ASTM A312 S31254 Stainless Steel Seamless Pipe , offshore and platform application 254 SMO is a high-alloy austenitic stainless steel developed for use in seawater and other aggressive chloride-bearing media.
The steel is characterized by the following properties:
The PRE is defined as, in weight of content %, PRE = Cr % + 3.3 x Mo % + 16 x N %
Standards
| C | Si | Mn | P | S | Cr | Ni | Mo | N | Cu |
|---|---|---|---|---|---|---|---|---|---|
| ≤0.020 | ≤0.80 | ≤1.00 | ≤0.030 | ≤0.010 | 20 | 18 | 6.1 | 0.20 | 0.7 |
254 SMO Applications:
| ASTM TP316 |
<150 h
|
Pitting
|
| '904L' |
No failure (1000 h)
|
Crevice corrosion
|
| Sandvik 254 SMO |
No failure (1000 h)
|
No attack
|
| Grade | Time to failure hours |
|---|---|
| ASTM TP316 |
105
|
| TP904L |
225
|
| 254 SMO |
425
|
254 SMO has a very low carbon content. This means that there is very little risk of carbide precipitation during heating, for example when welding. The steel passes the Strauss test (ASTM A262, practice E) even after sensitizing for one hour at 600–1000°C (1110–1830°F).
However, due to the high alloying content of the steel, inter-metallic phases can precipitate at the grain boundaries in the temperature range 600–1000°C (1110–1830°F). These precipitations do not involve any risk of intergranular corrosion in the environments in which the steel is intended to be used. Thus, welding can be carried out without any risk of intergranular corrosion.
The pitting and crevice corrosion resistance of stainless steel is primarily determined by the content of chromium, molybdenum and nitrogen. Manufacture and fabrication, e.g. welding, are also of vital importance for the actual performance in service. A parameter for comparing the resistance to pitting in chloride environments is the PRE number (Pitting Resistance Equivalent). The PRE is defined as, in weight-%, PRE = %Cr + 3.3 x %Mo + 16 x %N
Heat Treatment
The tubes are delivered in heat treated condition. If additional heat treatment is needed due to further processing the following is recommended.
Solution annealing 1150–1200°C (2100–2190°F), quenching in water. Thin-walled tubes min. 1130°C (2060°F), quenching in air/water.
| Wall thickness | Proof strength | Tensile strength | Elong. | Hardness | ||
|---|---|---|---|---|---|---|
| Rp0.2a) | Rp1.0a) | Rm | Ab) | A2" | HRB | |
| mm | MPa | MPa | MPa | % | % | |
| <5 | ≥310 | ≥340 | 675-850 | ≥35 | ≥35 | ≤96 |
| >5 | ≥310 | ≥340 | 655-850 | ≥35 | ≥35 | ≤96 |
| Wall thickness | Proof strength | Tensile strength | Elong. | Hardness | ||
|---|---|---|---|---|---|---|
| Rp0.2a) | Rp1.0a) | Rm | Ab) | A2" | HRB | |
| inch | ksi | ksi | ksi | % | % | |
| <0.187 | ≥45 | ≥49 | 98-123 | ≥35 | ≥35 | ≤96 |
| >0.187 | ≥45 | ≥49 | 98-123 | ≥35 | ≥35 | ≤96 |
a) Rp0.2 and Rp1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively.
b) Based on L0 = 5.65 √S0 where L0 is the original gauge length and S0 the original cross-section area.
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