Alloy Selection Guide

Get Started Choosing an Alloy Family

Fill in the below parameters to find your alloy family solution*

Temperature (*F)

Maximum Pressure (psi)

CO2 Partial Pressure (psi)

Chlorides (mg/L)

H2S (psi)

MARTENSITIC STAINLESS STEELS

Martensitic stainless steels are used extensively in sweet (CO2) environments where carbon and low alloy steels experience general corrosion.

13Cr-L80 is the most commonly used martensitic stainless for OCTG. The standard mechanical properties and quality requirements for this alloy are provided by API 5CT and ISO 11960. 13Cr-L80 can be used in mild sour environments within the guidelines of NACE MR017 and ISO 15156. Where chlorides or oxygen are present, 13 Chrome alloys are prone to pitting corrosion so higher alloys are required.

Modified 13 Chrome and Super 13 Chrome alloys provide improved pitting corrosion resistance along with higher strength and toughness. API 5CRA and ISO 13680 provide standard mechanical properties and quality requirements for Super 13 Chrome alloys at 95 ksi and 110 ksi yield strength. At 95 ksi these alloys are considered acceptable for mild sour service, within the guidelines of NACE MR0175 and ISO 15156.

Where higher strength and temperature resistance is required, 15 Chrome and 17 Chrome alloys should be considered. These alloys are available with 125 ksi yield strength, however, they are not recommended for sour service.

DUPLEX STAINLESS STEELS

Duplex stainless steels are used extensively in high chloride environments where pitting and crevice corrosion are of concern, and sweet HPHT environments where martensitic stainless steels won’t provide sufficient resistance to the combination of temperature and CO2. Duplex Stainless Steel tube is most commonly supplied in the cold worked condition with 110 ksi or 125 ksi yield strength. At these strength levels they are suitable for mild sour service, within the guidelines of NACE MR0175 and ISO 15156. API 5CRA and ISO 13680 provide standard mechanical properties and quality requirements for these alloys up to 140 ksi yield strength, however, they are not recommended for sour service in this highest strength condition.

Super Duplex Stainless Steels are alloyed to achieve a PREN (Pitting Resistance Equivalence) less than 40, which is necessary to prevent pitting corrosion in high temperature/high chloride environments. These alloys are also used in water handling systems where dissolved oxygen may result in pitting corrosion. They are suitable for mild sour service with a partial pressure of H2S less than 3.0 psi.

SOLID SOLUTION NICKEL BASE ALLOYS

Solid solution nickel base alloys are used primarily in sour environments where the partial pressure of H2S exceeds 3 psi. Nickel Base Alloy tube is most commonly supplied in the cold worked condition. API 5CRA and ISO 13680 provide standard mechanical properties and quality requirements for these alloys up to 140 ksi yield strength. NACE MR0175 and ISO 15156 provide the guidelines for sour service. Within these documents the cold worked nickel base alloys are grouped by alloy content. A range of sour service limits are provided for each group (designated as Types 4c, 4d and 4e). Types 4d and 4e are also recommended where high chlorides or dissolved oxygen necessitate a high pitting resistance.

For a comparison of sour service limits for CRA’s Nickel Base Alloys, click here.