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Gorman3 (Industrial) (OP)
30 Jul 08 13:37
Howdy all,

According to B16.34 there are 3 tables that define an acceptable casting, the tables are divided up by wall thicknesses . I am required to meet is Table I-1 for valves under 2" thick (page 100 in 2004 version). The table specifies gas porosity up to level 2, sand level 3, CA shrinkage lvl 2, etc.

My customers refer to castings that meet this table as level 3 castings. What are the other levels based on? Is there a table for it, API-6D maybe?

Any clarification would be great. Because every Xray tech I know just use the table in B16.34

thx friends!

PS - Does anyone have a scanned copy of ASTM E446 they can share. I have pages 707 - 710 but its from 1984!!
Helpful Member!  greg1950 (Mechanical)
30 Jul 08 16:18
Your customer is not quite correct. Those tables list various categories of defects along with the acceptable defect levels that must be met in order for the valve to meet "special class" in accordance with ASME/ANSI B16.34. Since at this time there is no other standard to reference for casting quality, B16.34 is used. A level 3 casting would be one in which all of the defect levels were no greater than level 3.

All of the casting defect levels are based upon reference radiographs published in the E446 reference radiograph comparative plates books. These radiograph books are what are referenced in the E446 standard. The last time we bought any reference radiograph books they were about $1200 (us dollars) each. They contain actual radiographs so they are very difficult to copy.

As for general valve casting acceptable radiographic quality standards, both MSS and API are working documents that address this issue.

Greg Johnson  
Gorman3 (Industrial) (OP)
30 Jul 08 16:47
Right, that table is the minimum requirement for acceptability as per B-16.34.


Now I understand what they mean by a level 2 casting, but they should be careful. By that logic a "level 3" casting could include CA3 shrinkage, or A3 Gas Porosity, both of which would not meet B16.34.

 
greg1950 (Mechanical)
30 Jul 08 18:04
That is correct. "Level 3" is kind of used as a defacto acceptance standard by many organizations. The problem is that it is a grade or level that exceeds the general casting quality of most of today's imported commodity cast steel valves. On the API RP591 "User Acceptance of Refinery Valves" workgroup, we have proposed a standard that is one level up (mostly level 4's) across the board, to identify a commodity (non-special class) valve casting. Of course things like hot tears are not allowed at all. In MSS we will be trying to do the same thing as well. Guaranteeing a level 3 on all valves today is impossible without expensive casting upgrades.
Gorman3 (Industrial) (OP)
31 Jul 08 9:28
I'm well aware of the difficulty of getting a special class RT level on a consistent basis. You'd be surprised by the number of OEMs at the same foundries with a perception of casting quality between the two brands is so different.

MSS is a whole other ball of wax. It is frustratingly subjective. It's easy enough to spot sand or gas and grind it out, but visually identifying a hot tear or surface shrinkage is hard and time consuming, even with the use of the SP55 manual. In SP55 D and E cracks are easy to identify, but type C is easy to miss when compared to the acceptable type A or B veining.

In respect to surface quality I think the biggest difference between "commodity" and special class is the amount of sand blasting performed at the foundries. Wouldn't you agree?
 

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