high strength pressure vessel materials

[ktgottfr]

Hello,
I am in the process of doing the preliminary design on a pressure vessel with a couple of unusual parts. The main part I am concerned about at the moment is a 'spring tube' that will be welded to an opening on the main pressure vessel body.
This spring tube is basically a series of tubes of increasing diameters that are nested inside eachother and welded at alternating ends. This means that the largest tube will be internally pressurized, the next smallest will be externally pressurized, the next smallest internally, etc. with the smallest tube being capped.
My question is two-part. The first part is, what are some good high-strength materials that I can use that comply with ASME section viii div 1 or 2 that can be used as pressure containing parts and have an allowable stress of 250Mpa (36Ksi) or so? Can I use SA 564 type 630 (S17400) for this? Any others?
My second question is whether or not it is possible to use section Viii div 1 to design such a fixture. It certainly is not a standard configuration, yet is really not all that different.
Does anyone have any insight on this? We are in the design phase right now so we do not want to design using any materials that we will have to change in future. Thanks!
-Kristjan

 

[metengr]

The answers to your questions are as follows;

The first part is, what are some good high-strength materials that I can use that comply with ASME section viii div 1 or 2 that can be used as pressure containing parts and have an allowable stress of 250Mpa (36Ksi) or so? Can I use SA 564 type 630 (S17400) for this? Any others?

Not enough information because the design service environment is unknown for proper materials selection.

My second question is whether or not it is possible to use section Viii div 1 to design such a fixture. It certainly is not a standard configuration, yet is really not all that different.

Seek help from an experienced pressure vessel design firm.

 

[gr2vessels]

Just a small complement to metengr post;- Titanium is a strong material and ASME VIII-1 does not preclude any vessel to be designed to its rulings, even if it is outside the scope of this code. Also, Uranus 52+ is another high strength material, not quite approved by ASME, but you can look for alternatives or even direct replacement. You could also look for a FEA design of your fixture, it is a very cool method and you'll impress anyone telling how you designed the fixture. Howzat?
Cheers,
gr2vessels

 

[ktgottfr]

So I am gathering that no one knows much about S17400 (otherwise known as 17-4) as it relates to pressure vessels?
As for design conditions, we are sealing helium at around 2000psi. The design and stress analysis of the vessel is very straightforward, that is not where we are having the issue so much. Our main problems is that ASME section viii seems to not allow any common high strength steels for holding pressure.
17-4 is perfect for our application, but it is not so clear from the code whether or not it is allowed.
metengr is probably correct in that we will need to talk to a PV design firm to settle this.
I had just thought that there would be some experienced pressure vessel design engineers out there who would know off the top of their head some approved for pressure steels with an allowable stress at room temperature of around 200MPa(29Ksi). In non-pressure vessel situations there are a lot of steels that meet this criteria, but the ASME section viii code seems mostly limited to low strength/high ductility materials, which does make sense from a safety perspective.
thanks again!
-Kristjan

 

[SnTMan]

ktgottfr, it's not so much no-one knows 17-4, it is more no-one KNOWS your design conditions & application in any detail.

ASME Code allows pressure vessels to be constructed of ANY material allowed in Sec II, Part D, subject to detailed requirements in the notes and in applicable sections of the design code. Other materials may be allowed per Code Cases and perhaps Interpretations to the Code.

To make a statement about whether this or another material is suitable can be very detailed determination.

Regards,

Mike

 

[ktgottfr]

Thanks SnTMan, that is more along the lines I am looking for. In ASME section viii div 1, section UCS-5 says that low carbon steels subject to stress due to pressure are limited to the steels listed in table UCS-23.
Likewise, section UHA-11 says that high alloy steels subject to stress due to pressure are limited to the steels listed in table UHA-23. These tables only list a fraction of the steels listed in Sec II, Part D and are very specific in what sort of shapes are allowed. 17-4 is listed, which is why I am hoping it can be used, but 4140/4340 is also listed. Since I have heard many people say that 4140/4340 cannot be used in pressure-stressed components due to their carbon content level, I cannot be sure that 17-4 would also be permitted.
This is where my problem lies. We do not want to design our vessel based on section viii div 1 requirements using allowable stresses from sec II part D, only to discover much later that the material we are using is not permitted to hold pressure.
So, to be more precise, has anyone here ever designed any pressure vessel for any conditions that used 17-4 in the pressure vessel walls or any other component subject to stress due to pressure and had it successfully code stamped?
Thanks again!

 

[SnTMan]

ktgottfr, Sec II Part D lists materials for several Sections, see the columns on the right hand page.

You will see which materials are permitted for Div 1 and Div 2, with temperature limitations.

An important consideration is often weldabilty, and so you may see a casting or forging permitted where a plate is not.

If a steel is listed in Table UHA-23 it is permitted, subject to limitations as stated earlier. Not every product form may be permitted however.

Depending on details of construction bolting may be important as well, see Sec II, Part D, Table 3.

Regards,

Mike

 

[ktgottfr]

Ah, there we go! Thanks Mike! I was not aware that sec II part D had a direct listing of whether or not is was permitted. I can see now that there are a set of columns for each code section that show availability and temperature range. That is exactly what I was looking for.
Thanks everyone for their help!
-K

 

[SnTMan]

To paraphrase...You can learn a lot about the Code by just reading it.

 

[MikeMet]

You also have to consider whether you can get materials in tubular form. UHDE and Bohler both make good high strength, polyethylene process tubing, but it not considered weldable by the code.

You would be hard pressed to find someone who makes 17-4PH sst, or 15-5PH sst in tubing in small quantities. Most very high strength materials are not made into tubing on a regular basis.

You don't mention what strength you need, but you can get 100 ksi yield strength tubing made of HY100 by gun drilling, which is weldable, but maybe that is overkill

 

[ktgottfr]

Thanks for that MikeMet! We are looking for something that has an allowable stress of 30Ksi+. There appear to be a few things of that strength in ASME Section II part D, but its slim pickings.
Our problem is that this spring tube device needs to hold the entire 2800psi pressure while retaining certain mechanical resonance properties. So while we can make it with weaker steel, it would require a lot of changes due to the requisite increase in stiffness, so we want to avoid that route if at all possible. The tubes are around an inch in diameter, and we have been making them from 17-4 barstock. But it looks as though 17-4 is not weldable according to section ii. We might just figure out a way to assemble the tubes without requiring a weld though...