Sulfide Stress Cracking
--NACE MR0175-2002, MR0175/ISO 15156
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The Details
NACE MR0175, “Sulfide Stress Corrosion Cracking Resistant Metallic Materials for Oil Field Equipment” is widely ud throughout the world. In late 2003, it became NACE MR0175/ISO 15156, “Petroleum and Natural Gas Industries - Materials for U in H 2S-Containing Environments in Oil and Gas Production.” The standards specify the proper materials, heat treat conditions and strength levels required to provide good rvice life in sour gas and oil environments.
NACE International (formerly the National Association of
Corrosion Engineers) is a worldwide technical organization which studies various aspects of corrosion and the damage that may result in refineries, chemical plants, water systems and other types of industrial equipment. MR0175 was first issued in 1975, but the origin of the document dates to 1959 when a group of engineers in Western Canada pooled their experience in successful handlin
g of sour gas. The group organized as a NACE committee and in 1963 issued specification 1B163, “Recommendations of Materials for Sour Service.” In 1965, NACE organized a nationwide committee, which issued 1F166 in 1966 and MR0175 in 1975. Revisions were issued on an annual basis as new materials and process were added. Revisions had to receive unanimous approval from the responsible NACE committee.
In the mid-1990’s, the European Federation of Corrosion (EFC) issued 2 reports cloly related to MR0175; Publication 16,
“Guidelines on Materials Requirements for Carbon and Low Alloy Steels for H 2S-Containing Environments in Oil and Gas Production” and Publication 17, “Corrosion Resistant Alloys for Oil and Gas Production: Guidance on General Requirements and Test Methods for H 2S Service.” EFC is located in London, England.
The International Organization for Standardization (ISO) is a
worldwide federation of national standards bodies from more than 140 countries. One organization from each country acts as the reprentative for all organizations in that country. The American National Standards Institute (ANSI) is the USA reprentative in ISO. Technical Committee 67, “Mat
erials, Equipment and
Offshore Structures for Petroleum, Petrochemical and Natural Gas Industries,” requested that NACE blend the different sour rvice documents into a single global standard.
This task was completed in late 2003 and the document was issued as ISO standard, NACE MR0175/ISO 15156. It is now maintained by ISO/TC 67, Work Group 7, a 12-member “Maintenance Panel” and a 40-member Oversight Committee
under combined NACE/ISO control. The three committees are an international group of urs, manufacturers and rvice providers. Membership is approved by NACE and ISO bad on technical knowledge and experience. Terms are limited. Previously, some members on the NACE Task Group had rved for over 25 years.NACE MR0175/ISO 15156 is published in 3 volumes.
Part 1: General Principles for Selection of Cracking-Resistant Materials Part 2: Cracking-Resistant Carbon and Low Alloy Steels, and the U of Cast Irons
Part 3: Cracking-Resistant CRA’s (Corrosion-Resistant Alloys) and Other Alloys
NACE MR0175/ISO 15156 applies only to petroleum production, drilling, gathering and flow line equi
pment and field processing facilities to be ud in H 2S bearing hydrocarbon rvice. In the past, MR0175 only addresd sulfide stress cracking (SSC). In NACE MR0175/ISO 15156, however, but both SSC and chloride stress corrosion cracking (SCC) are considered. While clearly intended to be ud only for oil field equipment, industry has
applied MR0175 in to many other areas including refineries, LNG plants, pipelines and natural gas systems. The judicious u of the document in the applications is constructive and can help prevent SSC failures wherever H 2S is prent. Saltwater wells and saltwater handling facilities are not covered by NACE MR0175/ISO 15156. The are covered by NACE Standard RP0475,
“Selection of Metallic Materials to Be Ud in All Phas of Water Handling for Injection into Oil-Bearing Formations.”日出日落图片
When new restrictions are placed on materials in NACE MR0175/ISO 15156 or when materials are deleted from this standard, materials in u at that time are in compliance. This includes materials listed in MR0175-2002, but not listed in NACE
MR0175/ISO 15156. However, if this equipment is moved to a different location and expod to different conditions, the materials must be listed in the current revision. Alternatively, successful u
of materials outside the limitations of NACE MR0175/ISO 15156 may be perpetuated by qualification testing per the standard. The ur may replace materials in kind for existing wells or for new wells within a given field if the environmental conditions of the field have not changed.
Sulfide Stress Cracking
春节服装--NACE MR0175-2002, MR0175/ISO 15156
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New Sulfide Stress Cracking Standard for Refineries
Don Bush, Principal Engineer - Materials, at Emerson Process Management Fisher Valves, is a member and former chair of a NACE task group that has written a document for refinery applications, NACE MR0103. The title is “Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining
Environments.” The requirements of this standard are very similar to the pre-2003 MR0175 for many materials. When applying this standard, there are changes to certain key materials compared with NACE MR0175-2002.
Responsibility
It has always been the responsibility of the end ur to determine the operating conditions and to specify when NACE MR0175
applies. This is now emphasized more strongly than ever in NACE MR0175/ISO 15156. The manufacturer is responsible for meeting the metallurgical requirements of NACE MR0175/ISO 15156. It is the end ur’s responsibility to ensure that a material will be satisfactory in the intended
environment. Some of the operating conditions which must be considered include pressure, temperature, corrosiveness, fluid properties, etc. When bolting components are lected, the pressure rating of flanges could be affected. It is always the responsibility of the equipment ur to convey the environmental conditions to the equipment supplier, particularly if the equipment will be ud in sour rvice.
The various ctions of NACE MR0175/ISO 15156 cover the commonly available forms of materials and alloy systems. The requirements for heat treatment, hardness levels, conditions of mechanical work and post-weld heat treatment are addresd for each form of material. Fabrication techniques, bolting, platings and coatings are also addresd.
Applicability of NACE MR0175/ISO 15156
Low concentrations of H 2S (<0.05 psi (0,3 kPa) H 2S partial
pressure) and low pressures (<65 psia or 450 kPa) are considered outside the scope of NACE MR0175/ISO 15156. The low stress levels at low pressures or the inhibitive effects of oil may give satisfactory performance with standard commercial equipment. Many urs, however, have elected to take a conrvative approach and specify compliance to either NACE MR0175 or NACE MR0175/
ISO 15156 any time a measurable amount of H 2S is prent. The decision to follow the specifications must be made by the ur bad on economic impact, the safety aspects should a failure occur and past field experience. Legislation can impact the decision as well. Such jurisdictions include; the Texas Railroad Commission and the U.S. Minerals Management Service (offshore). The Alberta, Canada Energy Conrvation Board recommends u of the specifications.
Basics of Sulfide Stress Cracking (SSC) and Stress Corrosion Cracking (SCC)
SSC and SCC are cracking process that develop in the prence of water, corrosion and surface tensile stress. It is a progressive type of failure that produces cracking at stress levels that are well below the material’s tensile strength. The break or fracture appears brittle, with no localized yielding, plastic deformation or elongation. Rather than a single crack, a network of fine, feathery, branched cracks will form (e Figure 1). Pitting is frequently en, and will rve as a stress concentrator to initiate cracking.With SSC, hydrogen ions are a product of the corrosion process (Figure 2). The ions pick up electrons from the ba material producing hydrogen atoms. At that point, two hydrogen atoms may combine to form a hydrogen molecule. Most molecules will eventually collect, form hydrogen bubbles and float away
harmlessly. However, some percentage of the hydrogen atoms will diffu into the ba metal and embrittle the crystalline structure. When a certain critical concentration of hydrogen is reached and combined with a tensile stress exceeding a threshold level, SSC will occur. H 2S does not actively participate in the SSC reaction; however, sulfides act to promote the entry of the hydrogen atoms into the ba material.
As little as 0.05 psi (0,3 kPa) H 2S partial pressure in 65 psia (450 kPa) hydrocarbon gas can cau SSC of carbon and low alloy steels. Sulfide stress cracking is most vere at ambient temperature, particularly in the range of 20° to 120°F (-6° to
49°C). Below 20°F (-6°C) the diffusion rate of the hydrogen is
Figure 1. Photomicrograph Showing Stress Corrosion Cracking
Sulfide Stress Cracking
--NACE MR0175-2002, MR0175/ISO 15156
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so slow that the critical concentration is never reached. Above 120°F (49°C), the diffusion rate is so fast that the hydrogen atoms pass through the material in such a rapid manner that the critical concentration is not reached.
Chloride SCC is widely encountered and has been extensively studied. Much is still unknown, however, about its mechanism. One theory says that hydrogen, generated by the corrosion process,
diffus into the ba metal in the atomic form and embrittles the lattice structure. A cond, more widely accepted theory propos an electrochemical mechanism. Stainless steels are covered with a protective, chromium oxide film. The chloride ions rupture the film at weak spots, resulting in anodic (bare) and cathodic (film covered) sites. The galvanic cell produces accelerated attack at the anodic sites, which when combined with tensile stress produces cracking. A minimum ion concentration is required to produce SCC. As the concentration increas, the environment becomes more vere, reducing the time to failure. Temperature also is a factor in SCC. In general, the likelihood of SCC increas with increasing temperature. A minimum threshold temperature exists for most systems, below which SCC is rare. Across industry, the generally accepted minimum temperature for chloride SCC of the 300 SST’s is about 160°F (71°C). NACE MR0175/ISO 15156 has t a very conrvative limit of 140°F (60°C) due to the synergistic effects of the chlorides, H 2S and low pH values. As the temperature increas above the values, the time to failure will typically decrea.
Resistance to chloride SCC increas with higher alloy materials. This is reflected in the environmental limits t by NACE
MR0175/ISO 15156. Environmental limits progressively increa from 400 Series SST and ferritic S
ST to 300 Series, highly alloy austenitic SST, duplex SST, nickel and cobalt ba alloys.用纸折枪
Carbon Steel
Carbon and low-alloy steels have acceptable resistance to SSC and SCC however; their application is often limited by their low resistance to general corrosion. The processing of carbon and low alloy steels must be carefully controlled for good resistance to SSC and SCC. The hardness must be less than 22 HRC. If welding or significant cold working is done, stress relief is required. Although the ba metal hardness of a carbon or alloy steel is less than 22 HRC, areas of the heat affected zone (HAZ) will be harder. PWHT will eliminate the excessively hard areas.
ASME SA216 Grades WCB and WCC and SAME SA105 are the most commonly ud body materials. It is Fisher’s policy to stress relieve all welded carbon steels that are supplied to NACE MR0175/ISO 15156.
All carbon steel castings sold to NACE MR0175/ISO 15156 requirements are produced using one of the following process:1. In particular product lines where a large percentage of carbon steel asmblies are sold as NACE MR0175/ISO 15156 compliant, castings are ordered from the foundry with a requirement that the castings be either normalized or stress relieved following
all weld repairs, major or minor. Any weld repairs performed, either major or minor, are subquently stress relieved.
2. In product lines where only a small percentage of carbon steel products are ordered NACE MR0175/ISO 15156 compliant, stock castings are stress relieved whether they are weld repaired by Emerson Process Management or not. This eliminates the chance of a minor foundry weld repair going undetected and not being stress relieved.
尿素偏高的原因及危害
ASME SA352 grades LCB and LCC have the same composition as WCB and WCC, respectively. They are heat treated differently and impact tested at -50°F (-46°C) to ensure good toughness in low temperature rvice. LCB and LCC are ud in locations where temperatures commonly drop below the -20°F (-29°C) permitted for WCB and WCC. LCB and LCC castings are procesd in the same manner as WCB and WCC when required to meet NACE MR0175/ISO 15156.
For carbon and low-alloy steels NACE MR0175/ISO 15156
impos some changes in the requirements for the weld procedure qualification report (PQR). All new PQR’s will meet the requirements; however, it will take veral years for Emerson Process Management and our suppliers to complete this work. At this time, we will require ur approval to u
HRC.
S -2
H
+
+
S -2
S -2
Figure 2. Schematic Showing the Generation of Hydrogen Producing SSC
Sulfide Stress Cracking
--NACE MR0175-2002, MR0175/ISO 15156
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Carbon and Low-Alloy Steel Welding hardness Requirements
• HV-10, HV-5 or Rockwell 15N.
• HRC testing is acceptable if the design stress are less than 67% of the minimum specified yield strength and the PQR includes PWHT.
• Other methods require ur approval. • 250 HV or 70.6 HR15N maximum. • 22 HRC maximum if approved by ur.
Low-Alloy Steel Welding hardness Requirements
• All of the above apply with the additional requirement of stress relieve at 1150°F (621°C) minimum after welding.
All new PQR’s at Emerson Process Management and our foundries will require hardness testing with HV-10, HV-5 or Rockwell 15N and HRC. The acceptable maximum hardness values will be 250 HV or 70.6 HR15N and 22 HRC. Hardness traver locations are specified in NACE MR0175/ISO 15156 part 2 as a function of thickness and weld configuration. The number and locations of production hardness tests are still outside the scope of the standard. The maximum allowable nickel
content for carbon and low-alloy steels and their weld deposits is 1%.
Low alloy steels like WC6, WC9, and C5 are acceptable to NACE MR0175/ISO 15156 to a maximum hardness of 22 HRC. The castings must all be stress relieved to FMS 20B52.
The compositions of C12, C12a, F9 and F91 materials do not fall within the definition of “low alloy steel” in NACE MR0175/ISO 15156, therefore, the materials are not acceptable.
A few customers have specified a maximum carbon equivalent (CE) for carbon steel. The primary driver for this requirement is to improve the SSC resistance in the as-welded condition. Fisher’s practice of stress relieving all carbon steel negates this need. Decreasing the CE reduces the hardenability of the steel and presumably improves resistance to sulfide stress cracking (SSC). Becau reducing the CE decreas the strength of the steel, there is a limit to how far the CE can be reduced.
Cast Iron
Gray, austenitic and white cast irons cannot be ud for any白浅图片
pressure-retaining parts, due to low ductility. Ferritic ductile iron to ASTM A395 is acceptable when p
ermitted by ANSI, API or other industry standards.
Stainless Steel
400 Series Stainless Steel
UNS 410 (410 SST), CA15 (cast 410), 420 (420 SST) and veral other martensitic grades must be double tempered to a maximum hardness of 22 HRC. PWHT is also required. An environmental limit now applies to the martensitic grades; 1.5 psi (10 kPa) H 2S partial pressure and pH greater than or equal to 3.5, 416 (416 SST) is similar to 410 (410) with the exception of a sulfur addition to produce free machining characteristics. U of 416 and other free machining steels is not permitted by NACE MR0175/ISO 15156.CA6NM is a modified version of the cast 410 stainless steel. NACE MR0175/ISO 15156 allows its u, but specifies the exact heat treatment required. Generally, the carbon content must be restricted to 0.03% maximum to meet the 23 HRC
maximum hardness. PWHT is required for CA6NM. The same environmental limit applies; 1.5 psi (10 kPa) H 2S partial pressure and pH greater than or equal to 3.5.
300 Series Stainless Steel
Several changes have been made with the requirements of the austenitic (300 Series) stainless steels. Individual alloys are no longer listed. All alloys with the following elemental ranges are acceptable: C 0.08% maximum, Cr 16% minimum, Ni 8% minimum, P 0.045% maximum, S 0.04% maximum, Mn 2.0% maximum, and Si 2.0% maximum. Other alloying elements are permitted. The other requirements remain; solution heat treated condition, 22 HRC maximum and free of cold work designed to improve mechanical properties. The cast and wrought equivalents of 302, 304 (CF8), S30403 (CF3), 310 (CK20), 316 (CF8M), S31603 (CF3M), 317 (CG8M), S31703 (CG3M), 321, 347 (CF8C) and N08020 (CN7M) are all acceptable per NACE MR0175/ISO 15156.Environmental restrictions now apply to the 300 Series SST. The limits are 15 psia (100 kPa) H 2S partial pressure, a maximum temperature of 140°F (60°C), and no elemental sulfur. If the chloride content is less than 50 mg/L (50 ppm), the H 2S partial pressure must be less than 50 psia (350 kPa) but there is no temperature limit.
软件工程简历There is less of a restriction on 300 Series SST in oil and gas processing and injection facilities. If the chloride content in aqueous solutions is low (typically less than 50 mg/L or 50 ppm chloride) in operations after paration, there are no limits for austenitic stainless steels, highly alloyed austenitic stainless steels, duplex stainless steels, or nickel-bad alloys.
团结Sulfide Stress Cracking
--NACE MR0175-2002, MR0175/ISO 15156
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Post-weld heat treatment of the 300 Series SST is not required. Although the corrosion resistance may be affected by poorly
controlled welding, this can be minimized by using the low carbon filler material grades, low heat input levels and low interpass temperatures. We impo all the controls as standard practice. NACE MR0175/ISO 15156 now requires the u of “L” grade consumables with 0.03% carbon maximum.
S20910
S20910 (Nitronic ® 50) is acceptable in both the annealed and high strength conditions with environmental restrictions; H 2S partial pressure limit of 15 psia (100 kPa), a maximum temperature of 150°F (66°C), and no elemental sulfur. This would apply to components such as bolting, plugs, cages, at rings and other internal parts. Strain hardened (cold-worked) S20910 is acceptable for shafts, stems, and pins without any environmental restrictions. Becau of the environmental restrictions and poor availability on the high strength condition, u of S20910 will eventually be discontinued except for shafts, stems and pins where unrestricted application is acceptable for the components.
CK3MCuN
The cast equivalent of S31254 (Avesta 254SMO ®), CK3MCuN (UNS J93254), is included in this category. The same elemental limits apply. It is acceptable in the cast, solution heat-treated
condition at a hardness level of 100 HRB maximum in the abnce of elemental sulfur.
S17400
The u of S17400 (17-4PH) is now prohibited for pressure-retaining components including bolting,
shafts and stems. Prior to 2003, S17400 was listed as an acceptable material in the general ction (Section 3) of NACE MR0175. Starting with the 2003 revision, however, it is no longer listed in the general ction. Its u is restricted to internal, non-pressure containing components in valves, pressure regulators and level controllers. This includes cages and other trim parts. 17-4 bolting will no longer be supplied in any NACE MR0175/ISO 15156 construction. The 17-4 and 15-5 must be heat-treated to the H1150 DBL condition or the H1150M condition. The maximum hardness of 33 HRC is the same for both conditions.
CB7Cu-1 and CB7Cu-2 (cast 17-4PH and 15-5 respectively) in the H1150 DBL condition are also acceptable for internal valve and regulator components. The maximum hardness is 30 HRC or 310 HB for both alloys.
Duplex Stainless Steel
Wrought and cast duplex SST alloys with 35-65% ferrite are acceptable bad on the composition of the alloy, but there are
environmental restrictions. There is no differentiation between cast and wrought, therefore, cast CD3MN is now acceptable. There are two categories of duplex SST. The “standard” alloys with a 3
0≤PREN≤40 and ≥1.5% Mo, and the “super” duplex alloys with PREN>40. The PREN is calculated from the composition of the material. The chromium, molybdenum, tungsten and nitrogen contents are ud in the calculation. NACE MR0175/ISO 15156 us this number for veral class of materials.
PREN = Cr% + 3.3(Mo% + 0.5W%) + 16N%
The “standard” duplex SST grades have environmental limits of
450°F (232°C) maximum and H 2S partial pressure of 1.5 psia (10 kPa) maximum. The acceptable alloys include S31803, CD3MN, S32550 and CD7MCuN (Ferralium ® 255). The alloys must be in the solution heat-treated and quenched condition. There are no hardness restrictions in NACE MR0175/ISO 15156, however, 28 HRC remains as the limit in the refinery document MR0103.
The “super” duplex SST with PREN>40 have environmental limits of 450°F (232°C) maximum and H 2S partial pressure of 3 psia (20 kPa) maximum. The acceptable “super” duplex SST’s include S32760 and CD3MWCuN (Zeron ® 100).
The cast duplex SST Z 6CNDU20.08M to the French National Standard NF A 320-55 is no longer ac
ceptable for NACE MR0175/ISO 15156 applications. The composition fails to meet the requirements t for either the duplex SST or the austenitic SST.
highly Alloyed Austenitic Stainless Steels
持盈保泰There are two categories of highly alloyed austenitic SST’s that are acceptable in the solution heat-treated condition. There are different compositional and environmental requirements for the two categories. The first category includes alloys S31254 (Avesta 254SMO ®) and
N08904 (904L); Ni% + 2Mo%>30 and Mo=2% minimum.
Sulfide Stress Cracking
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Monel ® K500 and Inconel ® X750
N05500 and N07750 are now prohibited for u in pressure- retaining components including bolting, shafts and stems. They can still be ud for internal parts such as cages, other trim
parts and torque tubes. There are no environmental restrictions, however, for either alloy. They must be in the solution heat-treated condition with a maximum hardness of 35 HRC. N07750 is still acceptable for springs to 50 HRC maximum.
Cobalt-Ba Alloys
Alloy 6 castings and hardfacing are still acceptable. There are no environmental limits with respect to partial pressures of H 2S or elemental sulfur. All other cobalt-chromium-tungsten, nickel-chromium-boron (Colmonoy) and tungsten-carbide castings are also acceptable without restrictions.
The cond category of highly alloyed austenitic stainless steels are tho having a PREN >40. This includes S31654 (Avesta 654SMO ®), N08926 (Inco 25-6Mo), N08367 (AL-6XN), S31266 (UR B66) and S34565. The environmental restrictions for the
alloys are as follows:
Nonferrous Alloys
Nickel-Ba Alloys
Nickel ba alloys have very good resistance to cracking in sour, chloride containing environments. There are 2 different categories of nickel ba alloys in NACE MR0175/ISO 15156:
• Solid-solution nickel-bad alloys • Precipitation hardenable alloys
The solid solution alloys are the Hastelloy ® C, Inconel ® 625 and Incoloy ® 825 type alloys. Both the wrought and cast alloys are acceptable in the solution heat-treated condition with no hardness limits or environmental restrictions. The chemical composition of the alloys is as follows:
• 19.0% Cr minimum, 29.5% Ni minimum, and 2.5% Mo
minimum. Includes N06625, CW6MC, N08825, CU5MCuC.
• 14.5% Cr minimum, 52% Ni minimum, and 12% Mo minimum. Includes N10276, N06022, CW2M.N08020 and CN7M (alloy 20 Cb3) are not included in this category. They must follow the restrictions placed on the austenitic SST’s like 304, 316 and 317.
Although originally excluded from NACE MR0175/ISO 15156, N04400 (Monel ® 400) in the wrought and cast forms are now included in this category.
The precipitation hardenable alloys are Incoloy ® 925, Inconel ® 718 and X750 type alloys. They are listed in the specification as individual alloys. Each has specific hardness and environmental restrictions.
N07718 is acceptable in the solution heat-treated and precipitation hardened condition to 40 HRC m
aximum. N09925 is acceptable in the cold-worked condition to 35 HRC maximum, solution-annealed and aged to 38 HRC maximum and cold-worked and aged to 40 HRC maximum.The restrictions are as follows:
Cast N07718 is acceptable in the solution heat-treated and precipitation hardened condition to 35 HRC maximum. The restrictions are as follows:
