US2985017A

US2985017A - Return bend

Info

Publication number: US2985017A
Application number: US796405A
Authority: US
Inventors: Hermann C Schutt
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-03-02
Filing date: 1959-03-02
Publication date: 1961-05-23
Anticipated expiration: 1978-05-23

Description

May 23, 1961 c, sc u 2,985,017

RETURN BEND Filed March 2, 1959 INVENTOR HEP/mu 6. 50/1/77 32 r Mm ATT RNEY United States Patent Ofitice 2,985,017 Patented May 23, 1961 RETURN BEND Hermann C. Schutt, 399 Belknap Road, Franiingham, Mass.

F lied Mar. 2, 1959, Ser. No. 796,405

2 Claims. (Cl. 73-343) My invention relates to return bends and more particularly to an improved return bend adapted to accommodate a housing projecting into the bend for the reception of a heat-sensitive element.

In the construction of apparatus for carrying out various chemical processes employing heat it is necessary, in order to control the process to measure the temperature accurately. This is commonly done by introducing a housing or tubing into the conduit through which the fluid being processed or the reactants flow. This housing is commonly known as a thermowell. Any appropriate temperature-sensing means may be positioned in the thermowell. Advantageously a thermocouple junction may be positioned in the thermowell adapted to produce a voltage which is a function of the temperature .to which the junction is heated. Such thermocouples may then be used automatically to control process conditions.

Most modern furnaces and heat exchangers are made of straight tubing joined at their ends by return bends, which may customarily change the direction of flow either through 180 or 90, although it is to be understood that any change in direction of flow may be chosen depending on the design of the particular equipment. It will be clear to those skilled in the art that thermowells may advantageously be positioned in the return bends since these are positioned at the extremities of the tubes and are thus readily accessible for insertion, removal or replacement of said thermowell and attachment of lead wires or conduits for the electrical or mechanical impulses created by the temperature.

It has been found that fluids flowing at high velocities and heated to high temperatures will erode thermowells. In addition to the erosion of the fluid itself, such fluids frequently carry abrasive particles such as finely-divided catalyst particles, or particles of carbon or other solids formed in the course of a conversion process. This erosive eifect is particularly severe in the pyrolysis of hydrocarbons where temperatures as high as l,600 F. and flowing velocities in the order of 1,009 feet per second may be encountered. In .addition to the high temperatures of the process, super-atmospheric pressures are employed and if the thermowellfails due'to erosive wear, reactant will escape into the atmosphere.

investigations of disastrous fires at oil refineries have shown'that in many cases they are directly attributable to the failure of thermowells. The escape of superheated hydrocarbon vapors .into the atmosphere will spontaneously produce .a violent .flash fire which willignite .any

combustibles in the environment.

Many efforts have been made to solve the problem of preventing the erosion of thermowells in return bends. It has been suggested to position a thermowell in the return bend inward of the outer wall of the return bend and perpendicular to the reactant flow. In this manner heavy particles would be thrown clear of the thermowell by centrifugal force to the outer wall. Unfortunately, erosion will occur even in absence of heavy particles since lighter or finer particles which will not be appreciably affected by the centrifugal :force are nevertheless quite abrasive. The abrasive elfect moreover is enhanced by elevated temperatures where metals become softer.

One object of my invention is to provide an improved return bend adapted to protect an inserted thermowell from erosion.

Another object of my invention is to provide an improved return bend formed with an integral baflie for protecting a thermowell inserted into the return bend adjacent to the bafile.

Other and further objects of my invention will appear from the following description:

In general my invention contemplates the provision of a battle in the interior of a return bend positioned on the upstream side of the bend. The bafile may advantageously be formed in the shape of a rib integral with the return bend and preferably formed by casting. The rib baflle is adapted to divert the fluid stream from the thermowell and thus shield it from the impact of the fluid passing through the return bend and the impingement of solid particles Whose impact is augmented by centrifugal force. The return bend casting is normally provided with a boss to which an external housing may be Welded, or

otherwise secured. The baflling rib may be shaped to follow the curvature of the bore through the boss and return bend wall.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

Figure l is a sectional elevation of my improved return bend in use, showing one embodiment of my invention.

Figure 2 is a fragmentary sectional View taken along the line 22 of Figure 1.

Figure 3 is a sectional View taken along the line 3-3 of Figure l with the thermowell and the thermowell housing removed.

Figure 4 is a fragmentary sectional view drawn on an enlarged scale taken along the line 44 of Figure 2 with the thermowell in place.

Referring now to Figure 1, the return bend, indicated generally by the reference numeral It may be formed of any appropriate material. Advantageously in the present invention the return bend should be made of cast steel, austenitic manganese steel, chrome-molybdenum steel, chrome-nickel steel or special hard alloys such as Stellite, which is an alloy containing cobalt, chrome, tungsten and molybdenum.

I prefer to use cast steels, and cast alloy steels, since castings have higher hardness and resistance to erosion at any given temperature than wrought materials of the same chemical composition. The hardness of cast materials at elevated temperature is usually 2 to 2.5 times greater than that of the wrought alloy of which the thermowells are usually made.

The return bend comprises a body member 12 formed with a curved passageway .14. The passageway may curve through any appropriate angle. Normally return bends are formed to curve through angles of either 180 or Figure 1 shows a turn return bend. The passageway 14 is provided with an outlet opening 16 and an inlet opening 18. In use, a tube 20, formed of any appropriate material such as wrought alloy steel, is welded to the outlet opening 16 by means of a weld 22. Similarly a tube 24 is welded by means of weld 26 to the inlet opening 18. The arrows in Figure 1 show the direction of flow of the fluid from tube 24 through the passageway 14.

The body member 12 is also formed with a bore 30, the axis of which extends in the direction of the inlet of the passageway 14 adjacent to the inlet opening 18.

Advantageously the bore 30 is positioned coaxially with the axis of the passageway 14 at the inlet opening 18; that is, coaxially with tube 24. It is understood, of course, that the bore 30 'may communicate with the passageway 14 at any desired point in the passageway 14 as long as the bore 30 extends in the direction of or substantially in the direction of the passageway at its inlet opening 18.

The purpose of bore 30 is to provide means for inserting the thermowell, in which the thermocouple or other temperature-sensitive measuring means is positioned, into the passageway 14. As shown in Figure 1 the bore 30 is formed with a boss 32 to which. a tube 34 is welded by means of circular weld 36. It is understood, of course, that the tube 34 may be secured to the boss 32 in any other appropriate manner such as by screw threads or the like. The tube 34 forms a housing for the thermowell. A circular plate 38 is welded to the tube 34 forming a flange. The thermowell 40 itself is formed of a smaller diameter than the bore of housing 34 and bore 30 which is coextensive therewith, as can readily be seen by reference to Figure 1. It may be formed in the shape of an elongated chamber of any appropriate hard material, as shown in Figure 1.

The outer end of the thermowell 40 is provided with a flange 42 secured thereto in any appropriate manner, such as welding or the like. A circular sealing ring 34 is clamped between the

flanges

42 and 38 by means of bolts 46. The upstream side of the thermowell 40 would normally be subjected to erosion and abrasion in use. I cast a rib '0 integral with the body member 12 adjacent to the inlet opening 18. This rib is slightly wider than the exterior diameter of the thermowell 40. In practice I make the rib between 0.03 inch and 0.1 inch wider than the diameter of the thermowell. The n'b will protect the wall of the thermowell projecting into the return bend from erosion by the flowing fluid. The rib also acts as a baffle diverting the fluid and solid particles carried thereby. Advantageously I curve the upper surface 52 of the rib 50 so that it conforms with the curvature of the surface 54 of thebore 30. Owing to the fact that the internal diameter of the bore 30 is larger, a space 60 will be provided through which vapors or reactant may pass into the thermowell housing 34. The space 60 makes for ease of insertion and removal of the thermowell.

In order to prevent coke and solid particles from accumulating between the thermowell and the batflling rib 50 and return bend body 12, I provide an arcuately molded filler 70. This filler may be made of any appropriate heat-resistant material. Advantageously it may be made of asbestos fiber impregnated with a silicone resin in partially polymerized form, which is adapted to set by heat to form a heat stable layer of resin bonded asbestos fiber. Any appropriate filler material may be employed, as will be readily understood by those skilled in the art.

It will be observed that the outer end 41 of the thermowell 40 is formed of increased Wall thickness since it will be subject to direct impingement by fluids flowing through the inlet tube 24.

The rib may be made with a streamlined nose, as can readily be seen by reference to Figure 3, so as to reduce resistance to flow of the fluid passing through the return bend at the same time parting the fluid in a streamline pattern reducing any erosive action on the rib itself.

It will be seen that I have accomplished the objects of my invention. I have provided an improved return bend in which a thermowell can be conveniently inserted and which will protect. the thermowell from abrasion and erosion from fluid passing through the return bend. My thermowell may be rapidly and expeditiously removed and replaced for inspection and will have much longer life when used in my improved return bend.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. A return bend for receiving a thermowell having an exterior diameter including in combination a steel casting formed with a curved internal passageway having an inlet opening and an outlet opening, a bore formed in said casting communicating with said passageway, said bore having a diameter larger than said exterior diameter, a rib integral with said casting positioned in said passageway extending from a wall of the passageway adjacent said inlet opening toward said bore, said rib being formed with a concave upper surface substantially forming a continuation of a portion of the interior surface of said bore, said rib having a thickness substantially equal to said exterior diameter of the thermowell, said bore being adapted to receive said thermowell with said thermowell disposed over said rib concave surface, and filler material on the surface of said rib.

2. A return bend for receiving a thermowell having an exterior diameter including in combination a member formed with a curved internal passageway having an inlet opening and an outlet opening, a bore formed in said member communicating with said passageway, said bore having a diameter larger than said exterior diameter, a rib carried by said member positioned in said passageway extending from a wall of the passageway adjacent said inlet opening towards said bore, said rib being formed with a concave upper surface substantially forming a continuation of a portion of the internal surface of said bore, said rib having a thickness substantially equal to said exterior diameter of said thermowell, said bore being adapted to receive said thermowell with said thermowell disposed over said rib concave surface.

References Cited in the file of this patent UNITED STATES PATENTS 301,964 Colby July 15, 1884 318,971 Evans June 2, 1885 490,723 Roney Jan. 31, 1893 779,398 Calkins Jan. 3, 1905 941,596 White Nov. 30, 1909 1,079,724 Roberts Nov. 25, 1913 1,193,911 Machlet Aug. 8, 1916 1,226,427 White May 15, 1917 1,441,581 Hilligardt Jan. 9, 1923 1,615,480 Poole Jan. 25, 1927 2,015,968 Ryder Oct. 1, 1935 2,560,455 Knight July 10, 1951 2,732,331 Wesh Jan. 24, 1956