Api Tr 2fc-2-2020

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

API TECHNICAL REPORT 2FC-2 FIRST EDITION, JANUARY 2020

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iii

Contents Page

1 Introduction........................................................................................................................................................ 1 2

Chain TN Fatigue Curves.................................................................................................................................. 1

3

Steel Wire Rope TN Fatigue Curves................................................................................................................. 7

4

Polyester Rope Fatigue Curves........................................................................................................................ 8

Annex A (informative) Polyester Rope Fatigue Test Data......................................................................................... 12 Bibliography.............................................................................................................................................................. 18

Figures 1 2 3 4 5 6 7 8 9

Proposed High-load Range/Low-cycle Corrections to API’s TN Curves for Chain and Wire Rope, and Polyester TN Curves including Spiral Strand × 6.............................................................................................................. 1 High-load Range Correction for R4 Studless Chain Based on API’s TN Curve for Studless Chain and Minimum Yield Stress for R4 Steel Grade........................................................................................................................ 4 Upper Bound, High-load Range Correction for R4 Studless Chain Based on the Mean Regression Curve for Studless Chain and a Yield Stress of 821 N/mm2 for R4 Steel......................................................................... 5 High-load Range Corrections for R3 and R4 Studless Chain Based on API’s TN Curve for Studless Chain and Minimum Yield Stresses for R3 and R4 Steel Grades....................................................................................... 6 High-load Range Corrections for R3 and R4 Studlink Chain Based on API’s TN Curve for Studlink Chain and Minimum Yield Stresses for R3 and R4 Steel Grades....................................................................................... 6 High-load Range Corrections for IWRC and Spiral Strand Wire Based on API’s TN Curves and Elastic Tension Range Limits of 40 % and 50 % of CBS............................................................................................................ 8 Polyester Rope Durability JIP Test Results for 10-tonne Rope Normalized by CBS and Average Break Strength (ABS)................................................................................................................................................................. 9 Polyester Rope Durability JIP Residuals (see Figure 7) for 10-tonne Rope Normalized by CBS and Average Break Strength (ABS)........................................................................................................................................ 9 Polyester Rope Fatigue Test Results Normalized by CBS compared with API 2SK’s TN Fatigue Curve for Spiral Strand Steel Wire Rope and Six Times API’s Spiral Strand Rope TN Curve.................................................. 11

Tables 1 2 3 4 5 A.1 A.2 A.3 A.4 A.5

API Studlink and Studless TN Fatigue Curve Parameters................................................................................ 2 Minimum IACS Requirements for Studlink and Studless Chain........................................................................ 3 API IWRC and Spiral Strand Wire TN Fatigue Curve Parameters.................................................................... 7 Polyester Rope Durability JIP—Loading Regime for 10-tonne Fatigue Tests (28).......................................... 10 Polyester Rope Durability 10-tonne Fatigue Curve Parameters..................................................................... 11 Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer A (NEL Table 6.2.1)......... 13 Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer B (NEL Table 6.2.2)......... 14 Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer C (NEL Table 6.2.3)......... 15 Polyester Rope Durability JIP Fatigue Data for 6-tonne Sub-ropes (ND Slide 3)........................................... 16 Polyester Rope Fatigue Data in API 2SM, First Edition.................................................................................. 17 v

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges) 1 Introduction This report summarizes the derivation of high-load range, low-cycle corrections to API 2SK, Third Edition studlink and studless chain fatigue curves, and in this respect supplements the derivation of standard fatigue curves reported in API TR 2FC-1, First Edition. In addition, low-cycle, high-load range corrections to API 2SK’s independent wire rope core (IWRC) and spiral strand (SS) wire rope fatigue curves are proposed, and polyester rope fatigue data are reviewed and compared with the recommendations presently contained in API 2SM, API 2SK, and ISO 19901-7. The proposed corrections to API’s TN curves and the chain and polyester fatigue test data are shown in Figure 1. The lower part of the piecewise linear TN curves (in the log-log space) are the same as in API 2SK, while the upper part is the correction or change proposed.

Figure 1—Proposed High-load Range/Low-cycle Corrections to API’s TN Curves for Chain and Wire Rope, and Polyester TN Curves including Spiral Strand × 6 Large tension ranges resulting from vortex induced motions of a Gulf of Mexico spar first led to the identification of the need to add a correction for high-tension range, low-cycle fatigue damage to the existing fatigue curves contained in API 2SK, Appendix H. More recently, a “Cyclic Integrity Test (20-hurricane test)” consisting of 20,000 cycles between 15 % and 45 % of the ropes break strength has been proposed for polyester ropes. Consequently, it seems appropriate at this time to review existing fatigue curves and test data, and propose corrections for lowcycle, high-tension range fatigue damage.

2 Chain TN Fatigue Curves Equation (1) expresses API 2SK’s TN curves for chain mooring lines in tension as: ​​log​  10​​​​(​​N​)​​​  =  m ​log​  10​​​​(​​T)​ ​​​  + ​log​  10​​(a)​

(1) 1

2

API Technical Report 2FC-2

where T is R divided by the catalog break strength (CBS) of oil rig quality (ORQ) chain of the same bar diameter; R

is the double amplitude tension range;

m

is the slope of fatigue curve;

​​log​  10​​​​(​​a​)​​​​

is the intercept of fatigue curve;

N

is the number of cycles.

API 2SK, Section 6.2.1, normalizes the tension range, R, by the reference break strength (RBS) and states “For chain, RBS is taken as minimum breaking strength (MBS) of ORQ common chain link of the same size for ORQ, R3, R4, and R4S common or connecting links. Guidance on increase of chain diameter for corrosion and wear and its effect on fatigue life calculation are given in Section 7.6. For wire rope, RBS is the same as MBS.” API 2SK, Section 7.2, then defines MBS as follows, “MBS is defined as the breaking strength guaranteed by the mooring component manufacturer. The minimum breaking strength of chain may be taken as the break test load (BTL).” To avoid introducing confusion and too many definitions and abbreviations catalog break strength (CBS) is used herein. Note that for the term minimum break strength to be meaningful, the MBS value shall be associated with a defined probability of exceedance and for a constant probability that break strength is above the minimum value, the value of MBS shall decrease as the length of the mooring line increases. The parameters of API 2SK’s chain TN curves are based on fatigue tests performed on studlink and studless chain links of ORQ, R3, and R4 steel grades, with nominal bar diameters between 2 in. (51 mm) and 4 in. (102 mm), in oxygenated saltwater [3]. API 2SK’s chain fatigue parameters are summarized in Table 1. Table 1—API Studlink and Studless TN Fatigue Curve Parameters Parameter m ​​log​  10 K

(​​​​ ​​a​)​​​​

Studlink

Studless

−3.0

−3.0

3.0

2.5

1000.0

316.2

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

3

Table 2 summarizes the minimum material properties and proof and break-test load requirements for studlink and studless chain for steel grades between ORQ and R5. Table 2—Minimum IACS Requirements for Studlink and Studless Chain R5

R4S

R4

R3S

R3

API ORQ

Quality assurance ISO 9000

Required

Required

Required

Required

Required

Required

Ultimate strength, MPa min.

1000

960

860

770

690

641

Yield strength, MPa min.

760

700

580

490

410

—

Reduction of area, % min.

50

50

50

50

50

40

Elongation, % min.

12

12

12

15

17

17

Design temperature, °C

−20

−20

−20

−20

−20

−20

Impact Joules (average of three minimum)

B

58

56

50

45

40

40

W

42

40

36

33

30

30

Stud chain

0.0251 × Z

0.0240 × Z

0.0216 × Z

0.0180 × Z

0.0156 × Z

0.0140 × Z

Stud less chain a

0.0223 × Z

0.0213 × Z

0.0192 × Z

0.0174 × Z

0.0156 × Z

0.0140 × Z

Break load (CBS), kN min.

0.0320 × Z

0.0304 × Z

0.0274 × Z

0.0249 × Z

0.0223 × Z

0.0211 × Z

Proof load, kN min.

NOTE 1 NOTE 2 NOTE 3 NOTE 4 a



Other intermediate qualities such as ORQ + 10 and ORQ + 20 may be considered. Stud welding is not allowed for R4S and R4 qualities; other qualities at client’s discretion. Chain weight per meter: stud chain = 0.0219 × d 2; studless chain = 0.02 × d 2. Z = d 2 (44 – 0.08d)

Loads for studless chain are 70 % of the break load in accordance with ABS Certification of Offshore Mooring.

The double amplitude tension range, Re, for which stresses first exceed the material’s yield stress on each cycle depends on the stress concentration factor, SCF, and the yield strength of the steel, ​​σ​ yield​​​. The elastic limit, Re, may be expressed in Equation (2) as: ​  ​​​​(​​2π ​r​​  2​​)​​​ / SCF​ ​​ e​  ​​  =  2 ​σyield R

(2)

where σ ​​ yield ​  ​​​

is the material yield stress;

r equals d/2; d

is the nominal chain bar diameter;

SCF

​  ​​​, where ​​σnom equals hot spot stress​/ ​σnom ​  ​​  =  tension / ​​(​​2π ​r​​  2​​)​​​.​

Figure 2 clearly illustrates that API’s TN curve is not conservative for high-tension ranges, as it predicts a fatigue life for R4 chain in excess of 100 cycles when the load range is approximately equal to the break strength of the chain, and ~10 cycles when the load range is approximately three times the chain’s break strength. That is, the dashed part of API’s TN curve, shown in Figure 2, should not be used in calculating fatigue damage, as it underpredicts fatigue damage. The proposed correction for R4 studless chain with a yield stress of 580 N/mm2 for SCFs of 4.16 and 10.4 (2.5 × 4.16) is shown on Figure 2. The SCF of 4.16 corresponds to the maximum SCF reported in reference [5] for studless chain links loaded in pure tension, while a SCF of 10.4 is used to illustrate the sensitivity to SCF that may result from poor support of chain links in fairlead pockets or out-of-plane bending. In Figure 2, the point on API 2SK’s TN curve that corresponds to the elastic limit, Re, is connected to the CBS of R4 chain at one load

4

API Technical Report 2FC-2

cycle. The two curves connecting these points represent a straight line in the log-log TN space and a straight line in the linear (T)-log(N) TN space.

Figure 2—High-load Range Correction for R4 Studless Chain Based on API’s TN Curve for Studless Chain and Minimum Yield Stress for R4 Steel Grade The correction to API’s TN curve for studless chain shown in Figure 2 is based on the minimum yield stress (580 N/mm2) for R4 grade steel. In practice, the average yield stress is often much higher than the minimum required by IACS. For a particular offshore project that used R4 studless chain the average yield stress, of 31 coupon tests, was 821 N/mm2 and combining this yield stress with the mean regression fit to the studless fatigue test data [3] results in the upper bound correction for high-tension range fatigue shown in Figure 3.

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

5

Figure 3—Upper Bound, High-load Range Correction for R4 Studless Chain Based on the Mean Regression Curve for Studless Chain and a Yield Stress of 821 N/mm2 for R4 Steel The tension range elastic limit, Re, for other chain grades may be calculated based on the minimum yield stress specified for the steel grade. Figure 4 shows corrections to API’s TN curve for studless chain based on the minimum yield stress for R3 (410 N/mm2) and R4 (580 N/mm2) steel grades. The correction for high-tension ranges to API 2SK’s TN curve for studlink chain may be calculated in the same way as that presented above for studless chain. The maximum SCF for studlink chain in pure tension is ~4.05 [6] . As this value is very close to the value of 4.16 for studless chain, 4.16 has also been used for studlink chain. Figure 5 shows the corrections to API’s TN curve for studlink chain based on the minimum yield stress for R3 (410 N/mm2) and R4 (580 N/mm2) steel grades.

6

API Technical Report 2FC-2

Figure 4—High-load Range Corrections for R3 and R4 Studless Chain Based on API’s TN Curve for Studless Chain and Minimum Yield Stresses for R3 and R4 Steel Grades

Figure 5—High-load Range Corrections for R3 and R4 Studlink Chain Based on API’s TN Curve for Studlink Chain and Minimum Yield Stresses for R3 and R4 Steel Grades

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

7

3 Steel Wire Rope TN Fatigue Curves API 2SK’s TN curves for IWRC and spiral strand mooring lines in pure tension are dependent on the mean tension, Tm, in the wire rope and may be expressed in Equation (3) as: l​​ og​  10​​​​(​​N​)​​​  =  m ​log​  10​​​​(​​T)​ ​​​  + ​log​  10​​(a)​

(3)

where T is R divided by the catalog break strength (CBS) of the wire rope; R

is the double amplitude tension range;

m

is the slope of fatigue curve;

​​log​  10​​(a)​

is the intercept of fatigue curve, and depends on the mean tension, Tm;

N

is the number of cycles.

The parameters of API 2SK’s wire rope TN curves are summarized in Table 3. Table 3—API IWRC and Spiral Strand Wire TN Fatigue Curve Parameters Parameter m ​​log​  10​​​​(​​a​)​​​​ K

IWRC

Spiral Strand

−4.09

−5.05

​3.20 − 2.79  ​T​ m​​​

​3.25 − 3.43  ​T​ m​​​

​​10​​  ​(​​3.20−2.79 ​T​  ​​​)​​​​

​​10​​  ​(​​3.25−3.43 ​T​  ​​​)​​​​

m

m

Figure 6 clearly illustrates that API’s TN curves for IWRC and spiral strand wire are not conservative for hightension ranges, as fatigue lives in excess of 100 cycles are predicted for load ranges that exceed the break strength of the wire. The dashed part of API’s TN curve, shown in Figure 6, should not be used in calculating fatigue damage, as it under-predicts fatigue damage. For IWRC and spiral strand wire, rope fretting damage to the individual wires within the rope occurs when the rope is subject to high cyclic tension ranges. It is recommended that the wire rope fatigue curves contained in API 2SK not be used for tension ranges above 50 % of CBS, as fretting will reduce the fatigue life below that predicted by API’s TN curves. The correction for high-tension ranges to API 2SK’s TN curves for wire ropes are calculated in the same way as for chain. Figure 6 shows the corrections to API’s TN curves for IWRC and spiral strand wire based on elastic tension range limits of 40 % and 50 % of CBS.

8

API Technical Report 2FC-2

Figure 6—High-load Range Corrections for IWRC and Spiral Strand Wire Based on API’s TN Curves and Elastic Tension Range Limits of 40 % and 50 % of CBS

4 Polyester Rope Fatigue Curves In API 2SM, First Edition, a regression fit to the results from 11 fatigue tests on polyester ropes, regarded as valid tests, were used to define the fatigue curve for polyester rope presented in Figure 4.6.7.2. Since that time the Polyester Rope Durability JIP performed fatigue tests on 10-tonne polyester ropes (28 valid tests) from three rope manufactures and reported nine fatigue test results for 6-tonne sub-ropes. The results from all these tests are summarized in the tables provided in Annex A. The Polyester Rope Durability JIP presents the results of the fatigue tests on 10-tonne ropes normalized by the average break strength (ABS) of similar ropes made by the three different rope manufactures. The ABS of the ropes from the manufacturers tested are reported to be 18.9 %, 3.6 % and 16.1 % higher than the CBS (10 tonnes), for the three manufacturers respectively. The ABS of the 6-tonne sub-ropes tested by the Polyester Rope Durability JIP are not defined, and these results are presented normalized by 6 tonnes in all cases. The introduction of ABS to normalize mean load and tension ranges, results in an increase in the scatter of the test results, the standard deviation of the residual increases from 0.172 (normalized by CBS) to 0.241 (normalized by ABS), see Figure 7 and Figure 8. Additionally, the use of ABS introduces yet another definition of strength that in most cases will be unknown to the mooring analyst at the time that the fatigue analysis of the mooring system is performed.

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

Figure 7—Polyester Rope Durability JIP Test Results for 10-tonne Rope Normalized by CBS and Average Break Strength (ABS)

Figure 8—Polyester Rope Durability JIP Residuals (see Figure 7) for 10-tonne Rope Normalized by CBS and Average Break Strength (ABS)

9

10

API Technical Report 2FC-2

As the use of catalog break strength (CBS) is consistent with the definitions of strength used for chain and steel wire rope used by API 2SK, and its use results in a reduction in the scatter of the test results, and it is a quantity that will be known to the mooring analyst; it is used in the presentation of the Polyester Rope Durability JIP results herein. It should be noted that the mean loads, load ranges, and maximum loads used in the Polyester Rope Durability JIP’s test program for 10-tonne ropes were extremely severe (see Table 4). Table 4—Polyester Rope Durability JIP—Loading Regime for 10-tonne Fatigue Tests (28) Mean Load (Mean/CBS)

Load Range (Range/CBS)

Maximum Load (Maximum/CBS)

Mean

0.479

0.465

0.712

Maximum

0.714

0.595

0.922

Minimum

0.415

0.339

0.586

Load

For the 28 valid 10-tonne test results, the average of the mean loads was ~48 % CBS, while the maximum mean load was ~71 % CBS. The average mean load range was ~47 % CBS with a maximum load range of 60 % CBS. While the average maximum load (mean + 1/2 load range) was 71 % CBS (well above API’s allowable intact tension limit of 60 % CBS), with the largest maximum load of ~92 % CBS. The use of these extreme loading conditions in the fatigue tests is an indication of the excellent fatigue properties of polyester rope which requires extreme loading conditions in order that the fatigue failures can be induced in a test program that may be completed in a reasonable time and is therefore economic to perform. Also note that the frequencies, between 1 Hz and 4 Hz, at which the fatigue tests were performed, were also extremely high. At present, API 2SK does not provide any guidance on the fatigue curve to be used for polyester rope. However, ISO 19901–7 contains the following: “The fatigue life of well-constructed polyester and HMPE rope lines may typically be assumed to be at least six times that given in Table 3 for a spiral strand wire rope at Q = 0.3 [i.e. K = 1000 in Equation (12)], for load ranges not exceeding 50 % of MBS.” Figure 9 presents all the fatigue test results for 10-tonne and 6-tonne ropes from the Polyester Rope Durability JIP along with the older results from API 2SM, First Edition. Also shown in Figure 9 are the mean regression fit and the mean minus two standard deviation curve and API 2SK’s spiral strand TN curve (with high-tension range correction) and six times the spiral strand TN curve.

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

11

Figure 9—Polyester Rope Fatigue Test Results Normalized by CBS compared with API 2SK’s TN Fatigue Curve for Spiral Strand Steel Wire Rope and Six Times API’s Spiral Strand Rope TN Curve The parameters of the Polyester Rope Durability JIP 10-tonne TN curves shown in Figure 9 are summarized in Table 5. Table 5—Polyester Rope Durability 10-tonne Fatigue Curve Parameters Mean

Mean – 2xStdev

m

Parameter

−5.08

−5.08

​​log​  10​​​​(​​a​)​​​​

4.848

4.504

70,4010

31,911

K

Note that the TN curves based on the Polyester Rope Durability JIP 10-tonne fatigue test data should not be used for design without qualification testing, as all the older API 2SM, First Edition, fatigue failures lie below these TN curves.

Annex A (informative) Polyester Rope Fatigue Test Data A.1 Introduction A.1.1 Tables A.1 through A.5 show examples of Polyester Rope Fatigue Test Data.

12

Table A.1—Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer A (NEL Table 6.2.1)

No.

Count

NEL ID

Mean Load (Mean/ ABS)

Mean Load (Mean/ CBS)

Load Range (Range/ CBS)

Max Load (Max/ CBS)

Cycles N

Test Freq. Hz

Valid or Not

1

1a

MPVQ_7

0.40

0.50

0.476

0.595

0.773

586,020

1

Valid

820 mm from pin center at moving end of machine.

2

2

MPVQ_8

0.40

0.35

0.476

0.416

0.684

7,085,340

2

Valid

1156 mm from pin center at moving end of machine.

3

3a

MPVQ_9

0.40

0.45

0.476

0.535

0.743

1,985,140

2

Valid

840 mm from pin center at moving end of machine.

Location of Failure and Comments

4

4

MPVQ_10

0.40

0.40

0.476

0.476

0.714

3,269,850

1.5

Valid

800 to 1150 mm from pin center at moving end of machine.

5

5a

MPVQ_11

0.40

0.50

0.476

0.595

0.773

629,650

1

Valid

820 mm from pin center at moving end of machine.

6

6a

MPVQ_12

0.40

0.50

0.476

0.595

0.773

663,320

1

Valid

760 mm from pin center at moving end of machine.

7

7

MPVQ_13

0.40

0.40

0.476

0.476

0.714

1,975,200

1.5

Valid

820 mm from pin center at moving end of machine.

8

8

MPVQ_15

0.40

0.40

0.476

0.476

0.714

1,558,880

1.5

Valid

900 mm from pin center at moving end of machine.

9

9

MPVQ_17

0.40

0.30

0.476

0.357

0.654

12,191,580

3

Valid

Clear length failure.

10

10 a

MPVQ_20

0.60

0.35

0.714

0.416

0.922

2,668,190

2

Valid

Clear length failure.

11

11

MPVQ_21

0.40

0.29

0.476

0.339

0.645

18,160,750

3

Valid

Clear length failure.

Not valid

Test abandoned after clevis failed. Rope may be used for . . .

12

1

MPVQ_14

0.40

0.40

0.476

0.476

0.714

1,031,140

1.5

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

Load Range (Range/ ABS)

13

14

Table A.2—Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer B (NEL Table 6.2.2)

No.

Count

NEL ID

Mean Load (Mean/ ABS)

1

1a

MPWM_7

0.40

0.50

0.415

0.518

0.674

2,046,520

1

Valid

Tail of splice at moving end of machine.

2

2

MPWM_8

0.40

0.40

0.415

0.415

0.622

8,181,270

2

Valid

Tail of splice at moving end of machine.

3

3

MPWM_12

0.40

0.45

0.415

0.466

0.648

3,624,620

2

Valid

Tail of splice at fixed end of machine.

4

4

MPWM_13

0.40

0.35

0.415

0.363

0.596

13,424,920

3

Valid

Tail of splice at moving end of machine.

5

5a

MPWM_14

0.40

0.50

0.415

0.518

0.674

3,272,080

1

Valid

Crotch of splice at moving end of machine.

6

6

MPWM_15

0.40

0.45

0.415

0.466

0.648

3,898,160

2 to 1.5

Valid

Tail of splice at fixed end of machine.

7

7a

MPWM_17

0.60

0.35

0.622

0.363

0.803

7,653,650

2

Valid

Tail of splice at fixed end of machine.

8

8

MPWM_20

0.40

0.33

0.415

0.342

0.586

21,582,120

3

Valid

Tail of splice at fixed end of machine.

Not valid

Test abandoned after clevis failed. Rope may be used for . . .

Not valid

Actuator seal went—affected test loads; test abandoned.

10

1

2

MPWM_9

MPWM_11

0.40

0.40

Mean Load (Mean/ CBS)

Load Range (Range/ CBS)

Max Load (Max/ CBS)

Cycles N

Test Freq. Hz

Valid or Not

0.45

0.45

0.415

0.415

0.466

0.466

0.648

0.648

509,680

838,240

2

2

Location of Failure and Comments

11

3

MPWM_18

0.30

0.06

0.311

0.062

0.342

15,063,960

4

Not valid

Electrical cable failure resulted in rope being broken; test repeated.

12

4

MPWM_19

0.30

0.06

0.311

0.062

0.342

40,000,660

4

Not valid

Sample sent for examination.

API Technical Report 2FC-2

9

Load Range (Range/ ABS)

Table A.3—Polyester Rope Durability JIP Fatigue Data for 10-tonne Ropes by Manufacturer C (NEL Table 6.2.3) Mean Load (Mean/ CBS)

Load Range (Range/ CBS)

Max Load (Max/ CBS)

Cycles N

Test Freq. Hz

Valid or Not

Location of Failure and Comments

No.

Count

NEL ID

1

1a

MQAN_9

0.040

0.50

0.464

0.580

0.755

1,858,440

1

Valid

Clear length failure.

2

2

MQAN_11

0.040

0.40

0.464

0.464

0.697

4,887,260

2

Valid

Clear length failure.

Valid

One sub-core mid-length; two sub-cores within tail of splice at fixed end.

3

3a

MQAN_12

0.040

0.45

0.464

0.522

0.726

2,029,750

2

4

4a

MQAN_13

0.040

0.50

0.464

0.580

0.755

1,908,020

1

Valid

Clear length failure but toward tail of splice at fixed end.

5

5

MQAN_16

0.040

0.40

0.464

0.464

0.697

4,173,530

2

Valid

Clear length failure.

6

6

MQAN_17

0.040

0.45

0.464

0.522

0.726

2,593,880

2

Valid

Clear length failure.

7

7

MQAN_18

0.040

0.35

0.464

0.406

0.667

12,807,610

3

Valid

Clear length failure.

8

8a

MQAN_21

0.060

0.35

0.697

0.406

0.900

3,834,130

2

Valid

Tail of splice at fixed end of machine.

9

9

MQAN_22

0.040

0.31

0.464

0.360

0.644

15,200,440

3

Valid

Tail of splice at fixed end of machine.

10

1

MQAN_10

0.040

0.40

0.464

0.464

0.697

1,228,960

2

Not valid

Test abandoned after clevis failed; rope may be used for . . .

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

Load Range (Rang/ ABS)

Mean Load (Mean/ ABS)

15

16

Table A.4—Polyester Rope Durability JIP Fatigue Data for 6-tonne Sub-ropes (ND Slide 3) Mean Load Load Range Mean Load (Mean/ (Range/ (Mean/ ABS) ABS) CBS)

Load Range (Range/ CBS)

Max Load (Max/ CBS)

Cycles N

Test Freq. Hz b

Valid or Not b

Location of Failure and Comments b

Count

NEL ID

1

1a

9

0.40

0.70

0.40

0.70

0.750

200

—

—

—

2

2

10

0.40

0.60

0.40

0.60

0.700

150

—

—

—

a

3

3

11

0.40

0.50

0.40

0.50

0.650

844,880

—

—

—

4

4

12

0.40

0.40

0.40

0.40

0.600

1,660,680

—

—

—

5

5

15

0.40

0.35

0.40

0.35

0.575

4,470,730

—

—

—

6

6

16

0.40

0.40

0.40

0.40

0.600

5,215,850

—

—

—

7

7

1

0.20

0.20

0.20

0.20

0.300

47,699,530

—

—

—

8

8

13

0.30

0.40

0.30

0.40

0.500

4,159,790

—

—

—

9

9

18

0.65

0.30

0.65

0.30

0.800

1,597,580

—

—

—

NOTE Average breaking strength (ABS) is unknown; coefficient of variation is unknown; Catalog break strength (CBS) = 58.9 kN (6 tonne); ABS/CBS is unknown. a b

Test results not used for developing TN curves. No data available.

API Technical Report 2FC-2

No.

Mean Load (Mean/ MNS)

Load Range (Range/ MNS)

Max Load (Max/ MNS)

Cycles N

Test Freq. Hz

Material

Location of Failure and Comments

Source

Test ID

OTC 5720

Table 2

No.

Count

Break Strength a kN

1

1

1156

0.39

0.62

0.700

914

0.095

PET

At eye splice

2

2

1156

0.29

0.42

0.500

61,376

0.095

PET

At eye splice

OTC 5720

Table 2 MJRT4

3

3

49.1, 66.6

0.40

0.70

0.750

2180

—

PET-855

Tail of splice

Fiber tethers 2000, 1992

4

4

49.1, 66.6

0.40

0.60

0.700

3360

—

PET-855

Splice pulled out

Fiber tethers 2000, 1992

MJRT5

5

5

49.1, 66.6

0.40

0.50

0.650

12,350

—

PET-855

Tail of splice

Fiber tethers 2000, 1992

MJRT7

6

6

49.1, 66.6

0.40

0.45

0.625

75,880

—

PET-855

Tail of splice

Fiber tethers 2000, 1992

MJRT8

7

7

1177, 1528

0.40

0.70

0.750

780

—

PET-785

Mid-length

Fiber tethers 2000, 1993

MLYI 04

8

8

1177, 1528

0.40

0.60

0.700

15,920

—

PET-785

Back of eye

Fiber tethers 2000, 1993

MLYI 05

9

9

1177, 1528

0.40

0.50

0.650

49,460

—

PET-785

Back of eye

Fiber tethers 2000, 1993

MLYI 06

10

10

1177, 1528

0.40

0.50

0.650

13,120

—

PET-785

Suspect dryness

Fiber tethers 2000, 1993

MLYI 07

11

11

1177, 1528

0.40

0.50

0.650

138,300

—

PET-785

Back of eye

Fiber tethers 2000, 1993

MLYI 09

The first value is the manufacture’s nominal strength (MNS, similar to CBS), which is used to normalize the loads; the second value is the average break strength (ABS).

a

Fatigue TN Curves for Chain, Wire, and Polyester Mooring Lines (Including Corrections for High-tension Ranges)

Table A.5—Polyester Rope Fatigue Data in API 2SM, First Edition

17

Bibliography [1] API Recommended Practice 2SK, Design and Analysis of Stationkeeping Systems for Floating Structures, Second Edition [2] API Recommended Practice 2SM, Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring, Second Edition [3] API Technical Report 2FC-1, Studlink and Studless Fatigue Curves for Mooring Lines, First Edition [4] ISO 19901-7, Petroleum and natural gas industries—Specific requirements for offshore structures— Stationkeeping systems for floating offshore structures and mobile offshore units [5] Finite Element Analysis and Strain Gauge Testing of 76 mm Studless Mooring Chain Link, part of the NDA/ NEL JIS on Corrosion Fatigue Testing of Studless Mooring Chain, NEL Report No. 079/2001, NDA Project No. 009, September 2001 [6] Yngve Bergstrom, Life of Anchor Chain, Department of Physical Metallurgy, Royal Institute of Technology, Stockhom, Sweden [7] OTC-5720-MS, Tension and Bending Fatigue Test Results of Synthetic Ropes, Offshore Technology Conference, 1988

18

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