WO1998054549A1

WO1998054549A1 - Midloop ultrasonic instrument

Info

Publication number: WO1998054549A1
Application number: PCT/US1997/022597
Authority: WO
Inventors: Donn M. Matteson
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1997-05-29
Filing date: 1997-12-11
Publication date: 1998-12-03
Anticipated expiration: 1999-11-29
Also published as: AU5897298A

Abstract

An ultrasonic instrument system (10) for measurement of fluid level in a horizontal run of pipe, comprising a horizontal run of pipe (12) having inner (42) and outer (36) surfaces defining a wall thickness therebetween, the pipe being constituted by a first material (32) which is internally clad with a second material (38); an inspection plug (46) of substantially uniform material composition imbedded in the pipe wall and having an inner end (48) at the inner surface of the pipe and extending outwardly to at least the outer surface of the pipe; an ultrasonic transducer (52) mounted on the outer end (50) of the inspection plug, for launching an ultrasonic beam (54) through the plug and onto fluid in the pipe, and for detecting a reflected ultrasonic beam (56) from the fluid in the pipe; and a processor (58) connected to the ultrasonic transducer and responsive to characteristics of the launched beam and reflected beam, for generating a signal (18) commensurate with the fluid level (44) in the pipe.

Description

MIDLOOP ULTRASONIC INSTRUMENT

Background of the invention

The present invention relates to a system for measuring water level or flow rate, especially in the horizontal run of pipe in a process plant, particularly a nuclear power plant.

U.S. Patent No. 5,541 ,969, issued July 30, 1 996 for "Midloop Water Level Monitor", describes a water level monitor responsive to the water level in a nuclear reactor vessel that is fluidly connected to a steam generator in a pressurized water nuclear steam supply system (NSSS). The measurement is made at a location in the horizontal run of pipe serving as a portion of the hot leg between the reactor vessel and the steam generator. A specially adapted measurement tank is supported laterally on the horizontal pipe, and fluidly connected thereto, such that the water level in a chamber of the tank is hydraulically balanced with the water level in the pipe. An array of heated junction thermocouples in the chamber, generate a signal indicative of water level in the pipe.

The ability to measure this water level accurately is particularly important during maintenance outages in a NSSS. During maintenance periods, water is drained from the steam generators to facilitate examination of the internals, i.e., heat transfer tubes. While the steam generator does not serve its heat exchanging function during these maintenance periods, the water in the reactor vessel is cooled by another heat exchanger as the water continues to function as a coolant for the reactor core. Since the hot leg pipe lies in essentially a horizontal plane, the precise level of water in the pipe is important. If the water in the pipe is permitted to be too high, the inside of the generator, where work crews are performing examinations, could be flooded. If the water level in the hot leg pipe is permitted to be too low, this could jeopardize proper cooling of the nuclear core. Because the hot leg has a direct fluid connection to the reactor vessel, the hot leg is in a convenient position for measuring the water level to ensure proper water level in the core. Therefore, accurate measurement of the precise water level in the hot leg pipe is of crucial importance for safety. Preferably, that the level may be measured from the NSSS control room where other safety equipment is monitored.

Ultrasonic sensors have also been used for this purpose, as described, for example, in U.S. Patent 5,31 9,972, issued June 14, 1 994 for "Ultrasonic Liquid Level Measurement System". According to a known technique an ultrasonic level measuring system includes a transducer mounted on the bottom of the pipe, whereby acoustic pulses are launched through the pipe wall into the liquid. The pulses are reflected from the water surface and received by the transducer along with pulses reflected by the pipe wall and reverberations within the pipe wail.

Ultrasonic techniques used in nuclear and other process plants where internal pipe corrosion can be a problem, must contend with the effect of cladding or other discontinuities in the pipe wall on the launched and reflected pulses. Typically, the pipe is low alloy steel with a corrosion resistant clad material applied to the inside surface of the pipe. The boundary between these two dissimilar materials increases the difficulty of using the ultrasonic instrument signal to accurately determine the water level, due to signal scatter at the boundary. Furthermore, the method of applying the clad material to the pipe, results in an irregular surface which also affects the operation of the ultrasonic equipment.

Summary of the Invention

It is an object of the present invention to improve ultrasonic measurement of fluid properties within a pipe composed of dissimilar materials.

It is a more particular object of the present to provide an ultrasonic water level measurement system for a horizontal run of pipe, which will not be degraded by the presence of dissimilar materials constituting the pipe wall.

The objects are achieved by providing a plug of material of uniform composition from the outside surface of the pipe to the inside surface of the pipe, and transmitting the launched and reflected ultrasonic signals through this material for use in the signal processing by which the liquid property, particularly liquid level, is inferred.

A system configured in accordance with the present invention includes at least one inspection plug of substantially uniform material composition embedded in the pipe wall and having an inner end at the inner surface of the pipe, and extending outwardly to at least the outer surface of the pipe. An ultrasonic transducer is mounted on the outer end of the inspection plug, for launching an ultrasonic beam through the plug and onto fluid in the pipe, and for detecting a reflected ultrasonic beam from the fluid in the pipe. The processor means connected to the ultrasonic transducer is responsive to characteristics of the launched beam and reflective beam, for generating a signai commensurate with the fluid property, e.g., level, in the pipe.

Preferably, in those plants where the pipe is covered with insulation, the inspection plug extends outwardly through the insulation, preferably so that the outer surface of the plug is outside the insulation. This permits permanent mounting of the transducer and associated processor onto the plug, and furthermore, reduces any heat or radiation effect on the transducer processor, due to the distance thereof from the heat and fluid in the pipe.

As a further preference, the inspection plug is generally frustoconicai with the larger end of the cone defining the inner end of the plug and the smaller end of the cone defining the outer end of the plug.

Those familiar with this field of technology, will appreciate the advantage that even when the pipe is constituted by dissimilar materials, the plug does not have dissimilar material, and therefore no dissimilar material boundary affects the ultrasonic beams.

Brief Description of the Drawings

These and other objects and advantages of the invention will be described with greater particularity with reference to the accompanying drawings, wherein:

FIG.1 is an illustrative view of the midloop water ievei monitor of the invention in operation between the reactor vessel and steam generator of a nuclear power plant;

FIG.2 is a cross-section view through the pipe and measurement device, which shows the configuration of the measurement system in accordance with the preferred embodiment; and

FIG.3 is a schematic of a plug array as utilized in an ultrasonic system for measuring flow rate.

Description of the Preferred Embodiment Figure 1 is an illustrative, schematic rendition of a portion of a pressurized water NSSS, showing the water level monitoring system 10 situated on a horizontal run of pipe 1 2 fluidly connecting the nuclear reactor vessel 14 to the nuclear steam generator 1 6. An electrical cable or the like 1 8 connects the monitoring system 10 to a console or other display device 20 in the control room 22 remote from the reactor and steam generator.

As is well known in the field of nuclear power plant design, relatively cool water enters the reactor vessel 14 through nozzle 28, is heated in the reactor core (not shown), and then delivered via hot leg 1 2 to the lower head 26 of the steam generator 1 6. The hot water passes through tubes (not shown) within the steam generator 1 6 and thereby heats the secondary side water, turning it into steam for use in the turbine/generator set, for generating electricity. After having given off much of its heat, water exits the lower head through cold line pipe 24, for delivery back into the reactor vessel through nozzle 28, to complete the so-called "primary loop" .

It is necessary during outages, to perform maintenance inside the steam generator 1 6, particularly in the lower head 26. Because of the orientation of the reactor vessel 1 and the steam generator 1 6, the hot water pipe 1 2 is in a substantially horizontal position at an elevation such that the upper region of the pipe 1 2 aligns with a portion of the steam generator head 26. As a result, even small changes in the level of water in the pipe 1 2 during an outage, can result in the flooding of the head 26. If the water level in the reactor 14 is not maintained high enough, however, the reactor core will not be sufficiently cooled, posing a different risk. Furthermore, if the level of water in the hot leg 1 2 falls to low, the shut-down cooling suction pipe (not shown) will form a vortex of cooling water while drawing the water from the hot leg pipe. This causes further problems during the maintenance activities.

Figure 2 shows the preferred implementation of applicant's water level monitoring system 10. The insulated pipe 1 2 as typically found in the nuclear plant, is shown in cross section. The insulated metal pipe 30 has a main portion 32 of low alloy steel, having an outer surface 34 and an inner surface 36. A corrosion resistant clad material 38, such as stainless steel, has been bonded to material 32, such that clad outer surface 40 is coextensive with inner surface 36. Clad inner surface 42 defines the innermost surface of the pipe. The radial distance between the innermost surface 42 and the outermost surface 34, establishes the pipe wail thickness.

An arbitrary water level 44 is shown within the pipe 30. An inspection plug 46 according to the invention, having substantially uniform material composition, is embedded in the pipe wall. The radially inner end 48 of the plug 46 is preferably contoured with the same radius of curvature as the inner surface 42. The plug preferably narrows in the radially outward direction, to a plug outer surface 50 which is at, or radially beyond, the outer surface 34. Preferably, both the inner surface 48 and the outer surface 50 of the plug 46, are machined to a smoother finish than present in the inner and outer surfaces 42,34. Although a variety of plug shapes can be utilized including cylindrical, it is preferred that the plug 46 be generally frustoconicai. In the preferred embodiment wherein the plug is permanently bonded to the pipe and exposed to a corrosive fluid within the pipe, the plug should be of a corrosion-resistant material such as stainless steel or Inconnel. Inconnel is particularly desirable because it can easily be welded to, and has a similar thermal expansion coefficient as, the low alloy steel.

At the outer surface 50 of plug 46, an ultrasonic transducer 52 is mounted in any well known manner. This mounting can be facilitated and performance enhanced if the outer surface 50 of the plug 46, is machined at least in one region 51 thereof, to be flat and normal to a pipe radius for receiving and achieving an intimate bond with a flat lower surface 53 on transducer 52. In a well known manner, various electronics and processing components, indicated at 58, are connected to the transducer 52. The transducer 52 and electronics 58 can be sealed within a housing 59, which in turn can also provide radiation shielding. Best results are typically obtained in operation of the inspection system, when the plug is located in the lower half, preferably at the bottom of the pipe, such that the launched beams 54 and reflected beams 56 pass through the relatively denser water 46 at plug surface 48, rather than through relatively less dense air (unless, of course, the pipe is empty).

The preferred shape of the plug 46, with the wider dimension on the inside of the pipe, reduces the potential for the plug to be forced out of the pipe due to the high pressure loadings during plant operation. Because the outer surface 50 of the plug protrudes well beyond the outside diameter of the pipe holes or other mounting recesses for the transducer and/or housing do not reduce the thickness of the plug available for resisting stresses imposed on the pipe during plant operation.

The plug 46 could be installed in the pipe during pipe fabrication. In the typical scenario wherein the invention would be installed as an after-market enhancement, a substantially cylindrical through bore is drilled through the pipe having a diameter larger than that of the inner, wide end 48 of the plug. The plug 46 is positioned in the bore, and a welding tool is inserted into the space between the bore wall and the plug. Weld beads are deposited progressively radially outward, until the plug is fully welded into place. In many plants where the present invention would find use, the pipe 30 is surrounded by insulating material 60. In this situation, it is desirable that the plug 46 extend outwardly through the insulation, with the outer surface 50 of the plug protruding several or more inches from the insulation, as shown in Figure 2. Ultrasonic instruments are adversely affected by high temperature. With the plug according to the invention extending through the insulation, the transducer and associated electronics are located in an area that is close to normal ambient temperature during normal plant operation. Ultrasonic instruments are also sensitive to radiation. Because, for regulatory purposes, it is desirable that the instrumentation remain permanently installed on the pipe, the feature of the invention whereby the plug extends outwardly beyond the pipe installation, has the beneficial advantage in that the components which are sensitive to temperature and radiation, are located at a distance which isolates them from these detrimental factors. Moreover, space can be provided for radiation shielding as desired or necessary for long-term operation of the instrument.

Relative to the lateral tank with hydraulic balancing as described in U.S. Patent No. 5,541 ,969, the present invention which is mounted directly on the hot leg pipe, offers other significant benefits. The amount and complexity of this system are considerably reduced, and there are no additional pipe connections to the pressure boundary of the hot leg loop. Furthermore, the potential for pipe breaks is also eliminated. Ultrasonic instruments provide a higher resolution that instruments with discrete measurement points, such as the heated junction thermocouple instruments. This provides additional information on the trend of the water level, to the operator.

It should be appreciated that the invention can also be utilized in a related end-use where ultrasonic techniques are utilized for measuring flow rate through a pipe having dissimilar materials. The physical configuration would be substantially the same as shown in Figure 3. Typically, four transducers 10a-d and associated plugs are located at four instrument locations. The details of the signal processing, differ from that associated with water level measurement, primarily in that the effects of turbulence during flow in a filled pipe are sensed ultrasonically. Importantly, one of the instruments 10a in a flow-rate measuring system 100 which is in use during plant operation, can easily be dedicated for level measurement purposes 200 during outages, by simply switching to a different mode of operation.

Claims

CLAIMS:

1 . An ultrasonic instrument system for measurement of fluid properties in a pipe, comprising: a run of pipe having inner and outer surfaces defining a wail thickness therebetween, the pipe being constituted by a first material which is internally bonded to a second material; at least one inspection plug of substantially uniform material composition imbedded in the pipe wall and having an inner end at said inner surface of the pipe and extending outwardly to at least the outer surface of the pipe; ultrasonic transducer means mounted on the outer end of each of at least one inspection plug, for launching an ultrasonic beam through the plug and onto fluid in the pipe, and for detecting a reflected ultrasonic beam from the fluid in the pipe; and processor means connected to the ultrasonic transducer means and responsive to characteristics of the launched beam and reflected beam, for generating a signai commensurate with the fluid property in the pipe.

2. The system of claim 1 , wherein the pipe is covered with insulation, and each inspection plug extends outwardly through the insulation.

3. The system of claim 2, wherein each inspection plug extends outwardly from the insulation.

4. The system of claim 1 , wherein the inspection plug inner and outer ends have surface finishes that are smoother than the pipe inner and outer surfaces, respectively.

5. The system of claim 1 , wherein the inspection plug generally resembles a truncated cone with the larger end of the cone defining the inner end of the plug and the smaller end of the cone defining the outer end of the plug.

6. The system of claim 5, wherein the inner end of the inspection plug is contoured to match the curvature of the inner surface of the pipe.

7. The system of claim 6, wherein the first material is a low alloy steel, the second material is a stainless steel, and the instrument plug material is selected from the group consisting of stainless steel and Inconnel.

8. The system of claim 7, wherein the plug is welded to the pipe wail.

9. An ultrasonic instrument system for measurement of fluid level in a horizontal run of pipe, comprising: a horizontal run of pipe having inner and outer surfaces defining a wall thickness therebetween, the pipe being constituted by a first material which is internally clad with a second material; an inspection plug of substantially uniform material composition imbedded in the pipe wall and having an inner end at said inner surface of the pipe and extending outwardly to at least the outer surface of the pipe; ultrasonic transducer means mounted on the outer end of the inspection plug, for launching an ultrasonic beam through the plug and onto fluid in the pipe, and for detecting a reflected ultrasonic beam from the fluid in the pipe; and processor means connected to the ultrasonic transducer means and responsive to characteristics of the launched beam and reflected beam, for generating a signal commensurate with the fluid level in the pipe.

10. The system of claim 9, wherein the pipe is covered with insulation, and the inspection plug extends outwardly through the insulation.

1 1 . The system of claim 1 0, wherein the inspection plug extends outwardly from the insulation.

1 2. The system of claim 9, wherein the inspection plug inner and outer ends have surface finishes that are smoother than the pipe inner and outer surfaces, respectively.

13. The system of claim 1 , wherein the inspection plug generally resembles a truncated cone with the larger end of the cone defining the inner end of the plug and the smaller end of the cone defining the outer end of the plug.

14. The system of claim 1 3, wherein the inner end of the inspection plug is contoured to match the curvature of the inner surface of the pipe.

1 5. The system of claim 9, wherein the first material is a low alloy steel, the second material is stainless steel, and the instrument plug material is selected from the group consisting of stainless steel and Inconnel.

16. The system of claim 9, wherein the plug is welded to the pipe wall.

17. The system of claim 9, wherein the inner end of the inspection plug is contoured to match the curvature of the inner surface of the pipe.