Introduction

NACE MR0175/ISO 15156 (Metals for Sulphide Stress Cracking and Stress Corrosion Cracking Resistance in Sour Oilfield Environments), often simply referred to as NACE, is a Materials Standard issued and mandated by the National Association of Corrosion Engineers in the United Nations of America.

Originally issued in 1975, the primary reason for the formation of NACE was for the assessment of materials suitability.

The standard of NACE MR0175/ISO 15156 indicates the kinds of corrosion-resistant substances encompassing stainless steels that can be utilized in particular oilfield settings. Along with that, it also sets margins on the hardness of the suitable materials. This pertains to parent material as well as weld material.

The concise and detailed information from the standard plays a significant role in the field of industry and marketing all around the world.

What is NACE MR0175/ISO 15156?

The basic description of NACE MR0175/ISO 15156 explains it as a Materials Standard that was originally formulated for the assessment of the appropriateness and suitability of specific materials based on petroleum and natural gas industries.

The standard has a very detailed and systematic layout that clearly states its role and purpose in modern marketing and industry. 

Structure

The structure of NACE MR0175/ISO 15156 has a very clear and concise pattern. The document of the standard is allotted into three parts which are:

Part One

The first part of NACE is General principles for the selection of cracking-resistant materials.

Part Two

The next part of this standard is based on Cracking resistant carbon and low-alloy steels and the use of cast irons.

 

Part Three

The third and final segment of NACE is about Cracking resistant CRAs (corrosion-resistant alloys) and other alloys.

At present, the data and information available on NACE MR0175/ISO 15156 are in four languages - English, Spanish, French, and Chinese.

Requirements

The standard of NACE demonstrates the various prerequisites and needs for the choosing and credibility of carbon and low-alloy steels, corrosion-resistant alloys, along with other alloys that are required for aid in devices employed in oil and natural gas generation and natural gas treatment plants in H2S-containing atmospheres.

A vast number of materials are addressed by the standard, and it comprises most categories and variations of stainless steel.

The absolute hardness is generally specified in terms of the Rockwell ‘C’ scale. No modification to any other kind of hardness measurements is provided in MR 0175. Only the systems of Rockwell ‘B,’ Vickers, or Brinell scales are used when determining the measurements.

A short overview is provided here that sheds some idea on how the NACE standard presents the requirements of multiple kinds of steel materials.

Type of SteelGradesAdditional Notes
Ferritic405,430, 409, 434, 436, 442, 444, 445, 446, 447, 448Hardness goes up to 22 HRC
MartensiticF6NMHardness is up to 23 HRC
AusteniticS20910 Hardness up to 35 HRC
Precipitation HardeningS6628635 HRC
Free machining grades like the 303 and 416 varieties are not included in the standard.

It must be noted that this given table is just a basic and short insight into the comprehensive summary provided by the NACE MR0175/ISO 15156. In no way can it be considered an acceptable replacement.


Chemical Properties

ChemicalsContent
CarbonC ≤ 0.10%
SulfurS ≤ 0.002%
PhosphorusP ≤ 0.020%

Mechanical Properties

Mechanical characteristics of tensile strength and yield strength are equivalent to that of general pipes referred to corresponding standards.

Yield StrengthTextile StrengthElongation Percentage
PSAMpaPSAMpaMinimum
35,500 minutes245 minutes60,200 minutes415 minutes-



Purpose and Objectives

The primary purpose and main objectives of NACE MR0175/ISO 15156 include

  • Prevention of expensive equipment faults and failures
  • Reduction in the hazards related to the health and safety of the public, faculty, and the environment
  • Protection of metallic elements from SSC (Sulfide stress cracking), SCC (Stress corrosion cracking), and all other forms of cracking that can occur due to H2S.

Manufacturers and sellers contribute materials only if they meet the following requirements:

  • The basic metallurgical requirements as dictated by NACE MR0175 
  • Proper chemistry, mechanical characteristics, hardness, and processing
  • Other user-based metallurgical necessities

The users of the materials are also responsible for a few significant matters. In the case of NACE standard requirements, the users are held accountable for the choice of the material and for determining the environment. They include:

  • The Oil company
  • The Contractor (only if delegated)
  • The Service (only if delegated)

The manufacturers or suppliers of the materials and units are not held liable in this particular matter.

Limitations

Provided that the standard is concentrated solely on sulfide stress corrosion cracking, it does not deal with the matters of common corrosion or pitting corrosion. 

Likewise, NACE does not specify the last version of mechanical aspects or an expected manufacturing process. Along with that, it does not prescribe general testing criteria, and nor does it give a finished and exact selection tool.

The hydrogen sulfide limitations have been ascertained depending on practical understanding and laboratory research. 

Conclusion

Despite all such limitations, NACE MR0175 has become an important industrial tool of the modern world. It is responsible for providing the conditions for metallic materials exposed to H2S in oil and gas generation settings.

Along with that, NACE also documents the prerequisites for carbon steels, low alloys, and corrosion-resistant alloys, and for each material category, it delivers the metallurgical injunctions related to hardness, chemistry, heat treatment, and much more.

Finally, in NACE standards, MR0175 is the criterion of material statutes for H2S involving oil and gas tools and production. For this reason, NACE pipe is employed in H2S comprising gas and oil transport.