P12 and P11 look almost identical on paper, yet P12 carries less chromium and silicon and a slightly higher minimum yield, so a certificate that satisfies one grade can fail the other. The difference is easy to miss on a busy certificate. ASTM A335 P12 pipe is a 1Cr-½Mo seamless alloy steel with 415 MPa minimum tensile and 220 MPa minimum yield. It appears mostly in boiler, feedwater and steam specifications from power and industrial plants across Oman. Other chrome-moly grades are on the alloy and chrome-moly pipes and tubes hub.
Where A335 P12 Pipe Is Used
- Boiler steam piping and headers built to specifications naming P12
- Feedwater and steam connections in power plants
- Replacement spools on existing P12 systems
- Moderate-temperature process lines
The closely related ASTM A335 P11 is more widely stocked, and P22 covers higher temperatures.
P11 vs P12: The Differences That Matter
|
Requirement |
P11 |
P12 |
|---|---|---|
|
Chromium |
1.00 to 1.50% |
0.80 to 1.25% |
|
Silicon |
0.50 to 1.00% |
0.50% max |
|
Molybdenum |
0.44 to 0.65% |
0.44 to 0.65% |
|
Minimum tensile strength |
415 MPa |
415 MPa |
|
Minimum yield strength |
205 MPa |
220 MPa |
|
ASME Section IX |
P-No. 4 |
P-No. 4 |
Worked example: one heat, two grades?
A heat analyses at 1.10% chromium and 0.65% silicon, with 240 MPa yield. It meets P11 (chromium and silicon both within range, yield above 205 MPa) but fails P12, because silicon exceeds 0.50%. A second heat at 1.00% chromium, 0.40% silicon and 215 MPa yield fails P11 on silicon (below 0.50%) and fails P12 on yield (below 220 MPa), even though it looks like a sound 1Cr steel. Dual certification to P11 and P12 is possible only when chromium, silicon and yield all fall inside both grades' limits, so each certificate needs checking line by line.
P12 in Sour and Hydrogen Service
In wet H2S service, NACE MR0175 / ISO 15156-2 hardness limits apply to P12 pipe and welds, with PWHT where required. Hydrogen service selection follows API RP 941. State any sour or hydrogen requirements in the RFQ; they are confirmed at quotation.
Pricing P12 Pipe
Each P12 enquiry is quoted individually, since alloy surcharges move with the market. What changes the figure:
- Pipe size, wall and total metres
- Mill minimum quantities, which matter for less common grades
- Whether the size is available now or has to be rolled
- Testing: PMI, hardness, NDT
- Certificate level (3.1 or 3.2) and inspection scope
- Delivery terms and destination port
Quotations are available in USD, OMR, AED, SAR, QAR, KWD and BHD, on EXW, FOB, CFR or CIF terms.
What to send for a quotation:
grade, NPS, schedule or minimum wall, length, quantity, end finish, supplementary tests, whether dual certification with P11 is acceptable, certification, inspection, destination port and required date.
Certification and Third-Party Inspection
P12 pipe comes with EN 10204 3.1 certificates as standard, and EN 10204 3.2 certificates on request. Inspection by the buyer's nominated third-party agency can be arranged; state your requirement in the RFQ. Review the chemistry, heat treatment details, tensile results and hydrostatic or NDE record, and specify PMI so every length is verified. See the MTC and EN 10204 certification guide.
Packing, Marking and Yard Storage
Lead time is confirmed at quotation. Each length carries the grade stencil, with end caps or bevel protectors fitted. On site, a separate, clearly labelled stack for P12 prevents mix-ups with visually identical grades, and storage off the ground with caps on keeps sand and moisture out of the bore.
Fittings and Flanges for P12 Pipe
Complete the line in the same grade: ASTM A234 WP12 buttweld fittings and ASTM A182 F12 flanges and forged fittings.
- Alloy steel fittings and flanges hub
- ASTM A213 T12 tubes, the tube form of the same alloy
- Alloy steel seamless pipes and tubes
P12 is used mainly in power generation plants and older refinery and petrochemical units.
ASTM A335 P12 FAQ
What is the difference between P11 and P12?
P12 has lower chromium (0.80 to 1.25%) and silicon (0.50% max) than P11, and a higher minimum yield (220 MPa against 205 MPa).
Can P11 pipe be used where P12 is specified?
Only with engineering approval, unless the pipe is dual certified and meets every P12 requirement, including silicon and yield.
What are the mechanical properties of P12?
Minimum tensile strength 415 MPa and minimum yield strength 220 MPa.
What is the EN equivalent of P12?
EN 10216-2 13CrMo4-5 is the nearest.
Is P12 still commonly used?
Less than P11, but it remains in many boiler and steam specifications and in replacement work.
What should I send for a P12 quotation?
Send the NPS, schedule, length, quantity, whether dual certification is acceptable, certification, inspection, destination port and required date.
Request a Quote for ASTM A335 P12 Pipes
Send the NPS, schedule and quantity, with the boiler or piping specification attached. Every enquiry is checked against ASTM A335 before the offer is prepared, so P11 and P12 requirements are never confused.