Product Information

Cracking tubes for ethylene

Ethylene is the largest volume petrochemical. It is an important basic chemical for many products. The principal source for ethylene is from the pyrolysis of ethane or naphtha. These furnaces are the hottest industrial furnaces using metal castings. Obviously, this is a very taxing environment for any alloy, not only do the alloy tubes and fittings have to endure the high temperature but must withstand carburization (carbon diffusion into the metal matrix), frequent heating cooling cycles and stresses due to coke build up. Kubota makes a variety of alloys specifically designed to resist carburization and high temperatures. High nickel-chromium alloys are designed to maintain high strengths, while resisting carburization. The coils are fabricated with gas shielded arc welding usingrotated hot wire machine welding or orbital welding.

Table.1 Chemical Composition of main KUBOTA cracking tube alloys (weight %)

Alloy C Si Mn Ni Cr Nb others
HK40 0.35/ 0.45 1.75 Max. 1.5 Max. 19/22 23/27 - -
KHR35CTHi-Si 0.45/ 0.55 1.5/ 2.0 2.0 Max. 33/37 24/27 1.0 Max. Add.
KHR45A 0.4/ 0.6 2.0 Max. 2.0 Max. 40/46 30/35 0.5/1.8 Add.

Catalyst reformer tubes

Catalyst reformer tubes are used to produce hydrogen from steam and natural gas. The hydrogen is subsequently converted to methanol, ammonia, town gas or is purified and used directly. Reformers operate at higher pressures and lower temperatures than pyrolysis coils. The gases are not reducing so alloy strength and creep resistance are the important properties rather than carburization resistance. Reformer alloys are usually HK or HP based with microalloys, modified to maximize high temperature physical properties. Microalloys are controlled and guaranteed to meet the published properties.

Table.2 Chemical Composition of main KUBOTA reformer tube alloys (weight %)

Alloy C Si Mn Ni Cr Nb others
HK40 0.35/ 0.45 1.75 Max. 1.5 Max. 19/22 23/27 - -
KHR24C 0.25/0.35 1.0 Max. 1.5 Max. 23/26 23/26 1.0 /2.0 -
KHR35C 0.4/0.5 1.5 Max. 1.5 Max. 34/37 24/27 0.6 /1.5 -
KHR35CT 0.45/0.55 1.5 Max. 2.0 Max. 33/37 24/27 1.0 Max. Add.
KHR MA7 0.4/0.8 1.0 Max. 1.0 Max. 16/25 23/27 1.0 Max. Add.