Modified Cr-Mo Steel Application

[Xeros]

Hi,I'm Xeros

My Client requests to fabricate the reactor with 2.25Cr-1Mo-0.25V steels.

I heard that 2.25Cr-1Mo-0.25V steels has following advantages:
- High strength therefore thickness could be decrease

However, I think that 2.25Cr-1Mo-0.25V steels has more disadvantage as follows:
- High Price for material (less thickness at same design condition but price is higher than 2.25Cr-1Mo Vessl)
- More difficult welding than 2.25Cr-1Mo steel
- More severe heat treatment than 2.25Cr-1Mo steel

THEREFORE,

I think that 2.25Cr-1Mo-0.25V steels has no advantage compared with 2.25Cr-1Mo steel except for weight decrease.


My question is why 2.25Cr-1Mo-0.25V steel is used for reactor.

 

[metengr]

Xeros;
Most of my exposure to this alloy steel has been with associates that use this material. It is common for use in heavy wall reactors because the vanadium alloy addition promotes elevated temperature mechanical property strength and creep strength in comparison to conventional Cr-Mo alloy steels. If a vessel designer can take advantage if weight reduction by lower wall thickness, this is a real savings to the client.

There is a significant downside risk of reheat cracking with this material during vessel fabrication because of vanadium. I have seen one recent presentation by a vessel manufacture at the ASME B&PV Code meeting in Los Angeles, CA in November. The cracks were a series of transverse cracks along the weld region of a reactor vessel under fabrication. The cracks were not detected by RT.

 

[stanweld]

Xeros,
The decrease in metal thickness appreciably impacts welding time and weight of deposited weld metal.

In terms of errection in the field, the decreased weight may permit the use of smaller cranes at considerably lesser costs.