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871 views
02:41 Aug-14-2002

luis marques

refinery inspector
petrogal,
Portugal,
Joined Jul 2002
5
How to monitor on line Naphtenic acid corrosion?

Naphftenic acid corrosion is produced on heavy crude oil cuts inside carbon steel and low alloy piping at temperatures above 180 ºC and bellow 350 ºC. Naphtenic acid corrosion increases with fluid velocity and is localized at fluid restrictions such as valves or pipe reductions and at elbows fluid direction changes. The results of Naphténic acid attack over metallic surfaces are great erosion and hard pitting. Because of high temperatures and its localized characteristics Naphtenic acid corrosion is difficult to monitor. Is there any ultrasonic device to monitor on line Naphtenic acid corrosion?

Tanks
Luis MARQUES


 
06:51 Aug-14-2002

Walter Wozniak

Engineering, -
Innovative Test Systems, Inc.,
USA,
Joined Jul 2002
4
Re: How to monitor on line Naphtenic acid corrosion? Greetings Luis ,

My first thought would be to bond an ultrasonic transducer, sized accordingly, at each critical area. You could then get a baseline reading of thickness. There are a number of off-the-shelf computer based UT instruments that can store wave forms, recall them, compare them, etc. In this case, all that is needed to monitor is the peak amplitude of the wave form. The storage of the wave form shape would be excess information that might be used to futher monitor the changes somehow.

The bonding method would be critical as there would have to be intimate contact for good transmission of the sound into the part. The bigger challange, I think, is that the chacterisitics of the bond cannot change over time as this would invalidate the test. The adhesive or other attachment method needs the most study. Also , is there any vibration that might fatigue the crystal of the transducer, causing a change in the characteristics?

This method will only work for the parts that are exposed to the outside.Items , such as the gates inside of valves, could not be examined, unless you put the transducer on the gate itself, in with the acid flow.

regards,
Walter Wozniak
Innovative Test Systems, Inc.

: Naphftenic acid corrosion is produced on heavy crude oil cuts inside carbon steel and low alloy piping at temperatures above 180 ºC and bellow 350 ºC. Naphtenic acid corrosion increases with fluid velocity and is localized at fluid restrictions such as valves or pipe reductions and at elbows fluid direction changes. The results of Naphténic acid attack over metallic surfaces are great erosion and hard pitting. Because of high temperatures and its localized characteristics Naphtenic acid corrosion is difficult to monitor. Is there any ultrasonic device to monitor on line Naphtenic acid corrosion?
.
: Tanks
: Luis MARQUES
.



 
08:34 Aug-14-2002
Lorrie Davies
Re: How to monitor on line Naphtenic acid corrosion? Pulsed Eddy Current or INCOTEST is a volumetric thickness measurement technique that can be used to monitor this damage mechanism on-line. I can forward information to you if you like. Contact me at ldavies@rtdquality.com

Best regards

: Naphftenic acid corrosion is produced on heavy crude oil cuts inside carbon steel and low alloy piping at temperatures above 180 ºC and bellow 350 ºC. Naphtenic acid corrosion increases with fluid velocity and is localized at fluid restrictions such as valves or pipe reductions and at elbows fluid direction changes. The results of Naphténic acid attack over metallic surfaces are great erosion and hard pitting. Because of high temperatures and its localized characteristics Naphtenic acid corrosion is difficult to monitor. Is there any ultrasonic device to monitor on line Naphtenic acid corrosion?
.
: Tanks
: Luis MARQUES
.



 
00:46 Aug-14-2002

Walter Wozniak

Engineering, -
Innovative Test Systems, Inc.,
USA,
Joined Jul 2002
4
Re: How to monitor on line Naphtenic acid corrosion? Hello again Luis,

Regarding my previous post using individual UT probes at critical locations. The next level of monitoring would be to used ultrasonic phased array transducers at each critical location. The ultrasonic beam can be electronically steered to map a region. It is a big leap up in cost from the previous system and perhaps not the same leap in performance.

It depends on how large the area of corrosion is. For lots of pitting or for large known areas of corrosion where a single element transducer can be aimed with confidence, the single element should work fine. For areas with scattered pitting or smaller randomly located areas of corrosion, I think the phased array system would be better.

regards,
Walter E Wozniak
Innovative Test Systems, Inc.

: Naphftenic acid corrosion is produced on heavy crude oil cuts inside carbon steel and low alloy piping at temperatures above 180 ºC and bellow 350 ºC. Naphtenic acid corrosion increases with fluid velocity and is localized at fluid restrictions such as valves or pipe reductions and at elbows fluid direction changes. The results of Naphténic acid attack over metallic surfaces are great erosion and hard pitting. Because of high temperatures and its localized characteristics Naphtenic acid corrosion is difficult to monitor. Is there any ultrasonic device to monitor on line Naphtenic acid corrosion?
.
: Tanks
: Luis MARQUES
.



 
02:27 Aug-16-2002

luis marques

refinery inspector
petrogal,
Portugal,
Joined Jul 2002
5
Re: How to monitor on line Naphtenic acid corrosion? Dear sirs

We have installed on line corrosion probes that measure instantaneous corrosion velocities. The probes are located in critical areas where is supposed to occur the greatest corrosion. Each probe is composed by a metallic filament of the same material of the pipe were it is installed. The thinning of the filament changes the electrical current signal that passes through it. This resistance electrical change is then transformed, by maths formula in corrosion thinning. This is a good tool to evaluate on line corrosion however it has some limitations because each probe filament has a short time duration and needs to be replaced several times. To complement this we also have installed corrosion coupons which ones are periodically replaced to evaluate corrosion rates and weight loss measurements. This probes and coupons are installed at high temperature point locations so their on stream replacement is dangerous for operator integrity. It is for the above reasons that we would like to have a less dangerous and operator dependent tool.

Tanks for your concern

Luis Marques



 
00:17 Oct-22-2002
Valeria Puértolas
Re: How to monitor on line Naphtenic acid corrosion? Dear Luis,

As far as I know, NAC is a quite localized type of corrosion, i.e.: any on-line-ultrasonic/probe device will not guarantee a reliable monitoring system for NAC specifically (though it´s a good method for other types of corrosion).
What I´d recommend is to determine NA concentration in crude oil and then decide if you should blend, use a special aditive or just follow the NAC concentration in gas oil streams.
After processing a naphtenic crude oil, radiographies can be taken in bottom elbows, heavy vaccuumm gas oil zones, etc.

Best Regards
Valeria Puértolas


: Naphftenic acid corrosion is produced on heavy crude oil cuts inside carbon steel and low alloy piping at temperatures above 180 ºC and bellow 350 ºC. Naphtenic acid corrosion increases with fluid velocity and is localized at fluid restrictions such as valves or pipe reductions and at elbows fluid direction changes. The results of Naphténic acid attack over metallic surfaces are great erosion and hard pitting. Because of high temperatures and its localized characteristics Naphtenic acid corrosion is difficult to monitor. Is there any ultrasonic device to monitor on line Naphtenic acid corrosion?
.
: Tanks
: Luis MARQUES
.



 


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