Dissimilar Welds in Refinery Services - B Jack

API Spring 2007API Spring 2007

Dissimilar Welds in Dissimilar Welds in Refinery ServicesRefinery Services

Brian Jack 510 245Brian Jack 510 245--46414641ConocoPhillipsConocoPhillips


This PresentationThis Presentation

Definition Definition –– what constitutes a dissimilar weldwhat constitutes a dissimilar weldWhere are they commonly used in RefiningWhere are they commonly used in RefiningWhat are the benefits of using dissimilar weldsWhat are the benefits of using dissimilar weldsWhat are the drawbacks/concerns with using What are the drawbacks/concerns with using dissimilar weldsdissimilar weldsConclusionsConclusionsPath forward Path forward –– Changes needed to API Changes needed to API documents (e.g. API 571, API 582 etc.)documents (e.g. API 571, API 582 etc.)


Dissimilar Weld DefinitionDissimilar Weld Definition

For the purposes of this presentation, a For the purposes of this presentation, a dissimilar weld is a weld joining a ferritic dissimilar weld is a weld joining a ferritic material and an austenitic materialmaterial and an austenitic materialCommon refinery ferritic materials include Common refinery ferritic materials include CS, 1.25 Cr, 2.25 Cr, 5 Cr, and 9 Cr CS, 1.25 Cr, 2.25 Cr, 5 Cr, and 9 Cr ––magnetic, often need PWHT, poor to OK corrosion magnetic, often need PWHT, poor to OK corrosion resistance, especially at high temps.resistance, especially at high temps.Common refinery austenitic materials Common refinery austenitic materials include 304L, 316L, 317L, 321, 347, Incoloy include 304L, 316L, 317L, 321, 347, Incoloy 800HT & 825, Inconel 625 & Hastelloy C 800HT & 825, Inconel 625 & Hastelloy C ––nonmagnetic, donnonmagnetic, don’’t typically need PWHT, good t typically need PWHT, good corrosion resistance, high expansion coefficientscorrosion resistance, high expansion coefficients


Common Refinery Dissimilar WeldsCommon Refinery Dissimilar WeldsH2 furnace 1.25 Cr inlet pigtails to Incoloy sockolets or H2 furnace 1.25 Cr inlet pigtails to Incoloy sockolets or weldolets on H2 reformer tubesweldolets on H2 reformer tubesHydrogen furnace Incoloy outlet cones to CS or 1.25 Cr Hydrogen furnace Incoloy outlet cones to CS or 1.25 Cr refractory lined transfer linesrefractory lined transfer linesAlloy transitions inside fired heaters (e.g. 9Cr to 317L in a crAlloy transitions inside fired heaters (e.g. 9Cr to 317L in a crude ude furnace)furnace)Welds joining clad pipe sections to themselves or to unclad Welds joining clad pipe sections to themselves or to unclad carbon or low alloy steel pipe (e.g. Hastelloy C276 clad CS carbon or low alloy steel pipe (e.g. Hastelloy C276 clad CS piping in CU OVHDs)piping in CU OVHDs)Inco welds joining socket weld valves in 5 and 9 Cr piping Inco welds joining socket weld valves in 5 and 9 Cr piping systemssystems300 series SS weld overlay in numerous refinery reactors and 300 series SS weld overlay in numerous refinery reactors and pressure vesselspressure vesselsLess common but used Less common but used –– overlaid CrMo exchanger/vessel overlaid CrMo exchanger/vessel nozzles to solid 321/347 SS piping in hydroprocessing servicesnozzles to solid 321/347 SS piping in hydroprocessing services


Example Dissimilar WeldExample Dissimilar Weld-- Wet Corrosion Wet Corrosion Refinery Environment Refinery Environment

( e.g. Wet H2S, NH4HS, HCL)( e.g. Wet H2S, NH4HS, HCL)


Example Dissimilar Weld Example Dissimilar Weld –– Hydro Hydro Processing UnitProcessing Unit


Benefits of Using Dissimilar WeldsBenefits of Using Dissimilar WeldsEliminates flanges, which themselves are a leak risk, Eliminates flanges, which themselves are a leak risk, especially inside a furnace and in high temperature/high especially inside a furnace and in high temperature/high pressure servicespressure servicesReduces installation costs by allowing for less use of Reduces installation costs by allowing for less use of flanges and by often allowing for more compact piping flanges and by often allowing for more compact piping layoutslayouts

Note: Using overlaid or clad construction versus solid Note: Using overlaid or clad construction versus solid austenitic is often desirable for several reasons:austenitic is often desirable for several reasons:Austenitics can experience chloride cracking in many Austenitics can experience chloride cracking in many refinery servicesrefinery servicesHigh expansion coefficient of austenitics can be difficult High expansion coefficient of austenitics can be difficult to accommodateto accommodateSolid austenitics can be prohibitively expensiveSolid austenitics can be prohibitively expensive


Concerns with Dissimilar WeldsConcerns with Dissimilar WeldsIn service cracking risk at austenitic to ferritic In service cracking risk at austenitic to ferritic fusion line is well recognized (see API 571). fusion line is well recognized (see API 571). Primary causes of cracking are thermal Primary causes of cracking are thermal fatigue or hydrogen embrittlement cracking at fatigue or hydrogen embrittlement cracking at hard zones along the fusion line.hard zones along the fusion line.There have been numerous failures of these There have been numerous failures of these joints in the power, ammonia and refining joints in the power, ammonia and refining industries and some of these failures have industries and some of these failures have been significant (e.g. complete weld been significant (e.g. complete weld separations). separations).


Two Significant Failures in 2006Two Significant Failures in 2006Failure 1Failure 1: Top 21: Top 21’’ of H2S stripper in hydrotreater of H2S stripper in hydrotreater unit is upgraded to solid Incoloy 825 (30unit is upgraded to solid Incoloy 825 (30”” D X D X 3/83/8”” t) to combat chloride corrosion in 2003. t) to combat chloride corrosion in 2003. Welded with 625, no PWHT, PT root & final & Welded with 625, no PWHT, PT root & final & 100% Xray. Operating conditions at weld are 100% Xray. Operating conditions at weld are 160 psig & 375F. Weld leaks late 2004; thought 160 psig & 375F. Weld leaks late 2004; thought to be bad weld so reto be bad weld so re--welded in entirety, again no welded in entirety, again no PWHT, same NDE. Weld leaks again in 2006; PWHT, same NDE. Weld leaks again in 2006; much of weld has nearly through wall fracture. much of weld has nearly through wall fracture. Cause of failure both times now believed to be Cause of failure both times now believed to be sulfide stress cracking (i.e. hydrogen sulfide stress cracking (i.e. hydrogen embrittlement) of hard zone at CS to 625 fusion embrittlement) of hard zone at CS to 625 fusion line.line.


Tower Failure at Fusion Line of Inconel 625 Weld Tower Failure at Fusion Line of Inconel 625 Weld to CS Base Metalto CS Base Metal


Hard Zones at AusteniticHard Zones at Austenitic--Ferritic Fusion LineFerritic Fusion Line


Significant Significant 2006 Failures2006 Failures ContCont’’dd

Failure 2:Failure 2: Furnace outlet weld fracture while reFurnace outlet weld fracture while re--starting a TCU furnace. Fracture at Inconel weld starting a TCU furnace. Fracture at Inconel weld joining a 5joining a 5”” diameter 347H furnace tube to a 9 diameter 347H furnace tube to a 9 Cr flange. Normal operating conditions at weld Cr flange. Normal operating conditions at weld were 920F & 500 psig. Weld was 12 years old at were 920F & 500 psig. Weld was 12 years old at time of failure. Failure cause suspected to be time of failure. Failure cause suspected to be thermal stress induced brittle fractures along thermal stress induced brittle fractures along hard carbide zone at fusion line between 9Cr hard carbide zone at fusion line between 9Cr flange & the Inconel weld. flange & the Inconel weld.


Fracture at Fusion Line Between Fracture at Fusion Line Between 9Cr Flange and Inconel Weld9Cr Flange and Inconel Weld


Dissimilar Weld ConstructionDissimilar Weld Construction

9Cr 347H

Inconel buttering (stress relieved)

Flange Tube

Inconel weld (NOT stress relieved)


Factors That Increase Cracking RiskFactors That Increase Cracking RiskThermal CyclingThermal CyclingTemperature: Temperature: above ~500F, high thermal stresses, above ~500F, high thermal stresses, above ~800F carbon diffusionabove ~800F carbon diffusionSevere hydrogen charging environments Severe hydrogen charging environments –– severe wet severe wet H2S/NH4HS environments at low temps & severe H2S/NH4HS environments at low temps & severe hydroprocessing environments at high tempshydroprocessing environments at high tempsFiller metal: Filler metal: 300 series worse than Inco types, especially 300 series worse than Inco types, especially at high temps (see API RP 582 for guidance)at high temps (see API RP 582 for guidance)Stress, either applied or residual. Stress, either applied or residual. Note that PWHT Note that PWHT benefit is questionable & may do more harm than goodbenefit is questionable & may do more harm than goodJoint type:Joint type: Butt welds more risk than socket weldsButt welds more risk than socket welds


Risk Risk ““ZoneZone”” in Hydroprocessing in Hydroprocessing EnvironmentsEnvironments


ConclusionsConclusionsDissimilar welds provide benefits but also Dissimilar welds provide benefits but also pose inherent risk; scrutinize them during pose inherent risk; scrutinize them during new constructionnew constructionDissimilar welds require regular inspection Dissimilar welds require regular inspection attention throughout their service life (e.g. attention throughout their service life (e.g. SWUT, PT etc.)SWUT, PT etc.)Hydrogen embrittlement failures can be Hydrogen embrittlement failures can be rapid and unpredictable so avoid using rapid and unpredictable so avoid using dissimilar welds in severe hydrogen dissimilar welds in severe hydrogen charging environments (whatcharging environments (what’’s severe?)s severe?)


Path ForwardPath Forward

See handouts on sections from API 571 See handouts on sections from API 571 and API 582 that pertain to dissimilar and API 582 that pertain to dissimilar metal welds. Following todaymetal welds. Following today’’s s presentations, letpresentations, let’’s discuss if our API s discuss if our API documents adequately address dissimilar documents adequately address dissimilar metal welds.metal welds.

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Dissimilar Welds in Refinery Services - B Jack