Eddy Current Testing vs Pressure Testing 3

[us1612]

Hi,
I would like to know if eddy current testing can fully substitute pressure testing of tubes.
THANKS

 

[Metalguy]

Don't know about your particular code or service, but you should be aware that eddy current testing can be blind to SCC until a fairly large % of the wall thickness is penetrated.

 

[us1612]

Well, it´s about manufacturing heat exchanger.
The code of the company we´re working for demands pressure testing of every single tube before welded in the tube sheet. The tube supplier says eddy current testing was sufficient and wants to double the price of the tubes if pressure testing is necessary.

 

[Metalguy]

If YOUR customer demands pressure testing, you had better use tested tubing. Ask them if THEY will accept EC instead-they probably won't.

 

[us1612]

As it is part of their code i guess they won´t.
But the exchanger will be pressure tested anyway, only after welding.
I see the advantages of pressure testing before welding: You can inspect the tubes easier and you won´t have any repair welding in case the bundle doesn´t pass the pressure test. But back to the question in this particular case: Are there any damages I would detect by pressure testing which I wouldn´t detect with EC???

 

[Metalguy]

Pressure testing verifies the strength of the tubing. EC only measures metal loss/cracks/etc.

I really don't see how you can avoid the PT-sorry.

 

[andyenergy]

metalguy -

Interested in your statement that EC is blind to SCC until a fairly large % of the tube wall is penetrated. Can you be a bit more specific on where you obtained this information? I'm inlvolved in a task where we propose to use EC for the detection of SCC and would like to know more. Rather than mix up in this thread, perhaps a new thread might be appropriate?

Thanks

Andy

 

[Rich2001]

eddy current testing tubes

http://www.pruftechnik.com/ndt/document/english/technic/tubfault.pdf

Andy, Take a look at ACFM testing kinda like EC on Steroids

http://www.tscinspectionsystems.com/tschome.htm

http://www.tscinspectionsystems.com/pdfdocs/Intro ACFM.pdf

 

[Metalguy]

Andyenergy,
The US nuclear power industry spends many millions of $ performing EC of steam generator tubing (Alloy 600) EVERY refueling outage. EC really measures metal loss or metal separation, so things like wear (from rubbing on tube supports) is easy to find/measure. But SCC, esp. the IGSCC we have has almost no loss or separation. Depending on the EC method used and the technique, it can be blind until the SCC is ~25% or more of the way thru the wall.

I am not an EC expert, but I can put you in touch with one of the world's leading experts (he used to be my boss).

 

[andyenergy]

Metalguy -

Many thanks for the info.

Andy

 

[stanweld]

When properly performed EC is a valuable test and may be used in lieu of Pressure Testing per the materials specification. The problem occurs when improperly performed as I have witnessed in numerous instances of welded pipe and tubes, accepted by EC, fail during pressure testing. In one of the cases the weld defects were only found after having been installed in a number of heat exchangers and subjected to Code hydrotest; costs exceeded over a million dollars to rectify. In all cases, EC was improperly performed by the mills.

I have had similar problems, when subcontracting similar field EC testing of oil field tubulars.

 

[andyenergy]

A bit of a late contribution to this thread I know, and it probably doesn't alter the earlier advice about the particular requirements of your customer and the good advice given by earlier correspondents. For information.

BS 1113 enquiry case 1113/1 -eddy current in lieu of hydraulic testing.

Does ECT of tubular components as required in BS 3059 Pt1, BS 3059 Pt2 (test category 2), BS 3601, BS 3602 Pt 1 (test category 2) and BS 3604 (test category 2) satisfy the requirements of clause 5.10.3.5 such that further hydraulic testing to the pressure specified in clause 5.10.2(a) is not required for components joined during assembly by circumferential butt welds in ordre for the completed boiler to qualify for the reduced pressure tests specified in clause 5.109.2(b)?

Answer:


ECT to the requirements of the standards described in the enquiry will satisfy the requirements of 5.10.3.5 providing the test pressure specified in 5.10.2(a) does not exceed 140 bar. Where the pressure specified in 5.10.2(a) exceeds 140 bart, the requirements of 5.10.3.4 apply.