9th Annual Sucker Rod Pumping

Workshop

Renaissance Hotel

Oklahoma City, Oklahoma

September 17 - 20, 2013

Modifying the Modified Goodman Diagram

Norman W. Hein, Jr.; P.E.

Chief Technology Professional

NPS & Norris/AOT Group Companies

Contents

• Latest proposed changes to API Spec 11B on rods and

couplings

• Background on fatigue & Goodman Diagram

• Development of API 11BR Modified Goodman Diagram

(MGD)

• Proposal changes to MGD for HA & HS rods

• Proposed changes to MGD to raise minimum allowables

• Summary & Recommendations

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New Table showing all info for rods

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New Table for couplings

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Fatigue Background

• Original fatigue work by Goodman in the 1920s developed a

linear relationship of load range based on steel tensile strength

• In 1960s API adopted and modified the Goodman work to

reduce the y-intercept from T/2 to T/4 and change the max

allowable load from T to T/1.75; this resulted in Modified

Goodman Diagram (MGD)

• In 1970s rod manufacturers developed special high strength

rods to provide competition to Oil Well patented Electra/EL

induction case hardened rod; Use to T/2.8 for these grades = 50

KSI which was same as EL

• Hein and Hermanson in 1993 discussed the very conservative

nature of MGD; recommended much higher life and even

increased allowable load range

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Background - Goodman Diagram 1926

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Original Goodman & API MGD (from API)

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Modified Goodman Diagram (from J. Lea)

T

T

T

T

T/2T/2 T/1.75

T/4

T/1.75T/1.75

T/4

Sa = Allowable Stre

ss

Sm

= M

in. S

tres

s

Sa = (T/4+ .5625(Smin))(SF)

Sa = Allowable Stre

ss

Sm

= M

in. S

tres

sSa = Allowable Stre

ss

Sm

= M

in. S

tres

s

Sa = (T/4+ .5625(Smin))(SF)

SaSaSa

SmSm

SySySa= Sa – Smin

Sa= max allowable

stress, psi

Sa = allowable range of

stress

.5625 = slope of Sa curve

SF = Service Factor

T = Minimum tensile

strength, psi

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Dynamometer Card

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000

Polished Rod Position

Lo

ad

, lb

.

Min Load = 9100 lbs.

Stress = 15141 psi

Pk Load = 17900 lbs.

Stress = 29768 psi

Rod Diameter is .875

Loading can be measured at top of rod string (from J. Lea)

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0

10000

20000

30000

40000

50000

60000

70000

0 10000 20000 30000 40000 50000 60000 70000

Smin = 15141 psiSmin = 15141 psi

Pk Stress = 29768 psi

Sa =(T/4+.5625(Smin))(SF)

= 37267 psi

Pk Stress = 29768 psiPk Stress = 29768 psi

Sa =(T/4+.5625(Smin))(SF)

= 37267 psi

Sa =(T/4+.5625(Smin))(SF)

= 37267 psi

Rod Loading =

29768 - 15141

37267-15141

= 66%

Rod Loading =

29768 - 15141

37267-15141

= 66%

Rod Loading - SF of 1.0: Grade D Rod (from

J. Lea)

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0

10000

20000

30000

40000

50000

60000

70000

0 10000 20000 30000 40000 50000 60000 70000

Smin = 15141 psiSmin = 15141 psi

Pk Stress = 29768 psiPk Stress = 29768 psi

Sa =(T/4+.5625(Smin))(.8)

= 29814 psi

Sa =(T/4+.5625(Smin))(.8)

= 29814 psi

Rod Loading =

29768 - 15141

29814 -15141

= 99.7%

Rod Loading =

29768 - 15141

29814 -15141

= 99.7%

Allowable stress, S

F = .8

Allowable stress, S

F = .8

Allowable stre

ss, SF = 1.0

Rod Loading: Grade D rods, SF=0.8 (from J. Lea)

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11BR Revisions – Adding HA & HS

• During API Task Group discussions of new 11BR, the

question was posed what allowable stress range should

be applied to new HS grade when these are

incorporate?

• T/2.8 as Y-intercept and T/1.75 were decided

• But one consultant and three users questioned why

normal API grades are not using this higher allowable,

especially since many users were applying a Service

Factor in their designs >1.0 (ranged 1.25 to 1.35) after

many years of field trials partially based on 1993 paper

& fatigue testing results

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11BR Revisions – New Higher Loads

• It was proposed that all API grades should have new

“modified” MGD with y-intercept being T/2.8 and max

T/1.75

• One manufacturer has been conducting fatigue testing

at ~56 KSI which is ~T/2.5 (or higher) for HA, HS and DA

• This load is higher than what industry is considering

and if testing results are correct, the new recommended

T/2.8 should not be a problem to achieve adequate field

fatigue life

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Current MDG & New Max – C/K

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Current MDG & New Max - D

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New MGD for HS & Comparison to Current Fatigue Testing

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Current D Grade and Proposed C/K Fatigue Testing Comparison

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Fatigue Life Graphs HA/HS & D

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Comparison of T/2.8 vs. T/2.5

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Summary & Recommendations

• New API Spec 11B is finally adding HA, HS and high

strength couplings

• Industry needs to decide what is the recommended

max allowable stress for HA & HS

• Industry should consider if other API rod grades

should have max allowable increased and to what

value (T/2.8)?

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Summary & Recommendations

• As a poll:

1. Should HA & HS be added?

2. What should be max allowable; T/2.8?

3. Which operators normally design rod strings with SF of

>1.0?

4. What is the SF that company recommends using?

5. Should API raise max allowable stress for C, K and D

grades?

6. If so, what should this number be; T/2.8?

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Contact Info:

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Modifying the Modified Goodman Diagram

by

Norman W. Hein, Jr., P.E. Chief Technology Professional

NPS & Norris/AOT Group Companies

Phone: 918.445.7619

Email: nhein@norrisrods.com

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