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Technical Discussions
Ahmed Raza
Engineering
Fauji Fertlizer Company, Pakistan, Joined Jul 2003, 2

Ahmed Raza

Engineering
Fauji Fertlizer Company,
Pakistan,
Joined Jul 2003
2
03:39 Jul-04-2003
Eddy current testing of furnace tubes

Gentlelmen,

I have a question regarding ET OF furnace tubes.
From what I have read about eddy current testing offered by some companies I understand that it is performed from outside the tube.Why it is not performed from inside the tube especially when it is effected by catalyst presence while performing from outside?
If anybody knows anything about it please do tell me.




 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 528

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
528
01:07 Jul-05-2003
Re: Eddy current testing of furnace tubes
Obviously Eddy current testing can be performed from either inside or outside a tube.

I'm not sure what knid iof furnace tubes you refer to, but since you mention a catalyst, I will assume you are refrring to centrifugally cast steel tubes as used in reformers/ ethylrnr crackers etc. (If I'm wrong please ignore)

These tubes are tested from the outside as:

a) access to the ID is difficult when in sewrvice (ID testing is used during manufacture)

b) The dominant failure mechanism is intergranular cracking from the inside. In a used tube there is always a lot of this, Noise level on a ID test would be far too high, the requirement is to find those tubes where cracking is deep enough to approach the ouside - This is easier from the OD.

hope this is relevant!

Joe

: Gentlelmen,
.
: I have a question regarding ET OF furnace tubes.
: From what I have read about eddy current testing offered by some companies I understand that it is performed from outside the tube.Why it is not performed from inside the tube especially when it is effected by catalyst presence while performing from outside?
: If anybody knows anything about it please do tell me.
.



 
 Reply 
 
Ahmed Raza
Engineering
Fauji Fertlizer Company, Pakistan, Joined Jul 2003, 2

Ahmed Raza

Engineering
Fauji Fertlizer Company,
Pakistan,
Joined Jul 2003
2
03:06 Jul-05-2003
Re: Eddy current testing of furnace tubes
Thanks Joe,

Yes you guessed right I am asking about reforming furnaces.

You have written that eddy current is used to detect only cracks reaching outer surface but why then its inability to detect inner cracks is said to be a limitation?
and Is catalyst removal required for eddy current testing from outside the tube?

: Obviously Eddy current testing can be performed from either inside or outside a tube.
.
: I'm not sure what knid iof furnace tubes you refer to, but since you mention a catalyst, I will assume you are refrring to centrifugally cast steel tubes as used in reformers/ ethylrnr crackers etc. (If I'm wrong please ignore)
.
: These tubes are tested from the outside as:
.
: a) access to the ID is difficult when in sewrvice (ID testing is used during manufacture)
.
: b) The dominant failure mechanism is intergranular cracking from the inside. In a used tube there is always a lot of this, Noise level on a ID test would be far too high, the requirement is to find those tubes where cracking is deep enough to approach the ouside - This is easier from the OD.
.
: hope this is relevant!
.
: Joe
.
.
.
: : Gentlelmen,
: .
: : I have a question regarding ET OF furnace tubes.
: : From what I have read about eddy current testing offered by some companies I understand that it is performed from outside the tube.Why it is not performed from inside the tube especially when it is effected by catalyst presence while performing from outside?
: : If anybody knows anything about it please do tell me.
: .
.



 
 Reply 
 
Richard D. Roberts
Engineering, Executive Managment
Quest Integrity Group, USA, Joined Nov 1998, 78

Richard D. Roberts

Engineering, Executive Managment
Quest Integrity Group,
USA,
Joined Nov 1998
78
06:11 Jul-07-2003
Re: Eddy current testing of furnace tubes
Mr. Raza,

Based upon the fact that you referenced “catalyst” I can only assume that you are referring to tubes in a Steam Methane Reformer (SMR) type unit. There are several companies who apply Eddy Current (ET) from the outside by attaching a crawler to the tube. I am unaware of any “field systems” which currently apply ET on the tubes interior. There are advantages and disadvantages of applying ET or any other type of inspection process (i.e. Ultrasonics, Laser, etc.) from the tubes exterior.

Some “advantages” of conducting inspection from the tubes “exterior” are:
a. Inspection can be carried out without the catalyst being removed

Some of the “disadvantages” of conducting inspection on the tubes exterior are:
a. Examining from the tubes exterior limits the inspection to only 60-70% of the tubes length since the tube penetrates through the floor and roof refractory.
b. Almost all external tube crawlers are too large to fit down into the tunnel (coffin) region of the SMR. In most cases when maldistribution of flue gasses is occurring, the damage is 6” – 12” below the top of the tunnel (coffin).
c. The tube exterior surface is a rough “as cast” profile. This induces noise into the ET data and can create erroneous results.
d. The circumferential weld at each tube segment is typically machined on the tubes exterior surface. This causes the ET sensor to rock back and fourth creating a “lift off” issue which can cause erroneous results in the ET data.
e. Since SMR tubes are operated at such high temperatures, made of high alloy spun cast materials and quite commonly are exposed to localized temperatures in isolated regions of the tube, it is very common to see variations of permeability down the tubes length. This can cause erroneous results in the ET data.
f. Most Eddy Current (ET) and Ultrasonic (UT) systems only inspect a very small portion of the tubes circumference. Damages from flame impingement, redirected radiation from the refractory, maldistrution of flue gasses can occur at any location around the tube circumference.

Over the last 6 years a very successful inspection process which utilizes “laser” is applied from the tubes interior. This process is not effected by any of the items listed above however it is limited to conducting the inspection during the catalyst is being changed out.

If you have any further questions please don’t hesitate in contacting me.

Regards, Rich Roberts

--------------------------- ORIGINAL MESSAGE --------------------------
Gentlemen,

I have a question regarding ET OF furnace tubes. From what I have read about eddy current testing offered by some companies I understand that it is performed from outside the tube.Why it is not performed from inside the tube especially when it is effected by catalyst presence while performing from outside?
If anybody knows anything about it please do tell me.



 
 Reply 
 

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