PRODUCT SUPPORT PROGRAM FOR REWORKING FRAME ASSEMBLY FRONT AND REAR PEDESTAL WELDS ON CERTAIN 794 AC, 796 AC, AND 798 AC OFF-HIGHWAY TRUCKS Caterpillar

PRODUCT SUPPORT PROGRAM FOR REWORKING FRAME ASSEMBLY FRONT AND REAR PEDESTAL WELDS ON CERTAIN 794 AC, 796 AC, AND 798 AC OFF-HIGHWAY TRUCKS

Usage:

TEBE9155-01

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10May2019

(Revised 17May2019)

U-279

A-234

D-247

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Before/After	PRODUCT SUPPORT PROGRAM FOR REWORKING FRAME ASSEMBLY FRONT AND REAR PEDESTAL WELDS ON CERTAIN 794 AC, 796 AC, AND 798 AC OFF-HIGHWAY TRUCKS
7755 0679 7051		PS46258

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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 "PS46258" 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 10May2019 Service Letter. Changes have been made to the Rework Procedure.

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TERMINATION DATE

31May2021

PROBLEM

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The frame assembly front and rear pedestal welds are undersized. The weld throat depth is insufficient to achieve expected frame life and can fail on certain 794 AC, 796 AC, and 798 AC Off-Highway Trucks as shown in Image 1. If an existing weld fails it can cause a frame crack to develop in the surrounding plate material.

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.

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Image1

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 10.0-hour job
This is a 10 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 the frame assembly front and rear pedestal welds. Welds on the 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 Image 1.2.1 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.

NOTE: If a through thickness crack is present across the width of a plate contact product support. Additional weld repairs may be required not stated in this service letter.

Refer to "PROCEDURE IF WELD THROAT CRACK ONLY IS PRESENT" section for a weld throat 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

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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 WELD THROAT CRACK ONLY IS PRESENT

Weld Throat Crack Repair

1. Inspect the right and left hand rear pedestal fillet welds at four locations (A) for cracks or defects.

Image1.10.1

2. If a crack or defect is present as shown in Image 1.11.1, excavate the fillet weld using air arc or grinding and reinstate the removed weld.

Image1.11.1

3. Inspect the right and left hand front pedestal groove welds at four locations (B) for cracks or defects.

Image1.12.1

4. If a crack or defect is present as shown in Image 1.11.1, excavate the groove weld using air arc or grinding and reinstate the removed weld.

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PROCEDURE IF NO WELD CRACK IS PRESENT

1. If no crack is present and no repair is required, additional weld material needs to be added to increase the fillet weld size at four locations (A). The fillet weld needs to increase from, 12 mm (0.47 inch) leg size to 18 mm (0.71 inch) leg size. Image 1.14.1 shows a cross section of the existing fillet weld size in red with the new 18 mm (0.71 inch) leg size in black applied.

Note: Disassembly of a mounting bracket for the inverter cabinet high voltage cables (right side), mounting brackets for brake hose assemblies (left side) and wiring harness connections (both sides) will be required to complete weld repair.

Image1.14.1

3. If no crack is present and no repair is required, additional weld material needs to be added to the existing 12 mm (0.47 inch) groove weld at four locations (B). Image 1.15.1 shows a cross section of how the finished weld profile should appear with the additional 8 mm (0.31 inch) fillet weld applied.

Note: Disassembly of the grab irons on the front pedestals will be required to complete weld repair.