Pulp Batch Digester Cracking Problem

I would consider evaluating the situation for chloride ion induced SCC (stress corrosion cracking). What makes me think that are:

1. High temperates

2. Cracks in heat affected (weld) zones

3. Presence of chloride ions in most paper process chemistry.

A visual exam should indicate by the presence if inter granular verses intra granular cracking.

Welders describe welding in many SCC areas as spider-webbing or chasing the cracks while they are welded.

This could aslo explain the success of the duplex steels and raise questions about welding materials.

I hope this helps.

My experience with 312 weld overlay it has high stresses after application which can lead to cracking issues and under bead corrosion problems. I have a number of vessels metallized with plain Inconel 625 that has lasted for over 14 years. Now there is a better material than Inconel 625 which is better for the process chemistry. This material out last anything currently being use until your retirement ("It is that good"). If interested in knowing more visit arcmelt.com web site and review their 3201 material and contact their Field Service Manager.

Good Luck

Tin-Man

Thanks for the replies. The reason we switched from 316 to 312 is because we were getting allot of SCC. This is the first 312 cladded flange I have had any cracks in so far out of all the ones I have put into service in the past 3 years. I have a job starting on 6/2/08 where a contractor utilizing a patented process will apply a 3/16" thick 312 s/s weld metal overlay to the entire inside wall of one of our digesters. I would like to have inconel cladding installed here but the cost is prohibitive in our case (we could just build a new digester for nearly the same amount) We get a 7 year "fix it for free" warranty on material and workmanship with the 312 cladding and this is the best warranty I have seen from the many different contractors. As I said we have one digester that is made from duplex stainless and we get hardly no wear or corrosion on this material. Duplex stainless steel has went up so much in cost that building any more from duplex is out of the question when one compares the ROI of the duplex digester with the carbon steel digester. Again, thanks for the replies all.

pipewelder

Pipewelder,

I would be interested on the 312 overlay detials and success. You indicated it was a patented process, could you provide more information, contractors, suppliers or website?

Paddler

paddler, I see your from "Sweet home Alabama". I am just across the line in North Georgia. Actually I was raised in (LA "Lower Alabama") myself. The contractor that is doing the cladding on our digester is Welding Service Inc. out of Norcross Georgia. The patented process they use is called Unifuse 312. They also do other alloys as well. Welding Services Inc. is one of the largest automated welding companies in the US if not the world. I had them do some base metal build up on one of my other digesters earlier this year and I was impressed with the whole operation. If you would like more information including contact names and phone numbers I can e-mail you direct if you give me your address. We are required to get at least 3 bidders on a job this size and I have a list of other companies that do this type of work as well.

pipewelder