0177 Method A test reports for the specific heat. Do not rely on the stencil. Ensure the certification proves survival at the required H₂S partial pressure and pH levels for 720 hours without cracking.
Does the SR 15.1.2 requirement impact lead times?
Generally, no. SR 15.1.2 only requires the reporting of the tempering temperature, which is already recorded during the mill's Quality Assurance process. However, enforcing a minimum temperature (e.g., >1000°F) may disqualify stock material, necessitating a custom rolling and extending lead times.
