Ultrasonic Testing of Welds on Plates

Ultrasonic Testing of Welds on Plates

For testing a weld satisfactorily, the following information should be available
(i) Material, (ii). Details of weld preparation, (iii). Welding process and probable defects expected, (iv) Applica­tion of the part and (v)Acceptance criteria.

Testing of a single 'V'butt joint welded only from one side using transverse waves.
The selection of probe frequency depends on the flaw to be detected and attenuation in the effects of the near zone and beam spread the minimum size of the material. Which varies with frequency should be considered. For mild steel welds usually, a frequency in the range of 1 MHz to 4 MHz will be satisfactory.

Ultrasonic Testing for laminations in plates

Ultrasonic Testing for laminations in plates 

Ultrasonic Testing for laminations in plates - A normal probe is brought into contact with the face of the plate through a couplant. The height of the back wall echo is kept at a fixed amplitude (50% or above F.S.H.)

Any drop  1n  back wall echo is considered to be caused by defective area.   Usually, the plate is scanned along grid lines only and wherever the back wall echo falls beyond a  set level or when a defect indication is present,  the adjacent area is also scanned to determine the area of defect.   Some­ times angle beam technique is also used to detect the presence of defects that are not oriented parallel to the surface.

SOME RADIATION CALCULATION FORMULAS AND EXAMPLES

SOME RADIATION CALCULATION FORMULAS AND EXAMPLES

SOURCE TO FILM DISTANCE CALCULATION

SFD (min)= t(1+d/ug)

t= thickness of job

d= source size

ug= 0.5 max

INTRODUCTION TO NON- DESTRUCTIVE TESTING (NDT)

INTRODUCTION TO NON- DESTRUCTIVE TESTING

INTRODUCTION

Non-destructive testing (NDT) Is a  method of quality control of materials without disturbing their aimed use.  The material under Inspection does not undergo any change In Its size, shape, physical and chemical properties. It is commonly used for:

Detection of flaws such as cracks, shrinkages, gas porosities, inclusions, and another weld, forging and casting defects.
Determining the material characteristics such as density, conductivity, hardness, grain structures, etc. to give clues about the strength of materials.
Dimensional measurements such as wall thickness, internal and outside dimensions, corrosion assessment coating/plating thickness, etc.
On-line monitoring of plants/ industrial systems.

IMAGE QUALITY INDICATORS

IMAGE QUALITY INDICATORS

Image quality indicator (IQI), also called penetrameter is a device used to judge the quality of radiography.  This is measured in terms of radiographic sensitivity. smaller the numerical value of radiographic sensitivity. better the radiographic quality. Image quality indicators are of simple geometric form and made of the same or similar material as the specimen being examined. The image of the IQI on the radiograph is permanent evidence that the radiographic inspection was conducted under proper conditions.

A number of  IQI designs are used by different authorities in the world. There are American Standards,  British standards, French, German, International and Indian standards. Some of the most commonly used IQI designs are mentioned below.

INDUSTRIAL RADIOGRAPHY

RADIOGRAPHY TERMS

MOTTLING - mottling is occurred in industrial radiography due to diffraction, this can be reduced by increasing KV and using lead foil screen.
in compare to 40kv film, 60kv film exposure film with time compensation film has lower contrast and greater latitude.

AVERAGE GRADIENT- It is a characteristic curve between exposure vs optical density.

LATITUDE- (X-Ray Film) the range of specimen thickness that can be adequately recorded on the radiography is referred to as the latitude.

DARK ROOM

DARKROOM

Dark Room is a room where industrial film loading & film development is done, a typical layout is shown above.

Every darkroom has a safe light in which all the above work is carried out (red light) called safe light.

Industrial Radiography Film Processing

Industrial Radiography Film Processing

It has 4 parts
1) Developing 5-8 min Temp 68deg F (20deg C)
2) Stop Bath (Arresting development) 65-70dec F 30- 60 sec
3) Fixation – 65-70 deg F, 8-15min
4) Washing – 20-30min

Developing- developing solution has the ability to reduce the silver bromide crystals on the exposed part of films to metallic silver.
The time required to develop is 5 to 8 min at 20deg cent of solution (developer)
Longer developing time will produce chemical fog and this will decrease the film contrast.
Low temperatures can slow the action while the high temperatures can fog the film or soften the emulsion on the film so that it will wrinkle or wash off.

Non Destructive Testing

WHERE & HOW TO QUALIFY, NDT LEVEL-2 (ISO: 9212)

The full form of "NDT" is Non-Destructive Testing, Today mechanical engineers, after their final year they try to qualify in NDT level-2 in ASNT (SNT TC 1A).  Qualify through a reputed organization. However,

My advice for these engineers is to go for NDT L-2 as per ISO scheme also

UT, MT, PT, RT L-2 as per ISO:9712 

After completion of above go for IWE or IWT exams, surely you will be absorbed by any reputed organization after completion.

In India, IWE/IWT training and exams are being conducted by IIW

Write to us for further details about the ISO 9712 qualification procedure.

Welding and NDT

WELDING AND NDT

WHY WE NEED NDT IN WELDING INSPECTION?
To find out welding defects in welding without destroying it is an NDT technique.

WELDING DEFECTS AND DISCONTINUITIES-
During the welding operation, many unavoidable volume changes occur that may cause
distortion, residual stresses or even cracking in the weldment. These changes are due largely to thermal expansion or contraction of the metal. If the rigidity of the structure Is high because of the stiffness of the members themselves, or support of previous welding or the use of fixtures, the amount of warping will be small. The forces set up by the weld contraction, however, will reach high levels by the time room temperature is reached. Cracking may result while the metal Is still hot or during cooling. Thus, the more highly con-strained the joint to be welded, the more plastic must be the weld metal that is used to complete the joint.