Question:

Our supplier is suggesting using A513 DOM tube for the alignment keys. A500 is not available in these dimensions. Our suppler is also suggesting to use 3" x .25" wall in place of the 3" x .216" as called out on the print because it would allow for better alignment.

NIST Response:

A500 Grade B steel is required for the inner HSS tube in the alignment keys (HSS 2.5x0.25). The ASTM A500 specification includes minimum requirements for yield strength, tensile strength, and elongation, which are necessary to ensure that the inner HSS tube is capable of resisting shear loads if the lowermost SRB were to slip relative to the base plates. The ASTM A513 specification does not include such tensile requirements, and A513 tubing therefore would not be acceptable for the inner HSS tube in the alignment keys.

HSS availability charts from Atlas Tube (https://www.atlastube.com/wp-content/uploads/2018/02/HSS-Availability-Chart.pdf) indicate that the inner HSS tube specified for the alignment keys (HSS 2.5x0.25) is readily available in A500 steel (rolled every 2-6 weeks) but that the outer HSS tube specified for the alignment keys (HSS 3.0x0.216) is not available. Keith-this is unique, I don't see an issue with recommending this supplier, since it's available, and is a requirement in the SOW.

NIST does not require contractors to use any specific supplier. This information is being provided only as an example to show availability of the required materials.

It would be acceptable to use HSS 3.0x0.25 for the outer tube in the alignment keys, in place of the HSS 3.0x0.216 tube. Either A513 DOM or A500 Grade B steel tube would be acceptable for the outer HSS tube in the alignment keys. It is noted that some material may need to be removed from the inside of the HSS 3.0x0.25 outer tube to allow the HSS 2.5x0.25 inner tube to fit inside.

Note that Section 3.2.5 of the Statement of Work includes the following statement: "As an alternative to welding of HSS tubes, the alignment keys may be machined from solid steel pieces, provided that this is indicated on the shop drawings and approved by the NIST COR."

All other terms remain unchanged.