MDMT for 430F Stainless Steel
MDMT for 430F Stainless Steel
(OP)
Does anyone know where I could find any published data on the minimum design metal temperature (MDMT) for 430F stainless steel, or at least some impact testing data for this material at low temperatures (-70C)?
Thanks
Thanks





RE: MDMT for 430F Stainless Steel
- Melting process at mill (electric, vacuum, etc.)
- Chemical elements (C, N, S, P - negative elements, etc.)
- Heat treatment (temperature, cooling methods, etc.) for base metal and new products
- Grain size
Additionally it also depend on the operating condition at high temperature (the temperature and duration time).
As a result, 430F SS has wide range of MDMT or impact test absorbing energy values. It normally ahs the MDMT over than -29 deg.C because it has been developed from 430 SS (-29 deg.C of MDMT) for the improvement of machining (increased S & P).
So it is recommended to do the impact test per the facility code and standard (and drop weight test per ASTM E208) with test coupons for the MDMT.
Probably you may get the MDMT, -29 to +21 deg.C from the tests.
Hope this helps.
Thomas Eun
RE: MDMT for 430F Stainless Steel
Considering the 0.15% min sulfur content for the F grade, this will increase the ductile to brittle transition temperature. The AISI Type 430 F is not recommended for use at -70 deg C, it will exhibit brittle fracture behavior (I would estimate the Charpy V-notch impact energy to be at or below 5 ft-lbs for this material at -70 deg C).
RE: MDMT for 430F Stainless Steel
RE: MDMT for 430F Stainless Steel
Your only other option is to use an alternative ferritic material, perhaps like one of the 3.5% Ni-bearing grades specified in SA 203. These plate steels are weldable to 304 SS, and can safely handle the low temperature service.
RE: MDMT for 430F Stainless Steel
RE: MDMT for 430F Stainless Steel
Can you give me more information regarding this "cold box" testing? Is it simply putting the valve in a chamber, reducing the temperature to the desired value, and operating the valve at its design pressure to see if it fails? That seems pretty risky given that we have a design pressure of 5000 psi! Also, how can you tell whether you have an appropriate safety margin? My understanding is that a vessel or pipe operating below its MDMT may not fail due to its internal pressure, but that some sort of impact may cause it to fracture and fail catastrophically. Do you subject the valve to impact while it is cold?
RE: MDMT for 430F Stainless Steel
1. You have a material that is brittle at -70 deg C. This means there is little margin for tolerance of flaws or stress risers under dynamic or even static loading conditions (like residual stresses from welding). Thick pieces as you described above can result in lower service stresses. However, this can also work against you by inducing a state of triaxial stress conditions that would exacerbate brittle fracture.
2. You have a weld that is an inherent stress riser in addition to brittle fracture behavior of one of the base metals that you are joining. There is concern for weld toe undercut, and you will require stress relief to assure the lowest possible residual stresses at these weld joints.
Any sudden impact loading, transient in service in conjunction with weld undercut can result in sudden fracture which would render the actuator inoperable in service. All of these operational scenarios needs to be carefully evaluated in this design.
RE: MDMT for 430F Stainless Steel
What physical properties does your application require?
Corrosion resistance?
Magnetic Permeability?
RE: MDMT for 430F Stainless Steel
Is there any chance that the operating rod can actually strike the 430 in service?
If so you have a problem. I don't think that you will find any martisitic or ferritic stainless that will handle -70 in the welded condition. The Ni steels are your best bet.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: MDMT for 430F Stainless Steel
The Cold Box is simply a refrigerated chamber for operational testing the valve under load. As has been previously stated, 430 SS is brittle and failure at the weld between the the 304 and 430 material is likely if subject to sufficient dynamic loading. The purpose of cold box testing is to prove your design in simulated operation. If a nickel steel will prove effective in this service, I, too, would recommend its use. Have you selected 430 SS from a corrosion standpoint or simply because it's ferromagnetic?
RE: MDMT for 430F Stainless Steel
RE: MDMT for 430F Stainless Steel
ed
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: MDMT for 430F Stainless Steel
Horse Sense is something that horses have that keeps them from betting on people. It also keeps them from voting for people.
Leonard
RE: MDMT for 430F Stainless Steel
RE: MDMT for 430F Stainless Steel
This is from a booklet From US Steel and a paper from Chicago Bridge and Iron.