The difference between galvanized pipe fittings and threaded pipe fittings

by | Feb 15, 2022 | Industry Knowledge

Galvanized pipe fittings and threaded pipe fittings are generally aliases for malleable iron pipe fittings. But they are different. Below, Jianzhi will give you a brief introduction from various aspects.

Malleable iron pipe fittings, made of malleable iron, have certain toughness and high ductility, but they can not be used for forging. Malleable iron pipe fittings are named by the material of the fittings.

The galvanized pipe fittings are named according to the surface treatment method of the pipe fittings (it is used for the connection of galvanized pipes).

Jianzhi Galvanized Pipe Fittings

Due to its iron material, malleable iron pipe fittings are prone to rust when exposed to air. In particular, our malleable iron pipe fittings are mainly used in fire protection and water supply projects. The pipe fittings are more likely to corrode when exposed to a humid environment for a long time. Therefore, the malleable iron pipe fittings need anti-rust treatment on the surface.

The surface anti-rust treatment of malleable iron pipe fittings is generally divided into two types: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing refers to a galvanizing treatment method in which the pipe fittings are immersed in a molten zinc solution at a high temperature of 700-800 degrees. The surface of the pipe fittings is covered with a layer of zinc. The principle of electro galvanizing is to rely on electrophoresis to transfer the zinc hanging on the anode to the surface of the pipe hanging on the cathode. This will form a thin and uniform zinc layer.

It is more expensive to hot-dip galvanize than to cold-dip galvanize, but hot-dip galvanizing produces a thicker galvanized layer, and the zinc layer reacts with the iron matrix at high temperatures, resulting in mutual penetration. During the transition, the zinc layer is firmly bonded to the surface of the pipe fitting, so it does not readily come off. The cost of the cold galvanized layer is relatively low, the zinc layer is uniform and beautiful. However, because electroplating only covers a thin layer of zinc metal film on the surface of the pipe fittings, the galvanized layer is thin and easy to fall off. In addition, electro-galvanizing produces a large number of toxic waste liquids.

Taking safety and practicality into consideration, we suggest purchasers choose hot-dip galvanized pipe fittings.

Since the malleable iron pipe fittings are connected by a thread, it can also be called a thread pipe fitting (thread pipe fitting). Different countries have different thread standards, as shown in the table below. Therefore, purchasers must pay attention to confirming the production standard of the thread when purchasing.

CountryMalleable Iron Pipe Fittings StandardSealed Pipe Thread StandardUnsealed Pipe Thread StandardMaterial Standard
EnglandBS143&1256BS EN10226BS2779BS6681
GermanDIN2950DIN2999DIN ISO228DIN1692
France/NF E03-004NF E03-005NF A 32-701
JapanJIS B2301JIS B 0203JIS B0202JIS G5705
BrazilNBR 6943NBR NM-ISO7-1ISO228NBR6590
IndiaIS 1879IS 554IS 8999IS 14329
Malleable Iron Pipe Fittings Standard

Common pipe threads are the following: NPT, PT, G, etc.

1) NPT is the abbreviation of National (American) Pipe Thread, which refers to the American standard 60-degree tapered pipe thread, which is used in North America. For the national standard, please refer to GB/T12716-1991.

2) PT (BSPT) is the abbreviation of Pipe Thread. A pipe thread with a 55-degree sealing angle. It is a Wyeth thread. Mostly used in Europe and the Commonwealth of Nations. Usually used for water and gas pipes. Taper 1:16, For the national standard, please refer to GB/T7306-2000. Also known as ZG.

3) G is a 55 degree unsealed pipe thread, which belongs to the Whitworth thread family. “G” stands for the cylindrical thread. For the national standard, please refer to GB/T7307-2001.

Jianzhi Male and Female 90 Degree Threaded Elbow

Nevertheless, it needs to be noted that most galvanized pipe fittings refer to malleable iron pipe fittings. For example, some welded pipe fittings, grooved pipe fittings, or other iron pipe fittings may also have a galvanized coating. In a strict sense, galvanized pipe fittings are not equivalent to malleable iron pipe fittings.

The same applies to threaded pipe fittings. Some iron and plastic pipe fittings are also threaded, but the materials are not malleable iron. Likewise, threaded pipe fittings are not equivalent to malleable iron pipe fittings strictly.

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