Case Studies - Field Failures

Those who don't know history are destined to repeat it. -- Edmund Burke

Case Studies

Paul Sedivy Director – High Purity Products 2505 Foster Avenue P O Box 389 Janesville, WI 53547 PaulSedivy@RathGibson.com Direct #800-586-4762 Mobile #608-436-8200

Widely varied problems, encountered in 25+ years

• All Tubing – No Pipe • All Stainless

• 304L & 316L • Duplex • Nickel • Titanium

• CPI & High Purity Industries

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Bending / Forming

Intrados

Extrados

CLR - Centerline Radius OD/T < 23 to avoid ID tooling RG can help with specifics

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Bending / Forming 4.000” 304/304L

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Please note grooves

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• Grooves • Sharp stress

concentrators

• Starter Cracks

• Saw cuts

• Burrs

• High cold-work (more stainless is formed) Makes metals ‘notch brittle’

Bends / Forming

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Black Spots in Hygienic

Orbital Tube Welds

Its All About Cleaning

Black Spots

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Black Spots

Near Orbital welds

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Spots in 1. Seamless Tubing 2. Welded Tubing 3. Fittings From Multiple Suppliers

Black Spots

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Rarely found in bead through tube welds.

Consistently found in prepared joints with no ID cleaning.

Black Spots

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Cleaning or removal of ID

particulate just before joint

closure.

Use “Best Practices” when

making orbital welds

Black Spots

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Particulate?

a. Dust, Lint, etc.

Cleaning Cloth Residual (PET)

b. Aerosols (oils)

c. Water Spots

d. Chips (stainless)

Black Spots

Black Spots

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Black Spots

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Black Spots

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Black Spots

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Analysis: FT-IR confirmed PET plastic

Black Spots

Clean Wipes

Caps / Plugs

Abrasives

Sleeving

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I. PET (Plastic) 1. Abrasives – Nylon, Silicon carbide 2. Black End Caps – Polyethylene 3. Blue End-Caps – Polyethylene 4. Sleeving – Polyethylene 5. Clean Wipes – PET

Black Spots

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Black Spots

White Clean wipes - PET

600 micron size, or 0.024”

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White Clean wipes - PET

10 micron fiber size, or 0.0004”

Black Spots

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Cotton cloth (white) Eliminates melting and adhesion Residue - Non adherent ash

Re-use of PET wipes? Not best practice.

Black Spots

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Solvent Cleaning IPA / water mixture can cause spotting (water).

Concentration > 90% IPA desirable. 70% IPA - Poor practice.

Black Spots

Black Spots

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Contamination – Cu - LME

Liquid Metal Embrittlement

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Understanding Fatigue Crack – But Why?

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6-Moly used for Bruschetta production

Understanding

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Tubing can only resist ID Pressure due to its round shape and tension in the wall – aka Hoop Stress!

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Expansion; aka Omega Loops

Δ = Change ΔT*MCLE*L = ΔL 150°F·9.2x10-6·150’ ·12 = 2.48”

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Expansion; aka Omega Loops

**Depth of loop should be twice width

Approx Expansion Capacity

(in) Width of expansion loop

Tube (in) 20 40 60 80 100

1.000 1.5 5

1.250 1 4 8

1.500 0.8 3 6

2.000 2.5 5 8

2.500 2 4 6 8.5

3.000 1.5 3 5 7.5

4.000 1.4 2.5 4.5 6

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Dark Welds

The Secrets of Stainless Steel The Protective Layer of Oxide

Air

Cr Cr

Cr Cr Cr Cr

Metal (mostly iron)

Cr2O3

Cr2O3

Oxide

Oxide

O2 O2 O2 O2

O2 O2

O2 O2 O2 O2

O2 O2 Air

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Dark

Marginal Alloys can be significantly affected

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Dark

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Dark

What's the fix? Better Cleaning, Better shielding Measure O2 before you weld Nitric Acid paste Neutralize Rinse, rinse Dry

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Dark

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Dark

AWS D18-2 Color Code Chart ASME BPE also has a chart

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Fatigue

Compressor – high pressure, high cycles, hot

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Fatigue

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Fatigue

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Fatigue

To Resist Fatigue Surfaces – Polished?

Putting surfaces in compression Shot blasting Peening

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Fumes

Drying action & condensation Most common modes of uncontrolled

failures

What are concentrations? Solubility limits!

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Fumes

Drying action & condensation If you can smell bleach (sodium

hypochlorite – NaClO

It’s concentrated bleach

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Fumes

Drying Action & Condensation Preventive actions Rinse often and completely Avoid foams Great ventilation Cleaning is good

Corrosion Inhibitors

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Fumes Dirt on top Drip-lines to bottom

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Fumes

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Fumes

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MIC SRB – Sulfur Reducing Bacteria MRB – Manganese Reducing Bacteria Every MIC case in stainless has been SRB 1. Cavernous pits 2. Sulfur in the corrosion by product 3. Terraced features 4. Stagnant Conditions 5. Often well water

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MIC

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MIC

Tube had a rotten egg smell

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MIC

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MIC

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MIC

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MIC

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MIC

1. Dissolving metal – corrosion damage (most of what we see)

2. Precipitation of metals out of solution – typically very visible (Rouging)

Corrosion-by-products a. Often oxidized

b. Sulfides

c. Chlorides

1&2 often (>90% of time) happen near each other.

Corrosion

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SRB with S

MIC

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Tubes within tubes Think air bubbles Think collapse from thermal fatigue Splashing up onto hot tube Will cause inner tube to Fold & Collapse

Nested Tubes

Excessive temperature Thermal fatigue - high stresses - deformation Drying action

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Vertical exchangers

Corrosion at top of exchanger! Cant get the last bit of air out! Hot & Cold Splashing and drying Thermal fatigue “Safe Ending” – Better alloy for last 3’

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Transverse section of intermediate tube near through wall cracking. Please note significant axial cracking from the tube ID toward the OD. Here imagine heat from OD and cooling from ID

Nested

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Orbital Welds

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Orbital

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Orbital

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Pitting

Pitting is typically cause by Chloride ions May be present as

Salts NaCl, MgCl, KCl Acids – HCl Bleach Solutions - Sodium hypochlorite – NaClO

Three things to be aware of:

1. Cl concentration 2. pH 3. Temperature

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Pitting Neutral water Crevices are BAD Stainless Steel likes clean

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Guidelines

Sports Drinks

Pasteurize then bottle => Pits & cracking What are your chloride concentrations? What is your pH? Electrolytes

NaCl, MgCl, KCl

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SCC – Stress Corrosion Cracking

Same Tube

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SCC – Stress Corrosion Cracking

Tends to occur in same environments as pitting (Chlorides), only at higher temperatures

May start as pitting, cracking may begin once

stresses are high enough

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SCC – Stress Corrosion Cracking

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SCC – Stress Corrosion Cracking

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SCC – Stress Corrosion Cracking

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SCC – Stress Corrosion Cracking

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SCC – Stress Corrosion Cracking

Duplex alloys are a good value

SCC – Stress Corrosion Cracking

Nickel Content (wt. %) Nickel Content (wt. %)

SCC – Stress Corrosion Cracking

ASTM G36 MgCl2 Solution Boiling at 155℃ Time to Cracking (hr)

2 hr 304L or 316L

25 hr 2205 (Duplex)

150 hr 4565

500 hr 2507 (Super Duplex)

1,000 + hr - No cracking, discontinued N08367 (6XN)

E-Brite, 29-4C, 439 + Indicates no cracking

SCC – Stress Corrosion Cracking

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Steel Defects

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Guidelines

1. Stainless likes flow - 5fps or more a) Fowling means more flow is needed! b) Flow induced erosion is rare c) Faster Flow => turbulent flow => cleaning

2. Minimize stagnant time

3. Much damage can occur during

a) Upsets b) Start-ups and shutdowns

4. Avoid drying action

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Thank you!