Corrosion under insulation - experiences with CSA and TSA?

[robsalv]

For such a world wide issue, the topic of CUI only got 10 hits in these fora!

I'm looking into methods available for CUI mitigation.

Our current official position where insulation of piping or equipment is required and the operating temperature is within the CUI range (now considered to be -4DegC to 175DegC), is to coat the equipment or piping with an epoxy phenolic system. These systems don't cycle very well though.


The worlds best practice appears to be Thermally Sprayed Aluminium (TSA), but this isn't a technique readily available in Australia - and certainly not a readily insitu friendly technique AFAIK. I'm fully on board with it being the bees knees ultimate system for new work preemptive CUI mitigation. We have no experience with it though, so I'd appreciate any experiences that folks would care to share.


The other main mitigation strategy (in my mind at least) is an International Paints product called CSA, "cold spray Aluminium". It's not technically correct to call their system cold spray aluminium, but that is how it is marketed. To me, this system has some inherent benefits, primarily that it is a coating system, inherently understood as one, can be utilised insitu in operating plant and since it's not a niche technology, there are many mobs who can spray, brush, roll etc coatings. There isn't much experience using CSA though. I'd appreciate folks sharing their experiences.

On the CSA front, would the aluminium pigment get in the way of UT testing once applied? This might be one thing that would limit it's use, particularly in an internally corroding services.


Look forward to your experiences/comments/discussion.

Thanks in advance.

Rob

- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[SJones]

Wrapping with aluminium foil is also a proven anti corrosion measure (useful around Xmas too!). No experience with UT through TSA but 'CSA' should not give too much bother to a pulse echo thickness measurement. TSA may impact the accuracy slightly.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[ndeguy]

robsalv

For precision ultrasonic thickness measurement using two successive backwall signals from the pipe ID to represent the pipe thickness will give an accurate reading. How the ultrasound is affected by the coating material on 1st introduction to the pipe depends on the characteristics of that material.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[robsalv]

Nigel, the question regarding UT is about whether anyone can confirm or deny if CSA interferes with sound wave transmission into the parent metal.

If the pipe/equipment is in a corroding service, losing UT as a technique is one large stroke against CSA.

Cheers


- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[ndeguy]

Rob

Interfere yes, its another interface for the sound pulse to traverse with different acoustic properties. However as a thin coating and as long as its soundly bonded to the substrate material all that will be required for corrosion thickness monitoring of the ID will be increased power of the sound pulse, perhaps a reduced frequency transducer (though probably not) and a skilled technician who knows to read between successive backwall echoes rather than just to the 1st backwall echo.

I would be very surprised if a thin coating significantly reduced the capability of performing an external scan of the plant or piework.





Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[ndeguy]

Sorry, I obviously did not run spellcheck - should be pipework and not piework!!

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[robsalv]

NDEGUY, if UT testing your pies floats your boat, then go right ahead! LOL. Thanks for the laugh.


Seriously though, we have some local experience, albeit this is third hand, that the UT could not punch through the Aluminimum flakes of the CSA. Hence my question. Does this change your opinion any?

Thanks in advance

- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[ndeguy]

No, one look at me and you would know i dont have the patience to test my pie before eating it! (Glad I didnt make another typo there!)

Rob, UT is used to test composites, concrete and many other heterogenous materials. Selection of the right probe will get you through the brushed-on or rollered layer of the CSA. You may lose some resolution but you will certainly be able to penetrate the coating and get to the steel for a thickness measurement.

If you are running a Risk-Based Inspection system you will only need make the baseline inspection on all your assets and then you can reduce and isolate the numnber of inspection points. After which point measurements become principally comparative to identify high corrosion rates.

Out of interest what does the coating system manufacturer say about transparency of their applied coating to the ultrasound? If they have no comment why not rig up a demo coated piece of known thickness as a calibration block.

Regards

Chief pie-eater



Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[robsalv]

Nigel, I'm waiting on International PC to make comment about the UT issue. Stay tuned. ( I almost said, stay tubed... perhaps that was a reference to both our love of pies??? lol)

What you said makes a heap of sense. Taaa. I'm looking to do a direct CSA UT test very soon. Will keep this thread posted.



SJones, apologies for not acknowledging your post. We've utilised aluminium foil wrapping on stainless lines that are to be insulated. The conventional wisdom says that it will help avoid Cl-SCC should the insulation get wet. Haven't used foil wrap on CS lines... might be an interesting experiment though...



Not much experience on TSA? ??

- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[rustbuster]

An alternative NDE method from UT is pulsed eddy current. It will provide volumetric readings on the carbon steel through the coating, Al cladding, and insulation. It is fairly accurate in my experience.

 

[ndeguy]

Rob, Look forward to reading of your trials on the CSA.

Thats right, rustbuster. For detection of CUI RTD have INCOTEST based on pulsed eddy currents and there is also the Lixi Profiler based on low-energy radiation. Each has its own advantages and limitations - INCOTEST is for ferro-magnetic materials only and the Lixi Profiler has pipe diameter and pipe product content limitations.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[robsalv]

We haven't used pulsed eddy current - but we trialled the lixi profiler. It's fine if you have a green fields plant and can set a base line... we didn't think it was all that practical for a working aged plant though... Flash Radiography is our preferred screening method.

There were also handling issues with the profiler for example on larger pipe diameters and in close packed pipe racks...





- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[ThermalSprayer]

Just last week I had a discussion with some ExxonMobil people regarding ultrasonic thickness measurements through TSA. They take a hammer and pound on the coating until it is flat and smooth, and then they take a reading they said this works fine and it is accurate.

I work for a large thermal spray equipment and materials manufacturer and for the last 5 years I have been working with petrochemical companies (ExxonMobil, Shell, etc.) NACE, and applicators developing low cost TSA coatings.

With the proper parameters, training, and equipment, TSA coatings can be applied at the thickness required for CUI at less than $1 per SqFt / $10 Sq Meter now (the cost of gasses and wire) and at 180 SqFt / 17 Sq Meters per hour , so they are pretty cheap! I have trained over 200 applicators on how to do this.

By the way, ExxonMobil has found a TSA coating applied to a vessel operating in CUI conditions that was coating in 1958. The 50 year old coating still looks fine! The vessel was reinsulated with no maintenance work done to the coating. It is pretty evident that there is no longer lasting, less expensive coating than "true" TSA.

 

[BenThayer]

for the temperature range you listed, what materials are you using?

we have had issues with heat transfer piping corroding for jacket service of vessels where use the piping to circulate both cold and hot fluids.

we are typically using 304 SS now because we don't want to use A333 carbon steel, both due to availability and due to the costs of coatings and CUI repairs.

by the time you install 2" SCH 40 A333 and do the coatings, you could had 2" SCH 10.

 

[robsalv]

Thermal sprayer, we meet again! Are you aware of any reputable mobs in Australia who are experienced in TSA? To the best of my knowledge there are mobs around who do sprayed Zinc on structures (e.g. offshore platform components), but experience with Aluminium (Aluminum for you US guys) is low.


Ben Thayer, for the quoted temperature range where process driven corrosion was not seen as an issue, we use A106B piping. We've looked at the CS vs SS piping a few times over the years, but in Australia, the figures don't add up to drive SS as the preferred piping material. It might at <=2" diameter however... it's certainly worth considering. Is this your experience?



- - - - - - - - - - - - - - -
"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[gr2vessels]

Rob,
Check out this website in Perth, there are also some people in Adelaide, I'd be surprised to not find several on the east coast...

http://www.wearprotection.com.au/products.html

cherrs,
gr2vessels

 

[gr2vessels]

Also, contact Trevor Overton at Austral Technologies in Perth on 08 9359 1544. This company has done this type of work before.
cheers,
gr2vessels

 

[ThermalSprayer]

gr2vessels - The problem with those companies is that they usually charge too much bot corrosion coatings. They are used to applying engineering coatings such as HVOF, plasma, and arc sprayed high alloy materials. For CUI/TSA, we need to think more like blasters and painters if lower cost coaints are needed. That's why I only train blasting, paining, and insulating companies to do TSA work for petrochemical companies. If you have a good blasting company, train them how to flame spray. It's easy!

 

[gr2vessels]

T.S.,
There is no disagreement with you and I wish many more of you would help this big yellow piece of world, Australia. The first step is to identify those willing to improve, then get them on the band wagon to lift their act first, then have them follow your example, for the benefit of everyone, not just a greedy bunch. I'll kep your details handy.
cheers,
gr2vessels