Bagaimana Flange Dilas?

Flensa merupakan komponen penting dalam sistem perpipaan, menyediakan yang aman, sambungan antar pipa anti bocor, katup, pompa, dan peralatan lainnya. Welding is one of the most common and reliable methods of attaching a flange to a pipe, ensuring strength, daya tahan, and resistance to high pressures and temperatures.

Di industri seperti minyak dan gas, pemrosesan kimia, pembangkit listrik, laut, dan pengolahan air, 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, persyaratan pemeriksaan, dan praktik terbaik.

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, bahan pipa, kondisi layanan, 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:

Flensa Leher Las – Has a long tapered hub and is butt-welded to the pipe. Ideal untuk tekanan tinggi, aplikasi suhu tinggi.
Flensa Selip – Slides over the pipe and is fillet-welded both inside and outside.
Flensa Las Soket – The pipe is inserted into the socket and fillet-welded at the outer joint.
Flensa Sambungan Putaran – Used with a stub end; only the stub end is welded to the pipe.
Flensa Buta – 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)

Proses – The flange hub is aligned with the pipe end, and the two are butt-welded together with a full penetration weld.
Keuntungan – Provides a smooth bore with minimal turbulence, excellent for high-pressure systems.
Aplikasi – Oil and gas pipelines, pembangkit listrik, high-temperature steam systems.

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

Proses – 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).
Keuntungan – Easier and faster than butt welding, but less resistant to high stresses.
Aplikasi – Low- ke pipa bertekanan sedang, sistem air pendingin, general industrial piping.

3. Seal Welding

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

Preparation Before Welding a Flange

Verifikasi Materi
- Confirm the flange and pipe materials match project specifications and are weld-compatible.
- Check certification documents for grade and standards compliance.
Inspeksi Dimensi
- Measure flange dimensions, pipe diameter, and wall thickness to ensure proper fit.
- Verify alignment tolerances per applicable codes.
Pembersihan Permukaan
- Hapus minyak, gemuk, kotoran, karat, 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.
Penyesuaian dan Penyelarasan
- 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:

Melangkah 1: Preheating (Jika Diperlukan)

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

Melangkah 2: Root Pass Welding

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

Melangkah 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.

Melangkah 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.

Melangkah 5: Pembersihan Pasca Pengelasan

Hapus terak, berhamburan, and oxidation using wire brushes or grinders.
Clean with appropriate solvents if needed.

Inspection and Quality Control

Setelah pengelasan, inspection ensures that the joint meets mechanical, dimensi, dan persyaratan keselamatan.

Inspeksi Visual – Check for cracks, meremehkan, incomplete fusion, or excessive reinforcement.
Dimensional Verification – Confirm flange alignment, squareness, and bolt hole orientation.
Pengujian Non-Destruktif (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.
Pengujian Tekanan – Hydrostatic or pneumatic tests verify leak-tightness in service conditions.

Welding Standards for Flanges

Flange welding should comply with recognized standards, seperti:

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.
Ensure Proper Alignment – Misalignment can lead to flange face damage and gasket sealing issues.
Protect Welds from Contamination – Shield from wind, kelembaban, and dust during welding.
Document All Work – Keep records of welding parameters, welder IDs, dan hasil pemeriksaan.

Common Welding Defects and How to Avoid Them

Porositas – 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

Pipa Minyak dan Gas – High-pressure transmission lines and offshore platforms.
Pabrik Pengolahan Kimia – Corrosion-resistant piping systems.
Pembangkit Listrik – Steam and water pipelines in thermal and nuclear plants.
Teknik Kelautan – Ship piping systems, pabrik desalinasi.
Pengolahan Air – High-capacity pumping stations and distribution lines.

Kesimpulan

Flange welding is a critical process that demands proper preparation, skilled execution, and thorough inspection to ensure reliable, leak-free joints. 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 lonjong ensures high-quality materials, adherence to international standards, and exceptional workmanship. With its expertise in flange production and welding, sasa lonjong provides solutions for even the most demanding applications.