Lap Joint Flange ASTM A815 UNS S31803 Duplex Stainless Steel 2”ASME B16.5

1. Product Description

This product is a Lap Joint (LJ) flange manufactured from UNS S31803 (Duplex 2205 / F51) stainless steel in accordance with ASTM A815 and ASME B16.5 standards. A lap joint flange (also called a "loose flange") is a two-part assembly consisting of a backing flange and a stub end. The stub end is butt-welded to the pipe, and the lap joint flange slips over the stub end. The flange itself is not directly connected to the pipe or stub end, allowing it to rotate freely. UNS S31803 is a dual-phase stainless steel with a microstructure of approximately 50% austenite and 50% ferrite, offering roughly double the yield strength of standard 300-series austenitic stainless steels such as 304/316L. This 2" flange is designed for applications requiring frequent disassembly, alignment flexibility, and high corrosion resistance.

2. Key Product Parameters

3. Application / Usage

This lap joint flange is ideal for corrosive environments and systems requiring frequent maintenance:

• Oil & Gas: Offshore platforms, subsea piping, chemical injection lines

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

• Marine Engineering: Seawater piping systems, shipbuilding, desalination plants

• Power Generation: Cooling water systems, heat exchangers

• Pulp and Paper: Bleaching lines, digester systems

• Low-pressure and large-diameter piping: Sizes above 24" are commonly produced as lap joints

4. Advantages

• Rotating Flange Design: The backing flange can rotate freely, allowing easy alignment of bolt holes even when pipes are misaligned

• Cost-Effective: Only the stub end needs to be made of duplex stainless steel; the backing flange can be manufactured from lower-cost carbon steel, significantly reducing overall system costs

• Superior Strength: Yield strength is approximately double that of 316L austenitic steel, enabling thinner wall designs

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

• Easy Maintenance: The lap joint design enables quick disassembly and reassembly without cutting or welding for pipeline inspection and cleaning

5. Functions

The lap joint flange provides a detachable, leak-proof bolted connection point for joining pipes, valves, or equipment in a piping system. The stub end is butt-welded to the pipe, and the backing flange slips over it, allowing the flange to rotate freely for bolt-hole alignment. The flange face accommodates a gasket to ensure a reliable seal when bolted to a mating flange. This design is particularly useful for systems requiring frequent maintenance, cleaning, or component replacement.

6. Installation Instructions

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

2. Surface Preparation: Clean the stub end weld bevel and adjacent area using dedicated tools; remove all oil, grease, and contaminants

3. Stub End Welding: Butt-weld the stub end to the pipe 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

4. Flange Assembly: Slip the lap joint backing flange over the stub end

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

6. Bolting: Align bolt holes by rotating the backing flange freely, 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

• Stub End Compatibility: Ensure the stub end type (A, B, or C) matches the lap joint flange design

8. Shipping & Delivery

• Standard delivery time is typically 15–30 days for standard sizes; larger sizes and custom specifications may require extended 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) available, 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.