NACE MR/ISO standard should be submitted to NACE. . NACE MR/ISO consists of the following parts, under the general title. Details of the software products used to create this PDF file can be pertaining to ANSI/NACE MR/ISO should be submitted to. Details of the software products used to create this PDF file can be .. ASNI/ NACE MR/ISO will be processed in the same way and.
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The revision of this part of ANSI/NACE MR/ISO involves a ANSI/ NACE MR/ISO will be processed in the same way and will lead to. This NACE International standard represents a consensus of those .. Adding New Materials for MR Section 4: Corrosion-Resistant Alloys (CRAs)—All. The document too frequently referred to simply as “NACE”, was first issued in by the National Association of. Corrosion Engineers, now known as NACE .
The overwhelming consensus was that the new document was much more conservative than the last version of the original document.
This is an important factor to bear in mind when considering some of the following. Differences between the Two Documents The definition of sour service has changed.
The NACE document allowed certain exemptions, for which materials did not need to meet the requirements. Sour gas systems operating at a total pressure less than kPa absolute 65 psia were exempt, regardless of H2S content. In oil effluent or multi-phase systems, exemption from the standard was more complicated.
If the total operating pressure was below kPa absolute and the maximum gas:oil ratio is and the H2S content is 15 mole percent and the H2S partial pressure is 70 kPa absolute 10 psia , materials were exempt.
ANSI/NACE MR0175/ISO 15156-2015-SG
While two 2 points on the hardness scale may not seem significant, when qualifying high yield strength materials weld procedures, those points may indeed mean the difference between pass or fail. CSA has not removed the strength restriction, the reason for which is unknown. CSA once again does not agree, as evidenced in Z , as well as, Z A minimum period of two 2 years experience was selected as the time criteria.
If the end user could demonstrate that the material has operated within a given environment for the time criteria, it became acceptable for continued service. This may sound logical and applicable, but there was an added stipulation stating that the material could not be exposed to more severe conditions than the documented experience.
This is also true for autoclave testing results, which essentially shortens the exposure period from two 2 years to hours. It is important to note that chlorides have no virtually no impact on cracking susceptibility. Nowhere in the document is there any explanation of how to use these regions. Section 7. This infers that somehow field experience can be extrapolated, without any discussion as to how.
That point selected is at an H2S partial pressure of kPa and an in-situ pH of 2.
The shaded area in Figure 3 depicts the area of exposure that this interpretation allows. This essentially precludes using materials based on field experience.
The operating conditions will define a certain H2S partial pressure, but the pipeline would likely have a significantly higher maximum allowable operating pressure MAOP , which would result in a higher H2S partial pressure. To illustrate, assume that the kPa H2S partial pressure is based on a historical operating pressure of kPa with 10 mole percent H2S in the gas phase.
If the MAOP of the pipeline is kPa, the H2S partial pressure could then theoretically reach kPa, which falls outside of the approved area depicted on Figure 3.
This approach also allows a material to be used in a large area within Region 3, but will not allow the material to be used in any area of Region 2 where the H2S partial pressure exceeds kPa. This approach seems to be more sensible in that it recognizes that while the H2S partial pressure might exceed the defined point, if the pH also increases, i.
Realistically however, it is extremely unlikely that the pH would increase, i.
As with the first interpretation, a material could qualify within Region 3, but could be disqualified for use in part of Region 2. One realization in using either of the above two interpretations is that it totally negates the need for identifying regions.
It needs to be understood that the total stresses working on a material are the combination of both the applied stress i. The higher the applied stress on a material the more susceptible to SSC it becomes.
Cold working will 1 alter the microstructure d 2 i th id l f t il t and 2 increase the residual surface tensile stresses. For this reason heat treatment is recommended for cold worked or cold formed low alloy steels before they are used in a sour environment. An annealing or normalizing heat treatment will return the material to its original SSC resistance following cold working SSC resistance following cold working.
Therefore additional high strength tubing and casing materials can be utilized above threshold temperatures However if a well is to be completed or operated in threshold temperatures. However if a well is to be completed or operated in a sour zone with a temperature above a threshold temperature for a particular material the engineer must confirm that the environment in contact with the material does not drop below that critical temperature.
Below this temperature these high strength materials are susceptible to SSC and cannot be utilized.
Under laboratory controlled conditions it is possible to determine the time to failure laboratory controlled conditions it is possible to determine the time to failure of a given alloy under a particular set of conditions.
However in actual field conditions projecting a time to failure is extremely difficult. The time it takes for a material to fail due to SSC is dependent on the aggressiveness of the environment and the degree of susceptibility of the material.
SSC can happen quickly or may take years to develop Therefore it is critical that a review of quickly or may take years to develop.
Therefore it is critical that a review of the materials and environment be conducted prior to specifying the completion equipment. SSC resistant materials should be utilized. Hardness by definition is the resistance of a metal to plastic deformation Hardness by definition is the resistance of a metal to plastic deformation usually by an indention.
Hardness testers utilize an indenter which is forced into the metal surface by a known loading. The relationship to the area or yg p depth of the indentions to the load applied is known as the hardness of the material. Controlling hardness is an acceptable method for preventing SSC. However if hardness control is to be utilized for approving a welding However if hardness control is to be utilized for approving a welding procedure for use in sour services specific locations and numbers of tests must be performed.
These illustrations must be followed for weld procedure qualifications These illustrations must be followed for weld procedure qualifications. When steel is welded the parent material and consumables are variables that must be welded the parent material and consumables are variables that must be reviewed and controlled.
But these are not the only variables that need to be considered when welding in sour service. The HAZ is that area around the actual weldment that has been exposed to high temperatures but not high enough to actually liquefy the material.
A parent material that was suitable and acceptable in regard to SSC in its as-received as-milled condition may be susceptible to SSC following fabrication that involves welding.
Therefore fabrication processes involving welding must be reviewed for their potential impact on the SSC potential of the parent material.
However in lieu of qualifying a weld procedure to NACE one also has the option to post weld heat treat PWHT following the completion of the welding option to post weld heat treat PWHT following the completion of the welding. The use of a PWHT technique tempers the welded material. This reduces the residual internal stresses created when the weld metal solidified and tempers t it th t b t i t fi ti f l i t l t i any martensite that may be present into a configuration of lower internal strain.
When ERW pipe was utilized the specification always called for full body normalizing following manufacturing verses only seam annealing full body normalizing following manufacturing verses only seam annealing following manufacturing.
In addition to its ability to crack metals it can also result in pitting corrosion with subsequent failures The release of H2S as a result in pitting corrosion with subsequent failures. The release of H2S as a result of corrosion or cracking can endanger the lives of people working around or in near proximity to the release point.
H2S can be fatal at py p concentrations as low as ppm. Therefore designing equipment resistant to H2S cracking is critical. Additionally prevention of corrosion by H2S is also highly recommended Inhibition of corrosion can be obtained through material highly recommended. Inhibition of corrosion can be obtained through material selection internal coatings or the application of corrosion inhibitor.
However to prevent cracking the NACE standard must be strictly adhered to and followed. Designing for SSC resistance is not only a prudent and good engineering practice but it is a requirement of many regulatory agencies. However producers should be aware of the changes published in the new standard and be prepared to make appropriate modifications to fabrication and engineering specifications.
It should be noted that hydrogen sulfide can be present naturally in produced fluids or can be introduced as a result of contamination by incompatible waters or sulfate reducing bacteria. All safety precautions should be exercised when determining the concentration of H2S in production fluids.
Because of the dangers associated with low concentrations of H2S it iddtl H2Si tdlftht is recommended to always assume H2S is present regardless of the past history of a field lease or individual well. This standard addresses the concerns for all types yp of cracking associated with sour production and makes recommendations for materials and operating conditions to prevent such failures.
NACE MR0175/ISO 15156: 2015 [pdf]
This type of attack occurs at elevated temperatures HTHA and is caused by atomic hydrogen permeating through the steel and HTHA and is caused by atomic hydrogen permeating through the steel and reacting to form other gases.
Accumulation of this methane at grain boundaries and other steel discontinuities results in localized high stresses from which cracks can occur. No externally applied stress is required for the formation of hydrogen-induced cracks.
This form of hydrogen-induced cracking is not related to welding. This type of cracking can be either discrete cracks or an array of cracks The cracks that cracking can be either discrete cracks or an array of cracks. This type of cracking can lead to catastrophic failures due to the potential for the cracks to propagate through the thickness of the material resulting in a considerable loss of strength and ultimate failure.
The linking of hydrogen-induced cracks to produce stepwise cracking is dependent on the local strain between cracks to produce stepwise cracking is dependent on the local strain between the cracks and the embrittlement of the surrounding steel by dissolved hydrogen.
This type of cracking is similar to HIC and SSC but the cracking is transgranular or across the grains in the through thickness direction. These cracks initiate and propagate in the direction normal to the applied stress and are typically observed in the HAZ of relatively high hardness typically observed in the HAZ of relatively high hardness microstructures. The application of a high external stress i.
It has been observed in t til flitdi ll lddi dithh t ff t d parent material of longitudinally welded pipe and in the heat-affected zone HAZ of welds in pressure vessels. SOHIC is a relatively uncommon phenomenon usually associated with low-strength ferritic pipe and pressure- py gpp p vessel steels. Blistering occurs when hydrogen enters the steel and combines into molecular hydrogen at defects present in the steel steel and combines into molecular hydrogen at defects present in the steel plate typically non-metallic inclusions such as sulfides.
Hydrogen blistering generally occurs in low pressure equipment such as tanks and pipeline equipment that are exposed to a corrosive environment that contains hydrogen sulfide. Because of the nature of the manufacturing process of rolled plates Because of the nature of the manufacturing process of rolled plates inclusions present in the steels become elongated with the larger inclusions present and aligned along the centerline of the plate.For the sake of argument, assume that if a version had been issued, it would not have substantially changed from the version.
Qualification by Field Experience - refer to Section 6. Maintaining gp y p g a constant pH in production would prove troublesome and impractical. This begs the question of why regions were created. Other test methods require the agreement of the equipment user. Api Latest Edition. The release of H2S as a result of corrosion or cracking can endanger the lives of people working around or in near proximity to the release point.
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If the end user could demonstrate that the material has operated within a given environment for the time criteria, it became acceptable for continued service.