Weld Neck Flange ASTM A815 UNS S31803 Duplex Stainless Steel 4”High Pressure

Product Specification

Weld Neck Flange ASTM A815 UNS S31803 Duplex Stainless Steel 4”High Pressure Pipeline Connecting Flange

1. Product Description

This product is a Weld Neck (WN) flange manufactured from UNS S31803 (Duplex 2205 / F51) stainless steel in accordance with ASTM A815 and ASME B16.5 standards. 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 such as 304L or 316L while maintaining good ductility and weldability. The Weld Neck flange features a tapered hub that transitions smoothly to the pipe wall, providing high strength, stress distribution, and sealing reliability. This 4" flange is designed for permanent butt-weld connection in high-pressure and corrosive service pipeline systems.

2. Key Product Parameters

3. Application / Usage

This Weld Neck flange is ideal for high-pressure and corrosive fluid systems:

• Offshore Oil & Gas: Seawater injection systems, process piping on platforms, subsea flowlines and risers

• Chemical Processing: Chloride-containing process streams, acid services

• Desalination Plants: High-pressure RO membrane feed piping

• Pulp and Paper: Chlorine dioxide bleaching lines

• FPSOs: Topsides process piping exposed to marine atmosphere

• Power Generation: High-temperature cooling water systems, heat exchangers

4. Advantages

• Superior Strength: Yield strength is 2.5 to 3 times that of 316L, enabling thinner walls and lighter piping systems for equivalent pressure ratings

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

• Weld Neck Design: Tapered hub provides smooth stress transition, excellent resistance to fatigue and thermal cycling

• Good Weldability: Compatible with standard welding procedures; solution annealing required post-weld to maintain the 50/50 austenite-ferrite microstructure

• Cost-Effective: Lower nickel content compared to austenitic grades offers material cost savings while delivering superior performance

5. Functions

The Weld Neck flange provides a permanent, leak-proof bolted connection point for joining pipes, valves, or equipment in high-pressure piping systems. The tapered neck is butt-welded to the pipe, forming a unified structure that distributes stress evenly and minimizes pressure concentration at the joint. The flange face (typically Raised 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 weld bevel and adjacent area using dedicated tools; remove all oil, grease, and contaminants

3. Alignment: Accurately align the flange neck with the pipe end, ensuring proper fit-up and squareness

4. Welding: Perform butt-weld following approved WPS with certified welders. For duplex materials, strict heat input control is essential. Solution annealing at 1020-1100°C followed by water quenching is required to maintain the duplex structure and corrosion resistance

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

6. Bolting: Install bolts and tighten in a cross-torque sequence to the recommended torque value

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

7. Precautions

• Ferrite Balance: Ensure ferrite content remains between 40-60% by volume. 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

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

• 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

• Quality Testing: Ferrite content testing per ASTM E562 and corrosion testing per ASTM A262 or ASTM G48 are required

8. Shipping & Delivery

• Standard delivery time is typically 15–30 days for standard sizes; super duplex grades and larger sizes may require 12-20 weeks lead time

9. Payment Terms

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

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) mandatory, including 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.

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.