Tensile stress areas are also located on the insides of the straight barrels, but these surfaces are similarly sheltered by their location. However, gouges can cause localized increases in the link stress and can be harmful if they are located in areas of tensile stress, especially if they are perpendicular to the direction of stress. Refer to Figure 1.
Figure 2 shows nicks of varying degrees of severity. Reading clockwise, at three o’clock there is a longitudinal mark in a compressive stress area. Since it is longitudinal and located in a compressive stress area, its effect is mitigated, but good workmanship calls for it to be filed out by hand.
At about five o’clock there is a deep transverse nick in an area of high shear stress. A similar nick is located at six o’clock in the zone of maximum tensile stress. Both of these nicks can create a potentially dangerous escalation of the local stress and must be filed out with careful attention to not damage other parts of the chain link or chain. A nick that was located at eight o’clock has been filed out properly. Although the final cross section is smaller, the link is stronger because the stress riser effect of the notch has been removed. The remaining cross section can now be evaluated for acceptablity by measuring it and applying the criterion for worn chain. See the “Wear Allowances Table” below.
Wear and Corrosion
When used in rigorous material handling applications, chain can easily become worn or corroded. It is important to inspect chain for defects on a regular basis to avoid an unsafe lifting condition or even operator injury. When corrosion and wear occur, it results in a reduction of link cross-section which can lead to decreased strength of the chain.
Corrosion can occur anywhere chain comes in contact with harsh chemicals, water or when it is used in tough environments. Wear can occur in any portion of a link that is subject to contact with another surface.
The natural shape of chain confines wear, for the most part, to only two areas. These are, in order of importance, (a) at the bearing points of interlink contact, and (b) on the outsides of the straight side barrels that may be scraped from dragging chains along hard surfaces or out from under loads.
This example illustrates the condition of interlink wear and shows how to inspect for it. Notice how easily such wear can be detected by collapsing the chain to separate each link from its neighbors. An operator or inspector can also check for corrosion using the same method.
When chain wear or corrosion is observed, the next step is to determine how severe the damage is and if the chain can still be safely used.
General surface corrosion can be removed by cleaning and oiling the chain. If pitting is observed after cleaning and oiling, remove from service. Next, the operator should take a caliper measurement across the worn section of chain and compare it to the minimum allowable dimension for that chain.
See the chart below for minimum section dimensions or chain wear allowances for Grade 80 and 100 Chain. If the chain does not meet these minimum dimensions, it should be removed from service and replaced.
Stretch and Chain Elongation
A visual link-by-link inspection is the best way to detect dangerously stretched alloy chain links.
Reach should also be measured from the upper bearing point on the master link to the bearing point on the lower hook. The smallest sign of binding or loss of clearance at the juncture points of a link indicates a collapse in the links’ sides due to stretch. Any amount of stretch indicates overloading, and the chain should be removed from service.
Note that a significant degree of stretch in a few individual links may be hidden by the apparent acceptable length gauge of the overall chain. This highlights the importance of link-by-link inspection.
Alloy steel sling chain typically exhibits well over 20% elongation before rupture. The combination of elongation and high strength provides energy absorption capacity. However, high elongation or stretch, by itself, is not an adequate indicator of shock resistance or general chain quality and should not be relied upon by riggers to provide advance warning of serious overloading and impending failure. Overloading must be prevented before it happens by selecting of the proper type and size of slings. Again, any amount of stretch is overloading and the chain should be removed from service.
There is no short-cut method that will disclose all types of chain damage. Safety can only be achieved through proper inspection procedures. There is no adequate substitute for careful link-by-link scrutiny.
OSHA Chain Sling Inspection
Since first published on July 27, 1975, the OSHA Chain Sling Inspection section has undergone very few changes. These regulations have and continue to serve as a comprehensive guide for those responsible for chain sling inspection.
Specifically, the applicable sections of the Code of Federal Regulations (29 CFR 1910.184) include:
Each day before being used, the sling and all fastenings and attachments shall be inspected for damage or defects by a competent person designated by the employer. Additional inspections shall be performed during sling use, where service conditions warrant. Damaged or defective slings shall be immediately removed from service.
1910.184 (e)(1) Sling identification
Alloy steel chain slings shall have permanently affixed durable identification stating size, grade, rated capacity, and reach.
1910.184(e)(2)(i): Hooks, rings, oblong links, pear-shaped links, welded or mechanical coupling links or other attachments shall have a rated capacity at least equal to that of the alloy steel chain with which they are used or the sling shall not be used in excess of the rated capacity of the weakest component.
1910.184(e)(2)(ii): Makeshift links or fasteners formed from bolts or rods, or other such attachments, shall not be used.
1910.184(e)(3)(i): In addition to the inspection required by paragraph (d) of this section, a thorough periodic inspection of alloy steel chain slings in use shall be made on a regular basis, to be determined on the basis of (A) frequency of sling use; (B) severity of service conditions; (C) nature of lifts being made; and (D) experience gained on the service life of slings used in similar circumstances. Such inspections shall in no event be at intervals greater than once every 12 months.
1910.184(e)(3)(ii): The employer shall make and maintain a record of the most recent month in which each alloy steel chain sling was thoroughly inspected, and shall make such record available for examination.
1910.184(e)(3)(iii): The thorough inspection of alloy steel chain slings shall be performed by a competent person designated by the employer and shall include a thorough inspection for wear, defective welds, deformation and increase in length. Where such defects or deterioration are present, the sling shall be immediately removed from service.
Please note that while the requirements under (d) for daily inspections are not explicit as to scope or maintenance of records, it is possible that individual OSHA inspectors may have different views on conformity.
However, the minimum 12-month interval inspections required under (e) call for a thorough inspection and written records. It is this thorough type of inspection that the procedures recommended in our Rigging Catalog and CMCO Training Classes are designed to satisfy.
Of course, the fundamentals are equally applicable to the more cursory daily inspections made by riggers, users or inspectors (individuals deemed a “competent person”) and will enable them to fulfill their responsibility efficiently.
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