US1091847A - Method of facilitating the detection of steam-boiler seam-cracks. - Google Patents

Description

S. F. J E mnmon or FAGILITA THE DETEOTI STEAM BOILER SEAM CRACKS. I I IGATION FILED DEC 20,1912. 1,09 1,847, Patented Mar. 31, 1914.

-fractured clear through.-

UNITED STATES PATENT OFFICE.

, SHERWOOD FRANK J'E'IER, OF HARTFORD, CONNECTICUT.

, METHOD or FACILITA'FING THE nn'rnc'rron or srEAM-BorLEn. seam-canons.

Specification of Letters Patent.

To all whom it may concern Be it known that I, SHERWOOD F. JETER, a citizen of the United States, residing at Hartford, in the county of Hartford and State"of Conhecticut, have invented a new and useful Improvement in Methods of Facilitating the Detection of Steam-Boiler Seam-Cracks, of which the following is a specification.

Disastrous boiler explosions have occurred as a result of the rending of boiler shells adjacent to the late joints. Such explosions have happene bothto beijlershaving plates lap-seamed and to boilersfhaving platcsfbut ted and strapped, and'werejnot caused'by'ex.-'

cessive steam pressure but by fractures coin-.v.

ing fromc'ra'ckswhich formed in theplates during normal service. These cracks generally are slow in forming and require long periods of time to develop to a dangerous condition, and they are. attributed to the weakening of the metal adj adent'to the riveted portions of the plates resulting from the manipulation necessary to make the edges conform to the true cylindrical shape of the shells, and to the changes in the stresses in the metal at those localities as the steam pressure varies during use and alters the distortion of the seams due to the thickening of the shellsby the over-laying of the plates. Cracks of this nature are generally very fine at first and are almost always concealed beneath the plies of metal which make up the seams. In lap-riveted joints the cracks usually start at the inner surface of the outer ply of the longitudinal seam and develop to the outer surface substantially parallel with the seam somewhere'intermediate the girth seams and inside of the inner row of rivet holes in that ply, or they start from the outer surface of the inner ply and work to the inner surface inside of the inner-row of rivet-holes in this ply. In the first instance the cracks can never be-observed from the inside, nor from the outside until the outer plate is fractured entirely through. In'the second instance the cracks never can be seen from the outside,

nor from the inside until the inner plate is In butt-strap seams the cracks generally occur between the girth seams back from the edges of the plates and they start from'the surfaces next the inner joint straps and develop from-the inner to the outer surfaces of the plates so that they never show from the inside and are 'not observable from the outside until the shows a plan of small sections in Fig. 5. p In forming a lap joint the edge of the. plate 1 is lapped over the edge of the plate fracture is of such an extent that an ex plosive condition is reached. Thus it is practically impossible to discover such a state until a serious condition exists, for the cracks being concealed do not 'give warning Patented Mar. 31, 1914. Application filed December 20, 1912. Serial N 0. 737,882.

by leakage. of steam or by leakage of water under a hydrostatic test until the plates are so far fractured that they have not suflicient strength to withstand the normal steam pressure.

The object of this invention is to provide .a very simple method and means by which concealed seam cracks lIl bollers can be detected by causal inspection before the plates are completely fractured and a dangerous state is reached. i ,T, h1s nvention can be utilized in connection wlth both'old and new boilers of either horizontal or vertical type having plates that are lap-jointed, butted and strapped or oined in any usual manner, and it is practised by. forming one or more small pockets in the metal of the plates adjacent to the joints in the localities where such cracks are liable to appear, or otherwise cuttin shallow slots or recesses in such manner and positions that while thestrength is not apthey are sufliciently great to extend completely through the plates, and'thus allow a leakage of 'steam which will give warning. that a fault has started, or exposethe defect under a hydrostatic test before a state has been reached. I

Figure 1 of the accompanying drawings 0 two plates of' a boilershell with a double riveted lapjoint treated according to this invention so as to facilitate the detection of anyconcealed seam cracks which may develop. Fig. 2 shows an edge view of the parts shown in Fig. 1. Fig, 3 shows a plan of a butt and dangerous double strapped joint triple riveted which is treated according to this invention. Fig.

.4 shows an edge view of the parts illustrated in'Fig. 3. 5 shows a plan of a modified form of butt-strap joint. Fig. 6 shows an edge view of the parts illustrated 2 the required distance and these two overlapped edges which' have been punched or drilled are secured together by rivets 3 ar-' ranged in any usual manner. -This of course makes the shell thicker where the plates are overlapped. The plates are usually bent by rolls to the arc of. a circle which coincides with the true cylindrical inside diameter of the boiler. In the first place, as the plates passfrom the forming rolls the edges are not ordinarily bent as much as the remainder of the plates, and in the second place overlapping the edge of one plate with the other tends. to distort the plates from the true curve, consequently,

it is necessary to swage or hammer the edges of the plates more or less to bring them together. As the steam pressure when the boiler is in use tends to expand the shell into a true cylinder there is more or less distortion of the plates at the joints. This distortion alters with the varying of the steam pressure when the boiler is in use, and consequently the stresses are constantly changing and those stresses come in the sections of the metal that have been bent down and weakened during manufacture in order to make a tight joint on as near a' true circle as possible. It frequently happens after long use as a result of these conditions that a crack 4 will start in the inner surface of the plate 1 over the edge of the plate2 and gradually work to the outer surface of the plate 1 extending parallel with the seam, or a crack 5 will form in the outer surface of the plate 2 under the edge of the plate 1 and gradually extend longitudinally to the inner surface of the plate 2. It will be observed that in the first case the crack 4 cannot be seen until it reaches the outer surface of the plate 1, and in the second case, that the crack 5 cannot be seen until it reaches the inner surface of the Plate 2, because both of these cracks start between the overlapped terial.

edges of the plates. Consequently these faults cannot be detected until "the conditions are dangerous.

In practising this invention one or more small recesses or slots 6 of any desired configuration can be made in'the outer surface of the plate 1. These slots are but only part way through the plate and they are run transversely of the joint in such positions that the strength'of the plate is not appreciably affected and yet if a crack occurs similar to the crack 4. it will run into or cross this slot before it has extended completely through the plate, and thus before a dangerous condition is reached the crack may be detected by observation or by the escape of steam if the boiler is in use or by the leakage of water if the boiler is under test. It is preferred that recesses be made in the form of shallow slots but the exact shape and number of the recesses is imma- To promote the detectionof cracks in the portion of the plate 2 that is under the plate 1, as the crack 5, one or more 'crack is likely to occur.

.cracks 14 occasionally develop and run apand they work'outwardly as time goes on.

tion of seam cracks in the p ate of a boiler slots? may be made on the inside of the plate 2 transversely of the line on which the In this case the crack will become exposed from the interior when the boiler is inspected before the crack has opened completely through the plate and become dangerous. The edge ofthe outer plate 1 may be cut transversely as at 8 sothat the crack may be seen from the exterior if desired, and if the opening thus formed is over a slot a crack passing across the slot will allow leakage and detection before the fracture is complete. Forming small transverse slots part way through the plates across the probable line of development of thecracks does not re move enough metal to appreciably impair the strength of the boiler shell and yet such slots provide means whereby a crack may be detected before it extends entirely through a plate and becomes dangerous, for the defect will become evident soon after starting, although it commences from a surface covered by a lap of the plates.

Where boiler plates are end butt'ed, as are the plates 9 and 10, the joint is ordinarily covered on the inside by the "strap 11 and on the outside by the strap 12, these being se cured together b rivets 13. When the inside strap is wi er than the outside strap proximately parallel with .thejoint just beyond the edge of the outer strap. These open first at the inner surfaces of the plates As they generally start from the inner surface which is covered by the inner strap they cannot be seen from the interior at any time, nor do they ordinarily show on the exterior until after the plates are fractured completely through and a dangerous condition is 7 reached. In order to discover these faults in boilers having a shell formed of butted and strapped plates, one or more recesses or slots 15 are made on each side of the joint 11o transversely of the probable line of the crack for a little distance in the outer surfaces of the plates so that a 'crack when it starts will open into these slots and cause leakage which will give warning of the defect before a dangerous condition is'reached. When the joint straps are the same width as in Figs. 5 and 6, sections 16 of the edges of the outer strap over the slots 17 may be cut away to facilitate detection of any cracks that may cross the slots beneath the outer strap. Thus cutting the edge of the strap does not impair the strength and in no case .does the formation of the slots remove enough metal to appreciably weaken the strength of the 'shell, and yet-the slots provide means for an early detection of any defect of this nature.

The invention claimed is:

1. The method of providin for the detec- Ill site to the surface in which the crack is liable to first occur, and in the probable path of development of the crack, whereby the crack will open into the recess and become apparent before it extends completely through the plate.

2. The method of providing for the detection of seam cracks in the plate of a boiler shell which consists in reducing the thickness of the plate by cutting an oblong recess adjacent to the scam in the surface of the plate opposite to the surface in which the crack is liable to first occur and transversely of the probable path of development of the crack,-whereby the crack will open into the recess and become apparent before it extends completely through the plate.

3. The method of providing for the detection of scam cracks in the plate of a boiler shell which consists in reducing the thickness of the plate by cutting a slot adjacent to the seam in the outside surface of the outer plate of the lap and transversely of the probable path of development of the crack, whereby the crack will open into the slot and become apparent before it extends completely through the plate.

4. The method of providing for the detec-' tion of seam cracks in the plate of a boiler shell which consists in reducing the thickness of the plate by formin a slot adjacent to the seam in the inner sur ace of the inner plate of a lap and transversely of the probable path of development of the crack.

5. The method of providing for the detectioncof seam cracks in the plates of a boiler shell which consists in reducing the thickness of the plates by forming slots partly through the plates adjacent to the seam and transversely of the probable line of the cracks in the outer surface of the outside plate of the lap and in the inner surface of the inside plate of the lap.

6. The method of providing for the detection of seam cracks in the plates of a boiler shell, which consists in removing portions of the metal from the plates adjacent to the seam, in the probable line of the cracks,

whereby the defect will become apparent before the plate is completely fractured.

7. The method of facilitating the detection of seam cracks in a boiler shell which consists informing openings from the exterior surfaces of. the plates a little distance into the interior of the metal of the plates in the paths of probable seam cracks, whereby outlets for steam will be cracks will be exposed be ore the plates are completely fractured.

SHERWOOD FRANK J ETER.

Witnesses:

HARRY R. WILLIAMS, JOSEPHINE M. STREMPFER.

rovided and the a

Images