Practical Implications of Impact Testing

[AgsMyDude]

I've always specified materials that don't require impact testing but I don't have a great understanding of what the practical implications would be if the testing is required (for instance if A53B is specified for use below its curve in Fig 323.2.2-1 of B31.3).

In a general sense...

Does it mean the fabricator needs to add some extra length that can be removed and sent off for testing? Or does the fabricator have certifications for materials (say A53B) that have already been tested that they can hand to you? If the former, what happens if the toughness comes back too low at the design minimum temperature given the pipe is already being fabricated? It seems like it would "too late" at that point and a re-design would be required.

How do we not already know the toughness of standard materials of construction as a function of temperature?

How would a field weld be tested?

Thanks in advance

 

[Doug Hunter]

When you buy the material it should be certified by the supplier to meet the requirements for impact strength as well as all its other rated properties.

I think that the toughness of standard materials of construction is already known as a function of temperature. You just need to find the right references.

I don't know how you'd handle weld impact strength. I would think that the welding process could add a lot of variation. You could always design using the fully annealed strength and add a safety factor.

 

[AgsMyDude]

Thanks for the response.

I read that toughness testing is typically required as a part of material specs but additional testing per Table 323.2.2-1 is required to use the material below its line in Fig 323.2.2-1. What happens in this instance? Are we just *hoping* the material comes back tougher (I am not sure why it would)?

Edit: I do see Table 323.3.5-1 with the minimum toughness energies but still looking for clarification on the other points.

 

[GD2]

I've always specified materials that don't require impact testing but I don't have a great understanding of what the practical implications would be if the testing is required (for instance if A53B is specified for use below its curve in Fig 323.2.2-1 of B31.3).

In a general sense...

Does it mean the fabricator needs to add some extra length that can be removed and sent off for testing? Or does the fabricator have certifications for materials (say A53B) that have already been tested that they can hand to you? If the former, what happens if the toughness comes back too low at the design minimum temperature given the pipe is already being fabricated? It seems like it would "too late" at that point and a re-design would be required.

How do we not already know the toughness of standard materials of construction as a function of temperature?

How would a field weld be tested?

Thanks in advance

The answer is simple. You will ask for impact tested materials at the time of order. Impact testing is determined by the process/mechanical determined MDMT. It's a design parameter.
Once you know the MDMT, you can use Fig. 323.2.2-1 to determine is an impact test will be required for the base material and also by using Table 323.2.2 for both base metal and weld metal.
There will be no practical implications for both base and weld metal if you know the impact test requirements prior to starting your material procurement and fabrication.
I believe you know the importance of impact test requirement for low temperature service. Many pressure vessels have encountered brittle facture during hydrotesting because they had high MDMT but didn't consider the room temperature for a hydrotest.

 

[Doug Hunter]

Thanks for the response.

I read that toughness testing is typically required as a part of material specs but additional testing per Table 323.2.2-1 is required to use the material below its line in Fig 323.2.2-1. What happens in this instance? Are we just *hoping* the material comes back tougher (I am not sure why it would)?

Edit: I do see Table 323.3.5-1 with the minimum toughness energies but still looking for clarification on the other points.

Sorry, I don't have access to Table or Figure 323.2.2-1, so I can't comment.

 

[AgsMyDude]

The answer is simple. You will ask for impact tested materials at the time of order. Impact testing is determined by the process/mechanical determined MDMT. It's a design parameter.
Once you know the MDMT, you can use Fig. 323.2.2-1 to determine is an impact test will be required for the base material and also by using Table 323.2.2 for both base metal and weld metal.
There will be no practical implications for both base and weld metal if you know the impact test requirements prior to starting your material procurement and fabrication.
I believe you know the importance of impact test requirement for low temperature service. Many pressure vessels have encountered brittle facture during hydrotesting because they had high MDMT but didn't consider the room temperature for a hydrotest.

Thanks GD2, I understand MDMT selection and the purpose of Fig. 323.2.2-1. What I'm struggling with is the fundamentals of specifying a material that requires impact testing.

Why would we expect an impact-tested material to perform any better than the same material that has not been impact tested? Does the request for impact testing actually change the material spec? How can we guarantee it will pass the impact test after you have specified it?