Shell Repair on a Furnace

[wagga]

HI All

I am planning to do a shell repair on a refractory lined furnace.
Bottom section of the furnace will have the refractory removed and shell cut out.

My concern is that do I need some kind of temporary structural support when the shell is cut out.
Mind you
- Refractory on the other part of the furnace will not be removed.
- The job should take about 3 days from cut out to replacement (excluding refractory work).
Shell thickness is 12mm, Plate is AS1548-7-430.

I have attached a sketch of equipment.
The furnace sits on a concrete support.

Any feedback or assistance is appreciated, especially from those who have done such job.

 

[hokie66]

Just my gut feel, but I don't think you need to support the shell temporarily.

 

[TLHS]

If you really need to, and there's no safety issue with whatever's in the furnace, you could weld stiffeners around the hole before you cut out the wall plate.

Do the walls of the furnace support the refractory? My concern would be that when you cut out the wall you break the internals.

 

[wagga]

Hi All

Thanks for the prompt reply.

We will break and remove the refractory inside the vessel where the shell shall be cut.
FYI, anchors are welded onto the shell to hold the refractory.
(After the new shell welded, will reinstate refractory).

I have attached another diagram below. From my understanding, the direction of movement (if any) would be towards the hole for the top section (as shown by the orange arrow).

The vessel is fully welded to the support saddle. I reckon welding two 3" sched 80 pipe with weld size of 10 (pipe to support) as stiffener should be sufficient. There is nothing I can use to support on top. The support bases are set in concrete.

What's your thought?

 

[SlideRuleEra]

IMHO, the pipes are a waste time, money, and make the job more difficult. The pipes don't do anything and are located where they will obstruct access to the repair area. Agree with hokie66, no temporary support needed.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[saplanti]

What is going to be supporting the refractory at the center uncut area above the cut section? Refractory in the complete circular condition is supporting itself. When lower partial section is removed the upper refractory will get loose under unsupported condition and fall. You either empty the full cross section of refractory or provide adequate support to keep upper refractory in place for safety.

The pipe connectivity close to the cut section for the stability of the vessel is necessary. You need to use the full section of the cut plate with some added margin in the selection of the pipe cross sections for the short term repair since the load path is going to change. The eccentricity that you will introduce will cause bending under the tension force on the pipes and saddle connections. Check the connections and pipes for this bending moment as well. For more detail you can check Zick analysis for pressure vessels for the available bending moment on the center cross section in the original position before cut, and figure out the tensile load on pipes and additional bending moment due to eccentricity.

You can drop the cut plate on the pipe slowly (additional weight load on pipe which will cause more additional bending on pipes) and slide the cut plate side way and remove. Do exactly opposite for the new plate, lift in place and weld.

 

[oldestguy]

The pipes do not have to be used for support of cut plate. Temporary wood blocking from the floor can do the job, with provision for the forks of an end loader or fork lift for removal. As stated by TLHS stiffeners alongside the long cuts will take care of distortion there, if any. I assume your welder personnel know about adding plate in an opening like this and the stresses developed and cared for. Looking at the loads and the location of the supports, that central area has practically no bending moment. That one large central arrow should be replaced by smaller arrows the full length of the furnace.

 

[saplanti]

One can even say that the lower portion is under compression, not in tension from the image. I believe that the image is not scaled, and the existence of bending moment needs to be checked adequately. The entire length of cut needs to be examined for the bending moment. Stability is the major concern during the repair.

 

[hokie66]

Much ado about nothing. The shell is 12 mm thick, and the thing only spans 2400. By inspection, it is OK to cut out the deteriorated part, replace it, then replace the removed refractory.

 

[SAIL3]

I suggest the OP calculate the stress in the vessel using the full section and may discover the stress in the shell so redicously low that it is ok by inspection and put an end to all this wild speculation...