DESTRUCTIVE TESTING A

DESTRUCTIVE TESTING ON WELDING TEST COUPEN -A

                  

Destructive testing is divided into 2 categories

a.   Test that measures mechanical properties.

Tensile test, hardness test, impact toughness etc.

b.   Test that measures joint quality.

Bend test, macroscopic examination, fracture test etc.

 

A.   TRANSVERSE TENSILE TEST

·         Test specimen is accurately measured before loading for testing.

·         Specimen is then fitted into jaw of tensile testing machine.

·         Then specimen is subjected to continuously increasing tensile force until the specimen fracture.

·         Tensile strength can be calculated by applied force to cross section area of specimen before applying load.

 

ACCEPTANCE CRITERIA

·         If the test piece broken into the weld metal it may acceptable only when the calculated strength is not less than the minimum tensile strength of the parent material.

·         If the test piece breaks outside the weld or in fusion zone then it may be acceptable when the calculated strength is not less than 95% of the strength of base material.

 

B.   ALL WELD TENSILE TEST

·         This test is carried out not only for tensile test but also yield strength (proof strength) and tensile ductility.

·         Test specimen is machined from weld parallel with their longitudinal axis and specimen gauge length must be 100 % of weld length.

·         Specimen is subjected to continuously increasing load in the same way that of transverse tensile specimen is tested.

·         Yield and proof stress can be calculated by means of Extensometer that is attached to parallel length of the specimen and is able to accurately measure the extension of gauge length as the load is increased.

         EXTENSOMETER & SPECIMEN 

      

·         Tensile ductility is measured in two ways:

% elongation of the gauge length &

% reduction of the area at the point of the fracture 

     

                                                                                            DUCTILITY MEASUREMENT

 

C.   IMPACT TOUGHNESS TEST

·         Charpy V- notch test is internationally have become internationally accepted method for accessing resistance to brittle fracture.

·         Material impact test is depends upon the design specification and product application to avoid brittle failure.

·         The dimensions of the specimen has been standardize internationally

·         Specimen are machined from welded test plates.

·         It having notch position at different location according to the testing requirements.

·         Typically notch position is the center of the weld and position across the HAZ.

  

METHOD

·         Test specimen is cooled at specified test temperature by immersion in an insulated bath.

·         Insulated Bath containing a liquid that is held at the test temperature.

·         After that allowing the specimen temperature to stabilize for a few minutes it is quickly transferred to the anvil of the test machine and a pendulum hammer quickly released so that the specimen experiences impact load behind the notch.

·         Energy absorbed by hammer when it strikes on test specimen is shown by the position of the hammer pointer on the scale of the machine.

·         Impact test specimen are taken in triplicate (3 specimen for each notch position) because there is always some variation in recorded energy for nominally the same test.

                          

ACCEPTANCE CRITERIA

·         Each test results is recorded and average value is calculated for each set of three test.

·         This value are compared with the specified values as per given standard or client specification.

·         After impact testing, examination of the test specimen provides additional information about their toughness characteristics and may be added to test reports.