ASTM A335 P91 Pipe Specification (Chrome Moly Pipe)

ASTM A335 P91/ ASME SA335 P91 pipe is made in Seamless Ferritic Chrome Moly Alloy used for high-temperature and anti-corrosion services. Chrome content at 8.00% to 9.50 %, Moly content 0.85% to 1.05%, Minimum yield strength 205Mpa and tensile strength 415MPa, similar to ASTM A335 P9 pipe.

Corresponding Material:

ASTM A335 P91 is for seamless pipe material, corresponding to:
ASTM A234 P91 for chrome moly pipe fittings in seamless
ASTM A182 F91 for forged flanges
ASTM A387 Grade 91 of chrome moly steel plate
ASTM A691 91 of welded chrome moly pipe

P91 pipe material has high toughness and high wear and tear resistance, it could be used in oil and gas pipelines and also could be used to manufacture pipe fittings like elbow, tee, reducers, and flanges with above standards. Differently, ASTM AA691 referred to welded pipe made from plates of ASTM A387.

Chrome Moly Pipe – ASTM A335 Pipe

ASTM A335 / ASME SA335 Pipe named chrome moly pipe as they have a high level of Chromium and Molybdenum.

Chromium will increase oxidation resistance and provides high-temperature strength, along with the better tensile & yield strength and proper hardness at room temperature. When the chromium content increased more than 12%, it can be classified as stainless steel.

Molybdenum increases the overall strength, resistance, elasticity, hardenability and overall quality, moly ensures that the material is more resistant to softening, restrains the growth of grains and lessens the chances of embrittlement. It is the single additive that is responsible for the increase in high temperature resistance (to 540-750°C) and it also improves the corrosion resistance to steel.

ASTM A335 P9/ASME SA355 P91 Data Sheet

Chemical Composition and for other P grade Pipe (P5, P9, P11, P22)

P91 Pipe Tensile Strength, Yield Strength

Elongation

Elongation in 2 in or 50mm or 4D minimum%:
For wall thickness 5/16 in [8mm] and over: Longitudinal 30% and Transverse 20%.

Elongation smaller 2 in or 50mm or 4D minimum%:
For wall thickness 5/16 in [8mm] and over: Longitudinal 22% and Transverse 14%.

For strip tests a deduction of each 0.8mm below 8mm shall be calculated with the Table 5 in ASTM A335.

Tolerances

Inside diameter not vary more than 1% from specified ID in the PO.
Outside diameter for 6mm to 40mm, vary +/-0.40mm.
For OD 40 to 100mm, +/-0.79mm.
OD 100 to 200mm, +1.59/-0.79mm.
OD 200 to 300, +2.38/-0.79mm.
Over 300mm 12 inch, +/-1% from specified OD in the PO.

Wall Thickness Tolerance

DN6 to 65, +20%/-12.5%
Abover DN65 t/D ≤5%A, +22.5%/-12.5%
Abover DN65 t/D ＞5%A, +22.5%/-12.5%

At= Specified Wall Thickness; D = Specified Outer Diameter

Referred standards of producing ASTM A335 P9 Pipe

a. ASTM A999/ A999M, Standard specification for common requirements for stainless and alloy steel pipe
b. ASTM A92, Hardness test methods for steel materials
c. E213, Instructions and practice for ultra sonic testing of steel pipe and tube
d. E309 Eddy-Current Examination methods for steel pipe products
e, E381, Inspection methods for steel bars, beams, profiles, billets and forgings.
f, E527, Numbering metals and alloys practices
g, E570, Instructions for flux leakage examination of ferromagnetic steel pipe products

Tests

Tensile tests: Transverse and Longitudinal
Flattening test
Hardness test not exceeding 250 HBW/265 HV30 [25HRC]
Bend Test shall be carried as per ASTM A370
Hydrostatic Test shall be carried , depending on the buyer a nondestructive examination shall be performed plus with hydrostatic test.

Heat Treatment

ASTM A335 P91 shall be heat treated with normalize and temper, or quench and temper, normalize temperature 1900-1975℉ [1040-1080℃], subcritical annealing or tempering temperature minimum or range 1350-1470 ℉ [730-800℃].

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