Wear monitoring construction for erosive/corrosive flow conducting devices

A wear monitoring device for use in a choke valve. The device includes a wear liner which fits in the flow annulus of the valve. The liner is sealed at either end from the fluid inlet valve and defines an annular void space in fluid communication with a port to the exterior of the valve. Leakage caused by flow cutting through the liner can be observed as fluid discharge from the port.

BACKGROUND OF THE INVENTION 
The present invention relates to flow conducting and controlling devices 
and more particularly to an improved internal erosion and corrosion liner 
construction for such devices, and even more particularly to an improved 
wear monitoring liner construction for such devices wherein an 
intermediate longitudinally extended annular element is positioned in the 
bore to be monitored between the body and a wear liner so constructed that 
the liner can be extended even beyond an end connection and wherein the 
wear monitoring device rather than the body wears, erodes or corrodes 
away. 
To simplify and yet clearly specify the function of the present invention, 
the discussion which follows is directed to an apparatus known as a choke 
valve. Choke valves are commonly used with oil and gas wells usually as 
part of an arrangement of valves and fittings that extend above the well 
head, commonly known in the industry as a "Christmas tree." While the 
discussion which follows is directed to an embodiment of the invention in 
a choke valve, it should be understood that the present invention in its 
broadest sense has applications to other types of valves and similar 
flowline devices. A Christmas tree normally includes an assembly of 
valves, tees, crosses, and other fittings including the choke valves at 
the well head. The assembly is used to control oil or gas well production 
and to give access to the well tubing. The choke valve is used to reduce 
the pressure of the fluid flowing from the well from a normally high 
pressure value to a lower pressure value. The pressure drop is 
accomplished in the choke valve by varying the cross-sectional area of the 
fluid flow stream to form a restriction for those fluids flowing from the 
well head. 
The fluid stream flowing from an oil or gas well typically contains 
material which can be chemically corrosion and/or mechanically erosive to 
the choke valve. Thus, for example, the fluid stream can contain sand, 
and/or particulate material as well as acids and corrosive harmful 
chemicals. Chemical corrosion and mechanical erosion are problems which 
have long plagued choke valve constructions. To complicate the matters, 
many applications, such as oil and gas well installations are in remote 
locations wherein a daily inspection of the choke valve is difficult or 
impossible. In these situations undetected wear can create a valve failure 
situation which can be not only damaging to the choke valve but dangerous 
and possibly catastrophic. If the choke valve becomes eaten away because 
of corrosion or erosion, leakage of gas and/or oil could create a fire or 
explosion with damage to property and the environment as well as possible 
loss of life or personal injury. 
In the past, various types of liners were used to protect choke valves from 
erosion and corrosion. The prior attempts, which did not provide 
satisfactory results, included such things as pistons, sleeves, cages, 
plating or linings of tungsten carbide, chrome stainless, Stellite and 
ceramics. In the past, the liner was placed directly upon the housing or 
body of the choke. In these prior configurations, when the wear sleeve or 
liner was fully eroded or corroded by the flowing media, damage to the 
choke valve body was immediate. This type of damage to the choke valve 
body required extensive repair which necessitated removal of the choke 
valve from the installation for repair at a machine shop or the like. 
Another problem with erosion and corrosion of choke valves was that 
associated with providing a valve liner which provided wear monitored 
length extending through the portion of the bore which is subject to wear 
and even beyond the connecting end portion of the choke valve body so as 
to minimize the chance that mechanical erosion or chemical corrosion could 
cause extensive damages to the choke valve body itself. Another problem 
with prior attempts to provide wear monitoring for choke valves was the 
alignment problem associated with the attachment of the liner to the bore 
of the flange or connecting portion. In the past, liners required a close 
tolerance fit so that if the parts were not machined within very tight 
tolerances, misalignment occurred. 
Several choke valve constructions have been patented wherein a protection 
of the downstream portion of the valve body was of concern. For example, 
the Wolcott U.S. Pat. No. 4,638,833 entitled "Choke Valve" disclosed a 
flanged choke valve body having an exterior surface with a choke valve 
body interior defining a flow annulus that included upstream and 
downstream sections. The valve body was provided with internal erosion and 
corrosion trim liners and means for detecting for leaks in the liners. 
Seals were provided for isolating a port through which leakage can be 
observed exteriorly of the valve body. The Wolcott device used a 
cylindrical seal which was carried by the valve body itself so that if 
flow cut through the liner, immediate damage resulted to the valve body 
itself. 
Various other patents illustrated the use of monitoring ports to detect 
leakage between seals in choke-type valves. The Renfrow U.S. Pat. No. 
4,518,148 disclosed a port between a seal and a packing element wherein 
the port allowed liquids and gases to escape. The Renfrow U.S. Pat. No. 
4,493,336 disclosed a leak-off port between seals for a hydraulic choking 
device used in controlling fluid flow from an oil or gas well. The Meek 
U.S. Pat. No. 4,469,122 disclosed a modular check valve having monitoring 
ports for minimizing the chance of fluid being forced into threaded areas 
of the valve and also for reducing the change of fluid pressure building 
up in the threaded region if the seals on the valve allow some leakage. 
U.S. Pat. No. 4,136,709 disclosed a ball valve using liners disposed on 
either side of a ball valving member. Wear indicators were provided 
between the liners and the valve body to detect erosion in the liners and 
spacers. Leakage was monitored along the length of the liners which 
extended to the flanged face portions of the ball valve on one end and to 
a seal on the other end. 
U.S. Pat. No. 4,413,646 disclosed a streamline coal slurry letdown valve. 
This patent disclosed liners extending beyond the flange face on the 
downstream portion of the valve wherein the valve seat and valve seat 
retainer were lined with erosion resistant material such as tungsten 
carbide. U.S. Pat. No. 4,503,878 disclosed a valve seat insert that 
included a sleeve with a blast tube secured within the sleeve. The blast 
tube was preferably made of a material such as tungsten carbide or silicon 
carbide which was resistant to the erosive action of high velocity fluid 
stream. A bore of the valve outlet was a continuation of the bore of the 
blast tube. 
GENERAL DISCUSSION OF THE PRESENT INVENTION 
The present invention solves the prior art problems and shortcomings in a 
simple, straightforward manner by providing an improved wear monitoring 
apparatus that includes a body having an an interior flow annulus that 
includes upstream and downstream bore sections. A flow restricting element 
such as an orifice, needle, cage or the like is positioned generally 
between the upstream and downstream flow bore sections for controlling 
flow within the annulus. An annular flow restricting element is removably 
mounted within the annulus and has a central longitudinal bore that 
coincides generally with the downstream bore section of the annulus. For 
ease of reference this flow restricting element will be referred to as a 
seat, although it should be understood that the present invention has 
applications to flow control devices in general. 
A first port extends laterally through the valve body for communicating 
fluid flow between the annulus and the exterior surface of the body. First 
and second exterior seat seals positioned on opposite upstream and 
downstream sides of the port isolate a section of the annulus between the 
choke body and the seat, which isolated section communicates with the port 
to define a monitoring window. A longitudinally extending wear liner is 
removably mounted within the seat bore for monitoring erosion or corrosion 
within the seat bore. First and second liner seals are positioned at 
opposite end portions of the liner for providing a sealed annular void 
space of monitored length between the first and second liner seals that 
can collect and isolate fluid leakage caused by flow cutting through the 
liner. A second port extends laterally through the seat and in 
communication with the first port for transmitting flow between the first 
port and the sealed void space of monitored length so that leakage caused 
by flow cutting through the liner can be indicated at the valve exterior 
by observing the first port. 
In one embodiment, the interior surface of the valve body and the seat 
include corresponding beveled surfaces which abut upon assembly. The first 
seat seal is preferably positioned at the corresponding beveled surfaces 
so that when the seat and body are assembled, a registration of the seat 
within the valve body perfects a seal when the beveled surfaces come 
together. The seat and body are arranged such that upon assembly positive 
axial alignment occurs. In this embodiment the positive axial alignment is 
provided by the interaction of the beveled faying surfaces but other 
constructions which provide such alignment might be used. 
In the preferred embodiment, the seat bore is stepped, having first and 
second sections of differing internal diameter with the larger seat bore 
section defining an annular space adapted to receive the liner so that 
upon assembly the liner and the seat have a common cylindrical bore of 
uniform diameter. Because the seat carries the liner, the seat can extend 
the full length of the downstream bore section of the valve body to give 
wear monitoring protection to the valve body even beyond the flanged end 
of the body. Thus, the liner is spaced radially inwardly of the annulus 
and carried by the seat so that the liner can be increased in length 
without any modification to the valve body.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
FIGS. 1-3 show generally the preferred embodiment of the apparatus of the 
present invention designated generally by the numeral 10. 
Choke valve 10 comprises a body 12 having an upstream flange 13 and a 
downstream flange 14. Each flange 13, 14 provides a flange face 15, 16 
respectively which typically aligns with a similar flange of another 
valve, or of a spool piece, or other section of pipeline or such ancillary 
equipment as is commonly found at a well head or other valve assembly. The 
body 12 includes a flow annulus comprising an upstream bore 17 and a 
downstream bore 18 with flow arrows 19, 20 showing the direction of flow 
through valve body 12 beginning with the upstream flow arrow 19 and 
continuing to the downstream flow arrow 20. The downstream bore 18 
normally has high velocity flow and is an area subject to 
erosion/corrosion. 
The present invention provides an improved wear monitoring apparatus for 
use in flow conducting and controlling devices such as choke valves. A 
typical choke valve includes one or more restricting orifices formed 
generally between the upstream and downstream flow bore sections for 
throttling flow within the valve annulus. In FIG. 1 there can also be seen 
a bonnet flange 21, assembly bolts 22, a bonnet 23, stem 24, cage 25, and 
cap 26 all of which are conventional parts of a choke valve and form a 
means for restricting flow between the upstream and downstream bore 
sections 17, 18 of the apparatus 10. 
The present invention provides an improved wear monitoring apparatus as 
part of an overall choke valve 10 which includes an annular seat body 27 
having a seat exterior surface 28. Seat body 27 is generally tubular and 
is formed having a stepped central bore defined by interior annular 
surfaces 29 and 30. Annular surface 29 defines a first interior bore of 
smaller diameter than the second interior bore defined by annular surface 
30. The seat interior surfaces 29, 30 intersect at annular shoulder 31. A 
pair of spaced apart annular seals 32, 33 are formed on the outer surface 
28 of seat body 27. Upstream seat seal 32 and downstream seat seal 33 form 
a seal with body 12. 
A removable liner 34, generally cylindrical in shape, is positioned within 
and carried by seat 27 abutting seat inner surface 30 of larger internal 
diameter. Liner 34 carries an upstream liner seal 35 and a downstream 
liner seal 36 which are positioned at the liner end portions respectively. 
Seals 34, 35 can be formed of any suitable seal material such as for 
example plastic, metal-to-metal, or the like. Seat 27 containing liner 34 
is assembled to body 12 by any suitable means such as with a threaded 
connection 37. 
Seat 27 includes a lateral port 39 which extends through seat 27 from 
inner-surface 30 to provide a fluid communication path through seat 27 
from the annulus defined between the outer surface of liner 34 and inner 
surface 30 of seat 27. A laterally extending port 39 extends through seat 
27. Body 12 includes another port 40 which extends laterally through body 
12 and in alignment with port 39 as shown in FIG. 1. Port 40 can be 
equipped with a high pressure fitting 41 for opening or closing bore 40. 
Liner 34 includes a central longitudinal cylindrical bore 42 that 
preferably has an internal diameter which is uniform and which is of the 
same cross-sectional dimension as the cross-sectional dimension of the 
seat body bore at seat inner surface 29 as shown in FIG. 1. The liner 
seals 35, 36 are positioned at opposite end portions of the liner 34 and 
provide a sealed annular void space of monitored length 38 between the 
seals 35, 36 which space can collect and isolate fluid leakage caused by 
flow cutting through the liner 34 as can occur because of chemical 
corrosion or mechanical erosion. Because the ports 39, 40 are aligned, 
they are in communication with one another so that fluid entering the 
annular space between liner 34 and seat 27 and isolated by seals 35, 36 
the leakage proceeds through ports 39 and 40 to the exterior surface of 
the valve body 12 by opening fitting 41. 
Seat 27 may be formed having a bevelled annular surface 50 which 
corresponds to a bevelled annular surface 51 formed in body 12. The 
surfaces 50, 51 abut upon assembly of seat 27 with body 12. Annular seal 
32 is positioned at the interface of surfaces 50, 51 so that as the 
threaded connection 37 is tightened, the annular seal 32 is compressed by 
surfaces 50, 51. 
Liner 34 is secured within seat 27 by a retainer ring 53. Seat 27 is sealed 
downstream of port 39 at downstream annular seal 33. Thus, the seat 27 can 
extend the full length of the downstream bore 18 portion of the valve 
annulus, even beyond the downstream flange face 16 as represented by the 
seat end 47 shown in phantom lines. This feature allows corrosion/erosion 
protection for the housing in the vulnerable downstream bore 18 section 
for its full length, even to the downstream flange face 16. 
FIGS. 2-3 illustrate an alternate construction of the removable seat and 
liner. In this alternative embodiment the seat 27a is connected to liner 
60 at downstream threaded connection 54. The interior end portion 55 of 
liner 60 forms a metal-to-metal seal with seat 27. The remaining elements 
of this alternative embodiment function as the similarly numbered elements 
in the preferred embodiment described above. 
The apparatus of the present invention may be manufactured of any suitable 
structural material depending generally upon its use. Parts may be made 
from common metals such as iron, steel, stainless steel, bronzes or the 
like or from "exotic" metals of any suitable type especially wear and 
corrosion resistant compositions. Under certain circumstances, dictated by 
service conditions, plastics, elastomers, monomers and polymers, and 
ceramics could be used. 
The foregoing description of the invention is illustrative and explanatory 
thereof, and various changes in the size, shape and materials, as well as 
in the details of the illustrated construction may be made without 
departing from the spirit of the invention.