Mặt bích được hàn như thế nào?

Mặt bích là thành phần thiết yếu trong hệ thống đường ống, cung cấp một cách an toàn, kết nối chống rò rỉ giữa các đường ống, van, máy bơm, và các thiết bị khác. Welding is one of the most common and reliable methods of attaching a flange to a pipe, ensuring strength, độ bền, and resistance to high pressures and temperatures.

Trong các ngành công nghiệp như dầu khí, xử lý hóa chất, phát điện, hàng hải, và xử lý nước, flange welding must be performed with precision to meet strict quality and safety requirements. This article explains in detail how flanges are welded, the different welding techniques used, preparation steps, yêu cầu kiểm tra, và các phương pháp hay nhất.

Introduction to Flange Welding

Flange welding involves joining the flange to a pipe or fitting by melting the base materials together, often with the addition of a filler metal. The goal is to create a joint that is as strong and corrosion-resistant as the base materials themselves.

Welding methods vary depending on the flange type, pipe material, điều kiện dịch vụ, and applicable industry standards.

Common Types of Flanges That Require Welding

Before understanding how to weld, it’s important to know the types of flanges typically welded to pipes:

Mặt bích cổ hàn – Has a long tapered hub and is butt-welded to the pipe. Lý tưởng cho áp suất cao, ứng dụng nhiệt độ cao.
Mặt bích trượt – Slides over the pipe and is fillet-welded both inside and outside.
Mặt bích hàn ổ cắm – The pipe is inserted into the socket and fillet-welded at the outer joint.
Mặt bích chung – Used with a stub end; only the stub end is welded to the pipe.
Mặt bích mù – Used to close the end of a pipe; welding is not typical but may be required for special sealing needs.

Welding Methods for Flanges

1. Butt Welding (for Weld Neck Flanges)

Quá trình – The flange hub is aligned with the pipe end, and the two are butt-welded together with a full penetration weld.
Thuận lợi – Provides a smooth bore with minimal turbulence, excellent for high-pressure systems.
Ứng dụng – Oil and gas pipelines, nhà máy điện, high-temperature steam systems.

2. Fillet Welding (for Slip-On and Socket Weld Flanges)

Quá trình – The flange is placed over or into the pipe end, and a fillet weld is applied to the outer edge (and inner edge for slip-on types).
Thuận lợi – Easier and faster than butt welding, but less resistant to high stresses.
Ứng dụng – Low- đến đường ống trung áp, cooling water systems, general industrial piping.

3. Seal Welding

Quá trình – A small weld bead is applied to create a leak-proof seal, usually in conjunction with another mechanical joint.
Thuận lợi – Prevents fluid leakage without adding significant structural strength.
Ứng dụng – Vacuum systems, low-pressure fluid lines.

Preparation Before Welding a Flange

Material Verification
- Confirm the flange and pipe materials match project specifications and are weld-compatible.
- Check certification documents for grade and standards compliance.
Kiểm tra kích thước
- Measure flange dimensions, pipe diameter, and wall thickness to ensure proper fit.
- Verify alignment tolerances per applicable codes.
Làm sạch bề mặt
- Loại bỏ dầu, dầu mỡ, bụi bẩn, rỉ sét, and moisture from welding surfaces.
- Use solvents, wire brushes, or grinding tools as needed.
Beveling
- For butt welding, bevel both the pipe and flange ends to the specified angle for penetration.
- Typical bevel angle: 37.5° for standard butt weld preparations.
Điều chỉnh và căn chỉnh
- Use clamps, fixtures, or tack welds to hold the flange and pipe in proper alignment.
- Ensure the bolt holes are oriented correctly for assembly.

Welding Procedure

The welding process depends on the selected method, but the general steps are:

Bước chân 1: Preheating (Nếu được yêu cầu)

Preheat certain steels, especially high-alloy grades, to reduce the risk of cracking.
Preheating temperature is determined by the welding procedure specification (WPS).

Bước chân 2: Root Pass Welding

Begin with a root pass to ensure full penetration and fusion at the joint.
TIG (GTAW) or stick welding (SMAW) is often used for root passes.

Bước chân 3: Fill and Cap Passes

Apply successive passes to fill the joint, ensuring each layer is cleaned before adding the next.
Use weaving or stringer techniques depending on joint geometry.

Bước chân 4: Fillet Welding (for Slip-On and Socket Weld Flanges)

Apply weld beads to the outer circumference (and inner circumference for slip-ons).
Maintain consistent bead size for uniform strength.

Bước chân 5: Làm sạch sau hàn

Loại bỏ xỉ, bắn tung tóe, and oxidation using wire brushes or grinders.
Clean with appropriate solvents if needed.

Inspection and Quality Control

Sau khi hàn, inspection ensures that the joint meets mechanical, chiều, và yêu cầu an toàn.

Kiểm tra trực quan – Check for cracks, undercutting, incomplete fusion, or excessive reinforcement.
Xác minh kích thước – Confirm flange alignment, squareness, and bolt hole orientation.
Kiểm tra không phá hủy (NDT) – Methods such as ultrasonic testing (UT), radiographic testing (RT), magnetic particle testing (MT), or dye penetrant testing (PT) to detect internal and surface defects.
Kiểm tra áp suất – Hydrostatic or pneumatic tests verify leak-tightness in service conditions.

Welding Standards for Flanges

Flange welding should comply with recognized standards, chẳng hạn như:

ASME B31.1 / B31.3 – Power piping and process piping codes.
AWS D1.1 – Structural welding code for steel.
ISO 9606 / EN 287 – Qualification of welders.
API 1104 – Welding of pipelines and related facilities.

These standards ensure welding is performed consistently, safely, and to the required quality level.

Best Practices for Flange Welding

Follow an Approved WPS – Ensure all welding is performed according to an approved welding procedure specification.
Use Skilled Welders – Welders must be qualified for the specific material and process.
Maintain Proper Heat Control – Avoid excessive heat input to prevent distortion or metallurgical damage.
Đảm bảo sự liên kết thích hợp – Misalignment can lead to flange face damage and gasket sealing issues.
Protect Welds from Contamination – Shield from wind, độ ẩm, and dust during welding.
Document All Work – Keep records of welding parameters, welder IDs, và kết quả kiểm tra.

Common Welding Defects and How to Avoid Them

độ xốp – Prevent by cleaning surfaces thoroughly and avoiding moisture in shielding gas.
Incomplete Fusion – Use proper heat input and electrode manipulation.
Undercutting – Control travel speed and electrode angle.
Distortion – Use balanced welding sequences and proper fixturing.

Applications of Welded Flanges

Đường ống dẫn dầu khí – High-pressure transmission lines and offshore platforms.
Nhà máy chế biến hóa chất – Corrosion-resistant piping systems.
Phát điện – Steam and water pipelines in thermal and nuclear plants.
Kỹ thuật hàng hải – Ship piping systems, nhà máy khử muối.
Xử lý nước – High-capacity pumping stations and distribution lines.

Phần kết luận

Flange welding is a critical process that demands proper preparation, skilled execution, and thorough inspection to ensure reliable, khớp không bị rò rỉ. Choosing the right welding method, following approved standards, and applying best practices are essential for achieving optimal performance and safety in service.

For industries seeking precision-manufactured and expertly welded flanges, partnering with a trusted supplier like sasa thuôn dài ensures high-quality materials, adherence to international standards, and exceptional workmanship. With its expertise in flange production and welding, sasa thuôn dài provides solutions for even the most demanding applications.