Std Material Specification for Wet H2S Services-Application to Carbon Steels [in-43]

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STANDARD MATERIAL SPECIFICATIONS FOR

WET H2S SERVICES

Application to Carbon Steels (IN-43)

This document contains confidential proprietary material belonging to Axens which may only be made available to personnel or organizations who have signed appropriate secrecy agreements. Fo43-5.dot/ Rév. 5 du 14.08.2003

IN-43-0.1(Standard Material Specification for wet H2S Services-Application Services-Application to carbon steels).doc


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GENERAL COMMENTS

The information given hereafter for Carbon Steels operated under sour services results from Axens experience in the field of refining units operated under wet H2S conditions. For instance, these specifications should be typically applied for pressure vessels, piping and accessories used under sour services. Specific codes, as well as Client and/or EPC Standards may also influence the choice in materials and methods. It shall be noted that, in case of interference, in the project frame, between the present specification and others (ex: issued by owner and/or EPC), or codes, etc, the more stringent criteria will have to be considered.

1.

SCOPE

This standard document specifies Axens requirements on Carbon Steels for equipments handling fluids containing free water and hydrogen sulfide. Appropriated rules described here after have to be applied when Axens process book calls for “wet H2S resistant steels” or “ HIC resistant steels” as well.

2.

PROCUREMENT

These kind of steels shall not be considered like standard carbon steels within the project framework but shall be cautiously considered by taking into account their technical specificities. When properly tackled, the procurement of such steels should be conducted by leading neither non justified extra-costs nor unacceptable delivery schedule. Project people should consequently be aware about this specificity at the very beginning of the project in the aim at anticipating the appropriated requirements dedicated to these steels.

3.

TYPICAL FORMS OF DAMAGE

Refer to Axens Standard IN-45 (Materials of Construction)


IN-43-0.1(Standard Material Specification for wet H2S Services-Application to carbon steels).doc

STANDARD MATERIAL SPECIFICATIONS

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WET H2S RESISTANT STEELS (Category 1)

Axens applies the following design requirements for Carbon Steel "wet H2S resistant” :

- Carbon steel must be Fully Killed Carbon Steel type, - Hardness of the base metal shall be below 22HRC, - Ni content less than 1%, - Carbon content shall be 0.20% maximum, - Plate material shall be supplied in Normalized condition, regardless of thickness, - Typical limitation of Carbon Equivalent are the following : . Ceq lower than 0.42% for thicknesses below 2” . Ceq lower than 0.45% for thicknesses above or equal to 2” With Ceq = C + Mn/6 + (Cr +Mo + V)/5 + (Ni + Cu)/15 These Ceq values are indicative and may be re-considered if needed regarding the used steel grade. In that case, new proposed values should be submitted to EPC for approval.

- Thermal Stress Relieving required for all welds (PWHT), even if it is not required by code, - Thermal Stress Relieving required for cold bend zones producing outer fiber deformation greater than 5%, even if it is not required by code , - Hardness of the production welds shall be lower than 200HB. This value uses to be slightly lower than the one defined for base metal (22HRC or 237HB) in order to anticipate potential non-homogeneity of certain weld deposits.




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ET H 2S R ESISTANT S TEELS (FOLLOWING) W

- Application to Plates (and Welded pipes) - As an example, a possible designation could be ASTM A516 gr60 (or P265GH according to EN10028-2) provided that all the specifications given here-above are guarantied and supplemented by following limitation: - Maximum allowable Phosphorus content 0.020% - Maximum allowable Sulfur content 0.015% - Welded pipes shall fulfill the same requirements as for plate material Note: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for Plates parts shall fulfill the same requirements as defined here-above. - Application to Process Piping and accessories - Process piping shall be seamless type, - As an example, a possible designation could be ASTM A-106 Gr.B (P265GH could also be used according to EN10216-2) provided that all the specifications given here-above are guarantied and supplemented by following limitation on impurities level : - Maximum allowable Phosphorus content 0.030% - Maximum allowable Sulfur content 0.020% Note: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for piping parts shall fulfill the same requirements as defined here-above.

- Application to Flanges and accessories - As examples, acceptable designations could be ASTM A-105 for forging (P280GH could also be applicable according to EN10222-3) and ASTM A-216WCB for castings (GP240GH could also be used according to EN10213-2) provided that all the specifications given here-above are guarantied and supplemented by following limitations on impurities level.: - Maximum allowable Phosphorus content 0.030% - Maximum allowable Sulfur content 0.025% Note 1: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for Flanges and accessories shall fulfill the same requirements as defined here-above.




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Note 2: The final specification concerning the P&S impurities contents, during the call-for-bids, might be reviewed by the EPC (based on its own standard if any) following its typical practice for “Piping in Sour Service”. In case of any discrepancy with the Axens specification, decision will be made under EPC responsibility.

Remark: It is Axens use to maintain PWHT on carbon steel made piping parts. As a matter of fact, the PWHT is considered by Axens as being the only way to be absolutely sure about the hardness level limitation in the welded and HAZ zones. However, the contractor may sometimes decide to avoid the PWHT on piping parts by considering that the appropriated welding procedure will be properly defined and controlled in order to guaranty the specified hardness level after welding. In that case, representative welding procedure qualifications shall be carried out on purchased piping material for the whole project such as to cover each grade of piping material, each type of welds (i.e. fillet welds and butt welds), maximum thickness without PWHT, highest CE, controlled base metal chemistry, controlled weld metal chemistry, etc. If it is considered, by the Contractor, that such qualified procedure will be properly followed for the whole piping product and thus guaranty fully achieved hardness restrictions, then the contractor may decide to avoid PWHT on piping parts. Decision shall be made under EPC responsibility.



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HIC RESISTANT STEELS (Category 2)

Axens applies the following requirements for Carbon Steel "HIC resistant":

It shall be noted that stresses have no influence on HIC phenomenon, however the material composition and structure do. The most important factor to avoid HIC is the purity (cleanliness) and the homogeneity of the steel. The non-metallic inclusions as well as any sites where hydrogen recombination might occur (e.g. elongated MnS inclusions) must be kept at very low content. In addition to the general recommendations relative to "wet H2S resistant steels”, when ”HIC resistant steel” is specified, the following requirements shall also be met:

- Carbon steel made by vacuum degassing process, - Oxygen content less than 0.0025% (target being 0.002%), - Calcium treatment, if any, shall be Ca/S ratio greater than 1.2 - It is required to pass the NACE standard TM0284 ( Evaluation of Pipeline and Pressure Vessels Steels for Resistance to Hydrogen-Induced Cracking ) by using the acidified test solution A specified in NACE standard TM0177 ( Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H 2S environments) with: Crack Length Ratio (CLR)

lower than or equal 5 %

- Mill test reports shall include the values for the crack length ratio (CLR), crack sensitivity ratio (CSR) and crack thickness ratio (CTR) as defined in NACE standard TM-02-84 and also carbon equivalent (CE),




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HIC R ESISTANT S TEELS (FOLLOWING)

- Application to Plates and Welded pipes - As an example, a possible designation could be ASTM A516 gr60 (or P265GH according to EN10028-2) provided that all the specification given here-above are guaranteed and supplemented by following limitations: - Maximum allowable Phosphorus content 0.010% (target 0.008%) - Maximum allowable Sulfur content 0.002% (0.007% if inclusion shape controlled by calcium treatment) - Welded pipes, if any, shall fulfill the same requirements as for plate material Note: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for Plates parts shall fulfill the same requirements as defined here-above.

- Application to Flanges and accessories - As examples, acceptable designations could be ASTM A-105 for forging (P280GH could also be applicable according to EN10222-3) and ASTM A216WCB for castings (GP240GH could also be used according to EN102132) provided that all the specifications given here-above are guaranteed and supplemented by following limitations on impurities level.: - Maximum allowable Phosphorus content 0.025% - Maximum allowable Sulfur content 0.020% Note: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for Flanges and accessories shall fulfill the same requirements as defined here-above. - Application to Process Piping and accessories - Basically, specification dedicated to the HIC resistant steels is not to be applied on process pipes provided that these latter are seamless type, - It is Axens viewpoint to consider seamless piping as intrinsically immune against Hydrogen Induced Cracking phenomenon; only “wet H2S resistant” steel specification shall then be applied, - However, welded pipe, if any, shall fulfill the same requirements as for plate material. Note: In case of Low Temperature applications under sour Service, dedicated Carbon Steel grades for piping parts shall fulfill the same requirements as defined in the specification for piping “wet H2S resistant”.




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Remark 1: Axens standard specification for HIC resistant carbon steel has been formulated in order to lower as much as possible the risk of potential Cracking induced by Hydrogen activity. Any deviation to the said Axens specification will be under the responsibility of the Engineering Contractor. Anyway, and whatever the criteria will be, Axens considers that it is mandatory to maintain, as a minimum, the whole here above specified requirements (including impurities content) in order to consider the steels as “HIC resistant steels”. Moreover, a quality control only based on NACE testing (without appropriated cleanliness control) may lead to a “pseudo-HIC” steel. In contrast to HIC resistant plates, pseudo HIC plates are not originally produced to be HIC resistant (i.e. using adapted production and quality assurance system) but are steels produced using conventional production methods which may be subjected to HIC testing in laboratory. Good results can be obtained but these are not representative of the whole plate and are only valid for the tested location. Homogeneous, constant HIC resistance can only be obtained if the entire plate production is consistently adapted to meet HIC resistance requirements. If not, the steels will not be considered as HIC resistant steels by Axens.

Remark 2: The final specification concerning the different impurities contents, during the call-for-bids, might be reviewed by the EPC (based on the owner specification if any) following its typical practice for “HIC resistant steels”. In case of any discrepancy with the Axens specification, decision will be taken under EPC responsibility.

Remark 3: the use of a standard carbon steel grade with SS cladding can be an alternative to “HIC resistant steels” specification especially for thick-wall vessels like cold HP separator since it should involve only a small cost premium over “HIC resistant steel” construction (the procurement could even be sometimes more easy). The resulting protection against corrosion would be enhanced provided that SS solution would not lead to other kind of corrosion and/or deterioration.



Std Material Specification for Wet H2S Services-Application to Carbon Steels [in-43]

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