Localized Corrosion Deterioration.

TB 9-2510-242-40

of the frame structure, chemical or erosive action, electrolysis, local wear, or an improper design feature. In some cases,

such as deep pitting and scrapes, deterioration is easy to detect and measure. In other cases, such as with the general

corrosion of age, it is impossible to establish the degree of deterioration without a very careful and thorough examination.

In these cases the only practical way of determining the degree of frame deterioration is to measure the thickness of the

member in question and compare it to the original thickness in undamaged areas of similar members. After detecting

deterioration and determining its degree, judgment is required to evaluate and determine to what extent repairs are

necessary.

b. Overall Corrosion Deterioration. Overall frame corrosion deterioration is an indication of inadequate

maintenance or improper application of the protective coating system. The extent (area) of corrosion deterioration and

loss of material thickness must be determined. An overall 10 percent loss of material thickness is approximately a 10

percent loss of frame strength. Overall strength losses of up to 15 percent can be tolerated as long as there are no signs

of greater losses at the higher stress areas: suspension support points, drawbar connection points, mounting brackets,

and points for carried loads. When overall loss of material thickness is 15 percent or less, remove all corrosion and old

paint and treat and repaint the frame as originally specified. Frames having more than a 15 percent overall loss of

material thickness are nonrepairable, and should be scrapped.

c. Localized Corrosion Deterioration. Localized corrosion deterioration in a frame is an indication of inadequate

structural strength at a specific location. The course of localized corrosion deterioration begins with excessive metal

flexing due to unknown stresses, proceeds successively with cracking of the structure's protective coating system and

admittance of moisture, and ends with the resulting corrosion damage. Examples of localized corrosion deterioration are

deep pits in a specific area, along the edges of structural shapes, and in bands/belts around welded or bolted joints.

Depending upon the degree of deterioration, repairs range from cleaning, treating, and strengthening the stressed area to

replacing a frame segment or member. Repairs are accomplished as follows.

(1) Remove Corrosion. Each corroded area shall be thoroughly cleaned down to a bright, bare metal surface.

To avoid stress concentrations, all cleaned surfaces shall be free of sharp corners and curves.

(2) Analyze Stressed Areas. Measure the area and residual material thickness of each cleaned corroded area.

Use these characteristics to determine the residual frame strength of the corroded area.

(3) Design and Fabricate Reinforcement Parts. Design and fabricate reinforcement parts necessary to

strengthen each damaged area. Determine the cross-sectional area of the damaged portion of the trailer and the cross-

sectional area of that portion when new. Areas having a frame thickness loss of less than 15 percent shall be reinforced

to their original design thickness. When deterioration results in a 15 to 50 percent loss of frame thickness, the thickness

of the reinforced area shall be increased to 50 percent more than the original design thickness.