NACE MR0175 / ISO 15156

NACE MR0175 / ISO 15156
• Discuss new standard & changes
• Describe failure mechanisms
• Discuss Kimray offering & changes
National Association of Cowboy Entertainers
National Association of Corrosion Engineers
• Interest begin in the 1950s after WWII. Natural
gas was beginning to be used by industry. Sour
gas was encountered in wells being drilled.
• Standard is based on 50 yrs of experience.
• Main goal is to prevent failures that would allow
exposures to people and the environment.
• Standard applies to down hole, Xmas Tree, &
surface facilities. NOT process plants, refineries,
• Fatalities from an accident in West Texas
prompted the Texas Railroad Commission
to ask the industry to write a document to
help prevent such incidents in the future.
• Failure mode identified as SSC & SCC.
• Materials failing were identified as
materials with HIGH HARDNESS & HIGH
• The new standard addresses issues which were not
considered in the previous version of NACE MR01752002.
• The new standard acknowledges, in addition to SSC,
other potentially catastrophic failure mechanisms
resulting from sour environments.
• Mechanisms specified in MR0175/ISO 15156 include
as chloride stress corrosion cracking,
hydrogen-induced cracking and stepwise cracking,
stress oriented hydrogen-induced cracking,
soft zone cracking
galvanically-induced hydrogen stress cracking;
The new standard:
– addresses the synergistic effects of H2S with
other environmental factors (chloride content,
temperature, pH, etc.) on the cracking
resistance of many listed materials;
– limits the use of many of the listed metals
through additional environmental restrictions
which were not taken into account by the
previous NACE MR0175 versions.
Structure of New Document
• The new NACE MR0175/ISO 15156 consists of 3 parts:
• Part 1- General Principles for Selection of CrackingResistant Materials
• Part 2- Cracking-Resistant Carbon and Low Alloy
Steels, and the use of Cast Irons
• Part 3- Cracking-Resistant CRAs (CorrosionResistant Alloys) and Other Alloys
CHANGES - Responsibilities
• “It is the responsibility of the user to determine the
operating conditions and to specify when this standard
applies. The manufacturer is responsible for meeting
metallurgical requirements. It is the user’s responsibility
to ensure that a material will be satisfactory in the
intended environment.”
• The owner company is a user.
• These are NOT users.
An equipment manufacturer is NOT a user.
An mill is NOT a user.
A distributor is NOT a user.
A consultant or contractor are NOT users.
It’s the User's Responsibility to:
• select the carbon and low alloy steels, cast irons, CRAs
(corrosion-resistant alloys) and other alloys suitable for
the intended service. (Part 1: Section 5 & Section 6)
• document the selection and qualification of materials
used in the H2S environment. (Part 1: Section 5 &
Section 9)
• assume the ultimate responsibility for the in-service
performance of all materials selected by the end user or
– For example, the end users is still responsible for materials
selected by delegated Engineering Consultants/
Engineering and Procurement Companies (EPC).
The Supplier/Manufacturer is responsible
• Although there is no direct reference to
supplier/fabricator responsibility in MR0175/ISO15156
the following sections imply responsibility.
– cooperate and communicate in an exchange of information
between the equipment users and materials
suppliers/manufacturers concerning required or suitable
service conditions. (Part 1: Section 5)
– ensure the material purchased meets the equipment users
requirements and the requirements of the standard. (Part
3: Section 7)
• The manufacturer is responsible for meeting
metallurgical requirements. It is the user’s
responsibility to ensure that a material will be
satisfactory in the intended environment.
• Paragraph 1.6.2 is a disclaimer-type of statement:
“Materials included in this standard are resistant to,
but not necessarily immune to, SSC and/or SCC in
stated conditions. Improper design, manufacturing,
installation, selection, or handling can cause
resistant materials to become susceptible to SSC
and/or SCC.”
• This is telling the user: You are responsible for
materials selection. We cannot guarantee successful
use or no failures or cracking, etc.
The new edition spells out more clearly that
materials selection is up to the user—NACE
cannot give advice and will not get involved
in negotiations or a dispute between users
and manufacturers.
Materials Included In MR0175 (with
Ductile Iron
Carbon Steel
304 Stainless Steel
316 Stainless Steel
17-4 PH Stainless Steel
Materials Excluded In MR0175:
Cast Iron
Free Machining Steel
303 Stainless Steel
Changes: Affecting only the Carbon Steel
Regions of environmental or SSC severity. (Figure 1 of Part 2: Clause
– Four severity regions are defined based on the effect of the in situ pH and H2S partial
pressure on the carbon and low alloy steels. This differs from previous editions where
only the partial pressure of the H2S was considered.
Hardness requirements for welds (Part 2: Clause
– Three different hardness test methods are acceptable for weld procedure qualification:
Vickers (HV10 or HV5), Rockwell 15N, and HRC (with specified restrictions). This
differs from previous editions where HRC was the primary basis of acceptance.
Consideration of HIC/SOHIC/SZC/SWC (Part 2: Section 8)
– These additional cracking mechanisms, which result from the synergy of H2S
exposure and various material factors (steel chemistry, hardness and manufacturing
methods) should also be considered.
Changes: Affecting only the CRAs
• Consideration of environmental limits for SCC and GHSC (Part 3:
Section 6)
• The new standard provides principles for selecting cracking resistant
materials for use in the presence of H2S in combination with other
environmental factors, such as chlorides. The cracking mechanisms
addressed include:
– SCC caused by the presence of chlorides in the H2S containing
– GHSC caused by the presence of dissimilar alloys, including
weldments in contact with an H2S environment
New Environmental Restrictions for Alloys
(Part 3: Clause A.1.3)
Depending on the alloy, environmental restrictions may include:
– maximum chloride content,
– maximum H2S partial pressure,
– maximum temperature,
– minimum pH
– application limits depending on the presence of free sulfur in the
In previous editions of MR0175, several legacy materials had no
environmental restrictions, implying they were suitable for any sour service
For example, wrought precipitation hardening nickel alloy 718 (UNS
N07718) had no environmental restrictions in previous editions of MR0175;
in the current standard this alloy has H2S partial pressure limitations based
on the maximum operating temperature.
Changes: New Environmental Restrictions for
Alloys (Part 3: Clause A.1.3)
Some alloys may have a range of acceptable environmental parameters
depending on the severity of the in-service conditions.
The environmental limits listed in Tables A.2-A.42 give the allowable
parameters for the H2S partial pressure, temperature, chloride content,
presence of sulfur and pH.
As cracking behavior can be affected by the complex interactions of these
parameters, there is some discretionary latitude for interpolation depending
on the material’s intended application or service conditions;
For example, austenitic steels such as AISI 316SS will have different
service limitations based environmental parameters such as partial pressure
of H2S, temperature, chloride concentration and in situ pH in the production
fluid. AISI 316SS and AISI 304SS have a new temperature limit of 140F
and H2S partial pressure limits. NACE is evaluating requests for changes.
Changes: Deletion of Previously
Approved Materials
• The general usage of some previously approved
materials has been restricted to specified components
• For example, 17-4 martensitic, precipitation hardening
stainless steel was deleted from the general usage
section, but remains an acceptable material for various
components of wellheads and Christmas trees, provided
a maximum H2S partial pressure of 0.50 psi and
minimum pH of 4.5. 17-4 martensitic is no longer
allowed as a pressure containing component.
Changes: Corrosion Resistant Alloy
Categories (Part 3: Clause A.1.1)
A CRA category is a broad-based group of alloys defined in terms of
chemical composition, manufacturing process, and finished condition.
These categories or materials groups (austenitic stainless steels,
martensitic stainless steels, etc.) are further split into material types (similar
compositional limits) and individual alloys.
• For example, Annex A, Table A.2 outlines the environmental and
materials limits for the general usage of austenitic stainless steels (AISI
304SS, AISI 316SS, etc).
• This table is sectioned into general materials type and individual alloys,
e.g. UNS S20910.
• The individual alloys tend to have broader environmental limits than
those set for the group.
• The UNS S20910 can be used at a slightly higher temperature than AISI
316 at similar partial pressures of H2S.
Equipment User’s Application Guideline
for MR0175/ISO 15156
• This section is to provide the equipment user with a
guideline on how to approach a material selection project
using the NACE MR0175/ISO 15156 Standard.
• 6.1 Select Qualification Method
• 6.2 Qualification By Field Experience
• 6.3 Qualification by Laboratory Testing
• Equipment user decision flow charts are included in
Appendix C and need to be used in conjunction with this
Other Considerations
• When using this document there are other considerations
that need to be taken into account. For example:
• Using previous versions of MR0175 will require
consideration of:
• changes in environmental conditions,
• regulatory requirements,
• the ability of the supplier and equipment user to
address conflicts between the previous and current
What chemical causes corrosion of steel by
• Hydrogen
• Fe + H2S > FeS + 2H0 (in aqueous solutions)
Hydrogen ions in aqueous solution from acid
waters and the H2S form on the surface of
the base metal. They migrate into the
crystalline structure and combine with
other Hydrogen ions to form H2 gas. 100s
to 1000s psi pressure can occur.
H0 + H0 > H2 gas
Forms of Hydrogen Damage
• Hydrogen Blistering (HB)
• Hydrogen-Induced Cracking (HIC)
• Stress-Oriented Hydrogen-Induced
Cracking (SOHIC)
• Sulfide Stress Cracking (SSC)
Stepwise Cracking (Linked HIC Cracks)
Concern is that HIC will link up through the wall by
stepwise cracking.
Sulfide Stress Cracking at Welds
Hydrogen Damage
• In high purity metal H2 gas does not collect as
readily, therefore damage is reduced.
• Kimray ensures the quality of materials used.
Other competitors materials have proven to be
• Damage is dependent on the H2 gas charge
rate. How fast the H2 gas is moving thru the
metal substrate.
• Sulfide Stress Cracking (SSC)
Hydrogen Damage
Residual Stresses from Welds can make
matters worse.
Hydrogen Damage
What temperatures are metals more
susceptible to Hydrogen Damage? (High,
Low or Moderate temps)
At High temps Hydrogen atoms pass right
thru the metal. At Low temps Hydrogen
charge rates are small. Worse damage
occurs at Room Temp. !
NACE at Kimray
NACE at Kimray
Kimray can provide most products for NACE
service. Certifications and documentation
are provided when NACE components and
products are ordered.
NACE at Kimray
There are some limitations:
• Bellows in the 75/150 PG
NACE at Kimray
There are some limitations:
• Bellows in the 50 PG Pilot
NACE at Kimray
There are some limitations:
• Glycol Pumps
NACE at Kimray
There are some limitations:
• Thermostats
The standard 112 pilot
plug is now produced
with NACE compliant
material (316 SS).
NACE at Kimray
Kimray has implemented a new Heat
Treating standard that documents the
procedures to properly heat treat NACE
Kimray also is improving our heat treating
process to better ensure NACE compliant
What about elastomers in sour gas?
• NACE does not apply
What is recommended?
• HSN up to 300F
• Aflas up to 500F (Not Recommended
below 25F)