What is a lap joint flange?

A lap joint flange isn’t welded to the pipe. Instead, a stub end, which is a short fitting with a flared edge, is welded to the pipe, and the flange slides over the pipe to sit loosely behind that edge. The stub end does the sealing, and the flange simply holds the joint together.

How does a lap joint work?

The stub end or collar is welded to the pipe, and it is the part that meets the gasket. The lap joint flange sits loose behind it, so when the bolts are tightened it pulls the stub end against the matching face.

Because the flange isn’t fixed, you can turn it to line up the bolt holes. That makes assembly easier, especially on long runs or awkward alignments.

What are the strengths and limits of lap joints?

Lap joints are a good choice for systems that are dismantled often for inspection or cleaning, because the flange rotates and the joint is easy to separate. Because the flange doesn’t touch the medium, it can also be a different material from the stub end.

The limit is pressure. Lap joints are generally suited to lower-pressure duties, so for demanding duties, an RFWN flange is the usual choice.

Why are our lap flanges BZP?

Our lap joint flanges are supplied BZP, which stands for bright zinc plated. This is a thin zinc coating that protects the flange from rust.

The flange can be plated rather than stainless because it sits behind the stub end and never touches the media in the pipe. The stub end or collar is the part that carries the media, so that is the part you specify in the grade your process needs. Each listing states the collar size the flange is made to suit, so match it to your collar.

What are EN1092-1 type 02 lap flanges?

In EN1092-1, type 02 is the loose plate flange, used with a weld-on plate collar or a lapped pipe end. In our names it appears as a code such as DN150 EN1092-1 PN16/02.

The wider EN1092-1 flange range includes other types, and our ANSI B16.5 flanges follow the American pattern.

Do we supply galvanised lap joint flanges?

We also supply ANSI B16.5 150LB lap joint flanges in a galvanised finish, made to suit NB stub ends. You’ll find them in our galvanised flanges range, which is aimed at outdoor and harsh environments.

If you work to American sizes, that range is the one to look at. If your system follows EN1092-1, the BZP lap flanges on this page are the match, so the choice comes down to which standard your pipework uses.

What are the common ordering mistakes?

The most common mistake is forgetting that the flange is only half of the joint. You also need the stub end or collar, and the flange has to be made to suit its size. The second is assuming the flange is stainless, when ours are BZP.

The third is mixing standards, so check whether your system follows EN1092-1 or ANSI B16.5.

What should you tell us when you enquire?

The detail that decides which lap joint flange fits is the size of the collar or stub end you’re using. Please tell us:

1. The DN size and the PN rating you need.

2. The standard, either EN1092-1 or ANSI B16.5.

3. The size of the collar or stub end.

4. How many you need.

5. Whether you need the BZP finish or the galvanised version.

If you haven’t chosen a collar or stub end yet, tell us the pipe size and the purpose and we can help you work out what the flange needs to suit.

Frequently asked questions

What is a lap joint flange?

A lap joint flange is a loose flange used with a stub end or collar that is welded to the pipe. The flange isn’t welded itself, so it can rotate around the pipe, which makes the bolt holes easy to align.

Why are lap joint flanges used where systems are dismantled often?

Because the flange rotates and the joint is easy to separate, lap joints suit systems that are taken apart for inspection or cleaning. The flange also doesn’t touch the medium in the pipe.

What does BZP mean on a lap joint flange?

BZP stands for bright zinc plated. It means the flange has a thin, shiny coating of zinc, which protects it from rust. The coating is only on the flange, which never touches the media in the pipe, while the stub end or collar is the part you choose in the grade your process needs.

What is an EN1092-1 type 02 flange?

EN1092-1 is the European standard for flanges, and it gives each flange type a number. Type 02 is the loose flange, which isn’t welded to the pipe. It is used with a collar or stub end that is welded on instead. Our lap joint flanges are all type 02, and each listing states the collar size the flange is made to suit.

Contact Anglo Stainless for more information

If you’re matching a lap joint flange to your stub end or collar, contact us and a member of our team will be happy to help. Lap joints sit alongside several other flange types and their uses, and the right one depends on how often the joint will be dismantled. You can also request our brochure using the form below.