Loose flanges — what they are

Loose flanges (often called lap joint flanges or loose backing flanges) are flanges that are not permanently welded to the pipe. Instead, they slide over a short stub end (lap joint stub end) that is welded to the pipe. The loose flange can rotate freely around the stub end, which makes alignment and assembly easier when joining pipe sections or equipment.

How loose flanges are used

Loose flanges are used wherever frequent dismantling, easy alignment or material separation between pipe and flange is required. Typical uses include:

• Pipework requiring regular maintenance — systems that need to be taken apart often for inspection, cleaning or replacement.
• Corrosive environments — where the stub end may be made of one grade while the loose flange is a different grade to reduce cost or improve performance.
• Systems with tight alignment needs — the rotating flange allows bolt holes to be aligned without moving the pipe.
• Applications using sanitary or specialty piping — food, beverage and pharmaceutical lines where joints must be disassembled and cleaned.

Who buys loose flanges

Typical buyers include mechanical contractors, pipefitters, plant maintenance teams, OEMs, fabricators and installers across small workshops to large industrial plants. They are also useful for DIY and garage projects where modularity and reusability are desirable.

Industries and sectors

• Oil & gas and petrochemical
• Marine and offshore
• Food & beverage and pharmaceuticals
• Water treatment and utilities
• HVAC and building services
• Automotive and general manufacturing
• Construction and fabrication workshops

Materials and steel grades

In this shop we offer loose flanges made only from stainless and corrosion-resistant steels. Common materials and their conventional designations you will see are:

• Stainless steel 304 (also listed as AISI 304 or EN 1.4301, sometimes called A2) — a versatile general-purpose stainless steel suitable for many indoor and mild outdoor applications.
• Stainless steel 316 / 316L (AISI 316, EN 1.4401 / 1.4404, often called A4) — contains molybdenum for improved resistance to chlorides and is common in marine and chemical environments. 316L has lower carbon for better weldability.
• Duplex and super duplex (for example grades commonly referenced as 2205) — used where higher strength and enhanced resistance to chloride stress corrosion are required, often in offshore and chemical industries.
• Heat-resistant stainless steels (such as 310/310S or other high-temperature grades) — used where sustained elevated temperature resistance is needed.

Using the correct combination of loose flange and stub end materials helps control cost while ensuring the required corrosion and mechanical performance.

Standards and compatibility

Loose flanges are manufactured to common pipe flange standards so they fit standard pipework and bolts. Typical standards include European and British standards such as EN 1092-1 and international/US standards such as ASME B16.5/B16.47. Always check product datasheets for the exact standard, face type (flat, raised, tongue and groove), pressure rating (PN or ASME class) and nominal size (DN or NPS) before ordering.

Practical benefits and selection tips

• Easy alignment: rotating flange simplifies bolting and assembly.
• Reusability: loose flanges can be reused when systems are disassembled.
• Cost control: stub ends can be made from more resistant (and more expensive) materials while loose flanges can be a different grade to reduce cost.
• Frequent maintenance: ideal for lines that require regular inspection or cleaning.

When selecting loose flanges, consider the operating pressure and temperature, the chemical environment (chlorides, acids), the required flange standard, and whether you need a matching stub end. If welding is involved, choose low-carbon versions (for example 316L) to reduce risk of sensitisation where appropriate.

Need help choosing loose flanges?

If you are unsure which loose flange or material grade is right for your project — whether it’s a small garage installation, building services, marine application or an offshore plant — contact our technical team with details: pipe size, pressure class, operating temperature and the medium being conveyed. We will recommend compatible loose flanges and stub ends that meet the appropriate standards and service conditions.