NDT Mechanical Testing

NDT Mechanical Testing
To establish the level of mechanical properties
Which properties?
1) Hardness
2) Toughness
3) Tensile Strength
4) Ductility

Introduction to Mechanical Testing
We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint
We divide tests into Quantitative & Qualitative methods.
1) Quantitative Tests: ( Have units)
2) Qualitative Tests: ( Have no units)
Types of Tests include:
1) Quantitative Tests:
Hardness tests
Toughness tests
Tensile strength tests
2) Qualitative Tests:
Macro Tests
Bend Tests
Fracture tests

Testing the Weldment
Charpy V Test : For Tensile Test
Bend Test: Macro / Hardness Test
Hardness Testing:
Generally we use a diamond or steel ball to form an indentation. We measure the width of the indentation to gauge the hardness.
Hardness Testing:
1) Vickers Diamond: Always uses a diamond
2) Brinell Hardness test: Always uses a steel ball
3) Rockwell hardness test: Uses a ball, or diamond depending on the scale

Toughness Testing:
1) Charpy V Test: 11x10 ( Specimen horizontal) Joules
2) Izod test: 12x10 ( Specimen vertical) ft. lbs
3) CTOD test: Specimen used is actual design size detailed fracture report. mm
Transverse Tensile Test:
A section of weld is cut, or machined out across the test piece and tested in tension to failure. The units are usually in N/mm

Ductility Elongation:
Firstly, before the tensile test 2 marks are made 50mm apart. During the test, Yield point & Tensile strength are measured. The Specimen is put together and the marks are re-measured.
A new measurement of 75mm will indicate Elongation E50%

 
Macro Inspection:
1) Excess weld metal height
2) Lack of sidewall fusion
3) Lack of Root fusion
4) Slag inclusion & Lack of inter-run fusion
5) Poor Toe blend
6) Laminations
7) Porosity
8) Root penetration

Bend Tests:
Bend tests are used to establish fusion in the area under test. Further tests include face, side and longitudinal bend tests. For material over 15mm thickness, side bend test may be used.
Mechanical Testing:
We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint.
We divide tests into Qualitative & Quantitative methods.
Macro Inspection:
The main difference between Macro & Micro is that Micro is the study of the micro-structure at much higher magnification.
The limit of Macro inspection is magnification< X15
The specimen is usually cut from a stop / start in the test piece
The Cut specimen is polished to a fine finish ( 530 grit)
The specimen must be inspected, before etching.
Welding Procedures:
A definition of the term “Procedure”
A systematic method of producing an aim
Therefore, a “Welding Procedure”
A systematic method of producing a sound weld
Most production welding procedures are formatted on written documents or computer spreadsheets, but they need not be written and may be a product of experience.
Most procedures are approved, but not all. An approved welding procedure is one that has been tested to ensure that the procedure as carried out, produces a weld that ensure that the procedure as carried out, produces a weld that satisfies a minimum level of quality for the mechanical, physical or chemical properties desired. If these are not required, then “Procedural approval is unnecessary”
A welding procedure is a recipe of variable parameters, which will produce the same results of certain quality & Properties if carried out in the same way each time. To evaluate a provisional welding procedure we need to check if all the parameters set will work together to produce the desired results.
Once the weld has been completed it is usually visually inspected, then Radiography or Ultrasonic testing is usually applied.
Finally, and most importantly, mechanically tested to ensure that the desire level of mechanical properties have been met.
If all the desired properties have been met, then a procedure qualification record is completed will all the test results.
 
Contents of Approval:
1) Diameter of pipe, or thickness of plate
2) Welding position, amperage range, or number of runs
3) Process( On multi process procedures only)
4) Certain material groups
5) Heat input rang (Kj/mm)
Welding Positions for Butt welds:
Graphical Representation:
1 G Flat Position (Rotated)
2 G Horizontal Position (Vertical position)
3 G Vertical position
4 G Overhead position
5 G Vertical position (PF Vertical up, PG Vertical down)
6 G Inclined position
Fillet welds:
1 F Flat position 45 degree
1FR (Rotated)
2F Horizontal vertical position
2FR (Pipe axis horizontal)
3F weld throat vertical
4F Weld axis horizontal ( Overhead position)
5F Pipe axis horizontal ( Vertical position, PG: Vertical Up, PG: Vertical down)
Reference by: welding books