Alloy pipes are tubular with higher percentages, than standard
carbon steel pipes, of alloying elements as Molybdenum (Mo),
Chromium (Cr), Nickel, etc. Actually, the ASTM A335 covers
“low-alloy” steel pipes, i.e. pipes that have a total amount of
alloying elements below 5%. The addition of higher percentages of
alloying elements (example Nickel and Chromium) transforms the
steel into higher alloys, like stainless steel, duplex, up to
super-alloyed materials like Inconel, Hastelloy, Monel, etc.
Alloy steel pipes are used in the energy industry for high
temperature and very low-temperature service (cryogenic), or for
applications with very high pressures.
GRADE
| Standard | Low-Alloy Steel Grade |
| ASTM A335 | P1 P2 P5 P5b P5c P9 P11 P12 P15 P21 P22 P91 P92 |
ASTM A355 Grade P1 ALLOY STEEL SMLS PIPE
ASTM A335 P1 Pipe is made up of 1% chromium, carbon, manganese,
phosphorus, sulfur, silicon and molybdenum.
The mechanical properties of the A335 P1 Vs P11 are similar with
205MPa minimum yield strength and 415MPa minimum tensile strength.
The pipes are of larger diameters. There are round, square,
rectangular, hydraulic and other forms of the Sa335 Gr.p1 Pipe. The
pipe ends differ in shape as beveled, plain and threaded ends.
These are useful in different application contexts. The thickness
of the pipes can vary from 3mm to 12mm. The ASTM A335 P1 Pipe can
be formed as cold drawn, cold rolled types. The pipes can come in
single random, double random and cut to length sizes.
A335 P1 Alloy Steel Pipe can also be further hardened by heat
treatment. The low carbon steel provides better welding capacities
in applications like petroleum, petrochemical, oil and gas and
other fluid transmission lines.
CHEMICAL COMPOSITION
| Element | C | Mn | Si | P | S | Cr | Mo |
| P1 | 0.10~0.20% | 0.30~0.80% | 0.10~0.50% | 0.025% | 0.025% | - | 0.44~0.65% |
| P2 | 0.10~0.20% | 0.30~0.61% | 0.10~0.30% | 0.025% | 0.025% | 0.50~0.81% | 0.44~0.65% |
| P5 | 0.15% | 0.30~0.60% | 0.50% | 0.025% | 0.025% | 4.0~6.0% | 0.44~0.65% |
| P5b | 0.15% | 0.30~0.60% | 1.00~2.00% | 0.025% | 0.025% | 4.0~6.0% | 0.44~0.65% |
| P5c | 0.12% | 0.30~0.60% | 0.50% | 0.025% | 0.025% | 4.0~6.0% | 0.44~0.65% |
| P9 | 0.15% | 0.30~0.60% | 0.50~0.10% | 0.025% | 0.025% | 8.0~10.0% | 0.44~0.65% |
| P11 | 0.05~0.15% | 0.30~0.61% | 0.50~0.10% | 0.025% | 0.025% | 1.0~1.5% | 0.44~0.65% |
| P12 | 0.05~0.15% | 0.30~0.60% | 0.50% | 0.025% | 0.025% | 0.8~1.25% | 0.44~0.65% |
| P15 | 0.05~0.15% | 0.30~0.60% | 1.15~1.65% | 0.025% | 0.025% | - | 0.44~0.65% |
| P21 | 0.05~0.15% | 0.30~0.60% | 0.50% | 0.025% | 0.025% | 2.65~3.35% | 0.80~1.60% |
| P22 | 0.05~0.15% | 0.30~0.60% | 0.50% | 0.025% | 0.025% | 1.9~2.6% | 0.87~1.13% |
| P91 | 0.08~0.12% | 0.30~0.60% | 0.20~0.50% | 0.02% | 0.01% | 8.0~9.0% | 0.85~1.05% |
| P92 | 0.07~0.13% | 0.30~0.60% | 0.50% | 0.02% | 0.01% | 8.5~9.5% | 0.30~0.60% |
ALLOYING ELEMENTS
The addition of Molybdenum (“Moly”) increases the strength of the
steel and its elastic limit, enhance the steel resistance to wear,
its impact qualities, and the hardenability. It also improves the
resistance to softening, makes chromium steel less prone to
embrittlement and prevents pitting.
Chromium, a key element also for stainless steel alloys, prevents
steel oxidation at elevated temperatures and increases the
resistance of steel to corrosion. It enhances the tensile, yield, and hardness properties of
low-alloy pipes at room temperatures.
Other alloying elements, present in various degrees in pipes of all
grades are:
- Aluminum: decreases oxygen from steelmaking
- Boron: used to produce fine grain size and enhance steel hardness
- Cobalt: used to enhance the steel’s heat and wear-resistance
- Manganese: gives better steel hardenability
- Nickel: Enhances toughness, hardenability and impact strength at low
temperatures
- Silicon: decreases oxygen, enhances hardenability and toughness
- Titanium: prevents precipitation of chromium carbide
- Tungsten: refines steel grain size and enhance the steel hardness,
especially at high temperatures
- Vanadium: gives steel enhanced fatigue resistance
As mentioned, low-alloy steels have a total amount of alloying
elements below 5%; high alloy steel has a higher percentage of
these elements.
