You get the answers in section 4.1.
API 650 does not discriminate between pressure and non pressure parts.
Rather it tells us to use plates for shell, bottom and roof and structural shapes for rafters, girders and trusses.

DHURJATI SEN
Kolkata, India

Our exact case is, we want to use S355-JR material for the anchor chair assembly, the assembly shall be prepared using the plate material except anchors. Since S355-JR is not a listed plate material as per clause 4.2. Other Codes such as ASME Section VIII-1 does not enlist the material specifications for non-pressure parts, so using the same analogy I posted the query that it seems to me 4.2 is applicable to the wetted parts and may not be applicable to anchor chair.

API 650 does not mention nor exclude anchor chairs (or other items such as guardrails, ladders, mixer support structures, lifting lugs, etc) in the Scope language but since it is welded to the tank shell and bottom I think you should use materials in the standard. API 650 refers to AISI Steel Plate Engineering Data, Volume 2, Part 5, “Anchor Bolt Chairs.” for design, look there for additional guidance. For materials, API is generally concerned about weldability, strength and toughness. If you can demonstrate that your material of choice meets or excesds all those requirements and get the tank owner to agree you may be fine. On the other hand, why not simply use a material that is in the standard?

Here is what API 650 says about using material not in the standard:

4.1.2 Material produced to specifications other than those listed in this section may be employed, provided that the material is certified to meet all of the requirements of an applicable material specification listed in this standard and the material’s use is approved by the Purchaser. The Manufacturer’s proposal shall identify the material specifications to be used. When this standard does not address material requirements for miscellaneous items and appurtenances, the Purchaser and/or the Manufacturer shall supply additional material requirements using a supplement to the Data Sheet.

Do what IFRS says.

When it comes to tanks he is one of the "experts" here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Quote (Abdul_Muiz

Our exact case is, we want to use S355-JR material for the anchor chair assembly,)

IFR has explained the case in detail and a big PS for his respond.

I just want to say my concern is ,about galvanic corrosion (from being welded to shell ). I would suggest to use the same mat plate with shell or S275 .

Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

Is your quality control system adequate to control all the different materials at all times?.

Regards