Mr Prabhukumar and Mr Mohamood,
I would like to add some more points in this discussion.
At the early part of my career in India(1980’s), I had handled welding and metallurgical requirements for urea plant equipments, reactors, strippers, carbamate separators/ condensers for a few fertilizer projects. Also had to travel few times to fertilizer plants to perform such weld repairs as needed.
Snamprogetti design specification SPC.CR.UR-510-Austenitic S.S in High Pressure Urea Equipments, typically involves 316L(Mod) and 310(Mod) urea grade base metals and welding consumables. The very basic welding and metallurgical requirements for urea service are :-
- Very low "C" (typically 0.025-0.03%) weld metal to safeguard against sensitization.
- Very Low (<1%) or Nil Ferrite so as to avoid duplex structures, avoid any chances of sigma phase during service and avoid aggressive corrosion of urea carbamate.
- Welding Procedure /PQR have to pass ASTM A 262 Practice C or Huey Test. This involved 48 hrs x 5 cycles = total 240 hrs of corrosion test.
- Passing this test is extremely tough. Unless both base metal, welding consumables meet this Practice C requirements comfortably, welding coupon will not pass this test.
In situ repair inside a vertical reactor with the smell of ammonia all round is not very easy. Generally area to be repaired should be steam cleaned, dried and thoroughly ground before executing any repair.All the process products shall be thoroughly removed prior to any welding work. Performing GTAW without proper clean up just causes misery.
Typically urea grade SMAW electrodes 316L(modified) and 310(mod) involve high manganese.Unless properly baked and handled as per manufacturers guidelines and without proper welder’s training, deslagging and achieving good welding quality could be difficult.
Thermanit 25/22 H, is higher alloyed than 316L base metal (liner) with better corrosion resistance. As per the attachment the reported corrosion resistance of 19/15H electrodes are max. 3.3 μm/48 h (0.54 g/m2h), while for Thermanit 25/22 H, the reported rate is 1.5 μ/48 h max., (0.25 g/m2h),(Huey test or ASTM A 262 Practice C). As a rule of thumb.this electrode would ensure better corrosion resistance of the weld but the interface/ HAZ could be a suspect, should the base metal and HAZ have corroded in the reported failure.
The change of electrode is easy but the root cause may involve something else. A few of the common causes for liner failures could be :-
- Weld defects- lack of fusion defects and wormholes ,could be easy initiators.
- Improper weld chemistry(not meeting any of the above requirements), higher ferrite in the weld
- Improper Welding Parameters and welding techniques (stringer beads with 40-50% bead overlap would be better)
Mr. Mahmood , should you perform failure analysis of the failed weld and then decide on the action plan as such change of electrodes, possibly the long term solution would be better. Also you need to take look at the operating conditions of the reactors also.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Prabhu Kumar L
Sent: Friday, June 25, 2010 1:25 AM
To: materials-welding@googlegroups.com
Subject: [MW:5737] RE: 5732] Urea reactor lining repair
Dear Mr. Mohamood,
ER310(mod) Thermanit 25/22H or ER310LMo Sandvik 25.22.2 LMn – Super austenitic stainless steel filler metal would be the better choice for welding/repair on urea grade 316L materials, since it will produce 100% austenite at all temperatures. The erosion corrosion would be more likely to occur in the welded area where there are high stress concentrations and HAZ as well due to high pressure/temperature involved in urea reactors.
For information, the best choice for urea reactor lining should be with Titanium in order to avoid erosion corrosion problems since it involves with high pressure and temperatures. (In my previous employer, we have carried out many reactors with 5mm Ti lining. Again it is depends on operating pressure/temperature and other service conditions)
In fact ER316L (mod) would meet the requirements of ferrite and better resistance to corrosive environments in urea reactors. Please check the ferrite content in the welds, it should be < 1% to avoid corrosion cracking and other related problems. The selection of filler metal from the selected manufacturers would be helpful since very limited manufactures are available to produce SS electrodes with nil ferrite such as Avesta, Sanvik etc.
In general welds in urea reactor shall have nil ferrite or less than 1 % ferrite in order to avoid stress corrosion cracking problems. One of the disadvantages of Ferrite will reduce resistance to stress corrosion cracking in service environments like urea reactors. In such cases, the weld metal is added with more than 5% Mn to take of hot cracking problems.
Regards,
L. Prabhu kumar,
Sr. Principal Engineer,
Equipments & Materials Dept.,
Saipem India Projects Limited,
Nungambakkam High Road, Chennai - 600 034, India.
Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,
Mobile Ph. No.: +91 9003010978.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Mehmood Javed
Sent: Thursday, June 24, 2010 3:56 PM
To: materials-welding@googlegroups.com
Subject: [MW:5732] Urea reactor lining repair
Dear Mr. Prabhu Kumar,
We are using ER Thermanit 19/15H for restoration of lining welds of our Snamprogetti Urea reactor. Material of lining is 316-L (mod) Urea grade. But after one year of service the repaired welds again undergo erosion/corrosion. Can we use ER Thermanit 25/22H instead, for a better life of repaired welds?
Regards,
Mahmood
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