Visual examinations

Visual inspection is the first method of quality control.

 

Forgings: 

The main type of defects is surface cracking, caused by excessive working on the surface and too low temperature, can be remedy by increase the work temperature.

 

There are until 25 visual inspection points for one manual valves.

The main visual examionation are:

Internal visual inspection, number of flange holes, examination of RF faces, checking the heat number, check the foundry logo, check the type of bolting, plug and injection fittings, direction of closing, type of gear box, type of hand wheel, type of lever, name plate, additional plate, tagging, Etc...  

 

 

Welding defects

Hot cracks:

This crack which is caused by shrinkage during cooling of metal.

Solutions to avoid this type of defect:

1 - Do not use excessive current.

2 - Avoid rapid cooling of weld metal.

3 - Preheatig is required.

4 - Especially when Si & C are rich, use low hydrogen type electodes.

5 - Do not use the electrodes which absorb moisture.

 

Cold cracks:

This type of crack occurs primarily in quench-sensitive areas, either in the weld metal or in the heataffected zone (HAZ).

The phenomenon occurs as a result of the coexistence of the following three factors:

1 - Brittle microstructure (martensite).

2- Tension stress (shrinkage upon cooling, restraint).

3 - Diffused hydrogen (H2) in sufficient concentration.

 

 

 

Welding defects in higher plate tickness.

Defects of lamellar tearing are dur to impureties in the base metal and presence of dendrites.

Casting

 

There are several casting methodes:

Centrifugal casting, static casting, die casting, core casting, investment casting, lost-foam casting, lost-wax casting, molding, sand casting, rapid casting and permanent mold casting.

Non destructive testing

 

There are 6 main types of weld defects:

Longitudinal cracks, transversal cracks, porosities in fillet weld, end crater, Incomplete penetration and excess penetration.

It is quite understood that there are others type of defects.

 

NDT by radiography:

What is the purpose of Image Quality Indicator (IQI) ,

Is to indicate the overall sensitivity of the technique and as measure of how well the radiograph will reveal discontinuities.

 

It is important that the end user of industrial radiography has some means to determine if the quality of the radiograph is satisfactory.

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