Metal material having excellent metal dusting resistance

Abstract

[Objective] To provide a metal material having excellent metal dusting resistance which is suited for using cracking furnaces, reforming furnaces, heating furnaces or heat exchangers, in petroleum refining, petrochemical plants, etc.[Means for Solution] A metal material having excellent metal dusting resistance, characterized in comprising, by mass %, C: 0.01 to 0.4%, Si: 0.01 to 2.5%, Mn: 0.01 to 2.5%, Cr: 15 to 35%, Ni: 20 to 65%, Cu: 0.05 to 20%, S: not more than 0.1%, N: not more than 0.25% and O (oxygen): not more than 0.02% and the balance Fe and impurities, and also containing, by mass %, one or more selected among the elements of P: more than 0.05% and not more than 0.3%, Sb: 0.001 to 1% and Bi: 0.001 to 0.5. It may further contain one or more selected among the elements of Nd: 0.001 to 0.15%, Co: not more than 10%, Mo: not more than 3%, W: not more than 6%, Ti: not more than 1%, Nb: not more than 2%, B: not more than 0.1%, Zr: not more than 1.2%, Hf: not more than 0.5%, Mg: not more than 0.1%, Ca: not more than 0.1%, Al: not more than 0.8%, Y: not more than 0.15%, La: not more than 0.15% and Ce: not more than 0.15%.

Description

TECHNICAL FIELD[0001]The present invention relates to a metal material which is high in strength at elevated temperatures, excellent in corrosion resistance and is to be used in particular in a carburizing gas atmosphere which contains hydrocarbon gases, CO gas, and in particular in a metal material having excellent metal dusting resistance, which is suited for use to cracking furnaces, reforming furnaces, heating furnaces or heat exchangers in petroleum refining or petrochemical plants.BACKGROUND ART[0002]The demands for such clean energy fuels as hydrogen, methanol, GTL (gas to liquids) and DME (dimethyl ether) are expected to grow markedly in the future. Therefore, the refining apparatus for producing such synthesis gases will become larger-sized and will be required to be much higher in thermal efficiency and suited for mass production. Also, the conventional refining apparatus in petroleum refining and petrochemical plants, the conventional ammonia production apparatus or hydro...

AI Technical Summary

Benefits of technology

[0043]The metal material according to the present invention has an effect of suppressing the surface reactions between carburizing gases and the metal and is excellent in metal dusting resistance and therefore can be used for constructing cracking furnaces, reforming furnaces, heating furnaces, heat exchangers in petroleum refining or petrochemical plants and can markedly improve the durability of apparatus and the operation efficiency.BEST MODES FOR CARRYING OUT THE INVENTION

[0044]The reasons for restricting the content ranges for the respective elements in the metal material in accordance with the present invention are as follows. In the description that follows, the designation “%” for the content of each element means “mass %”.

[0046]A C content of 0.01% is necessary for securing the strength at elevated temperatures. However, at levels exceeding 0.4%, the toughness of the metal markedly deteriorates, so that the upper limit is set at 0.4%. A preferred range is 0.03 to 0.35%, and a more preferred range is 0.03 to 0.3%.

[0048]Si has strong affinity for oxygen and encourages uniform formation of protective layers of oxide scales such as Cr2O3. Further, it forms Si-based oxide scales under the Cr2O3 layer, which shuts off carburizing gases. This effect is produced at content levels not lower than 0.01%. At levels exceeding 2.5%, however, the toughness decreases, so that the upper limit is set at 2.5%. A preferred range is 0.1 to 2.5%, and a more preferred range is 0.3 to 2%.

[0050]Mn is necessary for deoxidation and improvement in workability and a content level of not lower than 0.01% is necessary to obtain such effects. Since Mn is an austenite-forming element, it is also possible to replace part of Ni with Mn. However, an excessive content of Mn impairs the carburizing gas shut-off performance of the protective layer of oxide scale, so that the upper limit is set at 2.5%. A preferred Mn content range is 0.1 to 2%.

[0052]Cr stably forms oxide scales such as Cr2O3 and therefore it is effective in shutting off carburizing gases. For producing such effect, a content of not lower than 15% is necessary. Since an excessive content deteriorates the workability and also deteriorates the structural stability, the upper limit to the content thereof is set at 35%. A preferred range is 18 to 33%, and a more preferred range is 23 to 33%.

Problems solved by technology

However, the heat exchange in the lower temperature range might cause problematic corrosion due to the carburization phenomenon in a Fe alloy containing a high Cr and high Ni, which is used for reactor tubes and heat exchangers.

However, the surface of those parts in a relatively low temperature within heat exchanger causes carburization due to the penetration of C from the metal surface, because the forming of the oxidized dense layers effective in suppressing corrosion are delayed due to the insufficient diffusion of Cr and Si to the metal surface from the inside, and also because the gases containing hydrocarbons are converted to carburizing ones.

As a result, fine cracks tend to appear and, in the worst case, the metal pipe in use will burst.

Further, when the metal surface is exposed, a coking, deposition of carbon on the metal surface, is caused by the metal functioning as a catalyst, which is accompanied by decreases in the passage area in the pipe and this decreases the heat transfer characteristics.

Furthermore, the metal powder formed upon exfoliation acts as a catalyst, which causes coking.

Extension of such cracking, wear and clogging in the pipe may lead to a failure of the apparatus, and, as a result, there arises the possibility that the operation has to be discontinued; therefore, due care should be exercised in selecting the manufacturing apparatus parts.

However, no sufficient effect for suppressing carburization can be obtained by merely increasing the contents of Cr or Ni in Fe-based alloys or Ni-based alloys; a metal material more resistant to metal dusting is demanded.

However, while this method may be effective in the initial stage but, during a long period of use, the thin layer may possibly spall and accordingly, the effect may possibly be lost.

However, increased contents of Si and Al may lead to a decrease in hot workability and weldability in some instances; from the production stability and plant construction viewpoint, there is room for improvement.