ASTM A193 B7 and A320 L7 Stud Bolts: RFQ Checks Before Substitution

A stud that fits a flange is not necessarily an acceptable replacement for the specified bolting. When a quotation proposes A193 B7 instead of A320 L7, or the reverse, review the order requirements before comparing price. Matching diameter and length are only part of the decision.

Understand the two specification families

ASTM A193/A193M covers alloy-steel and stainless-steel bolting for high-temperature or high-pressure service and other special-purpose applications. A320/A320M addresses alloy-steel and stainless-steel bolting for low-temperature service. These are scope descriptions, not universal operating-temperature approvals for a completed joint. A193 scope · A320 scope.

State the exact grade and edition on the RFQ. B7, B7M, L7 and L7M should remain separate designations in the purchasing documents. Do not remove an ‘M’ suffix or interpret it as an optional spelling variation. The applicable standard, size and project specification determine the actual requirements.

Ask what evidence supports the proposed substitution

A supplier’s statement that two materials have similar chemistry is not enough. Ask the responsible design authority to confirm whether a proposed alternative satisfies the service conditions and governing code. Then identify the inspection evidence required for that particular order.

• What minimum and maximum service temperatures and other design conditions apply?
• Which specification, grade, edition and supplementary requirements are mandatory?
• What mechanical, hardness or impact testing must be reported under those requirements?
• Must results be linked to the supplied heat, manufacturing lot or finished components?
• Who has authority to approve a substitution, and how will that approval be recorded?

Specify dimensions and matched hardware

Write the stud diameter, thread system, pitch, overall length and thread configuration as separate fields. Include the dimensional standard or drawing, and clarify the length convention where necessary. Metric dimensions should not be inferred from a description prepared for an inch-based order.

List the required nuts, their specification and grade, the quantity per stud, and any washer requirement. A quotation for bare studs should not be accepted as a price for a complete assembly. Review the proposed finish or coating together with the thread fit and assembly specification; do not add a coating after the quotation without checking its effect on the agreed requirements.

Use a line-by-line quotation comparison

Create columns for ‘required’, ‘offered’ and ‘deviation’. Compare grade, standard edition, dimensions, heat treatment or supplied condition, testing, marking, matched nuts and documentation. Mark unanswered items as open rather than filling them with assumptions. This makes a lower price easier to assess: it may reflect a different inspection or supply scope.

Prepare the enquiry package

Include the drawing revision, quantities, destination, requested delivery date and required documents. A requested date is a procurement requirement to discuss, not a delivery promise. WISINE can review the A193 B7 / B7M, A320 L7 / L7M and stud bolt requirements against the supplied project documents. Any substitution should remain explicit and approved.

This article supports procurement preparation. Use the approved drawing, applicable standard edition and project requirements for design and acceptance decisions.