Paragraph 11.4 of the standard, which is titled "Compressors and Pumps," appears to not address many significant applications for pumps. None of the material classes addressed in Paragraphs 11.4.2, 11.4.3, 11.4.4, 11.4.5, 11.4.6, or 11.4.7 speak to applications in pumps in sour service. Is this intentional? It would appear that the limitations applied to compressors would be also applicable to pumps.
(MP INQUIRY #2003-20 Q2) ANSWER:
It is intentional that the paragraphs you have cited apply only to compressors. The Paragraphs 11.4.2 and 11.4.3 come from the previous 2002 edition. The other paragraphs were added as a result of the balloting process for the 2003 edition.
A.1.6 Table A.1 (Row “Any equipment or component”) QUESTION:
Are the bolting materials and nuts specified in Paragraphs 6.2.1.2 and 6.2.1.3, respectively, the only acceptable materials in compliance with MR0175-2003 for Exposed Bolting?
(MP INQUIRY #2003-22 Q1) ANSWER:
Bolting materials may be chosen in accordance with Sections 3 and 4 as described in MR0175-2003, Paragraph 6.2.1.1.
QUESTION:
Does Paragraph 6.2.1.1 allow other nuts and bolting materials besides the ones listed in Paragraphs 6.2.1.2 and 6.2.1.3?
(MP INQUIRY #2003-22 Q2) ANSWER:
Yes, in accordance with NACE Standard MR0175-2003 Sections 3 and 4. ISO 15156-3, Table A.1 (Row “Any equipment or component”) lists the tables which may be used to select bolting materials.
A.2.1 and A.2.2, Table A.2 QUESTION:
With the former MR0175-2000 the material 316L (bar and pipe material) and CF8M (casting material) was allowed for use for NACE applications. With the new revision (MR0175-2003) the 316L does not fulfill the new allowed limits of the chemical components any more and the allowed temperature range to use CF8M is drastically reduced (so that it has nearly no meaning anymore for the NACE applications).
According to our experiences these two materials have been very common for applications that require the "NACE conformity."
Now we are very interested in the reasons why these two materials are (nearly) not possible with the new specification any more.
--Do you know what have been the reasons to change the limits of the allowed alloys and the allowed maximum temperature in this way?
--Have there been serious problems with these materials in NACE applications in the past?
(MP INQUIRY #2003-30) ANSWER:
1. We are not aware of having restricted the general composition of 316 SS beyond that of an industry consensus that was reviewed during the balloting process for the 2003 edition. It is important to emphasize that the chemical compositions for any alloy category in the 2003 edition are those of the alloys as delivered and not from the specifications. 316L SS is within the range as specified in Paragraph 4.2.1 of MR0175-2003 and is acceptable.
2. The austenitic stainless steels were restricted because of industry and lab failures.
Please see the attached documentation. Upon the final ballot, there was a single negative that was not withdrawn. This negative suggested making the restrictions on 316 SS even more restrictive. You may choose for a future addendum to propose new limits based on the documentation described in NACE MR0175/ISO 15156.
This documentation may be either laboratory data or successful field experience.
A.2.2, Table A.2
The version of Table A.2 included in Reference 3 provides new guidance on the environmental limits of temperature, H2S, chlorides, pH and sulfur for austenitic stainless steels in sour service.
QUESTION:
Paragraph 4.2—Austenitic Steels (say 316 SS). One of the acceptance limits for these materials is a maximum H2S partial pressure of 15 psia at a maximum of 140°F when no chlorides are present. Can I assume that I can still use a material from this category at a higher temperature than 140°F if the partial pressure of H2S is lower than 15 psia?
(MP INQUIRY #2003-04 Q1) REVISED ANSWER 2005-09-01:
See Reference 3
QUESTION:
In the past we have used 300 series SS pipes and valves in sour service. We are not sure of the implications and use of SS in sour service according to NACE Standard MR0175-2003. Could you please advise whether 300 series SS (304/316, etc.) can be used at lower H2S partial pressures for temperatures above 60°C (140°F)?
(MP INQUIRY #2003-08) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3
Please see ISO 15156 Part 1 for guidance as to how to use field experience or laboratory data to qualify a material for H2S service.
QUESTION:
Paragraph 4.2.2 is new. Would you let us know which interpretation applies?
1. Paragraph 4.2.2 is intended to place a limit on acceptable H2S content under the conditions stated, i.e., when temperature does not exceed 60°C, when no elemental sulfur is present, but without restriction on chlorides.
2. Paragraph 4.2.2 places a maximum temperature limit of 60°C on the use of austenitic stainless steel under any conditions in which MR0175 applies, for example, at 0.1 psia H2S partial pressure with no chlorides present.
(MP INQUIRY #2003-23 Q1) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3 QUESTION:
In addition, please clarify the reason for the 60°C limit in Paragraph 4.2.2:
We have noted that a limit of 60°C is commonly cited with respect to chloride stress corrosion for austenitic SST in other publications, and that chloride is mentioned in Paragraph 4.2.2. Are we correct in assuming, therefore, that the 60°C limit in Paragraph 4.2.2 is based on chloride stress corrosion concerns above 60°C when chloride concentrations above 50 mg/L are present rather than H2S corrosion concerns? That is, the first sentence of Paragraph 4.2.2 does not have a limit on chlorides but does have a temperature limit, whereas the second sentence limits chlorides but does not have a temperature limit.
(MP INQUIRY #2003-23 Q2) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3
See Paragraph 1.1 in NACE Standard MR0175-2003 for the scope of MR0175. The environmental restrictions in Paragraph 4.2.2 were established to provide resistance to sulfide stress cracking (SSC) and/or stress corrosion cracking (SCC) in austenitic stainless steels.
QUESTION:
AISI 316: Technical justification of the temperature limitation to 60°C.
(MP INQUIRY #2003-27 Q5) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3
The austenitic stainless steels were restricted because of industry and lab failures.
Please see the attached documentation. Upon the final ballot, there was a single negative that was not withdrawn. This negative suggested making the restrictions on 316 SS even more restrictive.
QUESTION:
SUBJECT: Paragraph 6.2.1.1 of NACE MR0175-2003 Standard
QUESTION: It is not clear whether or not the word "restrictions" as used in Paragraph 6.2.1.1 of NACE MR0175-2003 includes any environmental restrictions for bolting and nuts exposed to sour gas environments. Are bolting and nuts, which are manufactured from wrought austenitic stainless steel materials in accordance with the applicable paragraph in Section 4 of NACE MR0175-2003, acceptable for use in exposed sour environments with no environmental limits with respect to chloride content, partial pressure of H2S, temperature, and free elemental sulfur?
QUESTION: Is the answer to the above question in agreement with ISO 15156?
(MP INQUIRY #2003-39) ANSWER:
Paragraph 6.2.1.1 requires materials to meet the requirements of Sections 3 and 4 as applicable to the base material. This paragraph does not specify just
"metallurgical requirements." If the bolting is non-exposed in accordance with Paragraph 6.3.1, then the environmental requirements are not necessary.
QUESTION:
NACE MR0175/ISO 15156-Part 3: From Table A.2 it seems that AISI 316/316L SS can no longer be used whenever the process temperature is above 60°C even if chlorides are totally absent from the environment. As this could have an enormous impact on the material selection for oil and gas processing plants, I would like to have a confirmation of the above.
(MP INQUIRY #2004-17) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3 QUESTION:
We are now in the detailed engineering design phase of a sour gas refinery, and we have implemented NACE MR0175/ISO 15156 for design purposes. NaCl (sodium chloride) will come to the refinery through three-phase flow pipeline from offshore, after liquid separation in slug catcher; then the sour gas will go to gas treatment units for further processing. Table A.2 refers to chloride content in aqueous solution as mg/L; my question is in sour gas treatment units in which we use austenitic stainless steel, what are the criteria for the limitation of application of austenitic stainless steel? My idea is we have to comply with the first row of Table A.2. There is no means to identify the chloride content in the gas stream.
(MP INQUIRY #2004-21) REVISED ANSWER 2005-09-01:
It is assumed in Table A.2 that this is a mixed-phase environment with both a gas phase and a liquid phase. This is always true throughout the document.
The operator is responsible for determining the service conditions, including chloride content (see ISO 15156-1, 6.1) and the ISO Maintenance Panel cannot provide advice.
As mentioned in ISO 15156-3, A.1.3, Paragraph 2: “The tables show the application limits with respect to temperature, pH2S, Cl, pH, S. These limits apply collectively.”
See also revised version of Table A.2 included in Reference 3
However, if, as an equipment user, you feel that ISO 15156-3, Table A.2 does not address your expected field conditions you have the freedom to test materials under alternative environmental limits and to use the outcome of successful tests to justify the use of a material outside the limits set in the standard. (See ISO 15156-3, 6.1, Para. 5.)
QUESTION:
Would you let me know whether our interpretation is correct? NACE MR0175/ISO 15156-3:2003 Para. A.2.2 states environment limits for austenitic stainless steel.
According to Para. A.2.2, austenitic stainless steel (304/316 SS) is applicable with max. H2S partial pressure of 15 psi at a max. temperature of 140°F and UNS S20910 for valve stem is applicable without environmental limit.
Austenitic stainless steel (304/316 SS) is applicable to valve stem material at a max.
H2S partial pressure of 15 psi and a max. temperature of 140°F. Over a temperature of 140°F, UNS S20910 is applicable material to valve stem.
(MP INQUIRY #2004-23 Q1) REVISED ANSWER 2005-09-01:
See revised version of Table A.2 included in Reference 3
"Any equipment or component" includes valve stems, pins, and shafts. Table A.3 allows the use of UNS S20910 without environmental restrictions for "valve stems, pins, and shafts" but not for other equipment.
See also "General Remarks" under ISO 15156-3, A.1.6 of this "Inquiries and interpretations" document.
QUESTION:
I have a technical query related to the latest edition of MR0175/ISO 15156 and the use of 316 stainless steel for sour service application. This latest edition of the standard imposes new restrictions on the use of 316 SS in environments operating above 60°C.
My question is can 316 SS be used above 60°C for non-stressed vessel internals or for items such as thermowells located into sour lines or vessels? I ask this because I note that the standard need not be applied to parts loaded in compression (Part 2, Table 1). The implication may be that parts have to be stressed for SCC to be an issue.
As a similar situation to vessel internals and thermowells, please could you advise on the use of 316 stainless steel for valve internals in a sour application, operating above 60°C. Of particular interest is the use of solid 316 SS balls for ball valves.
(MP INQUIRY #2005-03) ANSWER:
1.0 The scope of NACE MR0175/ISO 15156 Part 3, Paragraph 1, Sentence 1 defines the applicability of the standard. The standard need not be applied for equipment not covered by this sentence. In addition, in Table 1, parts loaded in compression are included among those considered to be "permitted exclusions."
SCC requires a tensile stress (applied and/or residual) to occur. There is no
provision for any of the alloys in the standard for a threshold tensile stress below which failure cannot occur.
2.0 The Maintenance Panel cannot analyze the design of equipment. It is up to the manufacturer and equipment user to agree whether or not the scope or any of the listed exclusions in Table 1 apply for a given design.
A.2.2 including Table A.2