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 P2 ALLOY STEEL SMLS PIPE
ASTM A335 P2 Pipe has 0.44% molybdenum and 4% chromium. It is a low
carbon steel with 0.015% carbon and can be welded without filler
materials and at room temperature because of the low carbon
content.The minimum yield strength of the products is 205MPa and
the minimum tensile strength is 415MPa. The ASTM A335 P2 Chrome
Moly Pipe also has manganese, phosphorus, sulfur and silicon in the
composition.
The pipes come in 3mm to 12mm wall thickness with 1/8NB to 24NB
nominal bore sizes. The products come in different pressure
capacities ranging with sch20 through XXS schedules. The A335 Gr P2
Pipe can also be further hardened by heat treatment. It could be
treated with full or isothermal annealing. There are round, square,
rectangular and hydraulic pipe forms. The Sa335 P2 Pipe can be
either cold drawn or cold rolled.
The length of the pipes can be single random, double random and cut
to length sizes. There are different pipe ends such as beveled,
plain and threaded ends for varying application types. The ASTM
A335 P2 Steel Pipe is a type of ferritic alloy pip that can be used
for high temperature services such as petroleum industrial pipe
lines, heat exchangers, oil and gas transmission pipes.
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.
