Hardness

[QC7]

Why most of codes only gives max hardness limit & not minimum??

Could someone explain briefly about minimum what level hardness can accept on A106 GR B as well as other common materials in pipe lines?

Also why most of client is asking hardness value on HAZ,if distance between two welds are less than 1 Inch.??

 

[Duwe6]

Minimum hardness is covered by the Minimum Yield, Minimum Tensile requirements.

 

[QC7]

Dear Duwe6 or anyone,

Can you explain it briefly,Including all my query?

 

[C2it]

Hardness values increase across a weld, often worst at the toe of the weld. If welds are in close proximity there can be an interaction. Excessive weld hardness can lead to brittle fracture or fatigue failure.

 

[QC7]

Dear C2it,

Thanks for valuable information.And pls give information about minimum Hardness value ,which can accept.

 

[C2it]

Acceptable hardness values depend on many parameters including the Design Code, material type, initial heat treatment and post weld heat treatment.

 

[stanweld]

Hardness maximums for carbon steels like A-106 B are generally imposed by Owner/Engineers to mitigate the possibility of stress corrosion cracking - usually in caustic and wet H2S environments.

The minimum expected a-106 B base metal hardness is approximately 120 BHN.

 

[QC7]

Dear Stanweld, - In which code is specifying ,minimum hardness value for various type materials.From where i have to compare minimum hardness value, if hardness value has gone below 120 BHN. Because we got minimum hardness value 110 BHN on parent metal and we don't know that whether it is acceptable or not.We fabricating pipe lines based on API 1104 and specification is B31.3 .

Pipe -8'' sch160
Preheat -150 C.
PWHT- ASME SEC VIII-DIV 1.

 

[stanweld]

There are no minimum hardness requirements specified in B31.3, B31.1, B31.4, B31.8 or API 1104. Hardness (BHN and Vickers) are reflective of the ultimate tensile strength of the material but is not absolutely indicative of it. 110 BHN approximates to a UTS of 55 to 57 ksi. If portable hardness test methods were employed, the hardness recorded may be in error; in any event, the accuracy is only + or - 5% when properly performed.

The acceptability of the material is based on the A-106 B tensile tests recorded on the MTR.

 

[SNORGY]

It may sometimes be necessary to specify minimum hardness. For example, if you have a carbon steel ring joint flange and are trying to use ring gaskets with higher hardness than the flange material, you might end up with a leak path that requires a flange repair to fix rather than a simple gasket change.

 

[QC7]

Stanweld,

Thanks for your valuable information...