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10:45 Apr-12-2009
krish
Hydrogen Induced Cracking using TOFD/Phased Array Technique

During routine HIC(Hydrogen Induced Cracking)survey of existing pressure vessel we got typical HIC indication by TOFD scanning.We want to verify those indication with alternate NDT method.I understand that PHASED ARRAY technique can be used for HIC Evaluation/verfication.My question in this regard is:
1)Which is the best method for detecting & evaluating the HIC indications(TOFD Vs Phased Array)
2)If volumetric defect like inclusions,lamination are present in the existing pressure vessel plate(uncleaned steel)which method can detect and size accurately(TOFD Vs PHASED ARRAY).
3)Any other alternate NDT techniques are available to detect HIC indications?

with advanc thanks,


    
 
10:08 Apr-13-2009

Abbas Bombaywala

NDT Inspector
Free Lance,
India,
Joined Jul 2007
91
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to krish at 10:45 Apr-12-2009 (Opening).

Well you can do the ToFD Line Scans, Back Scatter & Velocity Ratio Measurment for accurate sizing of Hyrdogen Attack

With Regards
Abbas Zoher bombaywala


    
 
14:50 Apr-13-2009

R Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to Abbas Bombaywala at 10:08 Apr-13-2009 .

Phased Array will be the best for sizing your indications, and can generate a graphic 'picture' of the indication. Engineers tend to enjoy having an X-ray-like picture to look at when evaluating the course of action required. One caveat, neither TOFD or PA can 'see' thru a delamination. However, PA will define the edges accurately and rapidly.


    
 
04:12 Apr-15-2009

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to krish at 10:45 Apr-12-2009 (Opening).

TOFD is good for HIC detection but may not be ideal for sizing. I am not sure you want to jump straight in with Phased Array unless you have good experience. The first question is to assess is it just HIC that you are dealing with and not SOHIC or SSCC which have mixed morphology and different response to UT. If true traditional HIC you should be able to get good representation using a narrow beam zero degree probe, small step increment and a C-Scan mapping system. This will give you excellent representation of the laminar morphology flaws. In tandem ideally you should use matched 45 degree shear waves from all sides of the HIC blister to look for the steps in the stepwise cracking. As to alternate NDE approaches not sure that anything else will give you as good an evaluation as UT. If you think the cracking is active a small array of AE sensors around the area on-line can indicate active crack growth.


    
 
13:58 Apr-15-2009

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
85
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to John O'Brien at 04:12 Apr-15-2009 .

zoom image[zoom]

zoom image[zoom]

I have sent some HIC images in which I used Phased Array. I hope these show up.

As John states, PAUT can better size the defects. Due to the beam configuration, 0 Degree Linear or a - 30 to +30 degree sweep I belioeve you will have better luck with Phased Array. Ideally with the beam sweep you can detect the laminar orientation and the planar orientation of the flaws.

Also, focusing is key here. You may be able to increase the Frequency to a 7.5 MHz or even a 10 Mhz with help due to the power of the number of elemenst you are firing. That is you get the penetration with the number of elements, but you have better detectability and sentivity with the inceased frequency. A 32 pulser Omniscan is even better.

Also, John makes a great point that a Visual is a good start.

    
 
15:27 Apr-15-2009

Luis Ganhao

Engineering,
USA,
Joined Sep 2008
25
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to Abbas Bombaywala at 10:08 Apr-13-2009 .

Sorry but if the problem is HIC those techniques that you mention are for High Temperature Hydrogen Attack (HTHA) this mechanism (HIC) is completely differente however I 'am agree with the use of TOFD

Reagrads
Luis Gnahao
Sr. Materials and NDT Specialist.
JACOBS Canada Inc.


    
 
15:29 Apr-15-2009

luis ganhao

Engineering,
USA,
Joined Sep 2008
25
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to R Duwe at 14:50 Apr-13-2009 .

I agreed that PA is one of the best technique to use for this case but is not the best I mean you can use TOFD with an adequate setting (frequency, size of transducers and angle) and you can detect and size precisely all you indications remember that PA is a reflect technique and TOFD is a diffraction technique in that sense TOFD is most sensitive. Inclusive corrosion mapping/C-scan can give you the idea of how much is the area of the demage

Regards



Luis Ganhao

Sr. Materials and NDT Specialist

Jacobs Canada Inc.


    
 
12:44 Apr-16-2009

Abbas Bombaywala

NDT Inspector
Free Lance,
India,
Joined Jul 2007
91
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to luis ganhao at 15:29 Apr-15-2009 .

I truly agree with my luis ganhao, TOFD is the best technique for sizing the defects and the sensitivity is also very high, and mode conversion also helps u in differentiate the indications.

Regards
Abbas Zoher Bombaywala
NDT Inspector


    
 
14:01 Apr-22-2009

Charlie Jackson

Consultant, - Trainer/Inspector
Northern NDT Ltd,
United Kingdom,
Joined Sep 2006
6
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to krish at 10:45 Apr-12-2009 (Opening).

The evaluation of HIC by TOFD can be very difficult mainly due to the saturation of the images by the high amplitude reflected signals. Pulse echo suits the application admirably as long as you consider the effects of original rolling direction on the flaw morphology. The use of large area high definition auto mapping followed by PE - manual, PA, Auto or mix would be best practise.
I know there are many out there who have TOFD systems and like to use them as often as possible but much of the original assesment can be done manually before you consider PA - AUT rasta etc.
This time spent manually scanning the areas is an important step in the understanding of the recieved signal shapes.

Kind Regards and hope this helps Charlie Jackson Northern NDT Ltd


    
 
11:54 Apr-30-2009
mark
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to Abbas Bombaywala at 12:44 Apr-16-2009 .

Abbas how mode conversions in TOFD helps to differentiate indications? Please explain


    
 
16:06 Apr-30-2009

Luis Ganhao

Engineering,
USA,
Joined Sep 2008
25
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to mark at 11:54 Apr-30-2009 .

The mode convert in TOFD help you to understand where is the ubication of your defects, I mean are those defects in the weld metal, HAZ or metal base and another thing is the the signal from this type of cracks should be in phase with your backwall but if one of those cracks have a diferent orientation (vertical) then have carfully to interpretate because now you will have 100% diffraction. Normallly this type of damage is between the HAZ and metal base, and TOFD can give you precisly in the detection and sizing in both modes Longitudinal wave and converted or Shear wave.

I hope thsi brief summary can help you.

Luis Ganhao
Jacobs Canada Inc.
403-6921037


    
 
05:46 Jun-11-2009
Bill Blanshan
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to Luis Ganhao at 16:06 Apr-30-2009 .

zoom image[zoom]

For the most part, I agree the most with John O'Brien and AUT raster scan using both 0 degree and shearwave probes simultaneously is the way to do it. I personally don’t see any benefit to using TOFD unless inspecting a weld, but then again, if you having blistering in the parent material, the TOFD data will look horrible due to the large ultrasonic footprint thus you will be seeing both indications in the weld and in the parent material, there is no way to distinguish. Phased array is a nice technique but I would suggest using it in three techniques; 1) 0 degree sweep of the parent material as what Mark Davis suggested to locate blistering; 2) Following up on the 0 degree detected laminar indications with a shearwave sweep looking for stepwise cracking; 3) Scan the welds with shearwave sweep with phased array for SOHIC detection.

As John stated, there are many different forms of hydrogen damage which all begin at the stage of being fabrication related defects such as inclusions and lamination, and then migrate into hydrogen accumulation, then blistering, then blisters with stepwise cracking, then you may have the welds with cracking in the HAZ (SOHIC). It is important to determine these stages and the best way to do this is by 0 degree AUT raster scanning. The 0 degree probe will detect these laminar indications with accurate sizing, and based on analysis, the technician can determine what stage or classification the damage is. For example, depending on the size and if the blisters exhibits a complete loss of back wall signal will tell you a lot about the severity of the damage; is it a blister caused by hydrogen or is in just dirty steel. Hydrogen blistering typically exhibits a loss of backwall signal, is round in shape, interacts with other blisters, and can have doomed tops. If you detect blistering, it is important to scan the blisters for stepwise cracking, the most detrimental stage of HIC. I personally have been called out to many job sites where poorly trained technicians called hydrogen blistering with stepwise cracking without using shearwave and only relying on 0 degree data, only to find that after destructive testing, it was only lamination from the fabrication process, this is bad. With the boom of phased array technology, many people are also going out in the field performing techniques as what Mark Davis suggested using a -30 to +30 sweep thinking they can achieve both 0 and angle beam coverage, this is also not a good idea as a standalone inspection technique; the reason being that refracted L-wave don’t always come back due to mode conversion. With hydrogen accumulation, you may have multiple layers of small laminar indications and they may appear on the screen as stepwise, but 0 degree data can be misleading, therefore shearwave data don’t lie. If there is cracking, your shearwave data will see it. With this said, we typically use a triplex transducer made by my company or Technisonics. This probe is of a unique design, containing a 0 degree transducer in the center and two outward facing 45° shearwave on each side. When using this probe on an automated 2-axis scanner in a raster scan pattern, you can cover large areas in a fast amount of time with exceptional data. When using this technique with acquisition/analysis software from Tomoview, AGR or Amdata, you will have the ability to superimpose the 0 degree and shearwave data together onto one image thus providing you with very detailed and accurate imaging of the damaged detected (as shown in the image). As far as I am concerned, this is the only way to do HIC inspection. I hope this helps.

Bill Blanshan
AUT Solutions

1    
 
10:21 Jun-11-2009

Asif ALi

NDT Inspector, -
Pakistan,
Joined Jul 2008
7
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to krish at 10:45 Apr-12-2009 (Opening).

Dear experts
I want to shear my experience with you peoples. A problem of Hydrogen attack inquiry is forward to us. The hydrogen attack in 0.5 Mo, steel pipe which is to be fabricated by welding technique,. When they try to weld the pipe they face the problem of Hydrogen attack (HA). We simply check the presence of HA by replica metallugraphy. And we easily find the fissure (Micro cracks on creak bounders) . The second task with us that how to weld this pipe . We use a technique which based on practical experience. by application of the said technique we able to weld the pipe with HA at stage of fissure’s.
Syed Asif Ali


    
 
23:46 Mar-31-2016

Jason Fry

USA,
Joined Mar 2016
1
Re: Hydrogen Induced Cracking using TOFD/Phased Array Technique In Reply to John O'Brien at 04:12 Apr-15-2009 .

zoom image[zoom] HIC using M2M Total Focusing Method

TFM improves the visualization and sizing accuracy for step wise cracking compared to having to use both an E-Scan (formerly Linear scan) and Sectorial Scan with conventional PAUT. TOFD can be used but does not give you a C-scan (top view) of the area, and as stated can only do line scans. Triplex probes work well but will not be able to scan an area as fast due to the size of the elements, when you can use a linear array that has a 60-70mm aperture.

    
 


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