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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
Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 2
New Table showing all info for rods
Sept. 17 - 20, 2013 3 2013 Sucker Rod Pumping Workshop
New Table for couplings
Sept. 17 - 20, 2013 4 2013 Sucker Rod Pumping Workshop
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
Sept. 17 - 20, 2013 8 2013 Sucker Rod Pumping Workshop
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)
Sept. 17 - 20, 2013 9 2013 Sucker Rod Pumping Workshop
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)
Sept. 17 - 20, 2013 11 2013 Sucker Rod Pumping Workshop
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
Sept. 17 - 20, 2013 12 2013 Sucker Rod Pumping Workshop
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)?
Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 20
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?
Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 21
Contact Info:
Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 22
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: [email protected]
Sept. 17 - 20, 2013 23 2013 Sucker Rod Pumping Workshop
Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 24
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Sept. 17 - 20, 2013 2013 Sucker Rod Pumping Workshop 25
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