MDMT for 430F Stainless Steel 1

[kjf1]

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

 

[TomEun]

The impact testing data mainly depend on the following factors;

- 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

 

[metengr]

The minimum design metal temperature for 430F SS will be much higher than -20 deg F, which is the typical minimum design metal temperature (MDMT) for AISI Type 430 SS, based on ASME B31.3 Appendix A material for pipe line applications.

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).

 

[kjf1]

The part in question has a tube of 304SS with relatively large chunks of 430F welded onto either end. The 430F is used due to its magnetic properties (this is part of a solenoid valve). Is it acceptable by B31.3 rules to use a material below its MDMT if there is a sufficiently large safety factor in the geometry (ie. the stresses in the material will be very low due to the large size of these pieces relative to the ID of part containing the process fluid)?

 

[metengr]

The 430F SS is a material that is NOT listed in Appendix A of B31.3. There are provisions in B31.3, see section 323.1.2 where unlisted materials can be certified for use (the second half of the sentence specifies the material will meet the requiremenets of B31.3). For 430F ss this material will exhibit brittle fracture behavior at -70 deg C, and therfore, cannot be certified for use at this service temperature.

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.

 

[stanweld]

The 430 SS as part ot the solenoid actuator and not a pressure retaining part; as such, it is not subject to B31.3. As metengr states, 430 SS will be brittle but if the operating loads are small in relation to its yield strength, 430 SS may prove acceptable. I would recommend cold box testing at the minimum operating temperature to verify operational safety. Cold box testing of valves was commonly used to prove cold temp. valve actuator operation during construction of the Prudhoe Bay oil & gas processing facilities.

 

[kjf1]

stanweld:

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?

 

[metengr]

Stanweld brings up a good point in terms of the applicability of B31.3 code. However, you must proceed with extreme caution on this issue. Several thoughts to consider;

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.

 

[unclesyd]

Adding a little to the above posts aside from the aforementioned required stress relief and low MDT, 430 SS requires a solution anneal for any weldment otherwise you have a very brittle material in HAZ of the 430 SS.


What physical properties does your application require?
Corrosion resistance?
Magnetic Permeability?

 

[EdStainless]

Hold the phone, is this an ammonia refrigeration valve by any chance? Is the 304/430 weld a pressure boundary? In your design is the 430 a plug that helps for the seal or is there a cap over it that seals?
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

 

[stanweld]

kjf1
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?

 

[kjf1]

We buy this welded assembly from Parker, so we did not design it or specify its materials. I don't know why Parker chose to use 430F SS. This part is a subcomponent of our valve. The reason this is coming up now is that we have a potential application for our valve which requires a -70 MDMT, so we were looking at the design as a whole to see if we could meet that requirement. Parker was not very helpful when we asked them about the low temperature capabilities of the part.

 

[EdStainless]

kjf1, please contact me.
ed

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[metman]

Very intresting thread with some well thought-out answers and interplay. Should have been a string of stars but everyone must be busy so just gave kjf1 a star.

Horse Sense is something that horses have that keeps them from betting on people. It also keeps them from voting for people.

Leonard

 

[Carburize]

Why not do a fracture toughness test on the material at the minimum operating temperature - plug in the stress and see what sort of tolerable defect size you come up with? If it is several inches there should be no problem if its less than say 0.25-inch then change material

 

[unclesyd]

Aside from the physical and HAZ metallurgical notch, which is brittle unless solution annealed, I can only find statements that emphasize that Ferritic and Martensitic Stainless Steels are not normally used nor recommended for Low Temperature or Cryogenic Service.

This is from a booklet From US Steel and a paper from Chicago Bridge and Iron.