NDE Methods for Insulated Plant Piping

[GL431]

We have a 10" CS line carrying sweet wet natural gas with a significant concentration of CO2. The line is insulated and runs at an elevation of 5 to 6 meters on supports for approximately 400 meters. Significant corrosion is expected in this line, despite dosing of anti corrosion agent.

We have previously done UT, which turned out to be very expensive due to the need of stripping the insulation and installing the scaffolding.

If anybody knows of advances in NDE which could allow testing of the line (while the plant is running) without the need of stripping the insulation, it would be a great help.

 

[hacksaw]

what was the result of your earlier testing?

 

[stanier]

Is it possible to run an intelligent pig? I suspect not as if the line is in plant then LREs would have been used insted of swept bends.

 

[stanier]

Have you considered the use of corrosion coupons inserted into the gas stream? These once permanently installed can be checked inexpensively with an external meter.

 

[unclesyd]

Here is one approach. I haven’t checked on the progress in several years so there ought to have been considerable improvement since I was involved. there are sevreral firms doing the work.

http://www.ndt.net/article/ecndt02/251/251.htm

 

[metengr]

We have used used the technique described below for detection of flow accelerated corrosion (FAC) damage in feedwater piping at several of our Power Plants. This system works well for detection of internal wastage of pipe material thru insulation or paint.

http://www.forgoodpower.com/fieldinspections.html

 

[SJones]

Why is significant corrosion expected "despite dosing of anti corrosion agent"? If the chemical has been selected properly (taking into account the flow regime in the pipe), and it is being injected in the right location, you should readily achieve corrosion rates of 0.2 mm year tops (actual rate to be determined by monitoring which can be at carefully selected UT windows in the insulation). If you go for PEC, which is a good technique, have you thought about the frequency of inspection based on predicted CO2 corrosion rates and how would this feature vis a vis changing out the carbon steel for a CRA from a life cycle cost point of view?



What were the results from the UT already performed?

Perhaps you are referring to corrosion under insulation (CUI) which will occur on the outside of the pipe. If this is the case, challenge the process engineers as to the need for insulation in the first place. If it cannot be totally justified, get rid of it. If the need for it is maintained, ensure that there is a quality coating on the pipe before the insulation goes on. Even with this approach, expect to have the insulation off again after 10 years to fully inspect and maintain the coating.

Steve Jones
Materials & Corrosion Engineer

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

 

[PVRV]

Guided Wave

 

[MOB1]

As stated by PVRV there is a system of ultrasonic inspection called guided wave which has been specifically developed to check for corrosion under insulation.
We have also used a real time X-Ray instrument to check for external corrosion under insulation.

 

[EdStainless]

Is your company a member of MTI?
They have invested thousands in this subject.
Look in to it.

http://www.mti-global.org

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[redrain63]

Try by Pulsed Eddy current technique.
More info on ndt.com

 

[rustbuster]

I have used both the pulsed eddy current and guided wave methods. Both are very usefull but you need to understand the type of damage expected.

Both methods are volumetric assessments where general wall loss is decectable but isolated pitting is difficult to detect.

 

[HermanQ]

You can try to use pulsed eddy current techniques when you need to know the status of your piping without the need for removing insulation and while the plant is running. One of those techniques is RTD-INCOTEST.

 

[stanweld]

Digital Radiography is being used by a number of petrochemical facilities for this purpose. RT is done at locations specified by plant/corporate metallurgist/corrosion engineers.

 

[googel]

You can use guided waves technologie to locate the corroded area then use DRT to size the flow. Such a combination will bring the cost of the inspection to quite reasonable level.