US2120525A - Method of building up pitted holes in a metal sheet - Google Patents

Description

June 14, 1938. I J, McKE RIHAN I 4 2,120,525

METHOD OF BUILDING UP FITTED HOLES IN A METAL SHEET Filed Jun 1, 1957 FIG: I FIGHZIZI 113 L6 1 1B 5 Z WITNESSES: I I N V EN TOR:

I Thomas J M Kerihan,

Patented June 14, 1938 UNITED STATES PATENT OFFICE METHOD OF BUILDING UP PITTED' HOLES IN A METAL SHEET My invention relates generally to the building up of corroded or worn metals and more particularly to a method of building up pitted holes in a metal sheet.

Becoming more specific my invention is immediately concerned with building up pitted holes in the crown sheet of a boiler in which the welding is done from the fire side of the sheet. In crown sheet boilers, where crown stays are used to support the pressure load, the part of the crown sheet surrounding the crown stay is subject to grooving action, which thins the sheet to the extent that the crown sheet, as a whole or in part, has to be renewed. Much difficulty is experienced in building up pitted holes by welding when the work is done from the water side of the boiler because of the cramped and obscured working space. In attempting to build up from the water side of the boiler sheet, long electrodes to reach the pitted parent metal are necessary for the autogenous or self-produced welding process and this has proved unsatisfactory for the operators vision is seriously obstructed. Work done in this manner has a rough corrugated surface which cannot be dressed smooth in order to prevent the accumulation of sediment.

Therefore the principal object of my invention is to provide a method of building up pitted holes in the crown sheet of a boiler by which the welding and other operations can be done from the fire side of the sheet. Another object is to provide a method for the rebuilding of any corroded sheet from the side opposite the corroded surface. Further advantages will become apparent from the following description of a preferred form of my invention, reference being had to the accompanying drawing.

Fig. I of the drawing shows a vertical section of a portion of the crown sheet of a boiler which has been pitted around a crown stay on the water side, the crown stay not being shown.

Fig. II shows a plan View of the same. Fig. III shows a vertical sectional view of the same after the corroded area on the water side of the crown sheet has been pressed into a smooth surface from the fire side.

Fig. IV is a vertical section of the same showing a building up by the addition of metal from the fire side.

Fig. V is a plan view from the fire side of the sheet showing the built up metal of Fig. IV; and, Fig. VI is a vertical section showing the built up crown sheet after the hole for the crown stay has been re-drilled and the excess building up metal smoothed off on the fire side of the crown sheet.

In the preferred practice of my method of building up a corroded area on the water side of the crown sheet of a boiler, I first heat the 5 parent metal in the corroded area 3 and then apply a backing element I against the water side A of the crown sheet 2, the crown stay having first been removed fromthe crown stay hole 5. This backing means I may be of any con- 10 venient form which can be easily positioned in the restricted area inside of a boiler. The backing means I should extend over a pitted area 3 in the water side A of the crown sheet 2 to be built up and must be securely positioned and 15 heavy enough to resist a pressure forcing out the pitted area 3 against the backing means I.

I then apply pressure to the fire side B of the crown sheet 2 until the corroded area 3 is forced out into a smooth surface on the water side A 20 against the backing means I, as shown in Fig. III, leaving a depression 6 on the fire side B. Any convenient pressure means may be used; I have used with success a pneumatic hammer of a well-known type. The next step is the build- 25 ing up of the depression 6 on the fire side B of the crown sheet 2 caused by forcing out the corroded area 3 against the backing means I. I use autogenous welding to build up this depression 6 from the fire side B, but other suitable 30 types of welding could be used, if desirable. Fig. IV shows welding material 1 after the aforesaid depressed area 6 has been built up by welding. The welding material 1 is distributed generously with a view to a final grinding and boring of 35 the hole 5. I then re-drill the hole 5 for the crown stay and grind off the excess of the welding material 1 on the fire side B. The finished product is shown in Fig. VI, ready to be re-tapped and to then receive the crown stay in re-assem- 0 bling for further use. The smooth surface on the water side A is substantially as good as the original surface.

Thus my invention provides a simple and practical method of building up the corroded area shown in Fig. I by working from the fire side B instead of the water side A which is so cramped and inaccessible. I have found that my method of repairing crown sheets has greatly reduced 50 the difficulty of building up these pitted areas and made it possible to repair corrosion in much less time than formerly was needed. The finished product is also much better than the results previously obtained by working from the water 55 10 said pitted area, applying pressure rigidly over the area of said sheet opposite the pitted side, pressing said pitted area outwardly against the backing means until a smooth surface is obtained on the previously pitted side, building up by autogenous welding the depressions caused by said application of pressure to the side opposite to the pitted area of said sheet, removing the excess Welding material, and redrilling a hole for the crown bolt.

THOMAS J. McKERIHAN.

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