Aluminum-lithium plates are butt-welded by juxtaposing the plates and making a preliminary weld from the rear or root side of the seam. An initial weld is then made from the face side of the seam, which may cause a defect in the root portion. A full-size X-ray is made and overlain over the seam to identify the defects. The defect is removed from the root side, and rewelded. Material is then removed from the face side, and the cavity is rewelded. The procedure repeats, alternating from the root side to the face side, until the weld is sound

McGee, William Floyd

Rybicki, Daniel John

NASA Technical Reports Server

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US005811755A 
nited States Patent [19] [ i l l  Patent Number: 5,811,755 
:Gee et al. [45] Date of Patent: Sep. 22,1998 
[54] WELD REPAIR METHOD FOR ALUMINUM 
LITHIUM SEAM 
[75] Inventors: William Floyd McGee, Slidell, La.; 
Daniel John Rybicki, Huntsville, Ala. 
[73] Assignee: Lockheed Martin Corp., New Orleans, 
La. 
[21] Appl. No.: 584,901 
[22] Filed: Jan. 11, 1996 
[51] 
[52] 
[58] 
Int. C1.6 ....................................................... B23K 9/00 
U.S. C1. ............................ 219/137 WM; 2191124.21; 
2281119 
Field of Search .................................... 2191137 WM, 
2191124.21, 125.1, 128, 137 R; 2281119; 
291402.01, 402.02, 402.09, 402.11 
~561 References Cited 
U.S. PATENT DOCUMENTS 
3,192,618 711965 Altgelt .................................... 2281119 
4,049,186 911977 Hanneman et al. . 
4,285,459 811981 Baladjanian et al. . 
4,458,125 
4,493,451 
4,575,611 
4,624,402 
4,959,523 
5,071,054 
5,156,321 
5,258,600 
711984 
111985 
311986 
1111986 
911990 
1211991 
1011992 
1111993 
Leis . 
Clark et al. . 
Bertossa . 
Pitcairn et al. . 
Fihey et al. .......................... 2191125.1 
Dzugan et al. ......................... 2281119 
Liburdi et al. . 
Arthur . 
Primary ExaminerXliEord C. Shaw 
Attorney, Agent, or Firm-W. H. Meise; S. A. Young 
[571 ABSTRACT 
Aluminum-lithium plates are butt-welded by juxtaposing the 
plates and making a preliminary weld from the rear or root 
side of the seam. An initial weld is then made from the face 
side of the seam, which may cause a defect in the root 
portion. Afull-size X-ray is made and overlain over the seam 
to identify the defects. The defect is removed from the root 
side, and rewelded. Material is then removed from the face 
side, and the cavity is rewelded. The procedure repeats, 
alternating from the root side to the face side, until the weld 
is sound. 
10 Claims, 4 Drawing Sheets 
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fuse and join the first and second objects at the heated 
location, and the heated location is moved to fuse and join 
the length of the unwelded root portion. The steps of 
removing the root portion of the defective weld, applying 
s heat to a location along the unwelded root portion of the 
seam and moving the location, removing the face portion of 
the defective weld, and applying heat to a location along the 
unwelded face portion of the seam and moving the location, 
are repeated in the specified order until no defective portion 
i o  of the weld remains. the initial weld may be preceded by a 
preliminary weld to form the root portion of the weld. The 
step of removing includes the step of applying a toothed 
cutting or abrasive tool, which may be a rotating tool, to the 
weld in the defective portion for removing metal. The heat 
is may be applied with an electrical torch, and inert gas may be 
applied to the heated region to reduce defects. 
In a particular method according to the invention, a 
radiographic (X-ray) overlay is used to identify the region to 
be cut away. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. l a  illustrates the juxtaposition of two aluminum- 
lithium plates to be welded, FIG. l b  represents application 
of a preliminary weld from the face side of the plates, to 
25 define a crown portion and a root region of a welded seam, 
FIG. IC represents the result of a radiographic image of the 
weld of FIG. lb,  FIG. Id  represents overlaying the image of 
FIG. IC on the weld of FIG. lb,  FIG. l e  represents the 
removal of material from the root side of the weld in the 
30 defective region, FIG. If represents welding repair of the 
material removed in the step of FIG. l e ,  FIG. lg represents 
a radiographic image of the repaired weld of FIG. If, FIG. 
l h  represents overlaying the radiographic image of FIG. lg 
on the repaired weld of FIG. If, FIG. l i  represents cutting 
35 away material from the face side of the repaired weld of FIG. 
l f in  the region identified as being defective in FIG. lh ,  FIG. 
lj represents welding on the face side of the region in which 
material was removed in the step of FIG. l i ,  FIG. l k  
represents a radiographic image of the repair of FIG. l i ,  FIG. 
40 1Z represents the overlaying of the radiographic image of 
FIG. l k  on the welded region, FIG. l m  represents removal 
of material from the root side of the weld in the region 
identified as defective by the image of FIG. lk, and FIG. In 
represents the result of welding the region in which material 
DESCRIPTION OF THE INVENTION 
It has been determined that a part of the original fusion 
microstructure a weld may be consumed, and a new fusion 
50 boundary or fusion line may form, when a second generation 
of weld is formed with lower heat input than the original 
weld. 
FIG. l a  illustrates a portion 10 of a lithium-aluminum 
alloy cylinder or dome, which is to be joined to a corre- 
ss sponding portion 12 of a second lithium-aluminum cylinder 
or dome along juxtaposed edges 10e and 12e. The cylinders 
or domes are sufficiently large so that, in the region depicted, 
they may be considered to be essentially flat plates. The 
illustrated portions of plates 10 and 12 are the side from 
60 which the weld is initially made, which may be considered 
to be the “outside” of the tank, and the illustrated portions 
of the plates are designated as being the “face” side. FIG. l b  
represents the face sides of plates 10 and 12 after an initial 
weld 16 made from the face side of the plates, by applying 
65 heat at a location along the future seam, and moving the 
location of the application of heat along the seam to fuse the 
material. 
20 
45 was removed in the step of FIG. lm. 
1 
WELD REPAIR METHOD FOR ALUMINUM 
LITHIUM SEAM 
This invention was made under NASA contract NAS 
8-36200, on which waiver number W-3047 has been 
granted. 
FIELD OF THE INVENTION 
This invention relates arrangements and methods for 
correcting or repair of defects in aluminum-lithium seams, 
especially for those of a lightweight propellant tank. 
BACKGROUND OF THE INVENTION 
The fuel tank for the space shuttle is made from a number 
of aluminum cylinders and two end domes, all welded 
together along seams to form a closed vessel for the storage 
of propellant, including liquid hydrogen. The internal pres- 
sure of the liquefied propellant, and the aerodynamic loads 
on the fuel tank during launch of the space shuttle, require 
extremely light weight and strong welds. Lithium-aluminum 
2195 alloy has been proposed as a substitute for the alumi- 
num currently being used for the fuel tank, because of its 
high strength and relatively light weight. 
Unfortunately, it has been found that the welding of 
lithium-aluminum alloy is more difficult than the welding of 
aluminum alone, and defects tend to form in the weld region. 
The lithium-aluminum alloy forms a fusion line at the 
location of the weld due to the temperature reached by the 
metal adjacent the weld due to the welding heat. The fusion 
line has a microstructure which consists of fine equiaxed 
grains coated with solute element second phases. 
It has been determined that the microstructure of the 
fusion line is detrimental to the integrity of the weld. 
However, repairs require re-welding. Too much heat input, 
including cumulative heat input from multiple and succes- 
sive heating cycles, accompanied by the build-up of residual 
stresses induced by weld solidification shrinkage, tends to 
result in cracking at the fusion line. Thus, attempts to 
re-weld defective regions of the initial weld often extends 
the region over which the defect occurs. 
SUMMARY OF THE INVENTION 
A method according to the invention for welding an 
aluminum-lithium seam includes the preliminary step of 
juxtaposing first and second plate-like aluminum-lithium 
objects to be welded along their edges, and holding them in 
position. When so held, the juxtaposed objects or plates 
define face and reverse principal sides. An initial weld is 
made from the face side of the juxtaposed objects, by 
applying heat to a location along the seam to fuse and join 
the first and second objects at the heated location on the 
seam. The heated location is moved to fuse the length of the 
seam, as a result of which a region of defective weld may 
occur in a root side of the seam adjacent the reverse side of 
the objects. When such a defect is identified, the root portion 
of the defective weld is removed in the defective region, 
which leaves an unwelded root portion. Heat is applied from 
the reverse side of the objects, to a location along the 
unwelded root portion of the seam, to thereby fuse and join 
the first and second objects at the heated location on the 
seam. The heated location is moved to fuse and join the 
length of the unwelded root portion. The face portion of the 
defective weld is removed, which leaves an unwelded face 
portion. From the face side of the objects, heat is applied to 
a location along the unwelded face portion of the seam to 
5,8 11,755 
3 
The weld can be examined by several methods. A pre- 
ferred method for examination is to make radiographic 
images of the weld region, which exposes the defective 
portions of the weld. FIG. IC represents a radiographic 
image of a portion of weld 16, illustrating a defective region 
designated 18. According to an aspect of the invention, the 
radiographic image is used to locate the site of the defect. 
This can be accomplished by making a full-size image of a 
selected region of the welded plates, and superposing the 
image on the welded plates to thereby identify the location 
of the defect. The tank is wrapped with a steel measuring 
tape having lead-impregnated markings during the exposure 
to the X-rays. The lead markings show up in the radio- 
graphic image, and allow the image to be registered with the 
tank to identify the location of defects. 
The full-size image may be made by starting with a 
full-size negative, or a smaller negative may have its image 
projected at full size onto the welded region. The initial weld 
16 made from the face side of the plates as described in 
conjunction with FIG. l b  defines a “crown” adjacent the 
face side of the plates and a “root” on the reverse side from 
the face side. The root side may be considered to correspond 
the “inside” of the tank. The inside of the tank is always 
accessible, even after fabrication, by way of access ports. 
According to another aspect of the invention, the first 
repair is made from the root side of the weld. Once the 
location of the defect is identified by examination, as sug- 
gested by FIG. IC, and by identifying the location of the 
defect, as by overlaying the weld with a radiographic image 
as described in conjunction with FIG. Id, the defective 
portion of the welded region is mechanically removed in the 
defect region. If the defect is visible only in the radiographic 
image, the material is removed only half-way through the 
thickness of the weld. It often happens that, as material is 
removed, the defect becomes visible to the naked eye, in 
which case sufficient material is removed to excise at least 
the visible portion. The mechanical removal is preferably 
performed by a suitable tool, such as an electrically or 
pneumatically driven rotary toothed cutter or abrasive disk. 
The result of the removal of the defective portion of the weld 
is illustrated in FIG. le ,  where the portion removed is 
designated 20. The next step is to again apply heat, in order 
to fuse region 20. Since material was removed, it may be 
necessary to supply additional material to aid in filling the 
void; no suitable lithium-aluminum wire is known, and the 
filling is accomplished with 4043 aluminum material. The 
result of the first repair weld is illustrated in FIG. If, where 
repaired region 20 is designated as 22. 
After the first repair from the root side, the weld is again 
examined. Ideally, the repaired weld will be sound, and no 
further repair will be required. Often, however, the weld will 
contain new fusion lines representing defects arising from 
the heat applied during the initial and first repair welds. The 
result of a radiographic examination which reveals a further 
defect is illustrated in FIG. lg, where a defective region 24, 
smaller than original defective region 18, is illustrated. FIG. 
lh  illustrates application of radiographic image 23 to the 
weld to identify the location of the new defect. According to 
the invention, the material in defective region 24 is removed 
from the original crown of the weld on face side of the plates 
being welded, as illustrated by region 26 in FIG. l i .  The 
weld is repaired by further application of heat to region 26 
as illustrated in FIG. lj, where the filled-in region is desig- 
nated 28. 
After the welding step illustrated in FIG. lj, the weld is 
again examined. Naturally, if no defect is identified, the 
procedure stops. If, however, a further defect is identified, as 
4 
suggested by region 32 of the radiographic image 30 of FIG. 
lk, the material is removed from the root side in the region 
of the defective weld, as suggested by the overlay step of 
FIG. 1Z and the removal step of FIG. lm. In FIG. lm, the 
s defective region 34 is likely to be smaller than the previous 
defective regions. FIG. In represents the result of fusing the 
region 34, to produce a repaired welded region designated 
36. 
After the step represented by FIG. In, the next step is to 
10 again examine the weld, and stop the repair process if 
appropriate. In effect, the repair process repeats steps lg, lh,  
l i ,  lj, lk, lZ, lm, and lm until the defect is cured. 
Thus, making a defect-free lithium-aluminum weld 
according to the invention involves starting the weld from a 
face side, examining the weld, and if it is defective, remov- 
ing material from the reverse side of the weld (the root side 
in the case of repair of the initial weld). The material is 
welded in the removed region, and again examined. If 
defects are found, material is removed from the reverse side 
2o of the last repair performed, and again welded. This alter- 
nation is repeated until the weld is defect-free. 
Other embodiments of the invention will be apparent to 
those skilled in the art. For example, while the removal of 
material from the defective region has been described as 
2s being performed with rotary power tools, other metal 
removal methods, such as hand tools or lasers, may be used. 
While radiographic images have been described, acoustic or 
other images may be used, or the defect may be located by 
various methods by the worker who performs the repair. If 
30 a suitable lithium-aluminum wire is found which can be 
used as a filler material, it may be used instead of the 
aluminum filler wire. The filler wire may be used in forming 
the initial weld, if necessary. While large tanks of lithium- 
aluminum material are the particular subjects of the welding 
3s method, it may be applied to any welds of lithium-aluminum 
material which, when initially welded, defines a crown and 
a root, and is, in principle, not limited to straight seams. 
What is claimed is: 
1. Amethod for welding a seam in a material which tends 
40 to generate defects arising from the application of fusion 
juxtaposing first and second plate-like objects of said 
material to be welded along a butt seam therebetween, 
said juxtaposing being such as to define face and 
reverse principal sides of said juxtaposed objects; 
making an initial weld from said face side of said juxta- 
posed objects by applying heat to a location along said 
seam to fuse said first and second objects at said 
location on said seam, and moving said location to fuse 
the length of said seam, as a result of which a region of 
defective weld may occur in a root side of said seam 
adjacent said reverse side of said objects; 
removing the root portion of said defective weld in said 
region, which leaves an unwelded root portion; 
from said reverse side of said objects, applying heat to a 
location along said unwelded root portion of said seam 
to fuse and join said first and second objects at said 
location on said seam, and moving said location to fuse 
and join the length of said unwelded root portion; 
removing the face portion of said defective weld in said 
region, which leaves an unwelded face portion; 
from said face side of said objects, applying heat to a 
location along said unwelded face portion of said seam 
to fuse and join said first and second objects at said 
location, and moving said location to fuse and join the 
length of said unwelded root portion; and 
heat, comprising the steps o f  
4s 
so 
ss 
60 
65 
5,8 11,755 
5 6 
repeating said steps of removing the root portion of said 
defective weld, applying heat to a location along said 
unwelded root portion of said seam and moving said 
location, removing the face portion of said defective 
weld, and applying heat to a location along said s 
unwelded face portion of said Seam and moving said 
location, until the defective portion of said weld is 
removed. 
prior to said making said initial weld, making a prelimi- 
nary weld along said seam from said reverse side of 
said juxtaposed first and second objects, to thereby 
form said root side of said seam. 
8. A method according to claim 1, wherein said material 
9. A method according to claim 1, further comprising the 
removing includes the step of applying a cutting tool to said 10 before said steps of removing, to thereby reveal said defec- 
weld in said defective portion for removing metal. tive portions, and making a full-size record of at least said 
3. A method according to claim 2, wherein said step of defective portions; and 
applying a cutting tool comprises the step of applying a 
rotating toothed cutter. after said step of examining, and before said steps of 
removing, placing said record over said seam to 
applying a cutting tool comprises the step of applying a thereby identify the location at which removing should 
rotating abrasive cutter. be performed. 
5. A method according to claim 1, wherein said step of 10. A method according to claim 9, further comprising the applying heat includes the step of applying plasma from an 
2o step of applying measurement indicia to said weld before electrical torch to said seam. 
6, A method according to claim 5,  further comprising the said step of examining said seam with penetrating radiation, 
step of applying an inert gas to said Seam during said step of for forming images of said measurement indicia on said 
applying heat. radiographic record. 
7. A method according to claim 1, further comprising the 
is lithium-aluminum 
2. A method according to claim 1, wherein said step of step of examining said Seam with penetrating radiation 
4. A method according to claim 2, wherein said step of IS 
step of  * * * * *  


Weld repair method for aluminum lithium seam

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