Skip to main content

MACRO SECTION


MACRO SECTION

Object: To examine a cross section of a weld for internal defects and soundness.

Method:  A transverse section of the weld is cut out. The cross section is then visually inspected. The section is filed down from rough to smooth, then emery or wet/dry papered down to a surface finish of 600 grit. The surface is then etched in NITAL (5% - 10% nitric acid in alcohol), washed off, rinsed and dried. (Possibly a final clean with acetone and mount in Bakelite) The specimen is then inspected at up to 10-x magnification.

MACRO SECTION


Reporting Results:
  1. Material.
  2. Welding process.
  3. Specimen identification.
  4. Sentencing standard.
  5. Thickness.
  6. Geometric flaws - type, size and location.
  7. Internal flaws - type, size and location.
  8. Parent metal flaws - type, size and location.
  9. Accept or reject, to standard, for each flaw.   
Comparison of macro section and micro section:

                                                                       MACRO                                            MICRO

Magnification                                                  x 10                                                 x 1000

Finish                                                            600 grit                                    1 micron (high level polish)

Features/ defects                                     cracks, slag, LOF, etc.                        inter granular structure

Uses                                                   procedure/welder qualification              research/failure analysis

Popular posts from this blog

BEND TESTS

BEND TESTS Object:   To determine the soundness of weld metal, heat affected zone and weld zone.These tests may also be used to give some measure of the ductility of the weld zone. It is not usual to use transverse and longitudinal bend tests for the same application. Method:   All specimens to be removed and prepared without causing significant distortion or heating. The cap and root are ground flush. The specimen is bent by the movement of a former of prescribed diameter, the relevant side of the specimen to be placed in tension. Angle of bend and diameter of former should be as specified in the appropriate standard. Reporting Results: Thickness of specimen Direction of bend (root or face) Angle of bend Diameter of former Appearance of joint after bending e.g. type and location of flaws

CHARPY V NOTCH IMPACT TEST

CHARPY V NOTCH IMPACT TEST Object : To determine the amount of energy absorbed in fracturing a standardized test piece at a specified temperature. Method : A machined, notched specimen is broken by one blow from a pendulum. Because scatter occurs in the results, at least three specimens are used to assess the joint represented. Testing is carried out at a temperature specified in the appropriate application standard. Reporting Results: Location and orientation of the notch.  Testing temperature. Energy absorbed in joules.  Description of fracture appearance. Location of any defects. The Charpy impact test, measured in joules, is an assessment of TOUGHNESS. Transition temperature (curve) in steel.

Part -5 Most commonly asked Mechanical Interview Questions

Most commonly asked Mechanical Interview Questions with answer 1. Why the Centrifugal Pump is called High Discharge pump? Ans. Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to push out the fluid. So the liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the liquid in high rate. It is given in the following formulae: Centrifugal force F= (M*V2)/R. Where, M-Mass V-Velocity R-Radius 2. How Cavitation can be eliminated by Pump? Ans. Cavitation means bubbles are forming in the liquid. To avoid Cavitation, we have to increase the Pump size to One or Two Inch To increase the pressure of the Suction Head  Decrease the Pump Speed. 3. Why Cavitation will occur in Centrifugal Pump and not in Displacement Pump? Ans. The form...