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Technical Discussions
11:41 Apr-20-2011
Andrew Liddell
NDT On Threads
Hi folks,

Can anyone confirm which is the best method of NDT to carry out inspections on threads, I have all ways been under the impression that MPI with a black light was the best. But someone has informed me that it can be done with black & and white sprays is this possible..

Any feed back would be grate thanks...

12:39 Apr-20-2011

NDT Inspector, ,
Joined May 2008
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

Fluorescent technique has greater sensitivity than contrast one.

14:43 Apr-20-2011

Steven Nabicht

Aerospace/ Orthopedic,
Joined Nov 2010
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

HI Andrew,

LK is exactly right the fluorescent method creates a greater contrast due to the luminescence of the dye and so is easier for the inspector to see. But the final judge of what method to use is always the customer.

14:49 Apr-20-2011

raffy lot
Engineering, NDE Level 3,
Honeywell Aerospace Pte Ltd, Singapore,
Joined Nov 2008
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

fluorescent LPI best does the inspection. you can read ASTM E1444.

15:05 Apr-20-2011
andrew Liddell
Re: NDT On Threads
In Reply to Steven Nabicht on 14:43 Apr-20-2011 .

So basically it is fine to do black and white, if saying the thread pitch is greater

17:03 Apr-21-2011

Scarpin Fabio
Technician 2° Lev. ,
Joined Apr 2010
Re: NDT On Threads
In Reply to andrew Liddell on 15:05 Apr-20-2011 .

Ciao on magnetic bolts certainly MT using fluorescent magnetic particles in black light offers excellent results (you can see from the foto in my profile),during the inspection on very narrow thread I use a special glasses to three magnifications because the indications are very thin end difficult to see . Another good but more complex technique if you have a lot of bolts whit same shape is UT method I use ultrasonic immersion test with a 10 MHz focused probe.

11:44 Apr-22-2011

Santosh Gaikwad
Director, Material Testing & Inspection Services(MTIS),
Material Testing & Inspection Services,
Joined Feb 2010
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

my opinion is
fluorescent magnetic particles in black light is the best method

13:50 Apr-22-2011

Michel Couture
NDT Inspector, ,
Joined Sep 2006
Re: NDT On Threads
In Reply to Santosh Gaikwad on 11:44 Apr-22-2011 .

I would go with FPI. Simply because fluorescent MT will give you an indications in the treads regardless. It maybe non-relevant because of the geometry of the tread or it may be a defect.

When doing FPI, if you remove your penetrant properly after your dwell time, you should only see you true indication. If you doubt what you see, you can always dab a little bit of remover on a tissue paper and wipe the area. Then reapply developer and watch for bleed back. You'll havee your answer.

12:41 Apr-24-2011


Engineering, QA/QC/NDT,
NOV (National Oilwell Varco),
Joined Mar 2006
Re: NDT On Threads
In Reply to Michel Couture on 13:50 Apr-22-2011 .


Fl MPI is the best with threads in OD or ID for Mag Material.
Fl DPI is the best with threads in OD or ID for Non Mag Material.

We are in OCTG as per DS.1 Std performing in this way.


22:06 Apr-24-2011
Jared Williams
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

I would suggest using a flourescent application as well. However, if you or someone else has UT experience I believe that is a superior technique, as I always opt to look for cracking coming from threads with UT before any other technique.

06:58 Apr-25-2011

Jon Wallis

NDT Inspector, - ,
Joined Feb 2010
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

If the standard you are working to allows the contrast method and you want to use this method then do it. If you have to post clean the parts that will be a little bit difficult (but not impossible).
Good people on this thread talk of the fluorescent method being 'better' than the contrast method. Yes, the fluorescent method may be more sensitive but if the code or standard allows a less sensitive method then the examination would still be a good one.

12:24 Apr-25-2011


NDT Inspector, Specially in the oilfield,
Tuboscope Vetco(Deutschland)Gmbh,
Joined Oct 1999
Re: NDT On Threads
In Reply to Jon Wallis on 06:58 Apr-25-2011 .

For pin threads i can agree to must answers , for coupling and box threads it is different.
Andrew never specified which threads he want to inspect .
In my opinion wet flourescent is the must apllied method in the oilfield.
UT on threads is questionable and when done then on pin threads only.
There is also the ACFM method applying eddy current.
All methods used have advantage and disadvantages , also you need to fellow the appliable specc and requirement from the customer.



05:32 Apr-28-2011

Holly Li
Consultant, ,
TCK Wire Rope Inspection Technology Co., Ltd,
Joined Apr 2011
Re: NDT On Threads
In Reply to Andrew Liddell on 11:41 Apr-20-2011 (Opening).

For ferromagnetic-material thread, currently two testing methods are popular in the world. 1. Strong magnetic testing method: to magnetize the thread to make it reach magnetic saturation, then using Hall element to look for magnetic leakage at broken place of thread. Weakness: magnetic saturation usually is not easily to reach, and can't test internal fatigue. 2. a more reasonable method--weak magentic testing method: to magnetize the thread to rule the disordered magnetic experience, remove away the magnetic loader, by the residual magnetic, use high-senstive Dou's Sensor(sensitivity is 250000 times higher than Hall element) to quantitativly test the rope flaws and fatigue. The The principle is the “Spatial Magnetic Field Vector Resultants”theory.
For more information about weak magnetic technology or related products, please contact me by iamhollyli@hotmail.com

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