Blind Flange ASTM A815 UNS S31803 Duplex Stainless Steel 4" Class 300# ASME B16

Product Specification

Blind Flange ASTM A815 UNS S31803 Duplex Stainless Steel 4" Class 300# ASME B16.5 

1. Product Description

This product is a forged blind flange manufactured from UNS S31803 (Duplex 2205 / F51) stainless steel in accordance with ASTM A815 and ASME B16.5 standards . A blind flange (also called a 'closure plate flange') is a solid circular disc with no center bore, installed at the end of a piping system to permanently terminate a pipe or provide access for inspection . Unlike other flange types, it has no hub, making it ideal for isolating pipelines, valves, or pressure vessels . UNS S31803 is a dual-phase stainless steel with a microstructure of approximately 50% ferrite and 50% austenite, offering roughly double the yield strength of standard 300-series austenitic stainless steels . This 4" Class 300# flange is designed for bolted connections in high-pressure and corrosive service pipeline systems.

2. Key Product Parameters

3. Application / Usage

This blind flange is ideal for high-pressure and corrosive fluid systems requiring permanent pipe termination or isolation:

• Oil & Gas: Pipeline termination, equipment isolation on offshore platforms, wellhead connections

• Chemical Processing: Isolating sections for maintenance in chloride-containing process streams

• Marine & Desalination: Seawater piping systems, desalination plant closures

• Power Generation: Pressure vessel openings, heat exchanger isolation

• Pulp and Paper: Digester systems, bleaching line closures

4. Advantages

• Superior Strength: Yield strength (450 MPa) is approximately double that of 316L, enabling higher pressure ratings with reduced thickness 

• Excellent Corrosion Resistance: PREN ~34-36 provides outstanding resistance to pitting, crevice corrosion, and chloride stress corrosion cracking 

• Complete Flow Isolation: Solid disc design provides 100% flow blockage and positive isolation

• Forged Integrity: Tighter grain structure than cast or plate flanges, ensuring superior performance under pressure and thermal cycling

• Good Weldability: Compatible with standard welding procedures; solution annealing required post-weld

5. Functions

The blind flange provides a permanent, leak-proof bolted closure for the end of a pipe, valve, or pressure vessel opening. Unlike other flange types that allow flow passage, the blind flange has no bore, completely blocking fluid flow. It is commonly used to permanently terminate pipelines, isolate equipment or piping sections for maintenance, or close off pressure vessel openings. The flange face accommodates a gasket to ensure a reliable seal when bolted to a mating flange.

6. Installation Instructions

1. Unpacking Inspection: Check for transit damage; verify markings, dimensions, and pressure class per ASME B16.5

2. Surface Preparation: Clean the flange face and stud bolt threads; remove all oil, grease, and contaminants

3. Gasket Installation: Place a suitable gasket (e.g., spiral wound, PTFE) on the flange face

4. Alignment: Align the flange with the mating flange bolt holes

5. Bolting: Install stud bolts and nuts, tighten in a cross-torque sequence to the recommended torque value

6. Hydrotest: Test pressure = 1.5 × design pressure; ambient temperature not below 5°C

7. Inspection: Check for leakage and retorque after system pressure stabilization

7. Precautions

• Ferrite Balance: Ensure ferrite content remains between 40-60% . Improper heat treatment is the most common cause of out-of-spec ferrite ratios

• Temperature Limitation: Not recommended for use above 300°C or below -50°C due to reduced toughness 

• Bolting Torque: Do not exceed recommended torque to prevent gasket damage or flange distortion

• Gasket Selection: Choose gasket material compatible with the service medium and pressure/temperature conditions

• Cleanliness: Requires a higher degree of cleanliness than carbon steel fabrication; use dedicated tools to prevent contamination

• Quality Testing: Ferrite content testing per ASTM E562 and corrosion testing per ASTM A923 recommended

8. Shipping & Delivery

• Standard delivery time is typically 15–30 days, subject to order quantity, pressure class, and specification availability 

9. Payment Terms

• Common international payment methods include T/T (Telegraphic Transfer) , L/C at sight (Letter of Credit) , and D/P 

10. Packaging

• Products are securely packed in plywood cases or wooden crates with internal cushioning to ensure safe transportation and prevent damage during transit 

11. After-Sales / Return & Warranty Policy

• All products undergo strict quality inspection before shipment, with Mill Test Certificates (EN 10204 3.1/3.2) available, including chemistry, mechanical properties, ferrite content, and corrosion test results 

• Third-party inspection (ABS, DNV, CCS, LR, BV, etc.) available upon request

• In case of quality issues, retain original packaging and provide relevant photos or third-party inspection reports

• Specific return, exchange, and warranty terms are subject to the final sales contract agreement.

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FAQ

1. Are you trading company or manufacturer ?
    We are manufacturer ,You can see the certification.
2. How long is your delivery time?
    Generally it is 5-10 days if the goods are in stock. or it is 15-20 days if the goods are not in stock, it is according to quantity.
3. Do you provide samples ? is it free or extra ?
    Yes, we could offer the sample for free charge but need pay the cost of freight.
4. What is your terms of payment ?
    Payment<=1000USD, 100% in advance. Payment>=1000USD, 50% T/T in advance ,balance before shippment.