There is a leakage from the
nozzle of our urea reactor through weep holes (02 weep holes in the
nozzle body), which indicate the liner inside is somewhere damaged. I am
attaching its drawing too. The nozzle is attached to the top hemihead.
Can somebody guide how to repair?
|
the first thing you have to do is
drop the pressure
gas free the reactor
do a LPT examination all around attachment weld for sleeve liner weld to shell and sleeve liner to flange.
find the bad spot if it is not visible
then write out your repair procedure depending on the type of repair to be done and notify your AI for NBIC
repair the weld or bad spot in liner
pt the welds
bolt it back up
|
|
The nozzle inside diameter is
92 mm and O.D is 237 mm (hence t=72.5 mm). The problem is: 1. How to do
LPT inside the liner sleeve; we can only do the LPT at the liner inside
joint (not the sleeve because of difficulty in accessibility)). 2. How
can we find the extent of corrosion in the nozzle body behind the line
(I mean corrosion of C.S portion). 3. If the damage is located by some
means inside the nozzle (the portion between nozzle flange and joint
with vessel hemihead), How to repair it. I am asking this because the
nozzle inside will not be accessible by welding repair.
Btw the liner material is 316L UG and the nozzle body material is C.S.
|
|
Thanks for reply ..I want to know:
1. How we can do LPT inside of nozzle (550 mm length from vessel inside to nozzle opening).
2.
Besides repairing the liner we also need to find the extent of damage
done to C.S portion of the nozzle; so that it may be repaired if badly
damaged due to corrosion by carbamate solution). (The O.D of nozzle
extended portion is 237 mm and I.D is 92 mm so thickness is 72.5 mm)
Note that material of liner is 316L UG and nozzle body is of C.S)
|
|
| roca (Mechanical) |
20 Feb 09 1:27
|
cut out the complete nozzle and replace with a new clad nozzle - unless it is absoloutely required to use a loose liner
|
|
 ak1965 (Mechanical) |
20 Feb 09 3:56
|
Dear franklin55
I have seen some difficult to find urea reactor leaks...and attended them..!
If
the leak rate is high and it warrants and immediate shut down....you
must shut down and evacuate the reactor...! Take care the leaky area
must be kept hot with the help of steam hose to avoid choking of passage
due to soildification of liquid carbamate....! Post opening the reactor
& proper purging....Enter the reactor with proper scaffoldings and
ladders....! Please do not allow any one to go inside with shoes with
Ferritic nails....dangerous to reactor.....!
The air @0.5
kg/cm.2 should be injeted through the leaky weep hole & the
corresponding weld seams on the liner inside, should be checked with
soap solution...you will see the bubbles coming out from leaky
point.....this must be done with extreme care and attention bacause the
leaky points get squeezed up after cooling of reactor and it becomes
difficult to locate the leak....! It is very much likely that you may
get a delayed response from leaky point after pouring soap solution on
it due to a very tight opening....so wait patiently after pouring Soap
Solution....! Do not rush...!
Once your are sure of the leak
location, you need to grind the affected point with a non magnetic
griding wheel...! Carry out DP Test on affected area to confrim the
extent of defect.Dont forget to clean the soap solution before DP
Test...!
In addition, carry out a visual inspection of weld
seams of whole reactor and mark out the points of undercuts , visual
porosities, pin holes etc. Also mark the weld seams that has appreciably
coorroded. It is a must because your company may not afford to open the
reactor again and again...!
Also DPI should be done on all suspected weld seams.
Once you are through with marking of defects. make a weld repair plan....I believe there could be 10 trays in your reactor....!
Repair all weld defects sequentially...using ER316L..i believe the Liner material SS316L. Ask your welder to
fill
the ground portion at leaky portion carefully using low currents and
fuse the small porosities found in visual inspection and DP test without
using a filler wire...! he has to just use the heat and fuse the parent
material.
After you are through with weld repair.....Check the
ferrite content on weld deposit...it should be less than 1....Carry out
DP Test again on the leaky portion....!
Clear all garbage from the reactor....and box it up...!
All the best to you.....!
|
|
Thank you very much Mr. ak1965 for your detailed reply.
You
have elaborated the repair procedure for the shell specifically. The
problem with our reactor is that the leakage is from the weep hole of
nozzle only ( not from the reactor shell weep holes). This nozzle is
attached to the top hemi-spherical head. The throat of the nozzle is
approximately 600 mm and inside diameter is 92 mm. Can I draw conclusion
from your discussion that: the liner can only leak from the weld joints
(i.e joint with the adjacent piece of liner)? and if for example the
leakage is from the inside portion of the nozzle , how can it be
repaired? Also I want to ask that the nozzle body (whic is of ASTM A266
Cl.2 material) may have been damaged by coming in contact with carbamate
solution. Is there any method to find the extent of damage to the
nozzle body from inside???(i.e. behind liner)
Note that the liner material is 316L UG
Please also check the picture attached at the beginning of thread for details.
|
|
| ak1965 (Mechanical) |
20 Feb 09 12:09
|
Dear franklin55
Nozzle
also should have a liner...my experience says that reactors always leak
from the weld joints of liner initially....however if the leak is not
attended and carbamate comes in contact with shell....the damages are
far beyond imagination....!
It is rare that liner parent metal
fails...as you know...weld joints are always more vulnerable to
fail....! I have always found the leakage from the weld joints in a Urea
reactor. The places having notches like corners of support cleats or
crevices in the weld joints are more prone for SCC...! that is why I
insisted for thorough inspection of all weld joints in reactor...! be
assured..may look tough...but it would improve the reliability of your
reactor...!
I am not aware the prodcution criticality in your
case...because it takes 2 or 3 days for reactor to cool down enough for
entry..& around a week to complete inspection , repair and box
up....you to decide on this...
It is very relevant to ask about
damage on nozzle body....!! Nozzle parent area being a small one and
without multi layering body...you can easily scan the area with
Ultrasonic flaw detection...that would reveal any thinning or damage if
had taken place in that region....! you must do this...this is very
critical....! However, before doing UT, do a simple experiment...inject
steam from one weep hole...steam should exit freely from the other weep
hole confrming that steam is not going elsewhere...
Normally the
neighbouring weep holes are interconnected....so refer the weep hole
drawing to know the exact lay out of weep holes. In your case 02 weep
holes are leaky so they must be interconnected..through internal
channels in engraved on nozzle body.
I used an innovative
technique in our urea reactor with multilayered sehll construction to
know the extent of damage caused during leakage from 02 weep holes in
the shell.......I did the radiography of affected area..results were
quite revealing...!and no damgewas seen on the sehll ...reactor is still
doing well even after 6 years of repair....though i have left that
organisation 2 yrs before...I still derive great satisfaction from the
success of that job.
Hope above info should further help...!!
I know the urea reactors act naughty and fuzzy..once leak...so be extra careful...!
All the best.....
|
|
Thanks again for your prompt reply.
We
had thought same thing here ( I mean Ultrasonic Flaw Detector) as a
means of detecting the damage to C.S portion material of the nozzle.
But the radiography technique as you mentioned is really an innovative
idea (In the sense that it can only give the comparison of the metal
thickness at different points, and not the exact thickness)..Now if the
nozzle thickness is reduced due to corrosion at some area..what should
be the next step, (thickness of the forged C.S portion is 72.5 mm,how
much reduction in thickness will be alarming
By the way your advice is directing us gradually towards the right direction.
Thanks in advance.
|
|
| ak1965 (Mechanical) |
20 Feb 09 17:25
|
It would be my pleasure if i could be of some use in reviving your the reactor...!
Radiography
is indeed innovative, however, you would need a cobalt60 radioactive
source for this thickness (72.5mm) but it ismore useful for urea
reactors with multilayered shell. so better to go for an easier method
i.e. UFD.
In my opinion, the chances of corrosion on forging is pretty less...& the leaky reactor can also run long unless
carbamate
solution comes in contact with the shell...! however if carbamte comes
in contact with shell material.. it can eat away CS at unbelievable
rate.
Consider a case when the repair of the damaged nozzle
forging is unavoidable...however, that would depend on the extent of the
damage...ideally a nozzle with any appreciable thickness reduction
should be replaced..but replacement being a big task, a local repair
with metal deposit by welding can also be a good solution. However, you
would need a nicely prepared WPS and a Post weld heat treatment for the
repaired portion. The liner of nozzle may also be replaced, if found
damaged.
So first inspect reactor carefully fix the extent & type of of damage......next action plan would come up accordingly.
Be
prompt now and move on....by the way... which part of the world your
plant is located is it Kellogg or Snam technology......?
|
|
Thanks once again. we have
planned the activity and I shall update as the course of events take
place. Our plant is situated in the indian sub-continent and our urea
plant is designed by TOYO of Japan (Its TOYO ACESS Process)
|
|
Dear ak1965,
You have
mentioned that things with ferritic content should not be taken inside
the reactor. What is the possible damage due to ferrite to urea
reactor???
|
|
| ak1965 (Mechanical) |
24 Feb 09 4:40
|
Dave5599
The presence of iron or ferritic materil can easily contamintae welding being done in the reactor......!
You
may be aware that a contamintaed weld joint would easily corrode under severe corrosive conditions with carbamate.....! This is alsois a reason
for using SS316 L with low carbon to avoid carbide preciptation due to
presence of ferrite....!
|
|
Dear ak1965,
You have
mentioned that things with ferritic content should not be taken inside
the reactor. What is the possible damage due to ferrite to urea
reactor???
|
|
Thank you ak1965 for explaining and sorry for repeating my question. (i repeated the question by mistake)
Anyhow
I had asked the question because we used to install C.S pipe
scaffolding during inspection work in reactor, but no welding job has
been performed uptill now ( after 11 years of its operation)..I think
that will not be harmfull..if there is no welding activity inside.
|
|
| ak1965 (Mechanical) |
25 Feb 09 13:09
|
dave5599
yes....normally
scaffolding material should not cause the problem unless ferrite gets
into the weld metal....risk is less....however...ferritic material
should be avoided especially during welding inside the reactor...because
any loose iron particle may prove catastrophic to welding repair.
I suggested franklin because they plan to weld inside...!
No comments:
Post a Comment