Micro alloy

The cracking susceptibility of a micro-alloyed HSLA-100 steel was examined and compared to that of a HY-100 steel in the as-received condition and after heat treatment to simulate the thermal history of a single pass weld. Slow strain rate tensile tests were conducted on samples of these alloys with these thermal histories in an inert environment and in an aqueous solution during continuous cathodic charging at different potentials with respect to a reference electrode. Both alloys exhibited reduced ductilities at cathodic potentials indicating susceptibility to hydrogen embrittlement. The results of these experiments will be presented and discussed in relation to the observed microstructures and fractography. 

In essence two types of carbonitride are formed in a Ti,Nb-hardened micro-alloyed steel. At high temperatures a predominantly TiN-rich carbonitride is formed. However, on cooling to lower temperatures a predominantly NbC-iich carbonitride also precipitates. Both caibonitrides are based on the NaCl structure and form part of a continuum usually described by a formula such as (TixNb. xXCzNi.2). This can be expanded to include elements such as V and Ta, so the formula becomes (TazTiyNb Vi.,. z)(CzNi.z). The formation of two types of carbonitride can be consisted due to phase separation and Fig. 10.54 shows a projected miscibility... 

Figure 10.55 Calculated mole % vs temperature plot for a micro-alloyed steel showing precipitation of TiN- and NbC-based carbides.

HP micro alloys were developed during the 1990 s. They contain traces of titanium (Ti), zirconium (Zr) and rare earths that are applied during casting. The... 

Figure 36. Benefits of Micro Alloy in reformer operation...

Recently a new-generation tube material has emerged, called Micro Alloy [1490]-[1493]. This contains not only niobium but also titanium and zirconium (or lanthanum), and has improved creep rupture strength still further. Table 24 shows the chemical composition of the tube materials. 

For the same outer diameter, the inner diameter and, therefore, the capacity of the tube can be increased. Thus more catalyst can be accomodated within a tube of a given outer diameter and, particularly when an optimized catalyst is used with improved packing and heat transfer properties, throughput is increased at (possibly) lower pressure drop than before retubing. Figure 36, demonstrates this by comparing HK 40 with Micro Alloy material. 

Description The feedstock (e.g. natural gas) is desulfurized, mixed with steam and converted into synthesis gas over nickel catalyst at approximately 42 bar and 800-850°C in the primary reformer. The Uhde steam reformer is a top-fired reformer with tubes made of centrifugal micro-alloy steel and a proprietary "cold outlet manifold," which enhances reliability. 

The carrier is a monolith with a shape similar to a honeycomb. The mineral cordierite (Mg, Fe)2Al Si50jg is used as the carrier material. Because of its system of chaimels, the carrier has an active surface of 30 000 m. The channels of the monolith are covered by a wash-coat of y-Al Oj. An alternative wash-coat carrier is a special stainless steel with 5% A1 and micro-alloyed with yttrium and cerium. By a carefully controlled heat treatment in an oxidizing environment AljO, whiskers are formed. On the wash-coat a layer of platinum metals is applied, which is responsible for the catalytic function. Platinum with 20% rhodium dominated earlier but nowadays palladium-rich alloys or pure palladium are mainly used. In 2001, the automobile industry accounted for nearly 72% of the total palladium demand. 

The reformer tubes are one of the most important pieces of equipment in a hydrogen plant. These tubes are built from micro-alloyed materials in order to handle the extreme environment in which they are exposed to. The industry standard for reformer tube design is for 100,000 hour life. To ensure that the tubes will last the designed 100,000 hour life, the reformer tubewall... 

High strength structural Micro-alloyed steels (Ti, Nb, V,B, Zr), Quality steels... 

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