PRODUCT SUPPORT PROGRAM FOR REWORKING WELDS IN THE CENTER SECTION OF THE FRAME ASSEMBLY ON CERTAIN 794 AC, 796 AC AND 798 AC OFF-HIGHWAY TRUCKS Caterpillar

PRODUCT SUPPORT PROGRAM FOR REWORKING WELDS IN THE CENTER SECTION OF THE FRAME ASSEMBLY ON CERTAIN 794 AC, 796 AC AND 798 AC OFF-HIGHWAY TRUCKS

Usage:

TEBE9049-01

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23Apr2019

(Revised 17May2019)

U-243

A-203

D-214

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Before/After	PRODUCT SUPPORT PROGRAM FOR REWORKING WELDS IN THE CENTER SECTION OF THE FRAME ASSEMBLY ON CERTAIN 794 AC, 796 AC AND 798 AC OFF-HIGHWAY TRUCKS
7755 7051 0679		PS46236

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NOTE:

Caterpillar’s obligations under this Service Letter are subject to, and shall not apply in contravention of, the laws, rules, regulations, directives, ordinances, orders, or statutes of the United States, or of any other applicable jurisdiction, without recourse or liability with respect to Caterpillar.

NOTE:

This Program must be administered either before or after failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS46236" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and "T" as the SIMS Description code. If administered after failure, use "96" as the Warranty Claim Description Code, and "Z" as the SIMS Description Code.

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NOTE:

The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.

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NOTE:	This Revised Service Letter replaces the 23Apr2019 Service Letter. Changes have been made to the Affected Product and Rework Procedure.

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TERMINATION DATE

30Apr2021

PROBLEM

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Certain welds in the center section of the frame assembly may not meet the weld criteria to achieve expected frame life and can fail on certain 794 AC, 796 AC and 798 AC Off-Highway Trucks. If an existing weld fails it can cause a frame crack to develop in the surrounding plate material as shown in Images 1 (bracket assembly for hydraulic lines routing), 2 (cold weather attachment mounting, 3 (drive pump plate assembly mounting) and 4 (frame doubler plate).

AFFECTED PRODUCT

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Model	Identification Number
794 AC	HRT00100-00102 MN500051-00056 MT500100-00143
796 AC	HRZ00500-00502
798 AC	ST700400-00402

PARTS NEEDED

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No parts needed for this program

ACTION REQUIRED

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Refer to the attached Rework Procedure.

NOTE: In some cases backing strips may be required as welding supplies.

NOTE: When applicable, it is recommended that this program should be implemented in conjunction with the 03Apr2019 Service Letter PI32985 - TEBE8746.

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Image1

Image2

Image3

Image4

SERVICE CLAIM ALLOWANCES

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Product smu/age whichever comes first	Caterpillar		Dealer Suggested		Customer Suggested
Product smu/age whichever comes first	Parts %	Labor Hrs%	Parts %	Labor Hrs%	Parts %	Labor Hrs%
0-48000 hrs, 0-60 mo	100.0%	100.0%	0.0%	0.0%	0.0%	0.0%

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NOTE: This is a 24.0-hour job
This is a 24 hour job, including time required for any disassembly, weld repair and any reassembly. An additional 2 hours will be allowed for a partial through thickness crack if present. An additional 4 hours will be allowed for a through thickness crack if present.

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PARTS DISPOSITION

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Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.

Rework Procedure

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Use the following procedure to rework welds in the center section of the frame assembly. Welds on the drive pump plate assembly mounting (Image 1.2.1), bracket assemblies for hydraulic lines routing (Image 1.2.2), cold weather attachment mounting (Image 1.2.3) and doubler plate (1.2.4) on the inside left and right sides of the frame will require weld repairs.

Image1.1.1

1. The first course of action is to identify if a crack exist such as shown in Images 1.2.1, 1.2.2, 1.2.3 and 1.2.4 and if so what is the extent of the crack. The next objective is to determine if the crack depth has propagated through the thickness of the plate. The crack depth will determine the extent of the repair. Utilize a grinder, or air arc rod and either magnetic particle, or dye penetrant testing equipment.

Refer to "PROCEDURE IF PARTIAL THROUGH THICKNESS CRACK IS PRESENT" section for a partial through thickness crack. Once crack has been repaired proceed to" PROCEDURE IF NO CRACK IS PRESENT" section.

Refer to "PROCEDURE IF THROUGH THICKNESS CRACK IS PRESENT" section for a through thickness crack. Once crack has been repaired proceed to" PROCEDURE IF NO CRACK IS PRESENT" section.

2. If no crack exists, proceed to "PROCEDURE IF NO CRACK IS PRESENT" section.

Image1.2.1

Image1.2.2

Image1.2.3

Image1.2.4

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PROCEDURE IF PARTIAL THROUGH THICKNESS CRACK IS PRESENT

Partial Through Thickness Crack Repair

The following section assumes that preheat (if required), crack excavation, and NDT verification have taken place and it has been verified that the crack has been completely removed and did not extend through the plate thickness. If so, the area excavated should appear similar (depending on crack depth to wall thickness) to that shown in Image 1.3.1.

Note: A previous crack repair must use ultrasonic testing to verify crack has been completely removed.

Image1.3.1

1. The following Images 1.4.1, 1.4.2 and 1.4.3 demonstrate the sequence of steps necessary to obtain the desired joint configuration prior to welding.

Image1.4.1

Image1.4.2

Image1.4.3

2. After the crack removal has been verified, reinstate by welding and sand the excess weld material flush to the profile of the surface of the surrounding plate.

Image1.5.1

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PROCEDURE IF THROUGH THICKNESS CRACK IS PRESENT

Through Thickness Crack Repair

The following section assumes that preheat (if required), crack excavation, and NDT verification have taken place and it has been verified that the crack has been completely removed and did extend through the plate thickness. If so, the area excavated should appear similar (depending on crack depth to wall thickness) to that
shown in Image 1.6.1.

Note: A previous crack repair must use ultrasonic testing to verify crack has been completely removed.

Image1.6.1

1. Images 1.7.1 and 1.7.2 demonstrate the approximate dimensions for a weld joint requiring a permanent backing strip.

Image1.7.1

Image1.7.2

2. The dimension of the permanent steel, backing strip will depend on the configuration of the excavation.

Every attempt should be made to accommodate a single, continuous strip that runs the full length of the weld joint. A 6.4 mm (0.25 inch) thick by 38 mm (1.50 inch) wide by the required length are the typical dimensions required for most applications.

The steel backing strip material can be any common structural steel such as ASTM A36. Attach wire (or other means) to the backing strip and insert through the root opening/gap and pull back flush to the inside of the plate surface.

The thickness of the backing strip should be kept to a minimum to assist with the insertion process. The thicker the backing strip the more difficult it will be to insert through the gap into an enclosed cavity. A 6.4 mm (0.25 inch) thick backing strip is the minimum that should be used and is sufficient enough to prevent burn through using the welding parameters specified.

Select a backing strip width that will ensure a minimum overlap of 3 mm (0.12 inch) of the backing strip to both sides of the weld joint along the entire length. Refer to Image 1.7.2. Minimize the gap (0 mm if possible) between the backing strip and the inside plate surface.

3. Tack weld backing strip in place. Remove wire/rod and grind one-half the thickness of the tack welds prior to finish welding to ensure proper fusion between tack welds and fill passes.

4. After the crack removal has been verified, reinstate by welding and sand the excess weld material flush to the profile of the surface of the surrounding plate. Refer to Image 1.5.1.

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PROCEDURE IF NO CRACK IS PRESENT

1. Remove four bosses on the inside right side of frame that are shown in Image 1.10.1.

Note: If bosses are being used for cold weather attachment, the bosses can not be removed and fillet welds on bosses must be TIG dressed.

2. After bosses are removed, fill and blend sand any divots remaining flush to the profile of the surface of the surrounding plate.

Image1.10.1

3. Locate the bracket assembly on the inside right side of frame that is shown in Image 1.11.1. Scribe lines to mark position of bracket assembly and center punch the four corner locations for reattachment of bracket assembly after the repair.

Note: Disassembly of hose assemblies and hose clamps from bracket assembly will be required to complete weld repair as shown in Image 1.11.2.

Image1.11.1

Image1.11.2

4. Remove intermittent fillet welds holding bracket assembly in place and as shown in Image 1.11.1.

5. Remove bracket assembly. Fill and blend sand any divots remaining flush to the profile of the surface of the surrounding plate.

6. Use scribe lines from Step 3 and dimensions as shown in Image 1.12.1 to relocate the bracket assembly.

Image1.12.1

7. Weld bracket assembly all around with 5 mm (0.20 inch) flare bevel groove weld. Refer to Image 1.13.1.

8. TIG dress the weld toe touching the frame side all the way around the bracket assembly. For details regarding TIG dressing follow the POSTWELD TREATMENT - TIG DRESSING section of this procedure.

Image1.13.1

9. Locate bracket assembly on the inside left side of frame that is shown in Image 1.14.1. Scribe lines to mark position of bracket assembly and center punch the four corner locations for reattachment of bracket assembly after the repair.

Note: Disassembly of hose assemblies and hose clamps from bracket assembly will be required to complete weld repair as shown in Image 1.14.2.

Image1.14.1

Image1.14.2

10. Remove intermittent fillet welds holding bracket assembly in place and as shown in Image 1.14.1.

11. Remove bracket assembly. Fill and blend sand any divots remaining flush to the profile of the surface of the surrounding plate.

12. Use scribe lines from Step 9 and dimensions as shown in Image 1.15.1 to relocate the bracket assembly.

Image1.15.1

13. Weld bracket assembly all around with 5 mm (0.20 inch) flare bevel groove weld. Refer to Image 1.16.1.

14. TIG dress the weld toe touching the frame side all the way around the bracket assembly. For details regarding TIG dressing follow the POSTWELD TREATMENT - TIG DRESSING section of this procedure.

Image1.16.1

15. Locate drive pump plate assembly mounting on the inside right side of frame that is shown in Image 1.17.1. Inspect weld all around mount assembly for correct 10 mm (0.39 inch) fillet weld size. If required, repair the weld to achieve the correct fillet weld size.

16. TIG dress the weld toe touching the frame side all the way around the mount assembly. For details regarding TIG dressing follow the POSTWELD TREATMENT - TIG DRESSING section of this procedure.

Image1.17.1

17. Repeat Steps 15 and 16 for the drive pump plate assembly mounting on the inside left side of frame.

18. Locate the doubler plate on the inside right side of frame that is shown in Image 1.19.1. Inspect the weld for the correct 12 mm (0.47 inch) x 19 mm (0.75 inch) fillet weld size. If required, repair the weld to achieve the correct fillet weld size.

Note: This assumes no cracks or defects are present. If a crack or defect is present, follow the PARTIAL THROUGH THICKNESS CRACK or THROUGH THICKNESS CRACK procedure to excavate the crack or defect and weld back to profile. Use magnetic particle, or dye penetrant testing equipment to verify crack or defect.

19. TIG dress the weld toe touching the frame side as shown in Images 1.19.2 and 1.19.3. For details regarding TIG dressing follow the POSTWELD TREATMENT - TIG DRESSING section of this procedure.

Image1.19.1

Image1.19.2

Image1.19.3

20. Repeat Steps 18 and 19 for the doubler plate on the inside left side of frame.

21. Locate the right side front cross tube to main rail transition on the inside right side of frame that is shown in Image 1.21.1. Inspect area for the correct weld joint transitioning between the cross tube and main rail.

Note: This assumes no cracks or defects are present. If a crack or defect is present, follow the PARTIAL THROUGH THICKNESS CRACK or THROUGH THICKNESS CRACK procedure to excavate the crack or defect and weld back to profile. In Image 1.21.2 examples are shown of unsatisfactory transitions and a previous crack repair. If existing weld repairs are present, use magnetic particle, or dye penetrant testing equipment to verify no cracks are present before blend sanding transitions.

Image1.21.1

Image1.21.2

22. After area is visually inspected, blend sand any transitions that are not currently transitioned. Image 1.22.1 shows a completed center tube to main rail transition. A 40 mm (1.57 inch) radius needs to be added to transition the tube weld to the main rail shown in Figure 1.22.1.

Note: It may be necessary to add weld material to the area shown in Image 1.22.1 to obtain a 40 mm (1.57 inch) radius. If weld material is added, extend any weld starts and stops 100 mm (3.94 inch) past the radius area shown in Image 1.22.1

Image1.22.1

23. Repeat Steps 21 and 22 for the right side rear cross tube to main rail transition on the inside right side of frame.

24. Repeat Steps 21 and 22 for the left side front and rear cross tube to main rail transition on the inside left side of frame.

25. Visually inspect the right side cross tube to nose cone fillet welds for cracks or defects as shown in Image 1.24.1 and 1.24.2. If a crack or defect is present, follow the PARTIAL THROUGH THICKNESS CRACK or THROUGH THICKNESS CRACK procedure to excavate the crack or defect and weld back to profile. Use magnetic particle, or dye penetrant testing equipment to verify crack or defect.

26. Repeat Step 25 for the left side cross tube to nose cone fillet welds.

Image1.24.1

Image1.24.2

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POSTWELD TREATMENT ? TIG DRESSING

The fatigue performance of fabricated structures involving fillet welded attachments to highly stressed members is, among other things, controlled by the profile or geometry of the weld toe. Fatigue performance improvement can be achieved through alteration of the original, as-welded toe profile by several post weld treatment options. This procedure describes a method whereby an electric arc is used to reduce and/or remove unfavorable profiles/stress risers thus creating a smooth, seamless transition from one component to the next.

Equipment Requirements:
? GTAW (TIG) Power Supply and torch capable of 200 amps (min. 60% duty cycle) with
hand/foot current control (Polarity ? DC Negative).
? Shielding gas ? 100% Argon (& flow meter)
? Electrode ? Lanthanated, Ceriated or Thoriated Tungsten [3/32? (2.4 mm) dia.]
? ER70S-2 filler metal (1/16? dia.) if needed
? Hand or foot current control
? Grinder - Pneumatic or Electric with Carbon Steel Wire Wheel Attachment
? Aluminum oxide grinding wheel to sharpen tungsten electrode.
? Radius Gages

Method:
The first steps to ensure a proper TIG dressing are cleanliness and tungsten electrode preparation. The fillet weld and surrounding base metal must have all contaminants thoroughly removed. It is imperative that all paint, rust, dirt, oil, scale, silicate islands, etc. are non-existent. This can be accomplished quickly via a grinder with a carbon steel wire attachment. Next, prepare a 3/32? (2.4 mm) tungsten electrode to the dimensions shown below. Grinding striations should run parallel not transverse.

Image1.25.1

Adjust shielding gas flow rate to 15-25 CFH and current control to approx. 200 amps. If a ramp down control is present on the power source, utilize to ensure proper crater fill control.

A number of different techniques exist for TIG dressing. This is due to the variability of the contour of the fillet weld toe that must be re-shaped. Therefore, either a stringer or weave manipulation of the torch can be employed so long as the goal of a smooth, contoured radius of 5 mm minimum exists between the base material and weld metal. Both the stringer and weave techniques are presented below.

Image1.26.1

Image1.26.2

Once TIG dressing is completed the area needs to be cleaned and painted to prevent pitting due to corrosion.

Note 1: Poorly shaped fillet welds with 90-100 degree transition angles to the base material will probably require several overlapping TIG dressing runs to properly smooth out the weld toe transition region.

Note 2: TIG dressing can be conducted in the vertical position as long as it is performed in a downhill progression.

Note 3: If undercut or other circumstances require the addition of filler metal, this can be accomplished by hand feeding ER70S-2 (1/16? dia.) into the weld pool and then repeat the TIG dressing to achieve desired toe radius/profile.

Inspect using a radius gage to ensure a 5 mm min. radius.

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Acceptance Criteria (Welding)