BS4504 STEEL FLANGES | PN10, PN16, PN20, PN25, PN30, PN40

The BS4504 steel flange is a round flange made of steel, with connection dimensions conforming to the British standard BS4504. The product is commonly used to join valves, pumps, equipment, and pipe sections by bolting in industrial piping systems. Each flange is designated by a pair of parameters, DN (nominal diameter) and PN (nominal pressure in bar), for example BS4504 PN16 DN100.

At the common PN ratings, the connection dimensions of the BS 4504 and BS EN 1092-1 standards are almost equivalent. BS4504 flanges can therefore be fitted to valves and fittings made to EN 1092-1, DIN 2501, or ISO 7005 at the same PN rating. However, for project orders, customers should still check against the technical drawings before ordering.

Overview of the BS4504 steel flange

The BS4504 steel flange is a disc-shaped pipe connection fitting. In the center is a bore for the fluid to pass through, and around it is a ring of bolt holes used to bolt two opposing flanges together with a gasket in between. This type of joint keeps the pipeline sealed and allows it to be taken apart when maintenance, valve replacement, or pipe section replacement is needed, something a continuous welded joint cannot do.

Advantages of the BS4504 steel flange

• Standardized connection dimensions, so BS4504 flanges of the same DN and PN fit valves, pumps, flexible joints, and strainers of the same standard without additional machining.
• A solid steel body withstands bolt tightening force, vibration, and pipeline loads better than cast iron or plastic flanges of the same size.
• A wide size range from DN15 to DN1000.
• A detachable joint shortens system downtime during maintenance, and the surface can be treated with a variety of coatings.

However, a flanged joint requires the correct grade of gasket and bolt set, tightened in a cross pattern so that the clamping force is even; otherwise it is very easy to get leaks at the edge of the gasket. For strongly corrosive media, carbon steel flanges should not be used, and switching to stainless steel flanges should be considered.

Practical applications of the BS4504 steel flange

The BS4504 steel flange appears in most large-scale industrial and civil piping systems, such as:

• Urban, industrial park, building, and apartment water supply and drainage
• Fire protection systems and sprinkler systems
• Pump stations, and the suction and discharge ends of pumps
• HVAC systems, chilled water lines, and chiller cooling water lines
• Wastewater treatment and industrial process water
• Hydropower plants, thermal power plants, and shipbuilding
• Auxiliary water and air lines in food and beverage plants
• Chemicals and oil refining, on pipelines whose materials and pressures are suitable according to the design

Classification of BS4504 flanges by pressure

The commonly used pressure ratings of BS4504 flanges are PN6, PN10, PN16, PN25, and PN40. PN (Pressure Nominal) is the nominal pressure in bar at a reference temperature of about 20°C.

Classification of BS4504 steel flanges by anti-rust surface coating

Quick comparison table of the 3 types of BS4504 steel flange

Plain steel flanges

This is a steel flange that has been machined and shipped from the factory, with only a layer of oil or a temporary anti-rust primer on the surface for transport and storage. This type suits pipelines installed in dry indoor locations, or lines that will be painted after installation, such as red-painted fire protection pipes or insulated pipelines. Compared with the other 2 types, this product line has the lowest cost, but it must be stored carefully and surface-treated as soon as installation is complete.

Hot-dip galvanized flanges

The BS4504 steel flange is dipped in molten zinc so that a zinc coating forms and bonds to the steel body. According to ISO 1461, the zinc coating must have a minimum average thickness of about 85 µm for steel flanges thicker than 6 mm. The thick coating lets the flange withstand outdoor environments, damp valve pits, and pump station areas far better than electro-galvanizing.

There are a few points to note when using them. Bolts, nuts, and washers should have the same protection so that the joint does not rust from the fasteners. The sealing face and bolt holes should be checked, because the thick zinc layer can make the holes tighter. If the flange is welded to a pipe on site, the weld zone will lose its coating and must be touched up with zinc-rich paint.

Electro-galvanized flanges

The zinc layer formed by electrolysis is much thinner and more uniform, typically about 5 to 25 µm, changing the part’s dimensions very little and giving a bright, attractive finish. This type suits indoor, dry pipelines, where appearance matters or tight tolerances must be kept. Because the zinc layer is thin, its rust resistance is poorer than hot-dip flanges under the same conditions, so avoid using it outdoors or in high-humidity locations.

A reputable flange supplier in Vietnam

The flange is the item most prone to being bought wrongly, because from the outside the different PN ratings look almost identical. When choosing a supplier, check four points: the CO and CQ documentation; the markings stamped on the flange (standard, PN, DN, material or brand); the actual measured dimensions against the standard table (outside diameter, bolt circle, number of holes); and the ability to supply matching gaskets and bolts together.

An Phu Thanh DV TM Co., Ltd. is headquartered in Hoc Mon, Ho Chi Minh City, and has operated for more than 17 years in industrial valves and pipe fittings. BS4504 steel flanges at An Phu Thanh are available in sizes from DN15 to DN1000, from reputable import sources in Korea, China, Taiwan, Malaysia, and Vietnam. Every shipment comes with full documentation, a certificate of origin, and a clear warranty policy. In addition, we support delivery nationwide.

See more real photos of An Phu Thanh’s BS4504 steel flanges below

If you need a quotation for BS4504 flanges by specific DN, PN, and coating, or need to choose a flange that matches the valves and pumps you are using, please contact Hotline 0946 729 913 or message An Phu Thanh’s Zalo OA. The experienced team at An Phu Thanh is always pleased to serve you.