15.techtips ropedefects en

7/27/2019 15.TechTips RopeDefects En

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Phone (US): 1.706.235.6315 Toll free: 866.54BRUGG (542.7844) Fax: 1.706.235.6035 info: [email protected] www.bruggrope.comTelfono (E.U.): 1.706.235.6315 Llamada gratuita: 866.54BRUGG (542.7844) Fax: 1.706.235.6035 info: [email protected] www.bruggrope.com

TECH TIPS: ROPE DEFECT

Hoist Ropes: Why mustthey be i nspected?

A hoist rope is not made to last forever. This is a

useful fact, as the kinds of wear that appear on a rope

can indicate areas of problems within an installation

and provide a professional with vital clues on how to

address them before catastrophic damage occurs.

If a rope were ever designed to be impervious to

system stresses, or even the forces of friction, it

could well prove to be destructive to surrounding

components that could never hope to be able

to achieve such high tolerances. In addition to

the impracticality and inefficiency of having a

perfectrope, such an item would not be economical

for use in any but the most rare kind of installation.

Since no perfect rope exists, it is up to the

industry professional to periodically review the ropeto make sure it is discarded before it becomes

operationally unsafe, and to detect any abnormal

damage caused by external influences.

Hoist Ropes: How oftenmust t hey be inspected?

ASME 17.1-2010/CSAT B44-10 recommends

periodic inspections for electric and hydraulic elevators

every 6 months, with evaluative tests performed every

12 months. This schedule is also dependent upon

environmental factors, the frequency of usage and

type of usage, quality of

maintenance, age and the condition of the installation.

In addition to routine inspections, professionals

also recommend that ropes be checked after initial

installation, and soon after the first wire breaks have

been detected. One should inspect ropes more fre-

quently in cases of abnormal loading. Ropes should

be reviewed prior to usage if machinery has been idle

for an extended period of time, or if that lifting system

has been dismantled, moved to another location, andreused.

Additionally, DIN standards mandate that sheaves,

rope drums and compensation sheaves be examined

whenever a new rope has been installed.

For questions concerning details on the frequency

of rope inspection, relevant rope discard criteria, or osheave and drum groove diameters, consult the

applicable international standards listed below.

Europe : EN, ISO or DINGreat Britain : BSJapan : JISUSA: ASME

Wire Defects

The following images detail obvious rope defectsand offer basic explanations for their cause. Should

evidence for any of these conditions be found upon

examining a hoist rope, international standardsmandate that the rope be discarded immediately.

figure 1

figure 2

figure 3

Wire Protrusion

Core Protrusion

Sunken Strand/ Local Reduction in Rope Diameter

Wire Protrusion

In this case certain wires or groups of wires rise up as loops on theside of the rope opposite to the sheave groove. Ropes found to be in

this condition should be discarded immediately.

Core Protrusion

An extremely rare form of deformation in NFC ropes, though it can maoccasionally be found in Mixed Core ropes, in which a rope imbalance is

indicated by either the protrusion of the core member through the outer

rope strands, or the protrusion of an outer strand of the core element

through the exterior strands of the rope.

Sunken Strand

Local reduction in rope diameter is evidence of core deterioration.This may be due to: internal wear and wire indentation; internal weardue to friction generated by bending between rope strands and wires;

fiber core deterioration; fracture of a steel core.

If such factors cause rope diameter to decrease by 10% of nominal

the rope shall be discarded, even if no broken wires are evident (ISO

4309 3.5.7).

Low values of deterioration may not be as apparent under actual

examination, particularly if rope stresses are well balanced in the outer

strands. Such a condition can lead to a large loss in rope strength.

Any suggestion of internal deterioration shall be verified through internal

examination procedures or with non-destructive testing. If deterioration

is confirmed, then the rope shall be discarded.

Brugg Wire Rope, LLCBrugg Wire Rope, LLC


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TECH TIPS: ROPE DEFECTS

figure 4

figure 5

figure 6

figure 7

Strand Protrusion

A basket or lantern deformation where an outer rope strand, or awire strand surrounding the core area, protrudes from the correct laid

position. This is normally evidence of a rope imbalance.

Flat tened Rope

Such damage is evidence of a failure of the rope wires to be able to

adjust to changes in length as they are bent. This normally occurs when

a rope becomes wedged in the sheave or through poor or less than

careful handling technique during the installation process. Flattened rope

segments which pass through the sheave will reveal broken wires and

quickly deteriorate. This may damage the sheave. The rope should be

discarded immediately.

Kinks or Tight ened Loops A deformation created when a rope loop has been tightenedwithout an allowance being made for rotation about the rope axis.

This can result in alteration of rope lay length which leads to excessive

rope wear. In severe cases the hoist rope becomes so distorted that it

loses all but a small proportion of its overall strength. Any rope with a

kink or tightened loop should be immediately discarded.

Waviness

A deformation where the longitudinal axis of the wire rope takesthe shape of a helix either in a loaded or unloaded state. While not

necessarily indicating a loss in strength, such a deformation can

transmit a pulsation throughout the entire rope length and create

irregular rope drive. This can lead to accelerated rope wear (as seen in

a rise in wire breaks) and excessive rope vibration, which is marked by

increased system noise.

Strand Protrusion

Flattened Rope

Kink or Tightened Loop

Waviness


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TECH TIPS: ROPE DEFECT

figure 8

figure 9

Birdcage or Basket/ Lantern Deformation

A deformation created by a difference in length between the ropecore and the outer layer strand layer. There can be many causes

behind such a condition, such as:

when running over a tight sheave (i.e., a sheave with a groove

radius that is too small for the rope) the entire wire rope is

compressed. This reduction in overall rope diameter

simultaneously creates an increase in overall rope length.

As the outer strands are naturally compressed to a greater

extent than the inner core, they also increase in length to a

greater degree than the core. A discrepancy between core

and outer strand length can lead to the deformation shown.

should a rope run over a sheave or drum at too great a fleet angle,

the rope will contact the flange of the sheave (or the drum) instead

of settling directly into the groove. This forces the rope to roll down

into the bottom of the groove, unlaying the outer strands of the

rope to a greater degree than the rope core, creating an alteration

in length of core and outer strand elements. (Note: See figure 9for an illustration of this condition).

In both cases the sheave and drum will displace the loose outer

strands, causing the discrepancy in core and outer strand lengths to

appear in one location as a basket or lantern deformation.

Birdcage or Basket/ Lantern Deformation

External Wear of Crown Wires

Large Fleet angle causing rope to roll down into groove.

figure 10

Ext ernal Wear

Abrasion of the crown wires of outer strands is due to the wiresrubbing the grooves of the sheaves and drums under pressure. Thisrope condition, which is marked by flat surfaces on crown wires, is

particularly evident at points of sheave contact when the load is being

accelerated or decelerated.



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figure 11

figure 12

figure 13

figure 14

Crown Wire Breaks

Crown breaks originate on the outside of a rope at the contactpoint between the rope and sheave, or drum. If there is no obvious

indication of rope wear the condition is normally cause by bending

stresses, or stresses placed upon the ropes wires as it bends under

load over a sheave. Close attention must be paid to a rope if two or

more valley breaks are found in one lay length. It is a sign that the

rope should be considered for discard.

Valley Wire Breaks Valley breaks originate within the rope itself and are a sign of ropecore deterioration. Should evidence of a valley break be found one

should inspect the rope segment closely. Two or more valley breaks

found in one lay length indicate that a rope should be considered for

discard.

Ext ernal Corrosion

Such a condition can be found in environments where debris anddirt are allowed to accumulate, or those where an excessive amount of

moisture is present (which can cause a rope to rust). External corrosion

will diminish rope breaking strength by reducing the metallic cross

sectional area, and accelerate fatigue by causing surface irregularities

which lead to stress cracking. Severe corrosion can cause decreased

elasticity in a rope.

Rouging

Rouging is a fine, red oxide crust that forms on a hoist rope giving it a rustyappearance. The debris exudes from within the rope and mainly deposits itsebetween the outer rope strands, and then accumulates lightly on the ropes

surface (only trace amounts on the crowns of wires), where it spontaneously

oxidizes. Though the red color is due to an oxidation of steel wire fragments,

it is not evidence of rustwhich indicates the presence of moisture. Instead

rouging is a sign of abrasion between rope strands and the core, or between

adjacent wire strands, and indicates internal rope degradation.

Rouging is generally due to the presence of heavy loads and vibrations

being placed on a rope and creating pressures that then work lubricant out

of the rope core. Note: field lubrication can only clean and retard further rope

damage, it cannot bring the rope back to its original state. The hoist rope

should be subjected to internal examination should rouging be detected.

Crown Wire Breaks

Crown Wire Breaks

External Corrosion

Rouging



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Detecting Wire Breaks:Why it s not so easy

The actual amount of hoist rope that a professional

can inspect is comparatively small. The outer wires of

the outer strands are not visible along the underside of

the rope, and for a zone of nearly 120 of the strands

circumference. This means that only 2/3 of the 50%

of any ropes metallic cross sectional area is available

for visual inspection (this is equivalent to an amount

equaling 1/3 of the ropes entire cross section).

Although the amount of area available for

inspection for a steel rope remains the same as that

for a Mixed or Fiber Core rope, the greater amount of

steel used in the construction means that the total

proportion of wire available for inspection drops even

further by some estimates to as little as 30% of the

total metallic cross sectional area.

Wire breaks that appear at the crowns of the

strands, and obvious breaks that appear in the

valleys, are relatively easy to detect. However breaks

at the contact points of two adjacent strands or a

ropes underside can be difficult to identify.

In many cases the only thing that can be done is for

a professional to review the rope, secure and removeits loads, and then physically bend it. One can then

inspect the rope more closely and identify any breaks.

As can be seen in Figure 15, at first glance the rope

appears free of wire breaks. However subsequent

bending reveals numerous breaks that have

developed at the underside of the strands where

they contacted the steel core. Long, free, wire ends

indicate that the breaks did not occur on the ropes

surface.

Though certain older industrial publications did

advise the use of certain invasive means to assess

the state of a ropes steel core or to examine the

underside of a ropes outer wires (through the use of a

Marlin Spike), we cannot recommend this procedure.

Any mechanical intrusion into a ropes construction (no

matter how carefully applied) can lead to damage of

the ropes design.

An Obvious Recommendation

Instead we recommend a passive, investigative

inspection technique that compares the total number

of wire breaks against relevant international

standards. The professional then should use that

criteria, as well as observations on rope diameter,

end connections, and an evaluation of surrounding

machinery (such as sheaves and drums) to assess

rope condition.

Rope Discard Recommendations

To obtain the most recent regulations concerning

rope replacement we urge you to consult the relevant

international standards that specifically affect you.

However, we do offer these general guidelines for

reference purposes that reflect information based

upon ASME 17.6-2010 Table 1.10.1.2-1 Wire Breaks

(Crown Wire Breaks Per Lay Length). These guidelines

are similar to those listed in on ISO 4344:2004 (E)

Table E.1, (Number of Visible Broken Wires). These

guidelines do not apply to Governor ropes

,

figure 15

Detecting Wire Breaks by Bending the rope

6-Strand Ropes

Type ofBreaks

WearConditions

Normal

WearConditionsUnfavorable

RopesShowRouge

DistributedBreaks (max) 24 12 12

UnequalBreaks (max) 8 4 4

4 Side-by-Side Breaks 12 6 6

8 and 9-Strand Ropes

Type ofBreaks

WearConditions

Normal

WearConditionsUnfavorable

RopesShowRouge

DistributedBreaks (max) 32 16 16

UnequalBreaks (max) 10 5 5

4 Side-by-Side Breaks 16 8 8

General Notes:

A. Provided tables do not apply to Winding Drum Machinesor Governor Ropes.

B.Unfavorable Conditions include, but are not limited to,corrosion due to external conditions, excessive wear ofindividual wires strands, unequal tension, poor sheave

grooves.

C. If fretting conditons indicated by a red dust or rouge existhe criteria to be followed are those indicated in Ropes

Showing Rouge. No more than one valley break per laylength and valley breaks per lay length are allowed if visiblerouge is detected.

D. Ropes less than 8 mm (.315 in.) in diameter shall bereplaced when rouging is indicated.

E. Ropes should be replaced if there is more than onevalley break per rope lay, or if valley breaks are indicated aany point where rouging may be found.


15.techtips ropedefects en

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