OPERATIONS – ASSET MAINTENANCE TRACK

TUESDAY, JUNE 13 | 10:00 A.M. – 11:30 A.M.

Strategies for Mitigating Ethanol and Methanol Stress Corrosion Cracking

The mandate for the use of biofuels has resulted in increased risk of stress corrosion cracking-related incidents caused by inadequate practices in the transport, handling and storage of ethanol and methanol. A panel of industry experts and facility operators will discuss the causes and effects of stress corrosion cracking. Sharing case studies and lessons learned, the panel will reveal effective practices for addressing stress corrosion cracking from methanol and ethanol at terminal facilities.

ABOUT THE SPEAKERS

Moderator

Daniel Leslie is a project engineer at Marathon Petroleum Company. He has 10 years of experience in industry, with five years’ experience in the refining and petrochemical industry. Leslie holds a Bachelor’s degree in chemical engineering and a Master’s degree in civil and environmental engineering from The University of Akron.

Panelists John Beaver, Ph.D., is a Corporate Vice President and Senior Principal Engineer in DNV GL’s Pipeline Services Department, North American Oil and Gas. He is in the Incident Investigation Section of DNV GL’s Materials and Corrosion Technology Center in Dublin, OH. His current job responsibilities include providing technical support on failure analyses, root cause analyses, litigation projects, consulting, and laboratory research programs. A major emphasis of Dr. Beavers’ research has been the mechanistic and practical aspects of corrosion and stress corrosion cracking (SCC). He earned a Bachelor of Science in Metallurgical Engineering with Highest Honors from the University of Illinois and received his Ph.D. in Metallurgical Engineering from the University of Illinois. Chuck Corr is the Biofuels Technical Service Manager for ADM, Inc. He has over 30 years of experience in the ethanol production industry and has spent his entire career with ADM. John Farrell is the Segment Engineer Technical Authority for Storage Tanks and Pipeline for BP Corporation. He received a Bachelor of Science degree in Civil Engineering from the University of Illinois, Champaign-Urbana, and a Master of Science degree in Civil Engineering from the University of Illinois – Chicago.

Russell Kane, Ph.D., is President of iCorrosion LLC. Dr. Kane has over 300 technical publications and five books on corrosion and metallurgical topics. He received his Bachelor’s degree, Master’s degree and Ph.D. in metallurgy and materials science from Case Western Reserve University. Chip Locke is Senior Project Manager at Kinder Morgan. In his current position, he has the lead role in the maintenance, development and implementation of all engineering and construction standards, maintenance procedures, preventative maintenance checklists and technical memorandums. Locke is responsible for advising on technical matters relating to terminal operations and serves as a facilitator for standards and procedures training. He is a registered Professional Engineer in Indiana and Ohio. He earned a Bachelor of Science in civil engineering from Purdue University and an MBA from Butler University.

Strategies for Mitigating Ethanol and Methanol Stress Corrosion Cracking

ModeratorDan Leslie, Marathon Petroleum Co.

PanelistsJohn Beavers, DNV-GLRuss Kane, iCorrosion

Chuck Corr, Archer Daniels MidlandJohn Farrell, BP

Chip Locke, Kinder Morgan

Topics at a GlancePart 1 - Research and Production

– Alcohol SCC Research– API Bulletins– Production & Experience

Part II - Operator Experience and Mitigation Solutions– SCC In Tanks– SCC In Pipes– eSCC Boot Camp

ALCOHOL SCC: RESEARCH SUMMARY

Dr. John A. Beavers, DNV GL

Major Technical Issues with Ethanol• Leaking of storage tanks

and piping due to SCC• Fuel quality• Corrosion in dispensing

systems (if wet)• Elastomer swelling

Experimental Methods• Constant Deflection/Load Tests (e.g., U-bends)

– Takes a long time and high loading– Lack of reproducibility

• Slow Strain Rate Tests (smooth or notched tensile specimens)– Strain specimen to failure in environment– Rapid and reproducible but does not represent field

conditions• Fracture Mechanics Tests (pre-cracked

specimens)– Most realistic test technique – Expensive and time consuming

Experimental Methods

• First Step – Reproduce the Cracking in the Laboratory

• Second Step – Evaluate Controlling Parameters

• Step Three - Determine Realistic Crack Growth Rates

• Step Four - Identify Mitigation Methods

Potent Environment

Susceptible Material Tensile

Stress

SCC

Susceptible Material

• No Evidence that Typical Line Pipe or Plate Steels are Resistant to e-SCC

• Weld Microstructures Have Similar e-SCC Susceptibility to Base Metal– Weld metal may be somewhat more resistant

SSR Tests if Different Steels Base Metal

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

DSAW

Seamles

s

Cast S

teel

X46 H

FERWX52

HFERW

X52 LFERW

SCC

CG

R m

m/s

E-95E-30

Effect of DSAW WeldsX46 DSAW

0.0E+00

1.0E-06

2.0E-06

3.0E-06

4.0E-06

5.0E-06

Base Metal HAZ HAZ Weld Metal Weld Metal

SCC

CG

R m

m/s

E-95E-30

Tensile Stress

• Primary Role of Welding in e-SCC is to Introduce Residual Tensile Stresses– Most failures occur near welds – Not in weld

microstructure • Low pressure piping and tanks

• In High Pressure Transmission Pipelines– Hoop stress from internal pressure may be

sufficient to cause e-SCC

Environment (Factorial Study)

• Oxygen and Steel Couple Are Most Significant Factors

• Chloride, Methanol and Acetic Acid May Be Important at Intermediate Oxygen Concentrations

• Water and Blend Ratio – Did Not Show up in Study

• Limited Range (Water)• Not Investigated (Blend Ratio)

Environment (Factorial Study)

Effect of Blend Ratio and Oxygen

Effect of Blend Ratio and Oxygen

• Dissolved Oxygen is Most Important Factor

• No SCC Below E-15– E-15?? On the edge of a cliff

• E-85 Susceptible• E-50 Appears to be the Worst!

Effect of Water

Hydrous Ethanol WillNot Cause SCC

Mitigation of e-SCC

• Reduce Tensile Residual Stresses– PWHT welds in piping– Grit Blast Tank Internals

• Not proven for e-SCC but works for other forms of SCC

• Internal Coatings for Tanks– Only will be fully effective when used with grit

blasting• Inhibitors and Oxygen Scavengers

– Transmission Pipelines

Methanol SCC

• Observed in Pipelines and Other Components Where Neat Methanol Used for Dewatering

• Similar Morphology and Controlling Factors to e-SCC– IG SCC– Oxygen necessary for m-SCC to occur– Water inhibits cracking

Summary• All Carbon Steels Susceptible to e-SCC• Residual Tensile Stresses are Primary Source of

Stress• Oxygen – Primary Promoter of e-SCC• Water – Inhibitor • e-SCC Mitigation

– Reduce Residual Tensile Stresses– Coatings– Inhibitors and Oxygen Scavengers

• Methanol Behaves Similar to Ethanol

API BULLETIN 939E-IDENTIFICATION, MITIGATION & PREVENTION OF ETHANOL SCC

Dr. Russell Kane, iCorrosion, LLC

What we know about Ethanol SCC• Made to ASTM D4806 or similar

standards; but some variable ethanol is out there.

• Ethanol processing methods, ethanol source, aeration, water content (maybe chlorides) can influence SCC susceptibility.

• In many cases, high stress intensity is required to initiate ethanol SCC: Areas of non-PWHT welds & stress concentration

• Lab / field information both suggest that severity of SCC is not constant over time. Failures can occur in 6 months to 10 years.

API 939E – Ethanol SCC Guidelines• This bulletin is based on

“lessons learned” from API surveys and research, supplemented by industry experience. It is in a form accessible and usable for field personnel.

• The focus of API Bulletin 393E:– Identification - Find– Repair - Fix– Mitigation – Eliminate

API 939E – Ethanol SCC Guidelines• Older equipment may not

conform exactly to API 939E, but this does not imply that such equipment is being operated in an unsafe or unreliable manner.

• It is recognized that facilities may vary and may need to be modified depending on specific:– operating conditions, – inspection and maintenance

experience. • Each user company is

ultimately responsible for its own safe and reliable operations.

Ethanol SCC Guidelines (API 939E)A total of 31 cases of eSCC have been reported in the API survey

efforts conducted from 2003 through 2013.

Failures from Experience Survey:•Facilities piping/fittings – 24%•Tank floor plates seam welds – 22%•Tank floor/sidewall fillet welds – 9%•Tank sidewall 1st course butt weld – 9%•Tank floating roof seam welds – 9%•Tank Roof Springs – 6%•Facilities piping/supports – 6%•Ancillary handling equipment – 6%•Tank nozzle – 3%•Shop built tank in E85 – 3%•Pipeline – 3%

API Bulletin 939E – Major Topics• Ethanol background, definitions & specifications• Citing of SCC examples

– Listing of documented SCC failures– Includes two documented cases of SCC in pipelines

• Summary of likely SCC locations and conditions• Guidelines for new construction & fabrication

– Minimize the use of lap seam welds– Minimize cold working and plastic deformation– Use of PWHT – mainly piping welds– Use of ethanol resistant immersion coatings for tanks– Encourages tank foundations and pipe supports

API Bulletin 939E – Major Topics• Inspection of existing equipment

– References to API 653, API 574, API 510 and API 570 as relevant to specific equipment

– Inspection for SCC is complicated:• Cracks are tight and can not be easily seen; leakage.• Cases of SCC have been observed in less than 12 months

– Encourages prioritizing inspection based on severity of service, location, prior cracking experience

– Option: Visual, WFMT, SW-UT, EM-ACFM, eddy current– Encourages (where possible) Ethanol sampling & analysis;

destructive metal sampling & examination for SCC confirmation.

API 939E – Major Topics - 3• Assessment & Repair of SCC Damaged Equipment

– Assessment of fitness-for-service and RBI - Methods of API 579 and API 581 are applicable.

– Temporary patches and permanent repairs – Repairs by grinding, flame or arc gouging/cutting, welding– PWHT of piping and use of ethanol resistance immersion

coatings for tanks.• Monitoring (with limitations)

– Sampling of ethanol per ASTM D4806

– SCC insitu testing. • Sampling & SCC Testing

– NACE TM0111 – SSR testing of sampled ethanol.

Summary• Sampling and SCC data suggests that there are

variations in ethanol• Source and manufacturing differences, and

contamination may occur.• We know:

– Where SCC is most likely to occur – SCC can occur in ethanol within ASTM D4806 range

• API Bulletin 939E provides guidelines for identification, mitigation and prevention of ethanol SCC.

• Experience since API 939E is good.

STRESS CORROSION CRACKING IN A DENATURED FUEL ETHANOL ENVIRONMENT: PRODUCER PERSPECTIVE

Charles Corr, Archer Daniels Midland Company

Overview• Represent broader industry – FETAG

• Production of denatured fuel ethanol• Industry experience• Thoughts

Denatured Fuel Ethanol• Story of glucose

– Photosynthesis• Fermentation• Distillation• Denaturation

• ASTM D4806 Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-Ignition Engine Fuel

Distribution of Ethanol • Ethanol Products are Distributed by

– Truck– Rail– Barge– Vessel– Pipeline

• Domestic and international

Producer Experience• Many Ethanol Products

– Undenatured and Denatured• Wide Range of Water Content

– Typically 5 percent to hundreds of ppm • Nearly all Ethanol Stored in Carbon Steel

Tanks• Not aware of SCC in any product other

than DFE– Limited to the Distribution System

Producer Experience• Confirmed with Multiple Producers

• No Reports of SCC in Tanks or Piping at Producer Facility or in Transport Container

• ADM tank evaluation– Professional Examination for SCC – Old tank with Fuel Oil Prior – No SCC Found

Clarification• SCC – Dependent on Conditions

– Material – Metal– Stress Conditions– Liquid Conditions

• Ethanol is Not the Cause of the SCC– Ethanol is Not Corrosive

• Solvent with Specific Properties - Polarity, Conductivity and Solubility

– Minor Contaminates

What Do We Need to Address SCC?• What Changes in Distribution System?

• If SCC in Tanks and Pipes is a Ongoing Problem –

• Fundamental Research

SCC IN TANKSJohn Farrell, BP

Ethanol SCC in Floating Roofs• Steel Pan IFT: a small ethanol puddle was found

on the deck near a fillet lap weld during a routine seal inspection. The tank was removed from service and two cracks were discovered in deck seams by wet fluorescent magnetic particle testing (WFMT). The cracked sections were analyzed and ethanol SCC was confirmed.

• Steel Pan IFT: a tank was removed from ethanol service for scheduled modifications including fillet welding the underside of the floating roof deck seams in preparation for installation of an ethanol resistant coating. Dye penetrant testing (PT) of the recently completed fillet welds identified 32 cracks.

Ethanol SCC in Floating Roofs

• Steel pan IFT: pusher springs that were part of a mechanical shoe seal had broken/snapped. This damage was found in two tanks that also experienced SCC in the bottom weld lap seams.

Ethanol SCC in Bottoms• Annular Ring: Annular butt weld seam

cracked. Additional WFMT revealed additional cracks in or very near bottom lap weld seams and in shell nozzle insert plate welds.

• Bottom Plate Seams: Lap weld seams, corner weld, and floating roof leg bearing pad fillet weld seams were examined by WFMT and cracks identified in 2 tanks located at same terminal.

Ethanol SCC in Piping• Terminal 1:

– Ethanol Piping at loading rack developed a seep at/near pipe to elbow butt weld joint.

• Terminal 2:– Minor seep/leak developed in carbon steel

piping in April. Seeps were located near pipe support fillet weld. Piping was constructed & placed in ethanol service in 1995.

– Upon detection of first leak, 3 more cracks were found at similar support weld locations.

– Several months later, other leaks developed at other support welds. Piping was replaced utilizing different support design and PWHT of completed piping installation.

Ethanol SCC in Shell• Tank Shell Seams: During routine internal

examination of an ethanol tank, WFMT of the uncoated shell vertical and horizontal weld seams revealed cracks in all 1st course vertical seams, most 2nd course vertical weld seams, and about ½ of the 3rd course vertical weld seams. Cracks were small (i.e. short, tight) and were not visible without magnification.

• Tank Nozzle Insert Plate Welds: During an internal inspection, WFMT examination of insert plate weld seams identified one small (i.e. short, tight) crack in insert plate to shell weld.

Ethanol Tank & Piping Practices Tank :

– Tank bottoms, shell and undersides of floating roofs are coated with epoxy coatings that are resistance to ethanol.

– Store in Internal floating roof tank (No EFTs) • Welded steel floating roofs are preferred • Bolted or welded aluminum floating roofs are

acceptable.• Mechanical shoe primary seal w/ stainless steel

shoes, hangers, & hardware. Piping:

– All new piping components shall be subject to PWHT – Welding of pipe supports to the parent pipe should

be avoided - the preference being to use clamp type supports (e.g. U-bolts).

– Pipe stresses should be minimised e.g. do not use maximum pipe support spacing, reduce spacing to reduce stresses over supports

Tank Inspection PracticeInternal inspection of a tank that has been in ethanol service, regardless of duration, includes Wet Fluorescent Magnetic-Particle Testing (WFMT) of the following areas:• Uncoated bottom lap welds.• Internal corner weld (remove any existing coating,

regardless of condition, to perform this inspection). • All uncoated internal shell welds beneath the first

horizontal shell weld, including vertical butt welds and nozzle welds.

• Uncoated carbon steel floating roof welds exposed to ethanol – if roof is not seal welded on the underside, the top side lap welds shall be WFMT inspected, including seams inside pontoons.– Note: WFMT requires surfaces to be cleaned to a near-white

metal finish The area extending 6 inches into the base metal on either side of the weld shall be prepared and WFMT inspected.

SCC IN PIPING AND CONSTRUCTION STANDARDS

Daniel Leslie, Marathon Petroleum Company

SCC in ball valve assembly• Assembly consisted of ball valve, reducing bushing, and nipple• Operating pressure was less than 150 psig – line from tank to load

rack• Sample sent to DNV for testing

– Intergranular facets were evident on the fracture surface and secondary intergranular cracks were present on the reducing bushing, which is consistent with ethanol SCC

SCC in ball valve assembly

SCC in Elbow• 4” line – Line was a dedicated prover line for ethanol• Leak occurred at elbow fitting near an adjacent girth

weld connecting a flange

SCC in Elbow• Intergranular cracks typical of eSCC

present• Crack interlinks

Northern Terminal - 2010• 6” pipe – ethanol line – less than 150 psi• Leak occurred adjacent to a girth weld

Northern Terminal – 2010 Findings• Traces of chlorine found on the fracture surface and intergranular

cracks typical of eSCC present• Circumferential external cracks were present on the piping fitting

side of the piping section, in the base metal just outside the heat affected zone of the girth weld

Single Terminal - Multiple Spots• Records of 8 welds being sent for analysis – 7 showed eSCC• Pipe installed in 2008• 8” standard wall (0.322”) A53 ERW piping – MOP of 225 psig.• Replaced piping to the rack – Approximately 500’• Location of the cracking not consistent with eSCC

– Cracks found in root of the weld, typically eSCC is found in base metal near girth weld

– Branched cracking and intergranular crack path consistent with eSCC

– Believed eSCC propagated from pre-existing hydrogen cracks formed during construction

– Some internal misalignment during construction (high-low) may have played a part where the cracks initiated

• The microstructure and chemical composition was typical for A53 piping

• There was no evidence of fatigue striations at the crack tip

Rack o-lets, Multiple terminals• Midwest Terminal #2 (under rack) – lateral-o-let – May 2013• Coastal Terminal #1 (lane 2) – thread-o-let – June 2013• Coastal Terminal #1 (lane 1) – thread-o-let – December 2013• Gulf Coast Terminal #2 (lane 10) – thread-o-let – December

2013• Gulf Coast Terminal #2 (lane 2) – thread-o-let – June 2014

• All of the above were reported as weeps/seeps• Repair included temporary repair utilizing Belzona™ and

within a year replacing the spool piece• All repairs and construction for ethanol lines includes 100% x-

ray and PWHT

Rack o-lets - PicturesTerminal #1 Terminal #2

Terminal #3

Construction Standards• Applies to systems with ethanol concentration >= 15%• Pipe Standards

– Piping must meet A106 Grade B– All welds to be Post-weld heat treated (PWHT) during fabrication– Valve assemblies to be uni-body– Receipt Manifold and ethanol offload line must not be connected

• Tank Standards– If shop fabricated (<14’ tall), entire tank to be PWHT– Ethanol tank bottoms and walls to be coated to at least 3’ from the floor, and

must be coated at least 6” above nozzles and or manway (whichever is greater)• Required coating: FastClad 105 ER or Carboline Phenoline 187 UHS

– Shell welds to be coated above 3’ line– High-deck Floating Roofs in ethanol service to be replaced

E-SCC BOOT CAMPLewis “Chip” Locke, Kinder Morgan, LLC

What is stress corrosion cracking?

• SCC occurs when material under high tensile strength is subject to a corrosive environment. SCC usually occurs in certain specific metal-environment-stress combinations.

• Tanks inherently have two of the factors - carbon steel and tensile stress

• Tanks in ethanol or methanol service introduce the third factor – dissolved oxygen

SCC

SusceptibleMaterial

(carbon Steel)

Tensile Stress(welding)

Corrosive Environment(ethanol)

DefinitionsTank Critical Zone – per API 653, the annular plate ring and 12” in on the floor and up on the shell.

eSCC – Stress Corrosion Cracking caused by ethanol exposure

FGE – Fuel Grade Ethanol

E85 – Vehicle fuel that is up to 85% ethanol and 15% gasoline

PWHT – Post Weld Heat Treating

OAP – Optically Activated Pigment for coatings

Stress Corrosion Cracking Data

• The impact of SCC on a material usually falls between dry cracking and the fatigue threshold of that material.

• The required tensile stresses may be in the form of directly applied stresses or in the form of residual stresses.

• The problem itself can be quite complex. The situation with buried pipelines is a good example of such complexity.

• Cold deformation and forming, welding, heat treatment, machining and grinding can introduce residual stresses. The magnitude and importance of such stresses is often underestimated.

• The residual stresses set up as a result of welding operations tend to approach the yield strength.

• The build-up of corrosion products in confined spaces can also generate significant stresses and should not be overlooked.

• Usually, most of the surface remains intact, but with fine cracks penetrating into the material.

• In the microstructure, these cracks can have an intergranular or a trans granular morphology.

• Macroscopically, SCC fractures have a brittle appearance.

• SCC is classified as a catastrophic form of corrosion, as the detection of such fine cracks can be very difficult and the damage not easily predicted.

A disastrous failure may occur unexpectedly, with minimal overall material loss.

Stress Corrosion Cracking Structure

Schematic of Stress Corrosion Cracking

Fe3O3  Fe3O4 Fe3O3  Fe3O4

Corrosion Build Up

Tensile ForceTensile Force

Advancing Crack Tip

(Corrosion Products) (Corrosion Products)

Common SCC Systems TableMaterial Environment Concentration Temp Mode

Carbon steel

Hydroxides high high INitrates moderate moderate ICarbonate/bicarbonate Low moderate ILiquid ammonia Low TCO/CO2/H2O low TAerated water very high T

Low Alloy Steel (e.g. Cr‐Mo, Cr‐Mo‐V) Water ‐ moderate T

Strong SteelsWater ( y>170 ksi) low M

Chloride ( y>120 ksi) low MSulfide ( y>90 ksi) low M

Austenitic Stainless Steel (including sensitized)Chloride high high THydroxide high very high M

Sensitized Austenitic Stainless SteelAerated water very high IThiosulphate or polythionate low low I

Duplex Stainless SteelsChloride high very high TChloride + H2S high High moderate T

Martensitic Stainless Steels Chloride (usually + high H 2S) moderate low THigh Strength Steels Water vapor ‐ low TAluminium Alloys Chlorides low low I

Titanium AlloysChlorides high Low TMethanol ‐ Low TN 2O 4 high high low T

Copper Alloys (excluding Cu‐Ni) Ammoniac and other nitrogenous low low I

Notes to SCC Table1. This Table presents the systems for which SCC problems are well established and of practical

importance. The absence of a metal-environment combination from this Table does not mean that SCC has not been observed.

2. There are rarely well-defined temperature or concentration limits for SCC, and the ratings given here are indicative only. As an approximate guide the terms used equate to the following ranges of values:

Concentration Temperature

Low Up to 10‐2M AmbientModerate Up to 1 M Below 100 °CHigh Around 1 M Around boilingVery high Near saturation Above boiling

Note that significantly increased local concentrations may be obtained under the influence of local boiling or evaporation, or by accumulation in pits and crevices, and cracking is often obtained for nominal concentrations that are much lower than is indicated here.

3. The fracture mode is classified as intergranular (I) where cracks go along the grain boundaries, trans granular (T) where cracks go across the grains, or mixed (M) where there is a combination of the two modes, or where the mode can vary depending on the conditions. There are often circumstances that can cause the fracture mode to change (e.g. chloride SCC of sensitized austenitic stainless steel may give intergranular cracking).

4. Very high temperature (> 200 °C) water environments are very aggressive, and will cause SCC of a wide range of materials. Expert advice is essential for materials selection for such conditions.

eSCC Industry Observations • No eSCC was observed at tanks or piping at ethanol producers.

• eSCC does not appear to affect first tier transportation (barges, etc.)

• eSCC appears in the first storage point (terminals and blending facilities)

• There have been no reports of eSCC after blending even in E85.

• eSCC occurs primarily in piping/fittings and tank floors. The shell and critical zone were less common but still had occurrences.

• eSCC also occurs in steel pan floating roofs and pontoons.

• eSCC has occurred in a little as 6 months to as long as 10 years.

• Both oxygen and chlorides seem to accelerate eSCC.

• Experimental SCC data is notorious for a wide range of scatter.

Tanks have several potential areas of stress at or near the bottom

– The critical zone with 1’ of the floor to shell weld

– Openings and nozzles such as manways

– Filet welds at lap weld plates

– Product weight on the floor and first course

– Small patches

API 650 and 653 shows details for openings, nozzles and patches that reduce stresses in these areas. Rounded corners on repads, for example 1/8 inch radius.

Fillet Weld

Greatest Stress

Overlapping plates

High Tensile Stress in Tanks

Construction Materials Affected by SCC

• Carbon Steel is the primary material affected

• Grade/strength of carbon steel apparently not a factor, but carbon equivalency may be.

• Aluminum does not appear to suffer SCC but will pit in ethanol service: An upgrade to marine grade aluminum could be justified.

• Stainless Steel does not suffer SCC from ethanol but will from chlorides

While ethanol is the primary cause of SCC because it is so common, methanol and anhydrous ammonia can also cause SCC.

API has issued two documents concerning SCC• API RP 939 D – a white paper explaining SCC • API RP 939 E – best management practice guidance

API 939 E recommends• Post Weld Heat Treating (more practical on pipes and fittings than

tanks)• Minimize lap joints in floor construction• Minimize cold working of metal (bending, forcing into place, etc.) • Use polymeric coating compatible with ethanol immersion• Consider periodic testing for chlorides and oxygen

Industry Best Management Practices to Mitigate SCC

Company BMP

Mitigating Stress Corrosion CrackingEngineering Standard, Mitigating Ethanol Induced Stress Corrosion Cracking of Carbon Steel During New Construction and Repairs - Revised: 06-16-2015

In reference to tanks,

• The tank shall be internally coated (lined) on the floor and above the first shell course weld.

• Coating the underside of the floating roof including the external rim and rim angle if it has any carbon steel components.

• Each new tank put in ethanol service shall have a stress coupon test station installed and monitored according to Pipeline Integrity Protocol.

• In lieu of PWHT, abrasive blast the tank to peen the surface with clean, new peen-shot-media. This relieves the surface tension on the steel.

• In addition or as an alternative, use new blast media (garnet or other mineral grit) to create a profile of 2 to 2.5 mils SSPC-10 Near White Blast.

• Coat the tank with the appropriate coating for the productMany coatings resist ethanol - most epoxies, including coal tar epoxy.Methanol requires a high solids, epoxy novolac phenolic or a vinyl ester

• The lining material should be made with OAP pigment to facilitate blacklight inspection

• The final step is to wet sponge holiday testing for coating milage of 20 mils or less. High voltage is utilized on coating thicknesses above 20 mils

Company BMP

Mitigating Stress Corrosion Cracking

Company BMP

Internal Tank Coating• Several internal company groups spent time updating the Protective

Coatings Standard• This standard now includes an Appendix that defines approved Coating

systems. It includes 3 systems for internal tank lining• First one has the tank is blasted to SSPC 10 and coated with an

epoxy novolac primer with OAP (optically active pigment) then an epoxy novolac up to 24 mils thick.

• Second is a Glass Reinforced Polymer using fiberglass mats to reinforce what ever resin is required for the product.

• Third is a Glass Flake System that uses the same epoxy novolac primer with OAP (optically active pigment) and then a high solids epoxy novolac amine, glass flake filled coating.

Company BMP

Internal Tank Coating• The lining systems in the previous slide are the proposed pre-approved

liners for both new construction and repair. • These are considered thick-film liners (over 24 mils). The glass-reinforced

and glass flake systems are generally used for repairing tanks that have minimal floor thickness or multiple leaks. The liner will extend the API internal inspection interval for these tanks to 20 years

• The First system will work for almost all products but many other coating systems are acceptable if they withstand the product in the tank.

• Other systems should be submitted to the Project Manager for approval

New tank construction often uses a thin-film liner (6 to 8 mills) of coating The theory is when the lining fails there is still the original floor thickness

This will still allow the 20 year inspection interval

Company BMP

Internal Tank CoatingLiners serve other functions than just carbon steel protection

• Lined tanks are easier and quicker to clean than carbon steel tanks• Lined tanks extend API internal inspection intervals • Lined tanks make switching products much easier and quicker• Tanks in white product service (alcohols, methanols, etc.) have much

less chance of rust bleed in lined tanks.• Many chemical tanks need to be fully lined including the bottom of the

roof to prevent product contamination.

Fully lining chemical tanks is economically viable because the tanks are usually small (10k to 30k bbls) and the chemical is valuable, with contaminated product creating a substantial cost to KM in terms of money and customer relations.

• Stress Corrosion Cracking is a infrequent but significant issue

• Chloride Testing should be performed using approved methods.

• Number of tests are determined on square footages

• SCC occurs when material, tensile stress and environment overlap

• eSCC is most common but methanol and other chemicals can cause SCC

• SCC can be mitigated by PWHT, Shot-peening and internal tank coatings

• Internal coatings (liners) must be carefully selected to resist the product

• Liner Quality Control using OAP and holiday testing is a must

• Liners serve other functions than just carbon steel protection

Thank you

Summary