Chemical & Process Technology

Sulfide -stress cracking is basically a hydrogen-embrittlement phenomenon .Atomic hydrogen enters the steel to cause cracking. The hydrogen is generated on the surface of the steel because of a corrosion reaction. Iron reacts with h2s to form iron sulfide and hydrogen .This hydrogen is generated in atomic form on the steel surface ,where it can either combine to form molecular hydrogen and leave the surface as bubbles or diffuse into steel .This latter process may result in hydrogen embrittlement .Hydrogen sulfide prevents hydrogen recombination & thus promote entry of atomic hydrogen into steel .It is important to note that water must be present for this mechanism to occur ;without it SSC will not be observed ,because the ionization of the hydrogen sulfide is required.

Following is a lecture presentation on NACE Standard MR0175  - Petroleum and Natural Gas Industries – Materials for use in H2S-containing Environments in Oil and Gas Production.

 

Download

• NACE MR0103 versus MR0175
• Common FAQs Related to NACE Standard MR0175 / ISO 15156
• Material Selection... USER Responsibility
• Error in NACE MR0175 / ISO 15156
• Guideline on Use of MR0175 / ISO15156
• What are the concerns related to H2S ?
• Safety Moment with H2S
• Pyrophoric Fire
• Pitting Corrosion - Mechanism & Prevention

NACE MR0103 "Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments" was developed by Task Group 231 to provide a standard set of requirements for materials used in sour petroleum refinery equipment. In the past, NACE MR01752, "Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment", was frequently referenced for this equipment, even though refinery applications were outside the scope of MR0175. The process used to develop MR0103 is described, followed by a review of the requirements in the standard accompanied by highlights of the differences between MR0103 and the previous and current versions of MR0175.

An Overview of NACE International Standard MR0103 and Comparison with MR0175 

Stainless steel is one type of material commonly used in oil & gas, refinery, petrochemical, pharmaceutical industries. Stainless steel is a material does not stain and corrosion resistance to many fluids. Stainless steel is rather "soft" and infact it is a cavitation resistance material. This has been discussed in "Stainless Steel SS316 resist to CAVITATION ?".

Recommended :
- Subscribe FREE - Processing Magazine
- Tips on Succession in FREE Subscription

Although Stainless steel is corrosion resistance to many corrosive fluids by formation of protective oxide film, it is still susceptible to pitting corrosion, one of the most destructive forms of corrosion which potentially cause equipment failures on perforation / penetration as discussed in "Pitting Corrosion - Mechanism & Prevention".

Beside pitting corrosion, stainless steel also susceptible to Chloride Stress Corrosion Cracking (CSCC) as discussed in "Chloride Stress Corrosion Cracking & Use correct MOC for seawater service". CSCC is initiation and propagation of cracks in a metal or alloy under tensile stresses and a corrosive environment contains Chloride compounds. Once the crack is initiated, it will propagate rapidly and potentially lead to catastrophic failure. There are more discussion on stainless steel can be found here.

Dr. David Jenkinson, Director of Nickel Institute has produced a series online training modules on "An Introduction to Selection of Stainless Steels for Corrosion Resistance". The online training modules are in audio format which can be read while listen to the explanation. Visual plus audio will quickly assist engineers in understanding the contents.

Click here to begin learning Stainless Steel and It Selection.

Following are complete listing of training module for Stainless Steel and It Selection.

01 - Disclaimer
02 - Module Abstract
03 - Module Information
04 - Chemical Symbols
05 - What Will We Cover?
06 - What Will We Cover? - What is Stainless Steel?
07 - How Stainless Steel Works
08 - Chromium is the Basic Building Block of Stainless Steels
09 - Damage to the Protective Oxide Film
10 - Penetration of the Protective Oxide Film
11 - Corrosion of Embedded Iron in a Stainless Steel Pipe Bend
12 - The protective passive film can be damaged mechanically or chemically in various ways.
13 - What Will We Cover? - Effect of Alloying Additions
14 - Effect of Alloying Additions
15 - 1. Corrosion Resistance
16 - Effect of Alloying Elements on Corrorsion Resistance - Chromium
17 - Effect of Chromium on Atmospheric Corrosion of Steels
18 - Pitting Resistance Equivalent Number (PRE)
19 - Effect of Alloying Elements on Corrosion Resistance - Nickel
20 - Addition of Nickel
21 - Nickel Provides Resistance to Reducing Chemicals
22 - Effect of Alloying Elements on Corrorsion Resistance - Molybdenum
23 - Effect of Alloying Elements on Corrorsion Resistance - Nitrogen
24 - Effect of Alloying Elements on Corrorsion Resistance - Carbon
25 - Hibernia Oil Production Platform
26 - 2. Crystal Structure
27 - Ferritic Stainless Steels
28 - Adding Nickel to Stainless Steels
29 - Austenitic Stainless Steel
30 - Duplex Stainless Steels
31 - List of Ferrite & Austenite Formers
32 - When Choosing a Stainless Steel
33 - What Will We Cover? - Families of Stainless Steels
34 - Families of Stainless Steels
35 - Ferritic Stainless Steels
36 - Typical Compositions of Common Stainless Steels
37 - Type 409 is hte most widely used ferritic stainless steel.
38 - Proprietary Grades
39 - Dishwashers
40 - Stainless Steel Refrigerators
41 - Hot Water Tank
42 - Austenitic Stainless Steels
43 - Typical Compositions of Common Stainless Steels
44 - Domestic Kitchen Sink
45 - Parliament House, Canberra, Australia
46 - Type 304 Stainless Steel Beer Kegs
47 - Chemical Plant
48 - Frederick R. Weisman Art Museum
49 - Wet Electrostatic Precipitator
50 - Duplex Stainless Steels
51 - Typical Compositions of Common Stainless Steels
52 - Type 316LN Stainless Steel - Example
53 - Pressurized Peroxide Reactor
54 - Stainless Steel Meat Racks
55 - Elevator Tower
56 - Families of Stainless Steels
57 - Martensitic Stainless Steels
58 - Typical Compositions of Common Stainless Steels
59 - Stainless Steel Products - Examples
60 - Martensitic Stainless Steel Blades
61 - Precipitation Hardening (PH) Stainless Steels
62 - Typical Compositions of Common Stainless Steels
63 - High Strength S45000 Precipitation Hardening Stainless Steel
64 - What Will We Cover? - Maximizing Corrosion Resistance
65 - Corrosion of Carbon Steel
66 - General Corrosion
67 - Localized Corrosion
68 - Pitting
69 - Once it gets started, pitting is difficult to stop and to repair.
70 - PRE Numbers for Some Ferritic, Austenitic & Duplex Grades
71 - Pitting Corrosion - Effect of Temperature and Chloride Level
72 - Crevice Corrosion
73 - Crevice Corrosion - Example
74 - Chloride Stress Corrosion Cracking (SCC)
75 - Chloride Stress Corrosion Cracking - Example
76 - Copson Curve
77 - Chloride Stress Corrosion Cracking - Effect of Temperature and Chloride Level
78 - What Will We Cover? - High Performance Stainless Steels
79 - High Performance Stainless Steels
80 - Pitting and Crevice Corrosion Resistance
81 - Three Families of High Performance Stainless Steels
82 - PRE Numbers for Some Ferritic, Austenitic & Duplex Grades
83 - Immersed in Seawater Without Cathodic Protection
84 - Heat Exchanger
85 - Flexible Hosing
86 - Heat Exchanger for Aggressive Chloride Service
87 - Zeron 100 Fittings
88 - Condenser Tubes
89 - What Will We Cover? - Nickel Alloys
90 - More Resistant Alloys
91 - Nickel Alloys
92 - Alloy C-276
93 - Summary

Further Reading

• Chloride Stress Corrosion Cracking & Use correct MOC for seawater service
• Pitting Corrosion - Mechanism & Prevention
• How Chloride stress corrosion cracking Lookslike ?
• Different Equation for Pitting Resistance Equivalent Number (PREN)
• Unified Numbering System for Metals and Alloys

A reader MT (abbre.) has read "Why Restriction Orifice is some distance from Blowdown valve ?" and drop me a note. The question are more-or-less as follow :

ii) If the Flare header is Stainless steel (SS), and the process piping is Carbon steel (CS), the Spec break between CS and SS will be shown at the blowdown valve (BDV), i.e. BDV is designed for the most conservative material - SS. In this case, i do not seen the reason of the minimum distance.

The intention of the proposed arrangement in "Why Restriction Orifice is some distance from Blowdown valve ?" is to avoid the BDV stem stuck at position in case the depressured fluid temperature is dropped to sub-zero (below zero degree Celcious).

i) In case low pressure drop and the depressured temperature is still higher than sub-zero, this requirement is NOT necessary. As long as there is NO risk of fluid temperature drop below zero degree Celcious, then this arrangement is not required.

ii) The process piping upto BDV (excluded BDV) is CS and from BDV onwards is SS. This is a good arrangement with good spec break. The 600mm requirement is mainly related to frozen of moisture content (below zero degree Celcious), it has no/less relationship with the material. Thus, as long as the depressured temperature can drop below zero degree Celcious, regardless what the material of construction (MOC) is, the 600 mm arrangement still applicable.

In earlier posts "Quick Estimation of CO₂ Corrosion Rate" and "CO₂ Corrosion Rate Estimation Using M-506 Model", two simple model i.e the DeWaard Milliam model and Norsok M-506 model have been introduced. The DeWaard Milliam model is just a simple chart while the M-506 model has been programmed into a software and available FREE for download.

In this post, another CO₂ corrosion rate estimation software FREECORP will be introduced. FREECORP has been released for use by the corrosion research community. It was developed by scientists and programmers at Corrosion Center using publicly available knowledge of oil pipeline corrosion and it is distributed under GPL (General Public License) for FREE use by researchers, practitioners, and students of corrosion phenomena.

"FREECORP V1.0 is a simple corrosion model, strongly rooted in theory, which has been developed exclusively based on public knowledge. Currently, this model is capable of predicting uniform corrosion of carbon steel at a single point in an environment containing carbon dioxide, acetic acid, oxygen, and/or hydrogen sulfide. Iron carbonate film formation, a key factor in carbon dioxide corrosion, is simulated using an empirical correlation to improve the accuracy of corrosion rate prediction. Contributions to corrosion of various corrosion species can be calculated, which enables the exploration of dominant corrosion mechanisms in the corrosion process. Furthermore, polarization curves for each individual electrochemical reaction, net cathodic and anodic reactions and polarization sweeps can be optionally displayed. In a case of hydrogen sulfide corrosion, film formation is calculated and concentration profile of H2S across mass transfer layers on steel surface is displayed."

Recommended :
Subscribes to FREE Hydrocarbon Processing

Plant debottlenecking and upgrading may involve some hot work and new tie-ins on existing facilities. To facilitate safe construction of new tie-ins, conventionally the existing system will needs to be shutdown and decommission to allow safe hot work. Production loss and inventory loss will incur a large cost for a simple modification. Thus, hot tap technology has been created to facilitate construction of new hot tap while allowing continue production and zero inventory loss. Read more on "Hot Tapping and Line Stopping Without Shutdown Services". You may view the the detailed hot tapping procedure by click this link.

In normal operation of a plant, certain unavoidable phenomena such as equipment wear and tear, corrosion, decay, etc would lead to valve deteriorate and required to be replaced / changed out. Similarly, this activities would lead production shutdown and inventory loss in order to carry out the change-out activities. Now a new technique has been introduced to remove and replace a ball valve without shutting down the plant. It has been successfully implemented in changed-out of a 6" ball valve located on a live cryogenic tank. This surely and significantly reduction in production and inventory losses. In principle, it apply the similar hot tapping procedure to carry out the valve change-out. Read more on "Ground-breaking procedure on live propane tank avoids costly shutdown".

Although hot tapping and online valve change-out is very attractive, nevertheless, there are still many established oil and gas operator keep them away from using this technology. The main concern still the risk involve and confident and success stories for these techniques. Having said that, it no doubt is a technique may be considered in special case.

What do you think ?

Related Post

• What are the concerns related to H2S ?
• Safety Moment with H2S
• Pitting Corrosion - Mechanism & Prevention
• Hydrogen present and it's impact to metallurgy
• Different Equation for Pitting Resistance Equivalent Number (PREN)
  
• Chlorride stress corrosion cracking and use of correct MOC for seawater

Recommended :
Subscribe FREE - Metal Finishing

NACE Standard MR0175 / ISO 15156 - Petroleum and Natural Gas Industries – Materials for use in H2S-containing Environments in Oil and Gas Production was established to provides limits of H2S partial pressure for precautions against sulfide stress cracking (SSC) and guidance for the selection and specification of SSC-resistant materials.

Following are some commonly asked question related to this standard.

Recommended :
Subscribe FREE - Metal Finishing

This is a brief history about how NACE MR0175 / ISO 15156 is established since 1950s. It begun after World War II with the establishment of Technical report 1A152 "Sour Oil Well Corrosion" and 1B159 "Well Completion & Corrosion Control of High Pressure Gas Wells" when the demand to gas increased. This followed by NACE 1B163 "Recommendations on Material for Sour Service" and NACE 1F166 "Sulfide Cracking-Resistance Metallic Material for Valves for Production and Pipeline Service" in 1960s. First published of MR 0175 in 1975 and TM0177 "Testing of Metals for Resistance to Sulfide Stress Cracking at Ambient Temperatures" in 1978 and followed by TM0284 "Evaluation of Pipeline Steels for Resistance to Stepwise Cracking" in 1990. MR0175 is then merged with some EFC reports i.e. EFC#16 & #17 and finally first published the NACE MR0175 / ISO 15156 in 2003/2004.

Critical Improvements
Several critical improvements in the NACE MR 0175 with the published of NACE MR0175 / ISO 15156 in 2003/2004 :

• Inclusion of Stepwise cracking (SWC), Stress Oriented Hydrogen-Induced Cracking (SOHIC), Soft-zone cracking (SZC), etc. Read more on these corrosion type in "What are the concerns related to H2S ?"
• USER who are specifying and/or operating the equipment has full responsibility to ensure a material is works satisfactory in the intended environment. USER is responsible for the material selection. On the other hand, MANUFACTURER is responsible for meeting the metallurgical requirements.
• For revamping/modification of existing facilities and the material was designed for previous revision of NACE MR0175, if USER has the opinion the fluid condition stayed as before, USER may keep the existing material.
• NACE MR0175 / ISO 15156 is solely a guide documents for a proper selection of material in H2S environment. This documents providing list of material resistant to H2S environment, however, the material is not immune to to H2S environment. It implies that improper design, selection, fabrication, etc. may still lead to these material susceptible to H2S environment.

USER Responsibility
From above statements, the use and implementation of NACE MR0175 / ISO 15156 in H2S environment is within the decision of USER. A metallurgist and material engineer with the assistance of process and chemical engineer within the USER group i.e. COMPANY, CONTRACTOR, and LICENSOR are playing a major role in defining and implementing this standard. DO NOT RELY ON MANUFACTURER & VENDOR !!!

Read more in "Changes to NACE Standard MR0175-2003"
Download

Related Post

• Error in NACE MR0175 / ISO 15156
• Guideline on Use of MR0175 / ISO15156
• What are the concerns related to H2S ?
• Safety Moment with H2S
• Pyrophoric Fire
• Pitting Corrosion - Mechanism & Prevention

Recommended :
Subscribe FREE - Plant Services

In earlier post "FAYF - Acid Solution Storage", Carbon Steel (CS) may be used for concentrated Sulfuric acid (H2SO4) at ambient temperature. However, diluted H2SO4 may severely corrodes CS. Non-metal material (PVC, PFA, FEP, PTFE) may be used for concentrated and diluted H2SO4 solution. Nevertheless, these materials lose it strength at high temperature and high pressure operation. Using non-metal material may not be cost effective at high temperature and high pressure design.

Thus for high temperature and high pressure operation, exotic material Zirconium and its alloy may be considered.

Zirconium has excellent corrosion resistance in all concentrations of sulfuric acid up to 70% and well above boiling.


Zirconium Limitation and its work-around...
H2SO4 concentration exceeded 55%, there will be preferential corrosion attack at weld. WIth H2SO4 concentration exceeded 65%, there may be Sulfide Stress Corrosion Cracking (SSCC) in Zirconium. Thus, stress-relief anneal (heat treatment) should be conducted to avoid above mentioned preferential corrosion and SSCC. However, In the presence of fluoride ions, Zirconium should not be used with sulfuric acid.

For H2SO4 concentration exceeded 70%, other material such as Tantalum may be considered. Tantalum can take any H2SO4 concentration with temperature upto 200 degC.

Read more details explanation in


Note :
*This article is only available FREE to Chemical Engineering Magazine registered user.
Login required. Registration FREE (Click HERE).
** Download immediately as article available FREE within short period (JUNE 2008 only)
*** Found lost link or unable to download, may contact me...

RELATED POST

• FAYF - Acid Solution Storage
• High Temperature Hydrogen Attack in metal & alloy
• Hydrogen Embrittlement TEST method
  
• Hydrogen present and it's impact to metallurgy
• Different Equation for Pitting Resistance Equivalent Number (PREN)
  
• Chlorride stress corrosion cracking and use of correct MOC for seawater
• Pitting Corrosion - Mechanism & Prevention

High demand in energy source i.e. petroleum, LNG, etc leads to high pricing of these sources. This has given addition incentive to explore those sour field. Sour field being Oil or gas contains high H2S which potentially lead to material cracking.

i) Sulphide Stress Corrosion Cracking (SSCC)
H2S dissolved in water to form weak acid promote corrosion and form free hydrogen. Free Hydrogen will penetrate the metal, reduce ductility of metal and potentially lead to stress failure below it yield stress, results Sulphide Stress Corrosion Cracking (SSCC).

Sulfide stress corrosion cracking (SSCC) is cracking of metal involving corrosion and tensile stress (residual and/or applied) in the presence of water and H2S. SSC is a form of hydrogen stress cracking (HSC) and involves embrittlement of the metal by atomic hydrogen that is produced by acid corrosion on the metal surface. Hydrogen uptake is promoted in the presence of sulfides. The atomic hydrogen can diffuse into the metal, reduce ductility and increase susceptibility to cracking. High strength metallic materials and hard weld zones are prone to SSC. (Source : NACE MR 0175)

Apart from SSCC, H2S also cause other cracking, including stress corrosion cracking (SCC), hydrogen-induced cracking (HIC) and stepwise cracking (SWC), stress-oriented hydrogen induced cracking (SOHIC), soft zone cracking (SZC) and galvanically induced hydrogen stress cracking.

Hydrogen Stress Cracking (HSC)
HSC refer to cracking that results from the presence of hydrogen in a metal and tensile stress (residual and/or applied). HSC describes cracking in metals that are not sensitive to SSC but which may be embrittled by hydrogen when galvanically coupled, as the cathode, to another metal that is corroding actively as an anode. The term galvanically induced HSC has been used for this mechanism of cracking.*

Stress Corrosion Cracking (SCC)
SCC refer to cracking of metal involving anodic processes of localized corrosion and tensile stress (residual and/or applied) in the presence of water and H2S. Chlorides and/or oxidants and elevated temperature can increase the susceptibility of metals to this mechanism of attacks. *

For Chlorides stress corrosion cracking (CSCC), read more in Chloride Stress Corrosion Cracking & Use correct MOC for seawater service

Hydrogen-Induced Cracking (HIC)
HIC refer to planar cracking that occurs in carbon and low alloy steels when atomic hydrogen diffuses into the steel and then combines to form molecular hydrogen at trap sites. Cracking results from the pressurization of trap sites by hydrogen. No externally applied stress is needed for the formation of hydrogen-induced cracks. Trap sites capable of causing HIC are commonly found in steels with high impurity levels that have a high density of planar inclusions and/or regions of anomalous microstructure (e.g. banding) produced by segregation of impurity and alloying elements in the steel. This form of hydrogen-induced cracking is not related to welding.*

Stepwise Cracking (SWC)

Stainless Steel (i.e. SS316) is "soft" compare to other material e.g Cast Iron, Duplex stainless steel, etc. due to it has high ductility. However, high ductility of stainless steel make a good material resist cavitation.

The main reason is due to work-hardening property of Stainless Steel. Hammering a SS316 strip would lead to surface work-hardens and difficult to change the shape.

Similar phenomenon occurs when microjet impacting on the surface of stainless steel and caused the Stainless steel work-hardens, and increase resistance to further cavitation.

SS316 resists cavitation about 10-15 times better than cast iron whilst CA6NM (modified SS316) is roughly 2-3 times more resistant to cavitation as compared to SS 316.

Related Topic

• Hydrogen present and it's impact to metallurgy
• Different Equation for Pitting Resistance Equivalent Number (PREN)
  
• Chlorride stress corrosion cracking and use of correct MOC for seawater
• Pitting Corrosion - Mechanism & Prevention

Chemical Engineering share a new FAYF in May 2008. This FAYF is related to some tips and requirements of Acid Solution Storage especially in Material of Construction (MOC).

Nano technology is getting important nowadays. Special characteristic of nano material such as high thermal conductivity, high electrical conductivity, high strength, etc would definitely will bring a great revolution in material selection and change the way we doing things.

There is a great detail introduction and substantial links to other websites related to nano-technology in here.

Let see simple presentation by Dr. Julie MacPHERSON, a researcher intended to find the way to produce nano-carbon in most affordable cost.

There are many head types attached to a vessel, column or drum such as hemispherical, semi-hemispherical, elliptical, flanged, etc. All these have been used in many application and however the selection of the head type is normally not documented in any process nor mechanical document and drawings. The question of application of head type has been raised many time by young engineers and the answer has been repeated many times. There is some incentive behind to list out some common reasons in application of head type.

There are few factors affecting the selection of head type :

• Allowable stress & Material used
• Access internals
• Constructibility / fabrication limitation
• Cost Saving

Allowable Stress & Material used
From stress and material saving perspective, for a vessel exposing to very high pressure hemispherical head is having highest allowable stress and minimum material. This will be followed by elliptical head and last flanged head (least allowable stress). Generally an elliptical head is in used.

Access Internals
In large vessel with the needs of accessing internals, normally an access hole (normally used manhole) will be provided.


However, in small vessel with internals, a flanged head is preferred. Most of the time a swing davit will be installed on the flanged head to held the flange without assistance of any hoist.

Constructibility / fabrication limitation
Flanged head some time is used due to complexity of fabrication. There are many event where a inline condenser is mounted on top of a column.


In some event where the column is small diameter (i.e. 1000mm) and a condenser with 800m ND needs to be mounted on top, there will be difficulties to use a elliptical head. those a flanged head with mating concentric reducer will be used. Apart it serve as manhole to access the internals such as demister.

Cost Saving
Sometime process and operation may required a manhole (for any specific reason) on a small vessel. Apart from construction limitation, providing a flanged head will solve the constructibility problem, it also act as manhole. Some cost saving is expected.


Above are some common reasons for selection of head type. I am sure there are others special reason(s) for the selection in Petrochemical & Chemical industry. If you have any example, why not sure with us ? OR if you have any photos for above applications, why not sent to me so that i can upload here ?

Related Topics

• Hydraulic Design Of Liquid with Pump Circuit - A revision kit...
• Hydraulic Design of Liquid Piping Systems - A revision kit...
• Is pressure drop increase with pipe schedule ?

In earlier post,<< High Temperature Hydrogen Attack in metal & alloy>> there are some discussion on how hydrogen attack in metal & alloy is initiated and a paper in recent activities in hydrogen attack.