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IS20

George C. Marshall Space Flight Center

Marshall Space Flight Center, Alabama

35812
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i

NASA/TM—2008–215411

The Repair and Return to Flight 

of Solid Rocket Booster Forward Skirt 

Serial Number 20022

T.W. Malone and C.S. Jones

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

J.H. Honeycutt, Sr.

JE Jacobs Sverdrup, Huntsville, Alabama

June 2008

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812
ii

Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076–1320

301–621–0390

This report is also available in electronic form at

<https://www2.sti.nasa.gov>

Acknowledgments

The authors wish to thank the following individuals and organizations for their assistance in this effort: 

James Hodo, Marshall Space Flight Center Materials & Processes (M&P) Laboratory, Mechanical Test Team, conducted 

mechanical testing. M&P Chemistry Team performed chemical analyses. M&P Nondestructive Evaluation Team conducted 

x ray and penetrant inspections. Clyde Jones, M&P Processes Development Team, recommended the methodology to correct 

the aft clevis pinhole misalignment and facilitated the repair using weld heat passes to locally shrink the skirt. Sam Clark, 

M&P Processes Development Team, was instrumental in determining the parameters for the weld passes. 

United Space Alliance provided photographic documentation and internal reports with supporting data. 

Susan Hessler, Snyder Technical Services, Inc., provided an editorial review of this Technical Memorandum.
iii

Table of Contents

1. INTRODUCTION .......................................................................................................................... 1

2. REPAIR PROCEDURES................................................................................................................ 3

2.1 Debuckling Solid Rocket Booster Forward Skirt Serial Number 20022 ................................ 3

2.2 Pinhole Realignment ................................................................................................................ 3

3. MATERIAL EVALUATIONS ........................................................................................................ 13

3.1 Buckled and Debuckled Al 2219.............................................................................................. 13

3.2 Al 2219 Stringer Reinforcements ............................................................................................ 17

4. CONCLUSIONS ............................................................................................................................ 25

Appendix A—TEST PLANS/REPORTS ....................................................................................... 26

REFERENCES ................................................................................................................................... 27
iv

LIST OF FIGURES

 1. S/N 20022 buckled forward skirt ....................................................................................... 3

 2. Hydraulic press debuckling S/N 20022 ............................................................................. 4

 3. MSFC demonstration panel weld locations/passes ............................................................ 5

 4. Typical microhardness curve for weld nugget on MSFC demonstration panel ................. 5

 5. Data curve showing MSFC demonstration panel shrinkage .............................................. 6

 6. General Products test panel 1, specimen locations 1–20 ................................................... 8

 7. General Products test panel 2, specimen locations 1–22 ................................................... 9

 8. General Products test panel 1 hardness values, from weld centerline 

into parent material ............................................................................................................ 11

 9. General Products test panel 2 hardness values, from weld centerline 

into parent material ............................................................................................................ 11

10. As-received, S/N 007 test section ...................................................................................... 14

11. As-received, S/N 007 test section, side view ..................................................................... 14

12. S/N 007 debuckled test section .......................................................................................... 15

13. S/N 007 debuckled test section, side view.......................................................................... 15

14. Specimen locations on S/N 007 debuckled test section ..................................................... 16

15. Two stringers fabricated by General Products ................................................................... 20

16. Exterior of S/N 20022 with callout of installed stringers .................................................. 23
v

LIST OF TABLES

 1. Shrinkage data for MSFC demonstration panel ................................................................. 7

 2. S/N 007 debuckled section mechanical test results ........................................................... 16

 3. Chemical composition of S/N 007 debuckled section ....................................................... 17

 4. Bulk chemical analysis for stored Al 2219 ........................................................................ 18

 5. Mechanical properties for stored Al 2219 .......................................................................... 19

 6. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 18 hr, first set of test samples........................................................................................ 20

 7. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 24 hr, second set of test samples ................................................................................... 21

 8. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 24 hr, third set of test samples....................................................................................... 22
vi

List of Acronyms, SYMBOLS, and Abbreviations

AMS Aerospace Material Specification

ANSI American National Standards Institute

ASTM American Society for Testing and Materials International

AWS American Welding Society

HKN hardness Knoop number

HRB hardness Rockwell B

ICP inductively coupled plasma

ipm inches per minute

JE Jacobs Engineering

M&P materials and processes

MSFC Marshall Space Flight Center

MTS Materials Test Systems Corporation

PEC Productivity Enhancement Complex

PQR procedure qualification record

RSRM redesigned solid rocket motor

SAE Society of Automotive Engineers International

S/N serial number

SRB solid rocket booster

STS Space Transportation System
vii

LIST OF ACRONYMS, SYMBOLS, AND ABBREVIATIONS (Continued)

TIG tungsten inert gas

TMC Technical Micronics Control, Inc.

USA United Space Alliance

USBI United Space Boosters, Inc.

UTS ultimate tensile strength

WPS weld procedure specification

WQP welding qualification procedure

YS yield strength

%El percent elongation
viii
1

TECHNICAL MEMORANDUM

THE REPAIR AND RETURN TO FLIGHT OF SOLID ROCKET BOOSTER 

FORWARD SKIRT SERIAL NUMBER 20022

1. INTRODUCTION

This Technical Memorandum discusses an effort to correct buckling sustained by solid rocket 

booster (SRB) forward skirts during water impact after Space Transportation System (STS) launches. 

By early 1991, five skirts—three left-hand and two right-hand flight units—had been damaged in this 

manner. Three had skin fracture damage and buckling, and one contained a tension failure in the aft 

clevis. The fifth skirt sustained damage levels that are unknown, as it was lost at sea during retrieval.

This effort involved several initiatives as follows:

• Determine whether damaged flight units might be repaired. The least damaged unit available 

was SRB forward skirt serial number (S/N) 20022 that buckled after the launch of STS–37. 

Special hydraulic tooling was used to debuckle S/N 20022. After the debuckling procedure, 

the aft clevis pinholes were found to be slightly out of alignment with the redesigned solid 

rocket motor (RSRM) check gauge. This misalignment was corrected using an experimental 

weld procedure.

• Additional testing and evaluation generated material property data that supported the decision 

to return S/N 20022 to the flight hardware flow. Postlaunch analysis indicated that S/N 20022 

performed nominally after being returned to flight during STS–100.

• United Space Boosters, Inc. (USBI) analytics personnel suggested that the structural integrity 

of the skirt might be improved by adding stringer reinforcements to its aft bay section. This 

change was made to S/N 20022 during repairs. It was later recommended as a fleet modification to be implemented on a case-by-case basis for other forward skirts.
2
3

2. REPAIR PROCEDURES

2.1 Debuckling Solid Rocket Booster Forward Skirt Serial Number 20022

After the STS–37 launch, S/N 20022 suffered water impact loads in excess of its design strength. 

The structural alloy (Al 2219) sustained damage that included skin buckling in the aft skin bay area as 

shown in figure 1. Depressions were observed to a depth of 1.6 cm (0.64 in) in the lower bay.

Figure 1. S/N 20022 buckled forward skirt. 

Using a hydraulic press, located at General Products in Huntsville, AL (fig. 2), buckling was 

removed within 0.5 cm (0.2 in). This operation restored the area contour within the experience base. 

2.2 Pinhole Realignment

After the debuckling procedure was complete, the flight direction of S/N 20022’s aft clevis pinholes was found to be slightly aft of and misaligned with some RSRM check gauge pinholes. As a result, 

nominal check gauge aft clevis pins could not be used to mate the two pinhole sets across a circumferential span (≈106-in long) located between aft clevis pinholes 66–96 outside the buckled area. Marshall 

Space Flight Center (MSFC) recommended that weld heat passes be conducted in an area of the skin 

adjacent to the misaligned pinholes to shrink the skirt so the pinholes would again match.
4

Figure 2. Hydraulic press debuckling S/N 20022.

2.2.1 Marshall Space Flight Center Demonstration Panel Weld

MSFC demonstrated a proposed methodology for a weld heat pass repair using a 2219–T87 test 

panel (12×24×0.24-in). This demonstration generated shrinkage and strength data to verify the amount 

of transverse weld shrinkage that would occur with respect to specific weld parameters, as well as subsequent mechanical properties in the weld zones (fig. 3). These data were used to qualify a similar weld 

schedule at the vendor and effect dimensional changes on S/N 20022.

Tungsten inert gas (TIG) welding was used without filler wire at a current of ≈185 amps and a 

weld speed of ≈15 ipm in accordance with procedures defined in MSFC–SPEC–504C.1 Two separate 

weld passes were made in the geometric center of the panel. Each weld pass was ≈0.25-in wide. The first 

pass was ≈9-in long. The second was ≈8-in long and overlapped the first weld pass by ≈1 in.

2.2.1.1 Metallography The degree of weld penetration was determined by measuring cross-sections 

of the weld nugget taken at three locations, with the average measurement indicating a penetration depth 

of ≈50 percent. Hardness surveys were taken transverse to the welding direction as shown in figure 4. 
5

Figure 3. MSFC demonstration panel weld locations/passes.

90

80

70

60

50

40

30

HRB

SRB22–M1 Root Hardness

Center Hardness

Crown Hardness

Distance From Weld Center (in)

–0.6 –0.4 –0.2 0 0.2 0.4 0.6

Figure 4. Typical microhardness curve for weld nugget on MSFC demonstration panel.

*Welded from 3.5-in mark on panel to 12.5-in mark, then welded from 19.5-in mark to 11.5-in mark

Notes: 1. Material 2219–T87 per QQ–A–250/30A (0.25-thick stock material)

 2. Prior to welding machine panel sides parallel +/– 0.01 in

 3. Conduct first weld pass per dimensions shown

 4. Panel orientation — longitudinal transverse

24

19.5

12

6

11.5

3.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

12

11

10

9

8

7

6

5

4

3

2

1

0

12.5

Start First Weld Pass

Start Second Weld Pass
6

2.2.1.2 Mechanical Properties Ten tensile specimens with parallel sides were taken at equal intervals transverse to the weld length. Mechanical properties were then determined in accordance with 

ASTM B 557–84.2 Data averages included ultimate tensile strength (UTS) of 47.2 ksi, yield strength 

(YS) at 0.2 percent of 27.1 ksi, percent elongation (%El) using a 2-in gauge length of 4.52 percent, 

and %El using a 1-in gauge length of 8.93 percent.

2.2.1.3 Shrinkage Two techniques were used to measure the panel before and after welding. Vernier 

calipers were used to take overall dimensions from the edges of the panel at 1-in intervals in both the 

transverse and longitudinal directions. Electronic measurements were taken across the weld area at 1-in 

intervals over a 2-in gauge length in the longitudinal direction using custom equipment developed by 

MSFC. The following measurements and shrinkage data were generated:

• In the transverse direction, maximum shrinkage (0.03 in) was observed at the midpoint of the 

panel. Minimum shrinkage (averaging 0.0025 in) occurred at the ends of the panel.

• In the longitudinal direction, maximum shrinkage (0.007 in) was observed at the two outer 

edges of the panel. Minimum shrinkage was zero at the midpoint of the panel (table 1). 

These shrinkage data are also presented graphically as curves in figure 5. 

0.035

0.030

0.025

0.020

0.015

0.010

0.005

0

0 5 10 15 20 25 30

Average Tensile Results

YS 27.1 ksi

UTS 47.2 ksi

%EI 8.93

Position (in)

Shrinkage (in)

Overall

Weld Face

Weld Root

Weld Panel Outline

First Weld Second Weld

12 in

Figure 5. Data curve showing MSFC demonstration panel shrinkage. 
7

Table 1. Shrinkage data for MSFC demonstration panel.

Panel ID: 12×24×0.25 MSFC Demo. Panel MSFC Demonstration 12×24 Test Panel Shrinkage Data Date: 10/31/97

2219–T87 Weld Pass For SRB Skirt Repair

Weld Side, Transverse Shrinkage Measurements **

Location 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Overall shrinkage 0.001 0.005 0.008 0.009 0.011 0.016 0.017 0.02 0.021 0.021 0.024 0.026 0.028 0.026 0.024 0.023 0.021 0.018 0.013 0.009 0.007 0.004

Preweld weld side 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013 12.013

Postweld 12.012 12.008 12.005 12.004 12.002 11.997 11.996 11.993 11.992 11.992 11.989 11.987 11.985 11.987 11.989 11.990 11.992 11.995 12 12.004 12.006 12.009

Weld Side, Longitudinal Shrinkage Measurements **

Location 1 2 3 4 5 6 7 8 9 10 11

Overall shrinkage 0.008 0.007 0.005 0.003 0.001 0 0.002 0.002 0.004 0.005 0.007

Preweld weld side 23.885 23.888 23.889 23.89 23.891 23.892 23.895 23.895 23.898 23.9 23.902

Postweld 23.877 23.881 23.884 23.887 23.89 23.892 23.893 23.893 23.894 23.895 23.895

Weld Side Face Measurement Over 2-In Gauge Length

Location 1.3 2.3 3.3 4.3 5.3 6.3 7.3 8.3 9.3 10.3 11.3 12.3 13.3 14.3 15.3 16.3 17.3 18.3 19.3 20.3 21.3 22.3

Weld Face Shrinkage 0.002 0.003 0.007 0.015 0.016 0.018 0.027 0.025 0.02 0.022 0.025 0.03 0.03 0.027 X 0.026 0.019 0.018 0.013 0.006 0.002 0.002

Pass Preweld weld side 1.987 2.003 2.002 2.004 2.003 2.002 2.005 2.004 2.005 2.004 2.003 2.001 2.002 2.003 1.93 2.003 2.003 2.002 2.004 2.003 2.003 2.004

1 First 9-in pass 1.986 1.998 1.995 1.991 1.984 1.983 1.979 1.980 1.987 1.986 1.987 1.989 1.995 1.999 1.976 1.980 2.002 2.001 2.002 2.003 2.003 2.002

1 Second 8-in pass 1.986 2 1.995 1.989 1.987 1.984 1.979 1.979 1.985 1.983 1.978 1.972 1.972 1.976 1.953 1.977 1.984 1.985 1.991 1.997 2.001 2.002

Root Side Measurement Over 2-In Gauge Length

Location 1.3 2.3 3.3 4.3 5.3 6.3 7.3 8.3 9.3 10.3 11.3 12.3 13.3 14.3 15.3 16.3 17.3 18.3 19.3 20.3 21.3 22.3

Weld Root Shrinkage X 0.002 0.007 0.013 0.013 0.013 0.016 0.013 0.014 0.016 0.020 0.023 0.022 0.017 0.019 0.015 0.013 0.01 0.006 X 0.001 X

Pass Preweld 2.016 2 2.002 1.999 2 2.001 2.002 2.001 2.002 2.002 2.002 2.003 2.002 2.001 2.003 1.999 2.002 2 2.002 1.999 2.003 2.002

1 First 9-in pass 1.998 2 1.998 1.991 1.986 1.987 1.986 1.987 1.988 1.988 1.991 1.994 1.999 2 2.003 1.998 2.001 2 2.001 2.001 2.003 2.002

1 Second 8-in pass 1.999 1.998 1.995 1.986 1.987 1.988 1.987 1.988 1.988 1.986 1.983 1.980 1.981 1.985 1.983 1.984 1.989 1.99 1.996 2.002 2.003 2.003

** Measurements taken with vernier calipers along the outer edge of panel*** Measurements taken electronically X Invalid measurements
8

2.2.2 General Products Additional Test Panels 

After the decision was made to shrink S/N 20022 using one or more weld heat passes, a plan was 

formulated calling for the vendor to develop a welding qualification procedure (WQP) and a procedure 

qualification record (PQR), in accordance with American National Standards Institute (ANSI)/American 

Welding Society (AWS) D1.2–90 (part 5C).3

General Products applied this procedure to test panel 1, which was a flat stock panel the same size 

as the MSFC demonstration panel (12×24×0.25 in). It was machined and welded, as shown in figure 6, 

generating the following results: 

• Before and after measurements showed an average shrinkage of 0.028 in at locations 8–12 near 

the center of the weld side of the panel.

• Welds were evaluated for defects using visual, penetrant, and radiographic inspections. Technical Micronics Control (TMC), Inc. of Huntsville, AL conducted the radiographic inspections in 

accordance with MIL–STD–453.4 No indications were observed.

• Average test data included UTS 44.5 ksi, YS (0.2 percent) 27.2 ksi, and %El (2 in) 5.2 percent.

• Weld nugget penetration averaged 46.9 percent, based upon 10 data points.

24

2

12

6

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Notes: 1. Material 2219–T87 per QQ–A–250/30A (0.25-thick stock material)

 2. Prior to welding machine panel sides parallel +/– 0.01 in

 3. Conduct first weld pass per dimensions shown

 4. Conduct second weld pass to overlap first weld pass by 2 in

 5. Conduct second weld pass in the same direction as the first weld pass

 6. All dimensions are in inches

 7. Specimen locations are at 1-in intervals

Second Weld Pass

Start First

Weld Pass

First Weld Pass

Panel Centerline

Finish Second Weld Pass

Figure 6. General Products test panel 1, specimen locations 1–20. 
9

Further qualification was conducted for test panel 2, which was fabricated to simulate the weld 

heat pass location on the flight hardware. It was machined and welded, as shown in figure 7, with the 

following results: 

• Before and after measurements showed an average shrinkage of 0.017 in at locations 10–14 

near the center of the weld side of the panel.

• Welds were evaluated for defects using visual, penetrant, and radiographic inspections 

 conducted by TMC in accordance with MIL–STD–453.4 No indications were observed.

• Average test data included UTS 48.8 ksi, YS (0.2 percent) 30.7 ksi, and %El (2 in) 5 percent.

• Weld nugget penetration averaged 39 percent, based upon 12 data points. The thick center section 

(0.5 in) had much lower penetration than the rest of the panel, causing a lower average than for 

test panel 1.

48

3

24

12

22 4

0.5 R TYP

0.25-in Thick Plate With 

0.5-in Thick Center Section

Flight Hardware Weld Qualification Test Panel Material 2219–T87

3

1 2 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Notes: 1. Conduct first weld pass to dimensions shown

 2. Conduct second weld pass in the same direction as the first weld pass to dimensions shown

 3. Second weld pass to overlap first weld pass by 2 in

 4. Before welding machine panel sides parallel +/– 0.01 in

 5. All dimensions are in inches

 6. Spacing between specimen locations is 2 in

Second Weld Pass

Start First Weld Pass

First Weld Pass

Finish Second Weld Pass

Figure 7. General Products test panel 2, specimen locations 1–22. 
10

A microhardness evaluation was conducted for the weld area on both test panels to define the limit 

of thermal impact on the parent material, as depicted in figures 8 and 9. These data show a return to the 

T87 tempered condition (i.e.: ≈76 HRB) at 0.5–0.6 in from either side of the centerline of the weld nugget.

These test results verified an attainable transverse shrinkage in the Al 2219–T87 panel (test panel 2) 

that mirrored the predetermined weld location on S/N 20022. When performed in accordance with the WPS 

and PQR documents, prepared by General Products, these welds contained penetration levels of less than 50 

percent and a return to parent metal strength at a distance of 0.5–0.6 in from the centerline. The qualification 

welded structure (test panel 2) had mechanical properties that included UTS 23.7 ksi, YS 39.8 ksi, and %El 

28.6 percent, which were lower than the reported minimum values in accordance with FED QQ–A–250/30.5

No anomalies were observed when the welds were subjected to nondestructive evaluation by visual, liquid 

penetrant, and radiographic techniques.

2.2.3 Serial Number 20022 Heat Pass Repair Weld 

General Products then performed a weld heat pass repair in accordance to their WPS and PQR 

documents for the qualification test panel (test panel 2). One weld consisting of two separate passes was 

made. The second pass was a continuation of the first, but overlapped its end by 2 in. In accordance with 

written instructions provided by USBI, the welds were conducted on the inboard side of the skirt between 

aft clevis holes 66 to 96, ≈111/8-in from the bottom of the aft clevis. The combined length of the two weld 

passes was ≈75 in. Allowances were made for determining additional welds/locations after completion of 

the first weld and any subsequent dimensional and/or pin-check evaluations, if required.

The area was measured before and after welding. It showed maximum shrinkages of 0.02 in 

across the weld nugget side (inboard) and 0.017 in across the root side (outboard). The weld pass area 

was allowed to stabilize to ambient temperature for ≈20 hr. Measurements were then made using a theodolite instrument that showed the aft clevis had shrunk ≈0.035 in. As a result, all RSRM check gauge 

pinholes were able to admit nominal, rather than reduced, diameter clevis pins. Afterwards, the skirt 

was installed with stringer reinforcements. Upon its arrival at Kennedy Space Center, a planarity check 

showed that all dimensions fell within the experience base.
11

140

130

120

110

100

90

80

70

≈76HRB

≈56HRB

≈32HRB

–0.64 –0.48 –0.32 –0.16 0 0.16 0.32 0.48 0.64

(in)

HKN 200 (g)

Average HKN vs Inches From Centerline of Weld

Figure 8. General Products test panel 1 hardness values, from weld centerline into parent material. 

140

130

120

110

100

90

80

70

≈76HRB

≈56HRB

≈32HRB

–0.56 –0.4 –0.24 –0.08 0.08 0.24 0.4 0.56

(in)

HKN 200 (g)

Average HKN vs Inches From Centerline of Weld

Figure 9. General Products test panel 2 hardness values, from weld centerline into parent material.
12
13

3. MATERIAL EVALUATIONS

Additional studies included material property testing and evaluation of buckled and debuckled 

Al 2219, as well as Al 2219 that was removed from long-term storage and reprocessed to fabricate 

stringer reinforcements.

3.1 Buckled and Debuckled Al 2219

To show the soundness of S/N 20022 as repaired, USBI analytics requested design values for 

similar materials that had been buckled and then debuckled. These values were used during an analysis 

that indicated the repair was acceptable for return to flight based, in part, on a strength reduction factor 

of 25 percent of the original design values. This knockdown factor was suggested by a consortium of 

M&P personnel from MSFC and United Space Alliance (USA) based on prior experience with the material rather than specific data. However, an independent assessment review required MSFC and USA to 

conduct mechanical testing to validate the knockdown factor.

In May 2000, a section of similarly buckled material from another damaged forward skirt, 

S/N 007, was selected for testing. This section was the same material (Al 2219–T87) and thickness 

(0.63 cm or 0.25 in) as the area in question on S/N 20022, with a maximum deflection or buckle of 

≈7.1 cm (2.8 in). The buckled panel was photographed as received (figs. 10 and 11). Following the 

removal of all coatings using a hydrolaser, radiographic and dye penetrant inspections were conducted. 

A 13⁄4-in long crack was found and trimmed away. No other anomalies were detected.

S/N 007 was debuckled and restored to within 0.5 cm (0.2 in) of the original surface by General 

Products, using the same tooling and expertise as for S/N 20022. Actual postdebuckling measurements 

indicated a flatness of 0.25–0.38 cm (0.1–0.15 in). The panel was photographed again after debuckling, 

as shown in figures 12 and 13. No indications were reported during another round of nondestructive 

evaluation. Tensile specimens were then fabricated from the repaired section, figure 14, per ASTM E 8, 

“Standard Test Method for Tension Testing of Metallic Materials.”6
14

Figure 10. As-received, S/N 007 test section. 

Figure 11. As-received, S/N 007 test section, side view.
15

Figure 12. S/N 007 debuckled test section. 

Figure 13. S/N 007 debuckled test section, side view.
16

Figure 14. Specimen locations on S/N 007 debuckled test section.

Tensile specimens were mechanically tested using an Instron series IX automated materials test 

system on a 100-kN (20-kip) Mechanical Test Systems Corporation servohydraulic load frame. Test 

results are provided in table 2. 

Table 2. S/N 007 debuckled section mechanical test results. 

Mechanical 

Property

Minimum 

Required 

MIL–HDBK–58

Using 25% 

Knockdown Factor

Axial Tests 

(8-Specimen

 Average) 

Hoop Tests 

(8-Specimen 

Average) 

UTS (ksi) 64 48 71.7 71.7

YS (ksi) 51 38.2 57 57.9

%El (2 in) 7 5.2 7.9 8.3

Hardness was measured in accordance with ASTM E 18, “Standard Test Methods for Rockwell 

Hardness and Rockwell Superficial Hardness of Metallic Materials.”7 A New Age Indentron unit 

was used to take HRB measurements on the grip end of several tensile test specimens and at various locations on the residual test material. A total of 12 measurements yielded an average hardness 

value of 79 HRB, well within the material acceptance requirements for Al 2219 given in the Society of 

Automotive Engineers International (SAE)/Aerospace Material Specification (AMS) 2658, “Hardness 

and Conductivity Inspection of Wrought Aluminum Alloy Parts (table 1),” which indicates a minimum 

acceptance value of 75 HRB.

9

A chemical analysis was conducted (table 3) to certify that the material was, in fact, Al 2219 

as stated in the drawing requirement. X-ray fluorescence spectroscopy revealed that all elements were 

within the acceptable ranges for Al 2219 as specified by FED QQ–A–250/30.5
17

Table 3. Chemical composition of S/N 007 debuckled section. 

Element Sample (Weight %) Al 2219 (AMS 2658)

Al (Balance)

Cr 0.005 –

Cu 6.39 5.8 to 6.8

Fe 0.23 0.3 (maximum)

Mg 0.02 0.02 (maximum)

Mn 0.25 0.2 to 0.4

Ni 0.01 –

Si 0.15 0.2 (maximum)

Ti 0.07 0.02 to 0.1

V 0.1 0.05 to 0.15

Zn 0.01 0.1 (maximum)

Zr 0.14 0.1 to 0.25

3.2 Al 2219 Stringer Reinforcements

This incident prompted a study by USA to reduce the risk of buckling SRB forward skirts during 

water impact after launch. As a result, Al 2219 stringers were installed in the aft bay area of S/N 20022 

during the repair procedure. Although skirt buckling had never been predicted analytically, a relative 

level of improvement was shown over the buckling strength of the current configuration. Therefore a 

fleet modification was recommended.

In recent years, it has become difficult to obtain Al 2219–T87 in sufficiently small quantities 

to fulfill needs as they arise, and material was not commercially available to meet this requirement. 

However, a substantial amount of Al 2219–T37 had been stored by the MSFC SRB Program Office for 

over 30 years. Unfortunately, the natural process of ambient temperature aging had left it in a condition 

that was not easy to recover.

USA took on the challenge of recovering this material to use in fabricating the forming stringers to reinforce the skirt structure. Three pieces of Al 2219–T37 measuring 122×244 cm (48×96 in) and 

0.63-cm (0.25-in) thick were obtained from NASA program stock for S/N 20022 stringer fabrication. 

Mechanical properties and chemical analysis needed verification since no supporting documentation 

was supplied with the material. It was also necessary to confirm that the recovered material met the 

requirements for T87 temper.
18

3.2.1 Chemical Analysis

A bulk chemical analysis was conducted using x-ray fluorescence spectroscopy that indicated 

two elements—copper and magnesium—were out of tolerance. A quantitative analysis was then conducted using inductively coupled plasma (ICP) emission spectrometry, a method with detection limits in 

the parts-per-million range, that indicated the material met specification requirements (table 4). 

3.2.2 Mechanical Properties

Thirty specimens were machined from three pieces of Al 2219–T37 plate that was 0.63-cm 

(0.25-in) thick, to evaluate natural aging properties that had developed during 30+ years of storage 

(table 5). The raw data and calculated minimum both exceeded the minimum requirements specified. 

These results indicated that a standard aging treatment would probably overage the material, which 

would then fail to meet the minimum requirements for T87.

Table 4. Bulk chemical analysis for stored Al 2219. 

X-Ray Fluorescence 1D 2D 3D Al 2219 Specification

Al (Balance)

Cr 0.01 0.01 0.01 0.05 max

Cu 6.95 6.95 6.94 5.8 to 6.8

Fe 0.16 0.16 0.17 0.3 max

Mg 0.025 0.029 0.026 0.02 max

Mn 0.25 0.26 0.26 0.2 to 0.4

Si 0.13 0.16 0.18 0.2 max

Ti 0.03 0.03 0.03 0.02 to 0.1

V 0.07 0.07 0.07 0.05 to 0.15

Zn 0.01 0.01 0.01 0.1 max

Zr 0.1 0.1 0.1 0.1 to 0.25

ICP Emission Spectrometry 1D 2D 3D Al 2219 Specification

Cu 6.41 6.51 6.52 5.8–6.8

Mg 0.011 0.01 0.012 0.02 max

Note: All values in weight%
19

Table 5. Mechanical properties for stored Al 2219.

Specimen No. Date Tested YS (ksi) UTS (ksi) Modulus (Msi) %El (1 in)

008–1C–1 04/10/1998 43.64 60.27 10.2 16.3

008–1C–2 04/10/1998 42.49 59.26 10.3 18.9

008–1C–3 04/10/1998 43.13 59.91 10.4 17.9

008–1C–4 04/10/1998 43.86 59.88 10.4 17.7

008–1C–5 04/10/1998 44.23 60.31 10.5 16.5

008–1C–6 04/10/1998 43.91 59.95 10.4 17.8

008–1C–7 04/10/1998 43.87 60.01 10.3 18.2

008–1C–8 04/10/1998 44.13 60.17 10.5 18

008–1C–9 04/10/1998 44.58 60.68 10.5 17.1

008–1C–10 04/10/1998 43.78 60.27 10.8 17.3

008–1C–19 04/10/1998 42.99 59.36 10.3 17.7

008–2C–2 04/10/1998 44.09 61.05 10.9 19.5

008–2C–3 04/10/1998 43.08 60.05 10.7 18.5

008–2C–4 04/13/1998 43.04 59.97 10.6 16.3

008–2C–5 04/13/1998 43.34 59.94 10.4 17.7

008–2C–6 04/13/1998 42.95 59.87 10.6 17.6

008–2C–7 04/13/1998 42.77 60.17 10.4 14.5

008–2C–8 04/13/1998 43.57 60.65 10.3 18.7

008–2C–9 04/13/1998 44.07 60.79 10.6 18.2

008–2C–10 04/13/1998 43.6 60.77 10.8 18.8

008–3C–1 04/09/1998 44.35 60.45 10.1 17.6

008–3C–2 04/09/1998 43.93 60.21 10.2 16.5

008–3C–3 04/09/1998 43.3 60.16 10 17.3

008–3C–4 04/09/1998 43.59 60.06 10.3 18.4

008–3C–5 04/09/1998 43.64 60.34 10.1 12

008–3C–6 04/09/1998 43.05 60.05 10.4 19.5

008–3C–7 04/09/1998 43.08 59.85 10.1 16.5

008–3C–8 04/09/1998 43.63 59.86 10.3 18.3

008–3C–9 04/09/1998 43.99 59.96 10.3 18.5

008–3C–10 04/09/1998 43.78 59.94 10.4 18.3

Mean 43.58 60.14 10.4 17.54

Standard Deviation 0.51 0.39 0.22 1.49

Direct Calculated A-Basis Value 42 59 – –

Minimum Required by

FED QQ–A–250/30 37 49 – 6
20

General Products Inc. fabricated two stringers according to the design requirements as shown 

in figure 15. They were heat-treated in accordance with MIL–H–6088, “Heat-Treatment of Aluminum 

Alloys” that requires aging at 177 °C (350 °F) for 18 hr to achieve a T87 temper.

10

Figure 15. Two stringers fabricated by General Products.

Five tensile coupons were sectioned from one stringer and tensile tested in accordance with 

ASTM B 557–84, “Tensile Testing.”2 These test results (table 6) clearly show the need for a modified 

heat-treatment to produce acceptable properties.

Table 6. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 18 hr, first set of test samples.

Specimen No. Date Tested YS (ksi) UTS (ksi) Modulus (Msi) Elongation (1 in)

SRB HT1 04/09/1998 45.4 60.7 10.1 9.8

SRB HT2 04/09/1998 44.7 60.7 10.5 9.5

SRB HT3 04/09/1998 45.5 61.1 10.5 10.4

SRB HT4 04/09/1998 45 60.4 10.6 11.6

SRB HT5 04/09/1998 45.4 60.9 10.7 10.8

Mean 45.2 60.76 10.48 10.42

Standard Deviation 0.34 0.26 0.23 0.83

FED QQ–A–250/30 51 64 6

Three additional specimens were sectioned from a plate originally intended for stringer fabrication to support the development of a longer aging treatment. These were aged in a modified Blue-M 

oven, programmed to ramp to an aging temperature of 177 °C (350 °F) at ≈2.5°C (5 oF) per min, hold 

at temperature for 24 hr, and then cool to 65 °C (150 °F). The samples were then removed and allowed 

to cool to ambient temperature. Mechanical testing, conducted in accordance with ASTM B 557–84, 

showed this process produced material that met the minimum requirements (table 7).2
21

Table 7. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 24 hr, second set of test samples.

Specimen No. YS (ksi) UTS (ksi) Elongation (1 in)

008–1c–11 51.87 66.03 10.8

008–1c–12 51.78 65.92 12.4

008–1c–13 51.51 65.84 10.5

Mean 51.72 65.93 11.23

Standard Deviation 0.187 0.095 1.021

Minimum Required by

FED QQ–A–250/30 51 64 6
22

Once the treatment cycle was established, 23 more samples were extracted from the panels and 

tested to verify the minimum requirement (table 8). The values were sufficiently close to the minimum 

requirement that USA recommended the modified heat treatment for this material.

Table 8. Mechanical property data for stored Al 2219, heat-treated at 177 °C (350 °F) 

for 24 hr, third set of test samples.

Specimen No. UTS (ksi) YS (ksi) Elongation (1 in)

008–1c–11 66.03 51.87 10.8

008–1c–12 65.92 51.78 12.4

008–1c–13 65.84 51.51 10.5

008–1c–17 64.2 50.3 10.5

008–1c–18 65.2 50.8 10.7

008–1c–09 65.7 51 10.6

008–1c–20 65.9 51.5 10.9

008–2c–11 65.9 51.2 10.4

008–2c–12 65.8 51 10.6

008–2c–13 66.1 51.3 10.5

008–2c–14 66.3 51.6 10.4

008–2c–15 65.7 51 10.5

008–2c–16 65.9 51.3 10.5

008–2c–17 66.1 51.1 10.7

008–2c–18 66.3 51.5 10.6

008–2c–20 66 51.4 10.6

008–3c–11 67 52.1 10.5

008–3c–12 67.3 52.4 10.3

008–3c–13 66.9 52.2 10.5

008–3c–14 67 52 10.6

008–3c–15 66.5 51.6 10.7

008–3c–16 66.8 51.8 10.5

008–3c–17 66.5 52.1 10.3

008–3c–18 65.8 51.4 10.5

008–3c–19 66.1 51.6 10.3

008–3c–20 65.8 51.1 10.8

Mean 66.1 51.479 10.623

Standard Deviation 0.627 0.481 0.393

Minimum Required by

FED QQ–A–250/30 64 51 6
23

As a result of these evaluations, stringers were fabricated and installed on S/N 20022 (fig. 16) in 

preparation for its return to flight. 

Figure 16. Exterior of S/N 20022 with callout of installed stringers.
24
25

4. CONCLUSIONS

Valuable methodologies were developed from this effort including the following:

• Using a hydraulic press to repair a damaged forward skirt.

• Correcting minor distortion that occurred during the debuckling procedure.

• Verifying material properties afterwards. 

All mechanical properties were found to either meet or exceed minimum design requirements, 

which supported the idea that a 25-percent strength reduction factor would provide a conservative estimate of the structure’s strength after repairs. S/N 20022 successfully returned to flight on April 19, 2001 

during STS–100. Plans call for it to continue in the SRB flight hardware flow.

Note: The original buckling problem was resolved at a later date by using saltwater-activated 

release mechanisms to keep the SRB parachutes attached until after splashdown.
26

APPENDIX A—TEST PLANS/REPORTS 

During the course of this work, the following test plans/reports were generated by USBI: 

JHH–002–97MP “Test Plan to Demonstrate Methodology for Locally Shrinking Forward Skirt 

S/N 20022 by Conducting Weld Passes,” USBI, 1997.

JHH–002–98MP “Results of Test Plan to Demonstrate Methodology for Locally Shrinking 

Forward Skirt S/N 20022 by Conducting Weld Passes,” USBI, 1998.

JHH–003–98MP “Vendor Qualification Requirements to Shrink Forward Skirt S/N 20022

by Conducting Weld Passes,” USBI, 1998.

JHH–005–98MP “Vendor Qualification Test Results for Shrinking Forward Skirt S/N 20022 by 

Conducting Weld Passes,” USBI, 1998.

JHH–005–99MP “Verification of 2219 Aluminum Material Properties After Long-Term Storage,” 

USBI, 1999.

JHH–002–00MP “Validation of the 25% Reduction in Material Properties for Forward Skirt 

S/N 20022,” Final Report, USA, MSFC–PEC Operations, August 11, 2000.
27

REFERENCES

1. “Welding Aluminum Alloys,” MSFC–SPEC–504C.

2. “Standard Methods of Tension Testing Wrought and Cast Aluminum and Magnesium Alloy 

Products,” ASTM B 557–84.

3. “Structural Welding Code, Aluminum,” ANSI/AWS–D1.2–90.

4. “Radiographic Inspection,” MIL–STD–453 (now superseded by “Standard Practice for Radiographic 

Examination,” ASTM E 1742).

5. “2219 Aluminum Alloy Plate and Sheet,” FED QQ–A–250/30.

6. “Standard Test Method for Tension Testing of Metallic Materials,” ASTM E 8.

7. “Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic 

Materials,” ASTM E 18.

8. Military Handbook, “Metallic Materials and Elements for Aerospace Vehicle Structures,” 

MIL–HDBK–5 (now superseded by “Metallic Materials Properties Development of Standardization 

Handbook.” MMPDS–03).

9. “Hardness and Conductivity Inspection of Wrought Aluminum Alloy Parts,” AMS 2658.

10. “Heat Treatment of Aluminum Alloys,” MIL–H–6088.
28

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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18

298-102

Unclassified Unclassified Unclassified Unlimited

The Repair and Return to Flight of Solid Rocket Booster Forward Skirt 

Serial Number 20022

T.W. Malone, C.S. Jones, and J.H. Honeycutt, Sr.*

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

National Aeronautics and Space Administration

Washington, DC 20546–0001

Prepared by the Materials and Processes Laboratory, Engineering Directorate

*JE Jacobs Sverdrup, Huntsville, AL

Unclassified-Unlimited

Subject Category 26

Availability: NASA CASI 301–621–0390

On April 5, 1991, a solid rocket booster (SRB) forward skirt serial number (S/N) 20022 sustained buckling damage 

during water impact after the launch of Space Transportation System Flight 37 (STS–37). As of that date, five 

forward skirts had been lost during water impact. Repair attempts began with the least damaged skirt available 

(S/N 20022). Special hydraulic tooling was used to remove buckled areas of the skirt. Afterwards, its aft 

clevis pinholes were found to be out of alignment with the redesigned solid rocket motor (RSRM) check 

gauge, but weld passes were used to correct this condition. Meanwhile, USA Analytics generated mechanical 

property data for buckled and subsequently debuckled material. Their analysis suggested that structural 

integrity might be improved by adding stringer reinforcements, stiffeners, to the aft bay section of the skirt. 

This improvement was recommended as a fleet modification to be implemented on a case-by-case basis. 

36

M–1231

June 2008 Technical Memorandum

NASA/TM—2008–215411

flight vehicles, Space Shuttle boosters, skirts, welded structures, stringers, aluminum 

alloys, aging (metallurgy), heat-treatment, mechanical properties, tensile properties, 

materials tests, and materials science.
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