API Standard 6A718 Inclusion of Additional Alloy 718 Strength Classes

Acceptance of alloy 718 at 140 ksi min yield strength

Rashmi BhavsarGlobal Materials Métier Manager Schlumberger Feb 2012

Agenda

• Background• Inclusion of 718 -140 • QC, heat treatment and microstructure • Corrosion testing

Inclusion of Additional Alloy 718 Strength Classes

Background•API Standard 6A718, 1st and 2nd Editions, have included only one strength class: 120K•A 120 KSI min yield strength is what has been historically required

Inclusion of Additional Alloy 718 Strength Classes

Background – Continued• API 6A718 at higher strength level used for other types of oil

and gas production equipment, such as down-hole safety valves• The manufacturers of down-hole safety valves specify Alloy

718 with minimum yield strengths of:– 120 KSI– 130 KSI– 135 KSI– 140 KSI

Inclusion of Additional Alloy 718 Strength Classes

• Background – Continued

•The 135 and 140 KSI grades typically need to be precipitation hardened at a lower temperature range than permitted by API 6A718, thereby rendering material heat treated in this manner out of API 6A compliance.

Or • hand picked to meet minimum yield strength –

not practical

Inclusion of Additional Alloy 718 Strength Classes

• The 130 KSI strength class could simply be added as another strength class without having to make any other changes.• The 135 KSI and 140 KSI strength classes cannot simply be added

in this manner. • It will require aging temperature to be changed to 1400 to 1475F

instead 1425 to 1475F for 140 grade• The yield strength range will be 140 to 150 ksi. (the current spec

limits yield strength to 145 ksi max for 120 grade)

Quality Control and Specification Requirements

Early failures were related to • Poor quality - several macros with inclusions • Chemistry control and Melt practices • Lower annealing temperatures • Poor microstructure - secondary phases and uneven grain size • Cold working for higher strength

Hence API 6A -718 spec was generated

Mechanical Properties

Performance tied to the Microstructure

500 Psi H2S, 500 psi CO2, 25%NaCl at 500oF

144 ksi actual yield strength at room temp – 100% stress level for six months

Courtesy: Foroni Metals

Testing also successful at 350F & 450F in high H2S/CO2 – No cracks (30 days test)

Suggested Change to Allow Higher Strength Alloy718

Heat Treatment:• Leave the annealing temp and time as is• Change the aging temperature range from 1425

to 1475F to 1400 to 1475F.• Leave the aging time of 6 to 8 Hrs.

The check is in the microstructure examination

Heat Treatment – Annealing

• Stay with the higher annealing temperature

Heat Treatment - Aging

Suggested Change to Allow Higher Strength Alloy718

Mechanical Properties: • Allow maximum yield strength to be 150 ksi• Keep the maximum hardness to 40 HRc.• Keep the Charpy toughness values the same

for all strength levels.

The check is in Charpy values

Initial ballots

• A Ballot in 1982 from various suppliers and Shell Development to change hardness to 40HRC max

• Hardness up to 45HRc and YS up to 165 ksi • Most data were at 750 and 1670F

Validation Testing • With 40 HRc Max per Current ISO 15156 – min 3 heats

– Perform 90 days four point bent beam or c-ring Or– Perform 30/90 days creviced bent beam or c-ring – Perform slow strain rate testing in duplicates for information and ranking – Test 130, 140 and 150 ksi actual yield strength – Test environment

• NACE level 6 (500 psi H2S, 500 CO2 and 121,300 mg/l cl at ) 350F) Or • H2S per NACE limits at 350F

Approximate cost $90 to 100K

Future Validation Testing • With 42/43 HRc max – three heats• The same annealing temp and lower aging temperature • To raise the limit in ISO 15156 to 43 Max HRc• Testing to be conducted after the 40 HRc max hardness testing

completed.• The max hardness to be tested with maximum yield strength

available and compare the data to 40 HRc max sample used as reference.

• Alternately test at 450F similar to alloy 935 and 945 and 945X. • Ballot for ISO 15156 / NACE MR0175

• Suggest validation testing if funded