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The main changes in ISO 15156:2015, the new NACE MR0175.
What are the changes in the new NACE MR0175? As I mentioned in a previous post, ISO 15156:2015 has been published on September 1st. There are several changes from the 2009 revision and in this blog we present the most relevant changes.
Since the publication of ANSI/NACE MR0175 / ISO 15156:2009 there have been several corrigenda and technical circulars, these are:
- ANSI/NACE MR0175/ISO 15156-1:2009/Cir.1:2014
- ANSI/NACE MR0175/ISO 15156-2 Technical Circular 1 (2011)
- ANSI/NACE MR0175/ISO 15156-2:2009/Cir.2:2014
- ANSI/NACE MR0175/ISO 15156-3 Technical Circular 1 (2011)
- ANSI/NACE MR0175/ISO 15156-3 Technical Circular 2 (2013)
- ANSI/NACE MR0175/ISO 15156-3:2009/Cir.3:2014
- ANSI/NACE MR0175/ISO 15156-3:2009/Cir.4:2014
Some users may not keep up to date with the technical circulars and corrigenda; for this reason in this blog we decided to compare the ANSI/NACE MR0175/ISO 15156:2009 with the new ISO 15156:2015.
Changes in ISO 15156-1: General principles for selection of cracking-resistant materials
There are two main changes in Part 1:
- Clause 5 has changed the use of the term “conventional elastic design criteria “to “load controlled designed methods”; this change is echoed in Part 2 and Part 3
- The standard now provides a better guidance for strain based design methods. Where as in the previous editions the strain based design scenario was address by indicating that the manufacturer and user “shall assess the need for other requirements”, the new version indicates that the manufacturer and user “shall define and agree other testing requirements and acceptance criteria”. This means that is a big step in terms of the qualification requirements.
Changes in ISO15156-2: Cracking-resistant carbon and low steels, and the use of cast irons.
As with clause 5 of section 1, the term “conventional elastic design criteria” has been replaced by “load controlled design methods”, but this is not the only change.
In the body of Section 2, the qualification and selection of carbon and low alloy steels with resistance to SSC, SOHIC and SZC is addressed. Two options are presented to the user, Option 1 is to select steels using annex A.2, the Option 2 is to qualify for specific applications.
When using Option 1, Section A.2 lists the properties required for the use of steels in different sour service conditions, these properties include chemical composition, heat treatment and hardness. A.2 also includes application to product making reference to qualified products listed in standards such as API 5L and API 5CT.
Option 2 includes the qualification of steels and low alloy steels, this is useful for non-listed materials, as well as fitness for purpose (e.g. equipment exposed to souring conditions). This is the route selected for qualifying proprietary grades for sour service.
The update of ISO 15156-2 in the 2015 revision allows extending the range of products listed in section A.2 by means of qualification using Annex B.
It is also important to mention that Part 2 now has spelled out the PWHT requirements as 620°C min for low alloy steels. The new text is also very explicit in defining that mechanical properties (other than hardness), as well as heat treatment method and duration shall be subject to approval of the user.
So in summary, Part 2 main changes are:
- The use of the term “load controlled design methods” replaces “conventional elastic design criteria”
- Qualification by option 2 allows opening the limits of materials listed in A.2.
- Explicit limits for PWHT for low alloy steels
Changes in ISO 15156-3: Cracking-resistant CRAs (corrosion resistant alloys) and other alloys.
Part 3 of ISO 15156 is the one that sparks the most interest, and this is because it addresses the limits for Corrosion Resistant Alloys (CRAs). This does not negate the importance of Part 1 and Part 2, but Part 3 always attract more attention. In this new ISO2015:2015 revision similar to Part 1 and Part 2 the term “conventional elastic design criteria” has been replaced by “load controlled design methods”; I also want to highlight the following changes
PREN
The limits for the PREN have been refined, now the PREN values shall be taken as absolute values as per ASTM E29. The importance of accurately presenting and comparing the PREN values is of high importance, some may consider as pernickety the need use ASTM E29 as a reference; but if you look at the 2009 edition where PREN values in table A.2 were defined as “>40”; you can see a storm coming when a test report present a PREN value of 39.5 and someone ask “can we round it to 40?”. In order to prevent these situations the use of ASTM E29 has been introduced and uncertainty is eliminated. This change is also shown in Table A.11, Table A.24 and Table A.25.
CRA limits:
Several changes have been included in the tables these include:
Austenitic Stainless Steels: Table A.2 has new limits for S31603. These changes were introduced in a previous technical circular and we have presented them in a different blog, you can follow this link. It is important to highlight that these changes are for S31603 (316L), not just for all austenitic alloys
Solid-solution nickel based alloys: Table A.12 has been updated to include Type 4f alloys, but note that this only covers UNS N07022, and the specific limits are included in table A.14 with temperatures limits for 204°C and 288°C for different ppH2S and a max Cl of 180000mg/l. But there is also a limit for the value of ppCO2+ppH2S. If you are planning to use this alloy contact us to complete a corrosion assessment and confirm the alloy is fit for purpose in your production environment. Hardness limits for UNS N07022 are also defined.
Duplex (and superduplex) stainless steels: Table A.24 and Table A.25 have been updated to refine the limits of the PREN, but also to define what is a rapid cooling. In this document, rapid cooling is defined as cooling rate that avoids the formation of deleterious phases.
Precipitation hardened nickel based alloys: Table A.32 has been updated and the limits for N09925 are updated. N09945 is now included. N07022 in wrought, annealed and aged condition is also included in table A.33
Titanium Alloys: R50250 is now included in Table A.41.
Annex F: this annex was controversial when introduced as a technical circular; some discrepancies between Annex F and the tables in Annex A meant that this annex will have to be reviewed and possibly added as a technical circular.
