Esshete 1250 (Tube and pipe, seamless)

Chemical composition (nominal), %

Forms of supply

Seamless tube and pipe in Esshete 1250 is supplied in dimensions up to 260 mm (10.24 in.) outside diameter, in the solution annealed and white-pickled condition or in the bright annealed condition.

Mechanical properties

1 MPa = 1 N/mm²

a) R_p0.2 and R_p1.0 correspond to 0.2% offset and 1.0% offset yield strengths, respectively.
b) Based on L₀ = 5.65 √S₀ where L₀ is the original gauge length and S₀ the original cross-sectional area.

At high temperatures

Creep strength

The creep rupture strength values correspond to values evaluated by Sterling tubes Ltd. The data from creep tests made by Sandvik correspond well to the given data.

* Values, which have involved extended stress/time extrapolation

* Values, which have involved extended stress/time extrapolation

Physical properties

Density: 7.9 g/cm³, 0.29 lb/in³

1) Mean values in temperature ranges

1) Mean values in temperature ranges (x10^-6)

1) (x10³)

Corrosion resistance

Air

Good resistance to scaling up to 800°C (1472^oF).

Gaseous corrosion

Good resistance to steam and flue gas atmospheres. In service conditions typical of coal-fired boilers, the alloy has a very similar fireside corrosion to alloys of the ASTM 316H type. However, the much increased high-temperature strength gives significantly improved service performance. Fireside corrosion resistance in coal-fired, biomass-fired or coal/biomass co-fired boilers is similar to that of type ASTM 347H. Steam-side corrosion is similar to that of type ASTM 347H.

Structural stability

As in other austenitic stainless steels, sigma phase can be formed after long heat treatment in the range 550–950°C (1022–1742^oF). Due to the low chromium content, Esshete 1250 is significantly less sensitive to sigma phase formation than steels of e.g. the ASTM 316 type, according to tests involving ageing for 100000 h.

Heat treatment

Tubes are delivered in the heat treated condition. If another heat treatment is needed after further processing the following is recommended:

Stress relieving

850–950°C (1560–1740°F), 10–15 minutes, cooling in air.

Solution annealing

1050–1150°C (1920–2100°F), 5–20 minutes, rapid cooling in air, gas or water.

Welding

The weldability of Esshete 1250 is good. Suitable welding methods are manual metal-arc welding with covered electrodes and gas shielded arc welding, with the TIG method as the first choice. Preheating and post-weld heat treatment are normally not necessary.

Since the material has low thermal conductivity and high thermal expansion, welding must be carried out with a low heat input and with welding plans well thought out in advance, so that the deformation of the welded joint can be kept under control. If, despite these precautions, it is foreseen that the residual stresses might impair the function of the weldment, we recommend that the entire structure is stress relieved.

As filler metal for gas shielded arc welding, we recommend filler metal type EN 12072 W Z 16 13 Nb. In manual metal-arc welding, covered electrodes type EN 1600-E Z 16 13 Nb B are recommended. The composition of these filler metals is designed to yield a weld metal with creep strength and oxidation resistance corresponding to the parent metal.

Bending

Esshete 1250 can be cold bent to narrow bending radii. Heat treatment after cold bending is not normally necessary, but this must be decided after considering the degree of bending and the operating conditions.

If post bending heat treatment is carried out, it should be in the form of solution annealing.

Hot bending is carried out at 1100–850°C (1832–1652°F) and should be followed by solution annealing.

Applications

The high creep strength of Esshete 1250, combined with its good resistance to steam and flue gas atmospheres, makes it a very suitable material for use in coal-fired boilers. The grade was developed in the United Kingdom in the 1960's, and the bulk of the material has been used in the UK power industry in 500 and 660 MW boilers.

The main application has been superheaters and reheaters operating at 570^oC (1058^oF), steam pressure 170 bar (superheaters) and 40 bar (reheaters). Typical metal temperature 600–700^oC (1112–1292^oF), in flue gas temperature 900–1200^oC (1652–2192^oF). The corrosion environment on the fireside in the UK boilers was historically very aggressive as the British coal has, typically a high chlorine content of up to 0.6%, sulphur at 1–2% and a high ash content of 20%.

Esshete 1250 has also been used successfully in superheaters in biomass boilers, burning various biofuels and producing steam at 580–540^oC (1076–1004^oF) at 60–200 bars pressure.

Trademark information: Esshete 1250 is a trademark owned by Corus