Valve Body Material - API 6D Requirements

[moodley]

I have gone out to tender for the purchase of a lubricated plug valves complying to API 6D 21st Edition. One of the suppliers have quoted to supply an API 6D & NACE MR-01-75 compliant valve.
However on reading the material specs the body is made of ASTM A216 Gr WCA. This is not listed in Table 3.1 of 6D. Paragraph 3.1 of 6D also says that the componnents are to comply with Table 3.1.
Paragraph 3.8 however allows alternate materials with certain conditions.
My opinion is that WCA is not an acceptable material for pipeline use and that it does not comply with 6D. In my experience I have not seen WCA bodies in this application.

Is the valve API 6D compliant ?
The manufacturer has API registration Q1 and a 6D number.

I understand that the differnces between WCA, WCB & WCC is in the Carbon & Manganese content as well as the Tensile Stength of the materials. What is the practical advantages/ disadvantages of each in use on pipeline valves?

Most importantly do I reject the offer based on Table 3.1 or does the valve comply under Paragraph 3.8 ?

Your help will be greatly appreciated. The valves offered are considerably cheaper than the competitors and as we are a public company cost saving issues are a big deal.

Thanx
Dev

 

[Hush]

WCA has a lower carbon content than WCB or WCC which makes it slightly easier to weld. The draw back is less carbon means lower yield and tensile. About 30K yield and 60K tensile as compared to WCB at 36K & 70K. The valve is 6D compliant. API allows the use of alternate materials providing the manufacturer backs it up with material specifications (in this case it could be as simple as: The material shall meet requirements of ASTM A216 Gr WCA) and a design package. You may want to check the valves maximum operating pressures to make sure they haven't been derated, other than that there shouldn't be a problem with this material.