MSS SP-70 vs API 599: Reading Valve Standards for Procurement and Testing

The Short Answer

MSS SP-70 and API 599 are two industry standards that buyers reference when procuring industrial valves, but they come from different organizations and serve different purposes. MSS standards are produced by the Manufacturers Standardization Society and cover a broad range of valve types and practices, while API standards are produced by the American Petroleum Institute and typically focus on the performance requirements and testing of valves for petroleum and related services. When a purchase specification lists both, the standard is the contract — the applicable edition, scope, and testing requirements should be confirmed before ordering.

Two Standards Bodies, Two Purposes

The Manufacturers Standardization Society (MSS) publishes voluntary standards that standardize dimensions, materials, and practices across the valve industry. MSS standards are widely referenced in North American procurement because they give a common technical language for a given valve type, covering areas such as face-to-face dimensions, marking, and material requirements. The American Petroleum Institute (API) develops standards for the oil and gas industry, and its valve standards typically emphasize the design, materials, testing, and inspection requirements that matter in demanding service. The two families overlap in practice: a purchaser may require an MSS standard for dimensional commonality and an API standard for performance and testing.

What a Buyer Should Check

Check Item	Why It Matters	Typical Source
Edition and revision date	Standards are updated; the contract should cite the exact edition	Procurement spec
Scope of the standard	Confirms the standard covers the valve type and size being bought	Standard’s scope clause
Material requirements	Body, bonnet, and trim materials follow the cited standard	Standard and data sheet
Testing and inspection	Shell test, seat test, and any required non-destructive testing	Standard and purchase order
Marking and documentation	Nameplate data, material certificates, and test records	Standard and delivery documents

The table lists the items a buyer should verify regardless of which standard family is cited; the specific values come from the cited edition.

Common Confusions in Practice

The most common confusion is treating the standard as a performance promise. A valve that meets a dimensional standard is not automatically suitable for a given pressure, temperature, or fluid — the rating and material still come from the data sheet and the applicable rating standard. Another confusion is mixing families: some purchasers assume any MSS valve can be substituted for an API valve of the same nominal size. In reality, the testing and inspection requirements can differ, and the purchase order should state which standard governs acceptance. Finally, the edition matters: standards are revised, and a contract citing an old edition may not reflect current requirements or current product builds. Some purchasers standardize on the latest edition to avoid managing multiple revisions, while others keep an older edition for continuity with existing installed equipment. Either policy works if it is written down and applied consistently, because the confusion comes from the in-between state — a specification, a quotation, and a delivered valve each referencing different editions.

How Standards Affect Procurement

In a typical purchase, the specification cites the governing standards in the front of the document, and the supplier quotes against that scope. At receipt, the inspector verifies marking, documentation, and the test results against the cited standard. If the delivered valve does not carry the required documentation, it fails acceptance even if the geometry looks correct. This is why the standard citation, not the product photograph, is the legal basis of the purchase. The same principle applies to every valve family: the standard is part of the specification, and the delivered documentation is part of the acceptance.

When Both Standards Appear in One Specification

It is common for a purchase specification to cite more than one standard, and the interaction is deliberate. An MSS standard may establish the dimensional and construction baseline so that valves from different suppliers are interchangeable in the plant, while an API standard may add the testing and performance requirements that the service demands. In this arrangement, the supplier must build to both, and the acceptance criteria come from both documents. The inspector checks dimensions against the MSS requirements and the test documentation against the API requirements. A valve that passes one but not the other is nonconforming, and the contract, not supplier confidence, settles the dispute.

For plants that maintain a valve standard, the practical benefit is consistency: every valve of a given type arrives with the same geometry, marking, and test records, which simplifies spares, installation, and documentation. The cost is that suppliers must be qualified to both families, which can narrow the vendor list. Most engineering teams accept that trade-off because the long-term reliability and traceability outweigh the initial procurement friction.

Application Scenario: Sourcing Valves for a Plant Standard

Consider a plant standardizing on a specific valve type across its North American facilities. The engineering team writes a purchase specification that cites the MSS standard for dimensional and material commonality and the API standard for the shell and seat testing requirements. When suppliers quote, the team compares not just price but whether the quoted valve meets both cited standards with the required documentation. One supplier offers a lower price but proposes a valve built to the MSS standard only; the team rejects it because the contract requires both. The lesson is that standards are procurement tools, and the citation in the purchase order — not general knowledge of the industry — determines what is acceptable. For more on how MSS and API standards interact for a specific valve family, see the comparison of MSS SP-67 vs API 609, and for the testing side, review the API 609 butterfly valve standard.

This article provides general educational knowledge only and is not professional engineering advice.

Tags: Valve Standards