60 Year Old 430 SS Vessel 1

[unclesyd]

Standing in the middle of large chemical plant is a scrubber column cobbled together from two 430 SS vessels from the early fifties. The structure is bottom 20 feet 430 SS, then 40 feet of CS, and the top 20 feet 430 SS. The jest of it is that the process changed and has virtually destroyed the CS section.
The internal supports for the structured packing in the bottom section were CS and they are gone too. The proposal as it stands now is to weld Austenitic supports to the 430 SS and hope for the best. The 430 SS in this section is .625 thick. As a friend of the court I made a suggestion that instead of welding bolt the support ring to the column using through wall bolts. In other words drill x number of holes though wall and attach the ring. The holes would be 3/4" or smaller. There is a tremendous amount of extra metal as the oringal 430 SS columns were designed for higher pressure and this column now operates around 20 psig at maximum.

Does anyone see a problem with this as proposed?

 

[metengr]

unclesyd;
Can you attach a basic sketch showing the above? I may have missed it, which is not that unusual, but what is the condition of the middle section (40 feet) of carbon steel shell cobbled between the two 430 stainless steel shells? At first blush I have no problem with the fastener concept for attachment versus welding; I was just trying to understand the constructability of this column.

 

[unclesyd]

I've not had any luck posting pictures or any thing of that order.
The 430 SS vessel absorber towers in a HNO# plant. The towers were in two flanged sections and used bubble cap trays with integral cooling coils. The trays were what we call "Vulcan" type. The trays were stacked from the bottom up using jack bolts for spacing and Blue African Asbestos Listing to wedge the tray and make it leak tight. They were taken out service when we got a single unit to replace 4 smaller HNO3 plants.
For this project it was deemed by someone that we would take a bottom 430 SS section make modifications, Reboiler and drain nozzle, add the CS packing support ring, and weld up all the gland holes for the cooling coils. a short section of CS was added for assembly . The bottom section was then stressed relieved.
The top section was taken from another like 430 SS absorber with essentially the same modifications except a 40' section of CS added and the whole thing heat treated, There was one final on-site weld CS/CS. Both thicknesses are the same 5/8". The 430 SS sections are pristine.

What was done was to take one 40' 430 SS flanged absorber column and make an 80' ft SS/CS/SS monolithic scrubber column.

I'll try to get a sketch up tomorrow to try to post post.

 

[unclesyd]

I think this will work. It is where the top 430 SS section meets the CS.

http://my.engineering.com/action/file/download?file_guid=231973

 

[unclesyd]

If you don't succeed, try, try, again.

As stated the column was cobbled together from several old 430 SS HNO3 Absorbers and the CS section as indicated. My area of concern where they proposed to weld is the cross hatch area in the original 430 SS section without the normally required anneal. As stated previously I think through wall bolting would have been the better option.

The column is now rated at 100 psig @ 275F and is to be rerated. The normal operating pressure is 20 psig.
The material of construction is 5/9" SA240 Gr-430 and 5/8" SA 516-70

http://my.engineering.com/action/file/download?file_guid=232379

 

[metengr]

I don't see a problem using a staggered bolt circle pattern to secure the austenitic stainless steel support ring directly to the 430 stainless steel shell. What were you looking to use for the fastener material - SA 193 Grade 8?

 

[unclesyd]

Yes. I suggested the use of 3/4' AS 193 B8 hex bolts as they are a stores stock item.

My idea may have lost out as I was told this morning that they had gotten information that you could weld on 430 SS all day without any problem, no source given.
If they go the welding I hope if it does crack the column wall will just shell out in the weld area.

 

[metengr]

unclesyd;
I did a little research on this topic using my copy of "Welding Metallurgy and Weldability of Stainless Steels" by Lippold and Kotecki.

Welding on 430 stainless steel with no post weld thermal treatment results in poor notch toughness from excessive grain growth and martensite formation. Not much you can do with the grain growth.

If the C and N levels are on the low side, despite the formation of martensite, it will be a low carbon variety that may still have adequate notch toughness. I would try an in-situ test and weld a small test bar of 304 stainless and see if you can break it loose from the 430 stainless shell. If the test bar bends against the 430 stainless steel, you should be ok with welding.

I would make sure that adequate preheat is used for the 430 stainless steel and a post weld NDT is used like Liquid PT.

 

[unclesyd]

Thanks for the information.

The varying composition of this material was my reason for concern initially. I knew the Carbon and Chromium were all over the map for the 430 SS used in fabrication of these vessels.

Just received word that the welding was accomplished with no problems.

Something very similar to the tab test, one of my favorites, was accomplish as the supports were straightened with a hammer and bar prior to the final PT.