A335 seamless ferritic alloy steel pipes for high temperature service

Dec 04, 2025

What is A335 pipe material

‌ASTM A335‌ is a steel specification widely employed in high-temperature and high-pressure environments, distinguished by exceptional heat resistance and creep performance. Its alloy composition-primarily chromium and molybdenum-confers superior corrosion resistance and elevated-temperature strength. Maintaining robust mechanical properties even above 500°C, A335 steel is extensively utilized in high-pressure boiler systems across petroleum refining, chemical processing, power generation, and aerospace industries.

Chemical Composition of Other Grades of Specification Chrome Moly Alloy Seamless Pipe A/SA335

Grade	UNS	C≤	Mn	P≤	S≤	Si≤	Cr	Mo
P1	K11522	0.10~0.20	0.30~0.80	0.025	0.025	0.10~0.50	-	0.44~0.65
P2	K11547	0.10~0.20	0.30~0.61	0.025	0.025	0.10~0.30	0.50~0.81	0.44~0.65
P5	K41545	0.15	0.30~0.60	0.025	0.025	0.50	4.00~6.00	0.44~0.65
P5b	K51545	0.15	0.30~0.60	0.025	0.025	1.00~2.00	4.00~6.00	0.44~0.65
P5c	K41245	0.12	0.30~0.60	0.025	0.025	0.50	4.00~6.00	0.44~0.65
P9	S50400	0.15	0.30~0.60	0.025	0.025	0.50~1.00	8.00~10.00	0.44~0.65
P11	K11597	0.05~0.15	0.30~0.61	0.025	0.025	0.50~1.00	1.00~1.50	0.44~0.65
P12	K11562	0.05~0.15	0.30~0.60	0.025	0.025	0.50	0.80~1.25	0.44~0.65
P15	K11578	0.05~0.15	0.30~0.60	0.025	0.025	1.15~1.65	-	0.44~0.65
P21	K31545	0.05~0.15	0.30~0.60	0.025	0.025	0.50	2.65~3.35	0.80~1.60
P22	K21590	0.05~0.15	0.30~0.60	0.025	0.025	0.50	1.90~2.60	0.87~1.13
P91	K91560	0.08~0.12	0.30~0.60	0.020	0.010	0.20~0.50	8.00~9.50	0.85~1.05
P92	K92460	0.07~0.13	0.30~0.60	0.020	0.010	0.50	8.50~9.50	0.30~0.60

Tensile Requirements of Chrome Moly Alloy Seamless Pipe A/SA335

	Seamless
	P-5	P-9	P-11	P-22	P-91	P91 shall not have a hardness not exceeding 250 HB/265 HV [25HRC].
Tensile Strength, min., psi
ksi	60	60	60	60	85
MPa	415	415	415	415	585
Yield Strength, min., psi
ksi	30	30	30	30	60
MPa	205	205	205	205	415

A335 Specification

A335 Pipe	Over		Under
NPS [DN]	in.	mm	in.	mm
1/8 to 1 1/2 / DN 6 to 40	1/64 (0.015)	0.4	1/64 (0.015)	0.4
Over 1 1/2 to 4 / DN 40 to 100	1/32 (0.031)	0.79	1/32 (0.031)	0.79
Over 4 to 8 / DN 100 to 200	1/16 (0.062)	1.59	1/32 (0.031)	0.79
Over 8 to 12 / DN 200 to 300	3/32 (0.093)	2.38	1/32 (0.031)	0.79
Over 12 / > DN 300	+/- 1% of the specified outside diameter

ASTM A335 vs ASTM A691 Comparison Table

‌Parameter‌	‌ASTM A335‌	‌ASTM A691‌
‌Standard Type‌	Seamless Pipe	Electric-Fusion-Welded Pipe
‌Manufacturing Process‌	Hot-rolled/Cold-drawn seamless forming	Plate rolling + Submerged Arc Welding (SAW)
‌Material Scope‌	Chromium-Molybdenum Alloy Steel (Cr-Mo)	Carbon Steel & Cr-Mo Alloy Steel
‌Common Grades‌	P1, P5, P9, P11, P22, P91	1CR, 1.25CR, 2.25CR, 5CR, 9CR
‌Wall Thickness‌	No weld limitations (thick-wall suitable)	Limited by welding process
‌High-Temp Performance‌	Superior (≤650°C, no weak zones)	Limited (≤550°C, weld seam vulnerability)
‌Inspection‌	Optional UT/ET	Mandatory 100% RT/UT for welds
‌OD Tolerance‌	Strict (±0.4%~1% D)	Moderate (±0.75%~1.25% D)
‌Key Applications‌	Supercritical steam lines, Hydrocrackers	Boiler feedwater, Oil/Gas transmission
‌Cost‌	Higher (complex process)	20-30% lower (welding efficiency)

Test and inspection of A335 Pipe

Non-destructive testing (UT ultrasonic, RT radiographic testing).
Hydraulic pressure test (to ensure pressure bearing capacity).
Supplementary requirements (such as grain size, hardness test, etc.).

test

Packaging and shipping

Bundles (hexagonal)
Wooden Boxes
Crates (steel/wooden)
Special crates for U-Bend tubes with each radius separated

shipping