DNV Approval of Manufacturer for Seamless Duplex Stainless Steel Pipe

Key facts

Certificate AMMM00003BT is a DNV Approval of Manufacturer issued to Zhejiang Xintongda Special Steel Manufacturing Co., Ltd. for its Songyang County factory. It covers one product family: seamless duplex and super duplex stainless steel pipe, cold finished and solution heat treated, in UNS S31803 and S32205 (duplex 2205) and S32750 (super duplex 2507), up to 323.9 mm outside diameter and 12.7 mm wall thickness.

The certificate was issued on 28 August 2025 and lists an expiry date of 27 August 2028. It is issued under the DNV rules for classification of ships and the class programme DNV-CP-0252 Steel pipes and steel pipe fittings.

It approves the factory, not a particular shipment of pipe. Material supplied to a DNV classed object still has to meet the requirements of the applicable class rules, and that check is made against the order, not against this certificate.

Who makes the pipe, and who handles your order

Manufacturer · Zhejiang Xintongda Special Steel Manufacturing Co., Ltd. (浙江鑫通达特钢制造有限公司), No. 209 Ruiyang Avenue, Xiping Street, Songyang County, Lishui, Zhejiang 323400, China. The certificate names this company and this address, so the approval attaches to pipe produced there and does not extend to pipe from another mill.

Export supplier · Wenzhou Xinzhe Tech Co., Ltd. (温州信哲科技有限公司) handles overseas enquiries, quotations, documentation and shipment coordination with the factory.

Manufacturer approval and order requirements

An Approval of Manufacturer is a factory-level approval. DNV assesses the manufacturing processes, facilities and quality system behind a product, then approves the factory to supply it. It is not a certificate for a particular heat, order or length of pipe, and it is not a substitute for the mill certificates that travel with the goods.

Confirm the applicable class rules and edition for the project, together with any testing, inspection and survey requirements for the order.

DNV certification of materials and components, including approval of manufacturers

Approved grades, sizes and delivery condition

The table follows the approval particulars on page 2 of the certificate.

The grade footnote on page 2 does not approve a single standard. It requires suitable pipe grades to be selected from a list of recognised standards: ISO 9329-4, ISO 9330-6, EN 10216-5, EN 10217-7, ASTM A269, A312, A358, A789, A790, A928 and JIS G3459. Check the ordered standard and edition against the grade, product form, manufacturing route and applicable DNV class requirements. Several of these standards also cover welded pipe or tube, but the approved scope is the one defined in the table: cold finished seamless duplex pipe.

Where the certificate stops

Read pages 1 and 2 together. Page 1 gives the application area as “Austenitic and Ferritic-austenitic (duplex) stainless”, but its steel type line reads “Ferritic-austenitic (Duplex) stainless”, and the page 2 particulars list duplex grades only. Do not quote this certificate for an austenitic grade such as 316L. If a project needs an austenitic scope, confirm it with DNV first.

Page 1 also describes the approval as covering “Steel Pipes and Fittings”, but the particulars record the product as pipes and the manufacturing method as cold formed seamless (shown on page 2 as CFS, Cold Finished Seamless). Welded pipe, tube and fittings are not listed as approved products. If your order includes them, ask DNV to confirm the scope instead of assuming this certificate extends to them.

Download and verify the DNV certificate

Download AMMM00003BT (PDF, 2 pages)Preview · 2 pages · 211 KB

Certificate number, dates and limits on this page are those printed on the supplied certificate, which carries form code AM 311, revision 2025-05. Check the current status using the certificate number or manufacturer name in DNV Approval Finder before an order is placed, or use the DNV certificate authentication service.

The same works under five other schemes

Approvals are granted independently, and a project spec often names more than one. The Songyang factory also holds an ABS Product Design Assessment and Manufacturing Assessment, a Bureau Veritas Materials Approval and Mode II Recognition, and a Lloyd’s Register Works Approval (LR25338152WA, valid to 30 October 2028). The BV documents cover a wider material range, including ASTM A312 austenitic grades. For duplex pipe, DNV and the BV Materials Approval each list a maximum outside diameter of 323.9 mm and a maximum wall thickness of 12.7 mm, while the BV Mode II Recognition lists a lower wall limit of 10.31 mm.

This DNV certificate has the narrowest product scope of the six: cold finished seamless duplex pipe only. The LR approval covers pipe and tube by material category, so an LR enquiry for a welded item or an austenitic grade still needs the LR scope checked against the ordered grade.

Two TÜV SÜD documents sit outside the classification system altogether. NORSOK M-650 qualifies the manufacturing route against a Norwegian petroleum standard, backed by material data sheets and qualification test records; the AD 2000 W 0 / PED certificate is the quality assurance route into EU pressure equipment supply, issued against EN 10216-5 and a listed set of ASTM and ASME specifications. Neither replaces a class approval, and neither is covered by it.

View ABS factory documents · View BV factory certificates · View the LR works approval · View the NORSOK M-650 qualification · View the AD 2000 W 0 and PED certificate

DNV manufacturer approval FAQ

Request a DNV scope check

Send the order data below and we will confirm whether the grade, size and standard fall inside the approval, and which documents the order is likely to need:

• Specification and edition — ASTM, EN, ISO or JIS
• UNS grade
• Outside diameter × wall thickness
• Quantity and delivery condition
• Class rules and project requirements
• Inspection and survey documents required

Wenzhou Xinzhe reviews the enquiry with the Songyang factory and replies with the applicable scope.

Contact Wenzhou Xinzhe

Page reviewed 7 November 2026 against DNV certificate AMMM00003BT, form AM 311 rev. 2025-05.