When engineers and procurement managers ask which loose flange dimensions best suit their application, the answer hinges on three variables: It is required that pipes have a certain minimum size (NPS or DN), pressure class, and length. Titanium-free flanges that meet ASME B16.5 or ASME B16.47 standards can work with pipes that are DN 15 to DN 600 and 12 to 40 psi. Before you buy, the most important thing is to figure out how to match the system's working area to the hole diameter, bolt circle, flange thickness, and outer diameter. The joint will stay sealed for decades if you do it right. Fixing it will cost a lot more than the price of the part itself if you do it wrong.
Understanding Loose Flange Dimensions – A Complete Overview
The bolt holes line up when you move loose flanges, which are also known as backing flanges or lapped joint flanges, around a stub end. The pipe does not move. The main technical benefit is that they can spin easily. However, this makes it even more important to get the ring size right than with fixed-bore types.
Every procurement specification should confirm these values before an order is released:
- Bore diameter (B): Must match the outside diameter of the stub end within the range shown in ASME B16.5 Table 1. This range is usually ±0.8 mm for sizes up to DN 300.
- Bolt-circle diameter (BCD) and bolt-hole count: The pressure class controls the bolt-circle diameter (BCD) and the number of bolt holes. There are 4 bolt holes on a 127 mm BCD Class 150 DN 100 flange, and 8 holes on a 149.2 mm BCD Class 300 DN 100 flange.
- Flange outer diameter (OD) and thickness: As the pressure class goes up, the thickness goes up as well. Class 150 flanges are about 24 mm thick at DN 200, while Class 300 flanges are 38 mm thick.
- Raised-face or flat-face height: Different heights for the raised face and the flat face: ASME B16.5 says that the raised face should be 1.6 mm for Class 150/300 and 6.4 mm for Class 600 and above.
LINHUI TITANIUM makes titanium loose flanges in all standard loose flange dimensions up to DN 600. The ends are machined to 45° welding tolerances according to ASME B16.5 and ASME B16.47 Series A/B. Two specialized plants with 30 titanium metal production lines can make up to 800 tons of titanium metal each year.
Comparing Loose Flanges with Other Flange Types for Your Application
Choosing between an open (lapped joint) flange and a weld-neck or slip-on flange is not just a matter of size. The choice also affects the cost of the materials, the freedom of the alignment, and the long-term maintenance plan.
Loose Flange vs. Weld Neck: Dimensional Trade-offs
A weld-neck flange is made as a single piece with a curved hub. This means that all of its dimensions—bore, hub length, and outside diameter (OD)—are set when it is made. The sealed surface (the stub end) is separated from the bolting ring by a loose flange. This lets engineers in chemical processing plants choose a high-alloy titanium stub end for fluid contact while using a cheaper carbon steel backing flange for the fastening structure. Industry data shows that this method can cut the cost of metal materials by up to 40% for corrosive-service lines with a large diameter.
ANSI vs. DIN Dimension Standards
The standard size on ANSI/ASME flanges is given in inches, and the bolt designs are based on the pressure class (Class 150 through Class 2500). The size of a DIN flange is given in DN millimeters, and the bolt designs are named by the pressure level (PN 6 through PN 40). LINHUI TITANIUM makes titanium loose flanges that work with both frames. This way, global EPC companies can get everything they need from a single source, no matter if the project specs are made in Hamburg or Houston.
It's also important that the gaskets work well together. Full-face gaskets fit flanges with a flat face, while ring gaskets fit flanges with a raised face. By double-checking the seal groove sizes before placing an order, you can avoid expensive interface mistakes during skid assembly.
How to Choose the Best Loose Flange Dimensions for Your Operating Conditions
The right loose flange dimensions series is chosen based on the temperature and pressure rating. In Class 150 service, ASME B16.5 says that titanium Grade 2 can handle about 19.6 bar of pressure at 38 °C. At 260 °C, the pressure drops to about 10.2 bar. It is not just an engineering problem to choose a flange that is one pressure class too low. It is also against the law.
The stub-end hole should match the inside diameter of the pipe, not its stated size. Even though both Schedule 40 and Schedule 80 pipes have the same NPS, their wall thicknesses and bores are not the same. It is about 154.1 mm wide for a DN 150 Schedule 40 pipe, and it is 146.3 mm wide for a Schedule 80 pipe. By ordering a short end that is bored for Schedule 40 and attaching it to Schedule 80 pipe, a step discontinuity is made that concentrates stress, which is a place where fatigue-loaded offshore pipelines can fail.
Customized flange measurements are the best choice when working conditions don't fit into standard tables, like when there is a high risk of crevice corrosion in desalination service or when weight limits are very strict in aircraft. The engineering team at LINHUI TITANIUM can help with unique bore, thickness, and bolt design issues. They can do this with CNC machining and full measurement inspection paperwork.
Procurement Considerations: Sourcing Loose Flanges with the Right Dimensions
If you want to find reliable sources, you should start by looking at approved measurement standard sheets instead of generic catalog pictures. On the specification sheets, it should say what standard applies, the tolerance class, how the heat number can be tracked, and whether the product has been inspected by a third party. Titanium loose flange suppliers with a good reputation, like LINHUI TITANIUM and well-known brands like Bonney Forge and Smith-Cooper, post measurement data that can be linked to mill certificates.
Here are the main supply-chain factors that always have an effect on how large industrial projects are bought:
- Lead time: Standard titanium loose flange sizes up to DN 300 are usually kept in stock. Sizes between DN 400 and DN 600 may have a 4–8-week production lead time, depending on how many are ordered.
- Certification compliance: Projects that need to follow the EU Pressure Equipment Directive need to be in line with PED 2014/68/EU. API-aligned projects need quality management that is certified by the API. LINHUI TITANIUM has certifications from TUV, ISO 9001, PED, DNV, ABS, CCS, and GL. This means that it can meet the needs of most global projects without having to go through extra qualification checks.
- Packaging and logistics: Titanium flanges are shipped in wooden cases or crates that are wrapped in plastic to keep them from rusting. People in North America, the Gulf region, Southeast Asia, and more than 60 other countries use LINHUI TITANIUM to send and receive DHL, FedEx, air freight, and sea freight.
Because of its strong supply chain, LINHUI TITANIUM is a qualified manufacturer of loose flange dimensions that can handle high-volume, time-sensitive project deliveries.
Practical Tips for Ensuring Dimensional Accuracy and Application Fit
The most common mistake in buying is to only order by standard size without mentioning the pressure class and facing type. Before sending out a purchase order, you should always compare the dimension drawing to your piping isometric, not just the part number.
A well-known example from a desalination development project in the Gulf shows this very clearly. As per ASME B16.47 Series A, the EPC contractor asked for titanium lapped-joint flanges to DN 400 Class 150. Before manufacturing, the team confirmed with the source the raised-face height and gasket contact surface finish (125–250 µin Ra). This saved about three weeks of schedule time and cut down on the need for two rounds of re-machining. The loose flange dimensions allowed for more movement, and they also fixed problems with misaligned bolt holes that were common in big prefabricated spool sections.
For custom sizes, you should always ask for a first-article inspection report, and you should keep source mill certificates with your own arriving inspection records. When DNV, BV, or SGS do third-party audits, these papers are very important proof.
Conclusion
Picking the right loose flange dimensions is a professional skill that directly protects the safety of the project, the life of the system, and the budget for purchases. When you match the bore, bolt circle, thickness, and pressure class to the exact operating envelope of your application (as tested against ASME B16.5 or ASME B16.47), there is no confusion and no need for expensive rework. Titanium loose flanges are a great choice for oil and gas, chemical processing, naval, and ocean uses because they don't rust and are strong for their weight. With the right supplier partnership, getting the right measurements and certifications stops being a project risk and starts being a reliable, repeatable outcome.
FAQ
How do I accurately measure a loose flange for replacement procurement?
Find the outside diameter, the diameter of the bolt circle, the number of bolt holes, the width of each hole, and the thickness of the plate as a whole. Write down whether the face is high, flat, or a ring-type joint. Check all of your measurements against the relevant ASME B16.5 or DIN EN 1092-1 dimension table to make sure you know the pressure class and nominal size before you place your order.
Which international standards govern titanium loose flange dimensions?
ASME B16.5 discusses NPS ½ to NPS 24 (up to about DN 600). The list of NPS 26 through NPS 60 is in ASME B16.47. In European projects, metric plates must follow DIN EN 1092-1. LINHUI TITANIUM products meet both ASME and metric standards, as well as PED 2014/68/EU for projects in Europe that use pressure equipment.
Can non-standard loose flange dimensions work in an existing piping system?
It is possible to have non-standard measures as long as the stub-end OD, bolt circle, and face type can all be switched out with the matching part. When you don't use standard bolt-circle or hole designs, you have to make your own fitting flanges for each joint pair. Before selecting non-standard loose flange dimensions on pressure-bearing systems, you should talk to a qualified engineering team.
Request a Quote from LINHUI TITANIUM – Your Trusted Loose Flange Dimensions Supplier
LINHUI TITANIUM has been making titanium products for 21 years, has two purpose-built factories, and can make 800 tons of titanium every year. Our titanium loose flanges come with certifications from TUV, ISO 9001, PED, DNV, ABS, and GL. They come in sizes ranging from DN 15 to DN 600 and can withstand pressures from PN 6 to PN 40. Our engineering team provides verified dimensional accuracy with full traceability, whether your project needs standard specifications or custom bore configurations. You can email us at linhui@lhtitanium.com or go to www.lhtitanium.com to get your next order's dimension charts, mill certificates, and competitive prices.
References
1. ASME B16.5 – Pipe Flanges and Flanged Fittings: NPS ½ Through NPS 24, American Society of Mechanical Engineers, 2017.
2. ASME B16.47 – Large Diameter Steel Flanges: NPS 26 Through NPS 60, American Society of Mechanical Engineers, 2017.
3. DIN EN 1092-1 – Flanges and Their Joints: Circular Flanges for Pipes, Valves, Fittings and Accessories, Deutsches Institut für Normung, 2013.
4. Becht, C., Process Piping: The Complete Guide to ASME B31.3, ASME Press, 2009.
5. Donachie, M. J., Titanium: A Technical Guide, 2nd ed., ASM International, 2000.
6. Nayyar, M. L., Piping Handbook, 7th ed., McGraw-Hill, 2000.
