Rope inspection or rather. pre-inspection

Be prepared with these five steps

By John Manka

John Manka is manager-cranes for Bridon American Corp., WilkesBarre Pa. He has served as a wire rope field engineer for Bridon for more that?. 21 years.

one of the easiest inspections someone can perform on a mobile crane is on the tires. The sidewall clearly shows the information you might need. It has the specifications, load rating, manufacturer name and brand, and even the manufacturing run lot number. The tread depth is easily checked, and the overall condition can be quickly evaluated.

When examining wire rope, we are not so lucky. There are no specifications, ratings, names or lot numbers printed on the rope's exterior. Therefore, we are faced with the potentially complex task of rope identification. If the rope is new, the rope manufacturer may be identified by a colored strand. However, not all rope manufacturers use colored strands; those who do may not have their full range identified. In addition, there are literally hundreds of different rope constructions on the market today from various manufacturers.

Usually wire rope inspection deals with the close examination of the wire rope itself with no regard to its construction, suitability for the application and/or breaking strength. Often these ropes are examined, pass inspection and are okayed for continued use. The danger is that the ropes may be incorrect in construction and required breaking strength, and that this information has not been transferred or calculated for in the load chart The bottom line is the crane may be operating with a wire rope that does not meet the requirements of OEM specifications and/or ASME/ANSI B30.5.

For the first-time inspection, or third-party annual inspection, the inspector should follow these steps:

´ Identify the rope.

* Verify breaking strength.

* Verify code for retirement criteria and design factors.

* Review inspection history.

* Inspect the rope.

Identify rope construction

The first step in inspection is to identify the rope diameter and construction. This is done by an actual measurement of the rope diameter, and a physical count of the number of strands and number of wires in each strand. The Wire Rope Users Manual is helpful in matching this information with certain rope constructions. It may also be necessary to match the rope construction to the particular rope manufacturer's catalog.

The wire rope manufacturer's test certificate should make this part of the inspection easier. The distributor or crane manufacturer should have these on file. Request a copy of this wire rope test certificate, and file it. Also keep a laminated copy in the cab so any inspector can see it on demand.

The wire rope construction is listed on the test certificate and should be compared to what is on the crane. If it matches, then it is now necessary to verify the rope breaking strength.

Verify breaking strength

The breaking strength of the rope is listed on the test certificate. This value can be confusing, but the following will attempt to clarify the terminology.

ASME/ANSI B30.5 Standards (Mobile and Locomotive Cranes) refer to nominal breaking strengths. Design factors specified in these standards use nominal breaking strengths in their calculations.

Nominal strength is the published catalog strength calculated by a standard procedure that is accepted by the wire rope industry. The wire rope manufacturer designs wire rope to this strength, and the user should consider this strength when making calculations.

Additionally, there is a minimum acceptance strength. Minimum acceptance strength is that strength that is two-anda-half percent lower than the catalog or nominal strength. This tolerance is used to offset variables that occur during sample preparation and actual physical testing of a wire rope.

For example, a rope with nominal breaking strength of 100,000 pounds would have to achieve an actual breaking load by test to destruction of at least 97,500 pounds.

When a minimum breaking strength is quoted, then it would be the same as the minimum acceptance strength. A minimum breaking strength of 100,000 pounds would require an actual breaking load by test to destruction of at least 100,000 pounds.

In addition to minimum breaking loads, some rope companies in Europe use a calculated minimum breaking force. The calculated minimum breaking force is the summation of the actual breaking force of all the wires in the rope multiplied by a spinning loss factor.

The spinning loss factor is determined by prior testing for each rope construction and wire grade. At the present time, this method is not acceptable for design factor calculations in the United States unless it is backed by an actual test to destruction certificate for the item supplied. If the certificate indicates that the minimum breaking load strength was confirmed by the International Standard ISO 3108-1974, or its latest revision, then it would be considered acceptable for design factor calculations in the United States. Note: The proposed National Wire Rope Standard uses the new terminology mint . mum breaking force in place of nominal and minimum breaking strength.

Again, the test certificate should be made easily available for the rope inspector. It is the only document that can assure that the rope in question is in compliance. Get a copy of this wire rope certificate with every new crane to avoid problems during inspection and future rope replacement.

Verify applicable code

Once the rope construction and its breaking strength are known, you will need to see if it meets the applicable code. 1330.5 states that the wire rope design factor is 3.5:1 for running ropes. If the rope is a rotation-resistant wire rope construction, then the design factor is 5:1 for the same application.

These two design factors have caused many cranes to operate out of code in the United States. To illustrate this, table A shows effective lifting capacities of a one inch diameter rope on a mobile crane.

A common practice is to substitute a 19x7 or 8x19 rotation-resistant construction for a 6xl9 wire rope classification to solve a block spinning problem. The chart shows that the crane's lifting capacity may be reduced by as much as 42.8 percent if a 19x7 wire rope is selected.

A similar practice is to substitute a 19x7 rope construction for Dyform-18 on rental hydraulic cranes. This is often done because users complain about the cost of replacement if the rope is damaged. This may be a valid argument only if the crane is de-rated by 26.6 percent before you hand the keys to the operator.

A 50-ton crane that has suddenly been de-rated to 36.7 tons does not sound very appealing. In addition, using 19x7 wire rope for multiple part reeving is not recommended. This is essentially why the higher strength high performance rotation -re s i stant ropes like Dyform34LR are finding their way onto cranes. They bring lifting capacities into line, and their improved rotation-resistance characteristics help prevent cabling on long falls.

Review inspection history and inspect the rope

Reviewing the inspection history is a time saver. If the rope history indicates rope removal due to localized damage in a particular area, then it would make sense to inspect this area first.

The final step is the actual wire rope inspection, which you can do with confidence now that you have identified the rope construction and verified it is correct for its intended application.

With all the new rope constructions in metric and imperial sizes. it is increasingly difficult to apply simple wire rope knowledge when performing a wire rope inspection. Good preparation prior to the actual inspection, along with the wire rope test certificate, makes the inspection easier, accurate and within compliance.

Reprinted with permission from: Bridon American Wire Rope. 1997