A 53 & A 106B Dual Certification?

I'm moving my office, so it'll be a couple of days before I find the boxes that have my ASME, ASTM books, so I can cite the particular references - but the answer is YES. Dual marking and dual certification is acceptable.

When I finish unpacking, I'll be back with more.

Actually it is possible, as long as we're comparing A-53 Type "S" (Seamless) piping to A-106, and assuming comparible material grades, normally Grade B. There's also only a certain range of pipe sizes where these specs overlap.

Reason being A-106 is the more stringent spec, anything made to A-106 also meets the requirements of A-53. It's important to note, however, the reverse isn't true. One example being your noted difference in Silicon. A-106 requires it, so as long as the pour has at least 0.1% Si content, it meets A-106. A-53 doesn't specify a maximum or minimum, so the presence of enough Si to satisfy A-106 requirements also meets A-53 requirements.

So, if you're buying A-106 pipe I think it's largely redundant that it's dual-certified also to A-53. If you're buying A-53 pipe, you're probably paying more than you otherwise would have to for the additional certification to A-106.

Another consideration will be what do the piping supply houses in your area actually stock? There's a big area of petro-chem & refinery operations not far from me.The suppliers there don't typically stock A53B seamless, but they have piles of A106B. They'll order the A53B if you really want it, but it'll take weeks/months to get, and cost a bundle as it's an odd item for them.