tube failure in Heat exchanger

[ryu.changmyong]

Dear sir,

pls let me ask you some technical advice for tube failure in Heat exchanger.

as shown on attached Tube failure status.

I would like to know that why 8~10 q'ty yearly tube failure occured in 3, 4 pass area near by
Condensate drain nozzle that is by 2nd baffle from Tube sheet especially
since 15 year operation.

1. Tube OD 19.05, thk 1.65mm
2. Shell Side Flash Vapor : 0.3% of Terephthalic Acid contained Water, Condensate water
pH 3.8

3. Tube side : Reactor Feed
4. Material : Shell-SS304L, Tube-SS316L
5. Tube side Pass ; 4 pass

6. Tube failure major status : Founded Pitting and Crack assumed by SCC
(Stress and Corrosion Cracking) at tube outside surface.
7. Pls see attached reference status

Could you advise me of your technical opinion in this regard.

Kind regards,
Ryu Chang

 

[Guest102023]

Pull some tubes showing representative failure modes and send them off to a recognized practitioner for metallurgical failure analysis.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[davefitz]

The specific failure and component geometry need to be reviewed by a metallurgist and structural engineer respectively. Being local to t a condensate nozzle suggests backflow of drain water up into a hot tube sheet, or the condensate nozzle is imposing a piping reaction onto the tubesheet.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[mrfailure]

This is why my job exists: You need to send a representative failed tube to a lab that practices failure analysis so the engineer can identify failure mode and characteristics that explain the failure. Nothing we can do with the information you presented so far.

 

[EdStainless]

You need some expert help.
With the location of these failures local variations in Temp and/or flow look like issues.
This may be a design issue, or you ma be operating outside of the design range.
As far as I am concerned in place ECT is worthless unless you are pulling tubes for lab analysis.
I have seen pit depth calls off by a factor of 5 (both over and under) based on standards used.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[ryu.changmyong]

For information, Let me show you Lab inspection data as attached file.
Most of Tube damage occured 3 Pass and 4 Pass area at condensate Drain nozzle where rear tube sheet
to 2ND baffle especially, this is issue why this area damaged rather than other zone.
at the moment, this is related to operating level of condensate water. and due to corrosion compound
when chemical cleaning.

Lab inspection repor for sample tube summarized as follows.
1. Major damage : Pitting and Stress Corrosion Cracking
2. Tube surface crack into tube inside : 1.1mm and growing slowly
3. Most damage area : It occured at back side of Tube sheet (2ND baffle area)
in 3 pass and 4 Pass zone in a length of 600mm.
Also,Scale cluster founded this area.
4. It founded S,Cl,Na at damage tube as corrosion factor. Chloride 0.75~0.99Wt%

 

[mrfailure]

You have stress corrosion cracking. The branch cracks indicate you have sec. SCC is driven by the combination of a susceptible, material, a corrosive species, and sufficient stress. In this instance the corrosive species appears to be chlorides which will cause SCC on austenitic stainless steels.

 

[metengr]

You need to contact a heat exchanger expert to determine the source of the contaminants and to perform an evaluation of the heat exchanger. You have only partial information of what you need to determine root cause.

 

[davefitz]

You may wish to trace the drain connections and the scenarios under which the drain is opened. It is possible a backflow of drain water is occurring due to the interconnection of the drains to a common drain header, and contaminated back-flowed drain water is contributing to the SCC.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick