Grain size requirement- SA 333 GR6 2

[ispengg]

Greetings,

Memebers please clarify the following:

1.SA 333 specification does not “explicitly” specify the fine grain requirement for GR 6 pipe. If I want to check the same, can I use the criteria that carburized austenitic grain size number of 5 or higher (finer) as determined by the McQuaid-Ehn test in accordance with Test Methods E112, Plate IV?

2. Why the plate specifications [for eg. For SA-516 & SA-515 ]explicitly specify the grain size requirement through SA-20 but for not pipes?

2. Is there any way to relate the austenitic grain size to the grain size [Ferrite/pearlite] determined at ambient temperature through in-situ metallography [Micro structure]?

Actually this exercise I just want to do check the material mix-up of SA 333 GR 6 and SA 106 GR B.

Thank you

 

[metengr]

I would perform Charpy impact testing of a sample removed from the unidentified pipe spools to sort out the difference in materials, SA 333 Gr 6 versus SA 106 Gr B. Grain size and other measures are not worth the time, effort and cost, and may not yield definitive results.

 

[ispengg]

Thank you Metengr..

Yes. Impact testing would be the best way to to sort it out. But the pipe spools are already fabricated and errected in the field. This was identified during final inspection. Now the contractor has taken some insitu metallography and screening /segregating the pipes with grain size less than 5 as SA 106 Gr B, which I don't agree. My understanding is that as per SA 20, fine grain is the one which is having "austenitic" grain size of 5 or higher. Can you please elaborate on the query No. 1&2 on the post.

Any how I have proposed to check the stress ratio of piping as per 323.2.2 of ASME B31.3 for exemption of Impact test as well.

 

[metengr]

ispengg
In that case, my suggestion is to remain solely with field metallography and compare microstructures between the various unidentified pipe spools. The SA 333 Gr 6 pipe material would be supplied either in a normalized or normalized and tempered condition. The pearlite colonies will exhibit much finer texture in comparison to the SA 106 Gr B, which is typically furnished in a hot formed condition.

Beyond this, regarding your query 1 and 2

1.SA 333 specification does not “explicitly” specify the fine grain requirement for GR 6 pipe. If I want to check the same, can I use the criteria that carburized austenitic grain size number of 5 or higher (finer) as determined by the McQuaid-Ehn test in accordance with Test Methods E112, Plate IV?

No. You are assuming a certain threshold for fine grain for plate with none given by the pipe specification so this would not be applicable. You would also need a material sample for this effort.

2. Why the plate specifications [for eg. For SA-516 & SA-515 ]explicitly specify the grain size requirement through SA-20 but for not pipes?

Because of the method of fabrication for plate and mostly because of pressure vessel use. Pipe specifications were originally developed by the American Standards Association during the 1950's, and the specific requirement for fine grain size was not a priority.

 

[ispengg]

once again thank you.

1.If there is no threshold for grain size for pipe to consider it as "fine grain" then how to ensure the fine grain manufacturing practice?

2. Why the definition for fine grain should be different for plate and pipe? [for my academic interest]. SA 671 is pipe specification even then it explicitly calls for fine grain practice for GR CC 60 [I agree it is made from plate].

3.Is it possible to define grain size of pearlite/ferrite microstructure?

Actually I have taken sample piece of SA 333 GR 6 pipe & SA 106 Gr B from the inventory and I am trying to study relation between austenitic grain size and ferrite/pearlite grain size.Please give your opinion.

 

[metengr]

1.If there is no threshold for grain size for pipe to consider it as "fine grain" then how to ensure the fine grain manufacturing practice?

The deliberate addition of aluminum to the melt results in fine grain practice.

2. Why the definition for fine grain should be different for plate and pipe? [for my academic interest]. SA 671 is pipe specification even then it explicitly calls for fine grain practice for GR CC 60 [I agree it is made from plate].

For plate, a specific grain size is called for as mentioned above. For pipe, fine grain practice means the addition of aluminum, which promotes a finer grain structure with no specific call out of grain size.

3.Is it possible to define grain size of pearlite/ferrite microstructure?

No, typically the spacing of the carbides within pearlite and size of the pearlite colonies are features that can be compared.

Your idea of using a template for each based on known samples is proably the best approach given no other type of testing (Charpy impact).

 

[ispengg]

Metengr,

Thank you...

 

[weldstan]

Also understand that a number of pipe mills are dual certifying pipe as A-106 B and A-333-6. Fine grain melting would then apply to both. As well as checking for Al (approximately .02%), also check for niobium and vanadium, which are also added (by some mills) to A-333-6.

 

[ispengg]

Weldstan,

My understanding is SA 106 GR B is intended for high temperature applications. Is it not killed with silicon for coarse grain practice? [but its not mentioned in the specification].I am curious to know then what makes SA 106 a specification for High temperature application.Can you elaborate more on this.

Even the [B 31.3] allowable stress values for SA 106 GR B and SA 333 GR 6 are same at all temperatures and only difference comes at the limitation on usage at lower temperature application .i.e. below -29 degC. If you see from this perspective yes, SA 333 GR 6 can be certified as SA 106 GR B but not vice versa.


I believe SA 333 GR 6 is killed with both silicon and aluminium for fine grain practice. Moreover SA 106 GR B is supplied in hot finished condition but SA 333 GR 6 in normalized,normalized & Tempered or quenched & tempered condition. There is a impact requirement as well.

Thank you

 

[weldstan]

In the new World Order, steel mills like to make one specification fill multiple specifications, not necessarily meeting the needs of the end user. A classic example was making A-515 to a fine grain melting practice to permit use as either A-515 or A-516 until the A-515 Specification was amended to state in 4.1, "The steel shall be killed and made to a coarse austenitic grain size practice." For many years the only requirement was that it be made "killed". A-516 required melting practice as killed and to a fine grain practice.

Quite possibly the same amendment should be made on A-106.

 

[metengr]

I might also add, that SA 106 being for moderate to elevated temperature service would not necessarily possess a fine grain structure because coarse or larger grains are preferred for elevated temperature strength, namely creep strength.

 

[weldstan]

metengr,
We recently purchased 106 B pipe, which was dual certified 106 B/333 6 (amongst others), from a Korean mill. The CMTR was supported with -50 F Charpy impacts and Al content confirmed fine grain melting. Whereas the pipe service was under 400 F, it was accepted.

There is a misconception by some steel mill manufacturers (Metallurgists) that fine grain, low temp., impact tested, carbon or low alloy steel is always superior for any service application.