ASTM A312 UNS31254/ 1.4547/ 6 Mo/ 254Mo Seamless Steel Pipe for Saltwater handling

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:

• A.Excellent resistance to pitting and crevice corrosion, PRE = ≥42.5%
• B.High resistance to general corrosion
• C.High resistance to stress corrosion cracking
• D.Higher strength than conventional austenitic stainless steels
• E.Good weldability

The PRE is defined as, in weight of content %, PRE = Cr % + 3.3 x Mo % + 16 x N %

Standards

• UNS: S31254
• EN Number: 1.4547
• EN Name: X1CrNiMoCuN20-18-7
• W.Nr.: 1.4529
• SS: 2378
• AFNOR: Z1 CNDU 20.18.06AZ
  
  Product standards
• Seamless tube and pipe: ASTM A269, A213, A312, NFA 49-217, EN 10216-5
• Norsok MDS R11/R18, IOGP S-563 MDS IR111/111S/IR118/IR118S
• Welded tube and pipe: ASTM A249, A269 , A312, A358, A409
• Fittings: ASTM A182
• Bar: ASTM A276, A479, EN 10088-3
• Forged products: ASTM A473

254 SMO Applications:

• 1. Equipment for handling of seawater, such as, seawater cooling, cooling water pipes, ballast water systems, firefighting systems etc.
• 2. Hydraulic and instrumention tubing
• 3. Equipment in pulp bleaching plants
• 4. Components in gas cleaning systems
• 5. Tanks and pipelines for chemicals with high halide contents

Intergranular corrosion

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.

Pitting 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.

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.

Weldding:

Recommended filler metals

TIG/GTAW or MIG/GMAW welding
ISO 18274 S Ni 6625/AWS A5.14 ERNiCrMo-3 (e.g. Exaton Ni60)
ISO 18274 S Ni 6059/AWS A5.14 ERNiCrMo-13 (e.g. Exaton Ni59)

MMA/SMAW welding
ISO 14172 E Ni 6625/AWS A5.11 ENiCrMo-3 (e.g. Exaton Ni60)
ISO 14172 E Ni 6059/AWS A5.11 ENiCrMo-13 (e.g. Exaton Ni59)