The short answer
API Spec 6D is the American Petroleum Institute's specification for axial, ball, check, gate and plug valves for the petroleum and natural gas industry, covering ASME Classes 150 to 2500. The current 25th edition (November 2021, with addenda to March 2025) is titled "Specification for Valves". A 6D marking doesn't prove a valve suits your service; check the manufacturer's licence for the exact facility on the API Composite List and hold the valve to your datasheet.
What API 6D covers
According to API's catalogue, the 25th edition sets requirements for the design, manufacturing, materials, welding, quality control, assembly, testing, marking, documentation and process controls of axial, ball, check, gate and plug valves, across ASME Classes 150, 300, 600, 900, 1500 and 2500. Earlier editions were titled "Specification for Pipeline and Piping Valves"; documents quoting that title may refer to the 24th edition (2014) or older.
This is a summary of API's published scope, not the standard's text. Your datasheet and project specification decide which edition, clauses and supplementary requirements apply.
What a 6D claim does and doesn't prove
| Claim you may see | What it can indicate | What it doesn't settle |
|---|---|---|
| "Designed and tested to API 6D" | The manufacturer states conformance to the specification | Whether that is independently licensed or verified |
| API Monogram on the valve | A facility licensed by API applied the mark | Suitability for your fluid, sour service, fire-safe or emissions requirements |
| ISO 9001 certificate | The manufacturer runs a certified quality-management system | That a specific valve conforms to API 6D or your datasheet |
Sour-service materials (ISO 15156), fire-type testing (API 607 for quarter-turn and non-metallic-seated valves) and fugitive-emissions type testing (ISO 15848-1) are separate requirements. Ask for them only where the datasheet calls for them, and ask for the evidence, not the logo.
How to verify a manufacturer's licence
- Open the API Composite List, API's free public directory of Monogram licensees.
- Search by company name or certificate number, or filter by specification 6D.
- Check the status. Only an active licence allows the facility to apply the Monogram.
- Check the facility's city and country: licences are issued per facility, not per brand.
- Match the certificate number to the one on the offer and the valve documents.
Then continue with the documentation guide or go back to the pipeline valve procurement guide.
Sources
External facts on this page come from these sources, each read on 15 October 2026. Regulations change; requirements for your vehicle are confirmed during quotation and clearance. This guide is not legal or financial advice.
- API SPEC 6D: Specification for Valves, 25th edition (Nov 2021; Addendum 3, Mar 2025) — American Petroleum Institute webstore
- API Composite List (Monogram licensees and registered companies) — American Petroleum Institute
- API STD 607: Fire Test for Quarter-turn Valves and Valves Equipped with Non-Metallic Seats, 8th edition (Oct 2022) — American Petroleum Institute webstore
- ISO 15156-1:2020: Materials for use in H2S-containing environments — International Organization for Standardization
- ISO 15848-1:2015 (Amd 1:2017): Industrial valves — fugitive emissions type testing — International Organization for Standardization