Comparison of conventional pipe prover and small pipe prover

1. Description

Conventional pipe prover refers to one-way or two-way spherical pipe prover, domestic model LJG type.

Small pipe prover refers to the piston pipe prover. 

The small pipe prover of the United States is about in the end of the 20th century 80's introduced to our country, the manufacturer is Smith, Brooks, Waugh, Calibron, etc. Kaifeng Instrument factory in the early 1990s also produced small pipe prover.

Kaifeng Instrument factory as a flow verification device production plant, it is not convenient to comment on the performance of these two types of pipe prover, so as not to mislead users. BOPP company, a flow verification device manufacturer in Germany, compares the performance of the two pipe provers as follows.

2. Performance comparison between spherical pipe prover and small pipe prover

2. 1 Spherical pipe prover

A. advantages

· High reliability.

· Easy to operate.

· It can be used to verify flowmeters with low pulse resolution, requiring only 10000 pulses of flowmeters output between detection switches.

· Fewer checks at a flow point.

· Insensitive to the reaction of solid particles in the tested liquid.

· Low maintenance cost.

· Displacer -- elastic ball is easy to replace.

· Good repeatability, better than 0.02%.

· Use four detection switches to reduce the number of tests.

B. shortcomings

· Large floor area.

· Unidirectional type with hydraulic system.

2.2 Small pipe prover

A. advantages

· Small footprint.

· Short verification time, the shortest verification time in one operation is 0.5 seconds.

· The measuring cylinder adopts non-electroplated nickel, with strong corrosion resistance.

B. shortcomings

· The standard volume is small (the maximum standard volume of existing products is 300 l) and is not suitable for testing flowmeters with low pulse resolution.

· The advantages of short verification time are offset by the large number of verification runs. According to the introduction of American product samples, 15 verification times are usually required for a flow point.

· The relative speed of the seal at the sliding seal and the moving part is up to 1.5m/s, so the seal is vulnerable and difficult to replace.

· It is sensitive to solid particles in the tested liquid, which is easy to cause damage to piston seals in the metering cylinder.

· High maintenance costs. 

· The use of pulse insertion method will lead to reduced repeatability. 

· When using the pulse insertion method, it is necessary to know the б T standard deviation of the output pulse period of the flowmeters. According to the provisions of GB/T17286.3, the number of pulses collected in a verification is N=500(б T)2 according to the formula below 

According to N and flowmeters coefficient K, the standard volume is determined, б T should be produced by the flowmeters manufacturer. However, flowmeters manufacturers usually do not provide, which makes it difficult to determine the small volume specifications. 

Note: The UK IP standard regulates this as follows: 

If a flow point fails 15 times, it can be increased by 30 times, if 30 times still fails. Conclusion: the flowmeters is not suitable for verification with small volume pipe. (without saying that the flowmeters is unqualified)

2.3 The standard deviation of the pulse interval б T 

As for the piston-type small-pipe prover, first know the time interval standard deviation of pulse output of the flowmeters: б T, the original ISO7278/3(BS6886) provides as follows: 

Standard deviation of pulse intervals The minimum number of pulses collected in a single stroke 

N б t (%) 

0.5 -- -- -- -- -- -- -- -- -- -- -- -- -- - 100 

1.0 -- -- -- -- -- -- -- -- -- -- -- -- -- - 500 

2.5 -- -- -- -- -- -- -- -- -- -- -- -- -- - 2500 

5.0 -- -- -- -- -- -- -- -- -- -- -- -- -- - 10000 

10.0 -- -- -- -- -- -- -- -- -- -- -- -- -- 40000 

15.0 -- -- -- -- -- -- -- -- -- -- -- -- -- 90000 

Now ISO7278-3-1988, has been adopted in Our country 

N = 500 (б t) 2 

According to the British IP standard, the turbine б T with high quality is ±1%, while the gear transfer pulse generator б T is up to ±10%. 

In Appendix A, this is the test of the small-volume standard compilation group in the United States. The pulse irregularity in the figure is different from that in б T, with irregularity =(maximum period -- minimum period)/ 2 average period 

A1 -- Turbine flowmeters, transmitter without regulator 

A2, A3, A4 -- Transmitter with gear regulator

3. Comparison of calibration flowmeters with small pipe prover and conventional pipe prover 

It was about 1993 that Xie Jiji, the main drafter of pipe prover verification regulation JJG209, made a test in Beijing Yanshan Petrochemical Plant.

flowmeters tested: DN100 waist flowmeters, Japan East machine products 

Prover: 

A. SVP150, American Smith product, standard volume V=57L 

B. Spherical pipe prover DN150, domestic, standard volume V=728L 

C. Spherical pipe prover DN250, domestic, standard volume V=2750L 

Tested medium: diesel oil 

The measured medium viscosity: 2.5cp 

Verification flow: 46.4m3/h 

pipe prover SVP150 DN150 DN250 

Instrument constant 10.0155 9.98053 10.0063 

Pulse count 570.62 7280 27521 

Standard deviation Sk 0.0151 0.00234 0.000058 

Repeatability δ K 0.39% 0.051% 0.0013% 

Number of checks 30, 12, 12 

Thus, it can be seen that the verification of small pipe prover is not qualified, so the flowmeters is not necessarily unqualified, but it is not appropriate to indicate that the flowmeters uses a small pipe prover of only 57L. 

The test records are in Appendix B, which were lost due to improper data storage and verification with DN250 pipe prover.

4. Verification of corioli mass flowmeters 

In theory, the mass of a liquid is equal to the product of its density and volume. The new technology has facilitated the success of high-precision in-line densitometers because the volumetric accuracy of the volumetric tube can reach 0.05%. Therefore, it is theoretically feasible to verify mass flowmeters with pipe prover and on-line density. Therefore, this method is also given in the mass flow verification regulation JJG897-95 in China. 

M = rho tVt = rho 20 v20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- (1) 

Where: M -- liquid mass 

ρt -- density of liquid at temperature t 

Vt -- volume of liquid at temperature T 

ρ20 -- density of liquid under reference conditions, given by density 

V20 -- The volume of the liquid under reference conditions, given by the pipe prover 

Reference condition -- 20℃, 101.325Kpa 

If we think of the liquid as incompressible 

20 - a rho t = rho (t - 20) = 20 [1 - a rho/rho, twenty (20) t - = rho, 20 argument -- -- -- -- -- -- -- -- -- -- -- -- (2) 

Argument = 1 - a/rho, twenty (20) t -, -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- (3) 

Where: a-- temperature correction coefficient of density, according to the national professional standards 

ν - temperature compensation coefficient of density 

The current imported densitometer reference condition is temperature 60℉(15.55℃), density from ρ15. 5 into rho 20, the work can only be solved through test, the liquid can be compressed, it involves the pressure correction, these technologies JJG897-95 did not give details, it is impossible to give, so use pipe prover and on-line densimeter on-line verification is not theoretical issues of mass flowmeters, but through practice, accumulated experience, Develop a good operational procedures. 

In the world, oil trade is settled by volume, the volume of oil calculation norms have been very mature. The flow verification system composed of volumetric flowmeters and pipe prover has been widely used in many countries. However, the use of mass flowmeters method is still in the research and development of foreign countries, there is no mature and recognized verification standards, in JJG-897 procedures, the verification method of Coriao mass flowmeters is only a general guiding principle, but lack of operability, there is no precedent for mass flowmeters as trade handover in China. Therefore, from the perspective of reliability and comparability, oil delivery, still use GB9109.1~5 standard, there will be no trade disputes. 

Weighing method is usually used in off-line verification of mass flowmeters, which is widely used in France. Domestic Qilu petrochemical has 380 coriolis flowmeters, in order to verify these flowmeterss, built a set of weighing verification device.