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Classification and introduction of pipe thread-(3)

December 7, 2020

Sealing pipe thread (R)

The basic dimensions and tolerances of inch sealing pipe threads

Cooperate way

There are two matching methods for inch seal pipe threads: cylindrical internal thread and conical external thread form a “column/cone” fit; conical internal thread and conical external threa

NPT thread picture

d form a “cone/cone” fit.

European countries mainly use “column/cone” matching threads; countries outside Europe mainly use “cone/cone” matching threads. The inspection gauges for the two types of threads are somewhat different; the current ISO inch seal pipe thread gauge standard (ISO 7- 2:2000) is designed according to the “column/cone” coordination system.

mark

The complete mark of inch seal pipe thread is composed of thread feature code, thread size code and rotation direction code.

The characteristic code of inch sealed cylindrical internal thread is: RP;

left &right hand thread

The characteristic code of the inch sealing cone internal thread is: RC;

The characteristic code of the inch sealing cone external thread is: R1 (used with the inch sealing cylindrical internal thread);

R2 (used in conjunction with inch sealing cone internal thread);

The rotation code of the left-hand thread is LH; the rotation code of the right-hand thread is omitted and not marked.

For sealing pipe threads, use RP/R1 and RC/R2 to indicate “column/cone” and “cone/cone” thread pairs respectively.

Unsealed pipe thread

The basic size and limit deviation of the imperial unsealed pipe

mark:

The complete mark of inch unsealed pipe thread is composed of thread feature code, thread size code, pitch diameter tolerance grade code and rotation direction code.

The characteristic code of inch unsealed cylindrical thread is: G

For inch non-sealed cylindrical internal threads, the codes for the tolerance grades of the median diameter are omitted and not marked; while the codes for the pitch diameter and metric grades of the inch non-sealed cylindrical external threads are A and B respectively.

When indicating the thread pair of the inch unsealed pipe thread, only the marking code of the external thread is marked.

Example:

Right-handed, non-sealed cylindrical female thread with size code 2: G2

Class A with size code 3, right-handed, unsealed cylindrical external thread: G3A

Grade B with size code 4, left-handed, unsealed cylindrical external thread: G4 B-LH

Thread pair consisting of a right-handed, non-sealed cylindrical internal thread and a grade A cylindrical external thread with a dimension code of 2: G2A

The inner thread is processed by pipe thread taps, and the outer thread has die.

Note: 2, 3, 4 above are code names, not inch sizes, don’t confuse

other

Conversion of 55° tapered pipe thread

55° tapered pipe thread means that the thread angle is 55° and the thread has a taper of 1:16. This series of thread is widely used in the world, and its code is different from country to country.

China UK France Japan iso

Code ZG R (outside) G PT R

R (external thread) Rc (internal) R R Rc

Conversion of 60° Conical Pipe Thread

The 60° tapered pipe thread refers to a pipe thread with a tooth profile angle of 60° and a thread taper of 1:16. This series of threads is used in the machine tool industry in my country, the United States and the former Soviet Union. Its code name was previously designated as K in our country, and later designated as Z, now it is changed to NPT.

Classification and introduction of pipe thread-(2)

December 7, 2020

“Cylinder/cone” and “cone/cone”. Two inch seal pipe threads use different thread ring gauges (cylindrical thread ring gauge and tapered thread ring gauge) and thread plug gauge (the position of the datum plane is different, the two datum planes are different Half-tooth apart). Pipe threads that pass the inspection in European countries may be unqualified if they are inspected by countries outside of Europe. In international trade, you must pay attention to this difference, otherwise there may be waste. Before 1994, the ISO standard for sealed pipe threads and their gauges The standard is designed according to the “cone/cone” coordination system. China’s imperial sealed pipe thread products can directly enter the international market. However, the pipe thread products of European countries are in a disadvantageous position. After 2000, ISO’s imperial seal The pipe thread standard and its gauge standard are designed according to the “column/cone” matching question system. Our country’s original inch seal pipe thread products will encounter difficulties when entering the international market. For this reason, China revised the inch seal pipe in 2000 Thread national standard. Change the original one thread standard into two thread standards to remind the designer to pay attention to the difference and correct selection of the two mating threads. Japan still insisted on adopting 1994 when it revised the inch seal pipe thread standard in 1999 The ISO standard a year ago. Therefore, the international inch seal pipe thread market after 2000 is more complicated, and domestic

NPT thread picture

manufacturers must be careful.

Inch sealing pipe thread is a general purpose sealing pipe thread. Sealing filler should be added to the thread pair during use. Its characteristics are economical and the processing accuracy requirements are moderate. Without sealing fillers, it can ensure that the sealed connection thread is dry sealed Pipe thread. There is no dry seal pipe thread in the inch pipe thread system.

Sealed pipe threads have two functions: mechanical connection and sealing; non-sealed pipe threads have only one function of mechanical connection. Therefore, the accuracy of sealed pipe threads is stricter than that of unsealed pipe threads. Some people see unsealed pipe threads The tolerance of the pitch diameter is half of the tolerance of the sealed pipe thread. It is considered that the accuracy of the unsealed pipe thread is higher than that of the sealed pipe thread. This view is incorrect. The sealed pipe thread has requirements for the accuracy of the tooth shape. Its large diameter, The tolerances of the pitch diameter and the minor diameter are the same; the flank angle and pitch error have a greater impact on the sealing performance. The non-sealed pipe thread basically has no requirements for the accuracy of the tooth form. The top diameter tolerance is greater than the pitch diameter tolerance; the bottom diameter There is no tolerance requirement. In addition, some people think that it is possible to use non-sealed cylindrical internal threads and sealed cylindrical external threads to form a fit. This view is also wrong. This is equivalent to relaxing the accuracy requirements of sealed internal threads, and the sealing of pipe threads There may be a problem.

Due to differences in the use of sealed pipe threads, processing accuracy, assembly and testing techniques, the pipe thread standard cannot guarantee that all threaded parts that meet the standard can be sealed. In the imperial sealed pipe thread standard, a unified thread item cannot be proposed. The accuracy requirements of the parameters. These individual thread parameters have a direct impact on the sealing performance. The fundamental way to solve the problem is to formulate their own internal control measures for their specific products. Each industry or company formulates its own internal control measures. The internal control indicators of these parameters are generally confidential. Companies in other industries are not universal, and manufacturers must have a clear understanding of this. Sealing pipe thread standards are not omnipotent, and sealing problems may require manufacturers to pay attention to them. Before 1987, China did not have American and British pipe thread standards. But In production, these two internationally commonly used pipe thread standards cannot be avoided. For this reason, the old mechanical drawing standards once stipulated the marking codes for American and British pipe threads. These thread codes are derived from the Chinese Pinyin alphabet, and have not considered the foreign Whether the standard codes of standard pipe threads are consistent. Since this standard only specifies the thread codes and not the thread parameters, the same thread code may have different thread parameters in different companies or industries. There is no basis for judging who is right and who is wrong when there is a scrap .From 1987 to 1991, China promulgated the British pipe thread standard. From then on, the pipe thread code and marking should comply with the pipe thread standard. The pipe thread code specified in the old mechanical drawing standard should be abolished immediately.

Classification and introduction of pipe thread-(1)

December 7, 2020

Pipe thread is a thread used for connection on the pipe wall to the valves. There are 55-degree unsealed pipe threads and 55-degree sealed pipe threads. Mainly used to connect pipes to make the internal and external threads fit tightly. There are two types which are straight pipes thread and tapered pipes thread.
Common pipe threads mainly include the following types: NPT, PT, G, etc.

NPT thread picture

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

2) PT (BSPT) is the abbreviation of Pipe Thread. It is a 55-degree sealed tapered pipe thread. It belongs to the Wyeth thread family. It is mostly used in Europe and the Commonwealth countries. It is often used in the water and gas pipe industry. The taper is 1:16. Refer to GB/ T7306-2000. The domestic name is ZG.

3) G is a 55-degree non-sealed pipe thread, which belongs to the Wyeth thread family. Marked as G stands for cylindrical thread. Refer to GB/T7307-2001 for the national standard.

Metric and inch threads

Metric threads are expressed by pitch, while American and British threads are expressed by the number of threads per inch;

Metric thread is 60-degree equilateral profile, inch thread is isosceles 55-degree profile, and American thread is isosceles 60-degree profile;

Use metric units (such as mm) for metric threads, and use imperial units (such as inches) for American and British threads;

“Insiders” usually use “minutes” to refer to the thread size, one inch equals 8 points, 1/4 inch equals 2 points, and so on.

In addition, there are: ISO—Metric Thread Standard 60°; UN—Unified Thread Standard 60°; API—American Petroleum Pipe Thread Standard 60°; W—British Wyeth Thread Standard 55°.

The difference between various threads

NPT, PT, G　 are all pipe threads.

NPT is the abbreviation of National (American) Pipe Thread, which belongs to the American standard 60-degree tapered pipe thread and is used in North America. National standards can be found in GB/T12716-1991

PT is the abbreviation of Pipe Thread. It is a 55-degree sealed tapered pipe thread. It belongs to the Wyeth thread family and is mostly used in Europe and Commonwealth countries. Commonly used in water and gas pipe industry, the taper is 1:16. National standards can be found in GB/T7306-2000

G is a 55-degree non-thread sealed pipe thread, which belongs to the Wyeth thread family. Marked as G stands for cylindrical thread. National standards can be found in GB/T7307-2001

In addition, the 1/4, 1/2, and 1/8 marks in the thread refer to the diameter of the thread size, and the unit is inch. Insiders usually use points to refer to the thread size, one inch equals 8 points, 1/4 inch equals 2 points, and so on. G is the general name of pipe thread (Guan). The division of 55 and 60 degrees is functional, commonly known as pipe circle. That is, the thread is processed by a cylindrical surface.

ZG is commonly known as pipe cone, that is, the thread is processed by a conical surface. The general water pipe joints are like this. The national standard is marked as Rc metric thread to indicate the pitch, and the American thread is 60 degrees. Metric units are used for metric threads, and imperial units are used for American and British threads. Pipe thread is mainly used to connect pipelines. The internal and external threads are closely matched. There are two types of straight pipes and tapered pipes. The nominal diameter refers to the diameter of the connected pipe, obviously the thread diameter is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameters of inch threads, and the unit is inches.

Inch pipe threads are derived from British Wyeth threads. The combination of Wyeth threaded pipe series and Wyeth thread profiles establishes the basic dimensions of British pipe threads. According to the 1/16 taper relationship, the radial diameter tolerance of Wyeth threads is converted into British sealed tubes. Tolerance of the axial number of threads (there is a certain amount of rounding and adjustment). Then refer to the tolerance value of the inch seal pipe thread to propose the tolerance of the inch unsealed pipe thread (the tolerance changes from one-way distribution to one-way distribution, relax the top Diameter tolerance, let go of the bottom diameter tolerance). The time for the three types of threads is:

In 1841, the British Wyeth thread was proposed, and in 1905, the new Wyeth thread standard (BS 84) was promulgated.

In 1905, the British Sealed Pipe Thread Standard (BS 21) was promulgated.

From 1905 to 1940, Wyeth Thread performed the responsibility of the imperial unsealed pipe. In 1940, the unsealed pipe thread series (BSP series) of Wyeth Thread was proposed; in 1956, the British unsealed pipe thread standard (BS 2779) was issued separately.

European countries and Commonwealth countries first accepted the imperial pipe thread standard. The ISO/TC5/SC5 Pipe Thread Standardization Technical Committee and its secretariat are controlled by European countries, and the imperial pipe thread standard was adopted by the ISO standard. In 1955, the ISO proposed the imperial sealed pipe thread Standard (ISO R 7); In 1961, ISO proposed the standard for imperial unsealed pipe threads (ISO R 228). In 1978, ISO promulgated two official standards for imperial pipe threads (ISO7-1 and ISO228-1). Threads have been generally accepted by countries outside North America and are widely used in international trade.

The inch pipe thread in the ISO standard has been converted to the metric system. The metric method of the inch pipe thread is very simple. Multiply the inch size of the original pipe thread by 25.4 to convert it to the millimeter size. The inch pipe thread size is being eliminated. The so-called use of real pipe thread standards is unrealistic. There is no distinction between real metric pipe threads and fake metric pipe threads.

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Classification and introduction of pipe thread-(3)

Classification and introduction of pipe thread-(2)

Classification and introduction of pipe thread-(1)

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