Galvanized Flange
Galvanised flanges, also spelt galvanized, have a zinc coating that keeps moisture and other corrosive elements away from the steel underneath. We supply galvanised and BZP backing flanges, including ANSI B16.5 150LB galvanised lap joint flanges made to suit NB stub ends.
What is a galvanised flange?
A galvanised flange is a steel flange coated in zinc, which protects it from rust and corrosion. BZP stands for bright zinc plated.
Our galvanised and BZP backing flanges are best used outdoors or in harsh environments where they’ll be exposed to the elements. The coating gives a durable, long-lasting layer of protection.
How does a zinc coating protect a flange?
Steel rusts when it meets moisture and oxygen. A zinc coating sits between the steel and its surroundings, which stops moisture reaching the steel underneath.
An uncoated steel flange left outdoors or in a harsh environment would be exposed, so the coating matters. The protection depends on the coating staying intact, so it’s worth handling the flanges with care.
Why do lap joints use backing flanges?
A backing flange is the loose flange used in a lap joint. It sits behind a stub end that is welded to the pipe, so it doesn’t touch the medium in the pipe.
Because the stub end carries the media, it can be specified in the grade your process needs, and a coated steel flange simply holds the joint together. If you work to EN1092-1 instead, you’ll find that version in our lap joint flanges range.
Which ANSI B16.5 150LB galvanised flanges do we supply?
Our galvanised range includes ANSI B16.5 150LB lap joint flanges, each made to suit an NB stub end and available from 1 inch upwards. Check the size against your stub end before you order.
The wider ANSI B16.5 flanges range includes slip-on, blind, threaded and weld neck forms.
Should you choose galvanised or stainless?
It depends on what the flange will touch and where it will sit. Choose galvanised when the flange works as a backing flange behind a stub end, because it never touches what is in the pipe and the zinc coating protects it from the weather. That makes it a sensible choice outdoors and in harsh surroundings, and it is usually the more economical option.
Choose stainless when the flange will be in contact with the process fluid, or when you need full stainless corrosion resistance. Pick 304 stainless steel flanges for general use and 316 stainless steel flanges where chlorides or harsh chemicals are present. If you’re unsure which, it helps to know the difference between 304 and 316 steel.
What are the common ordering mistakes?
The most common mistake is treating a galvanised flange as a stainless one. It’s a coated steel flange, so it suits backing duty and outdoor protection, not contact with aggressive liquids or gases.
The second is ordering without the stub end size, and the third is forgetting that the flange is only one part of a lap joint.
What should you tell us when you enquire?
The galvanised lap joint flanges are made to suit NB (nominal bore) stub ends, so the stub end comes first. Please tell us:
1. The nominal bore of the stub end the flange will sit behind.
2. The standard you want, which for our galvanised flanges is ANSI B16.5 150LB.
3. How many you need.
4. Where the flange will be used, especially if it’s outdoors or in a harsh environment, because that’s what the coating is for.
If you’re not sure whether a galvanised flange is right, describe the application and we’ll say whether stainless would suit it better.
Frequently asked questions
What is the difference between galvanised and BZP finishes?
Both are zinc coatings that protect steel from rust. Galvanising is a thicker coating, so it lasts longer outdoors or in harsh conditions. BZP, which stands for bright zinc plated, is a thinner, shinier coating that suits milder conditions.
Can I weld a galvanised flange?
Welding burns off the zinc coating and gives off fumes, so you need good ventilation and protective equipment, and the weld area should be treated afterwards to restore protection. Our lap joint flanges aren’t welded to the pipe themselves, because it’s the stub end that is welded.
Can I paint a galvanised flange?
Yes, but the surface needs preparing first, because paint doesn’t stick well to bare zinc. Clean it and use a primer made for galvanised steel, and check the paint suits the conditions it will face.
What does NB mean on a stub end?
NB stands for nominal bore, the size name for pipe and stub ends. In our ANSI range it’s given in inches, such as 2 inch NB, while EN1092-1 flanges use metric DN sizes.
Contact Anglo Stainless for more information
Our galvanised lap joint flanges are made to suit NB stub ends. If you’re not sure which size you need, contact us on 01924 430044 or email sales@anglostainless.co.uk and our team will be happy to help. You can also request our brochure using the form below.
