1972 -2012

Alternative Approach to Essential Welding Variables

An Alternative Approach

API - 19 Jan 2016Marie Quintana

Yong-Yi Wang

Aditya Dekhane

Presentation Overview

• Traditional treatment of welding variables

• Elements of the alternative approach

• Practical tools accessible to industry

• Opportunities for improvement

• Benefits demonstrated in case studies

• What is “essential”?critical or profound impact on making compliant welds

• Typical basis . . .Empirical . . .

Experiencial . . .Equipment settings

• 29 “essential” variables among all four standards• Less than half are consistent across standards• Even less consistency in method of control

Consistent result until boundary conditions change.

Historical Approach

API 1104 ASME IXCSA

Z662.03BS 4515-1EN288-9

# Essential Variables 15 17 23 27

Alternate Approach• Necessary because boundary conditions have shifted

– Pipe & weld materials ⇒⇒⇒⇒ alloy & micro alloy strategies

– Welding technology ⇒⇒⇒⇒ complexity of waveform welding⇒⇒⇒⇒ new welding processes

– Tendency to higher design factors ⇒⇒⇒⇒increasing demand for mechanical properties

• Without alternative approaches . . .– Difficult to accommodate new welding technologies in a

meaningful way– Difficult to meet performance expectations with new materials– Cost and productivity implications– Layer on requirements w/o addressing primary drivers

• Reconsider “essential” . . .primary drivers of mechanical properties

resulting in changes that can be reliably measured

• Expand the basis . . .Empirical . . .

Experiencial . . .Correlated with Fundamentals

• Interactions more relevant than individual, independent variables

Alternate Approach to Essential Welding Variables

Alternate Approach

Weld Properties (Fusion Zone or HAZ)

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

Primary Drivers Based on Fundamentals

How fast does it cool?How fast does it heat?Peak temperature?How many cycles?

Specified elements?Unspecified elements?Recovery?Dilution?Slag-metal reactions?

Current codes do not address these directly.

Alternate Approach

Weld Properties (Fusion Zone or HAZ)

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

Primary Drivers Based on Fundamentals

Significant Impact on Three Major Industries . . . So Far

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Weld Properties (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

Alternate ApproachPrimary Drivers Based on Fundamentals

Alternate ApproachIndustry Response to Unexpected Weld Performance

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Regulatory reaction . . . . . . without change mechanism.

• Military Shipbuilding ⇒⇒⇒⇒ weld metal properties

– Mandated heat input ranges based on survey of applications and process control tools in use at the time

– Complete change to PQR for those applications– Pushed “burden of proof” to consumable suppliers

• High & low cooling rate tests for initial qualification & lot certification(thickness, preheat/interpass, average heat input)

Alternate ApproachIndustry Response to Unexpected Weld Performance

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

INDUSTRY response . . . . . . WITH a change mechanism.

• Structural Fabrication ⇒⇒⇒⇒ weld response to seismic load

– FEMA guidelines for demonstrating material performance• Lowest and highest heat inputs possible for the product

(did not include other factors)• Dilution effects

– AWS refined the approach in consensus based fabrication specifications and filler metal standards

– Regulators & owners rapidly adopted guidelines

Alternate ApproachIndustry Response to Unexpected Weld Performance

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

INDUSTRY response . . . . . . WITH a change mechanism.

• Heavy Fabrication & Power Generation ⇒⇒⇒⇒ GMAW-P weld properties not reproducible

– ASME added True Heat Input option for heat input control (targeted at advanced waveforms)

– Used for welding procedure qualification in critical applications

– Further modifications to procedure qualification under consideration

Waveform Welding (schematic)cu

rren

tcu

rren

t

time

curr

ent

Error is constant

Error varies with waveform

Error is <1%

Traditional Average HI vs. True Heat Input

Alternate Approach

Weld Properties (Fusion Zone or HAZ)

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

Opportunities for Improvement Over Traditional Approach

• Direct measurement not feasible

• Traditional control by HI, thickness and PHT / INT is indirect

• Waveforms change the game− HI error up to ± 17%

• Need real HI with a meansto determine thermal cycle

• Traditional “control” is indirect . . . at best− strength range− alloy group− carbon equivalent− mfg. trade name

• Need to document the interaction with thermalcycle or cooling time . . .

Alternate ApproachSTEP 1 – COOLING TIME, ∆T800-500

Controlled by welding process variable interactions and computed with confidence

STEP 2 – MICROSTRUCTUREGleeble simulations used to document

interaction between chemistry & welding thermal cycles. Establishes

lower bound properties.

STEP 3 – PERFORMANCEEstimate properties from

microstructure & mechanical test history

Weld Properties (Fusion Zone or HAZ)

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

The Methodology

Tool set now in Beta includes numerical model for ∆∆∆∆T800-500validated for GMAW -P with limited properties prediction.

• Single Torch GMAW -PValidated experimentally . . .

using True HI

Tool Validation – Thermal Cycle Prediction

300

800

1300

1800

2300

3080 3100 3120 3140 3160 3180

Welding Time (s)

Tem

pera

ture

(K)

Trailing torch

leading torch

• Dual Torch GMAW -PUnderstood best using thermal cycle prediction(key variable is torch spacing)

Cooling Time is Key ⇒ function of HI, T, t

• “Garbage in, garbage out” . . .maximum reliability obtained with True Heat Input

Current Capabilities & Limitations

INPUTS OUTPUTS

HeatInput

Baseline MaterialData

∆T800-500Hardness &

StrengthCv TT

TrueActual

Estimated

AverageActual

Estimated

Most accurate estimates from the most reliable inputs

Self-consistent trend estimates

Use with caution

Situation: Determine Essential Welding VariablesDistinguish primary from secondary drivers in controlling weld properties

• Engineering judgement ⇒⇒⇒⇒ reduced variables (29 to 13)

• Predictive tools ⇒⇒⇒⇒ 39 virtual welds in 2 weeks(∆T800-500 , hardness)

• Weld Experiments ⇒⇒⇒⇒ 27 physical welds in 8-10 weeks(∆T800-500 , hardness, Cv, strength)

• $50K and 3 months saved

Case Study A

Situation: Accelerated Procedure Development & QualificationDeliver required weld strength overmatch with significant change in X100 pipe wall thickness & joint type

• Predictive tools ⇒⇒⇒⇒ 12 -15 virtual welds over 2 weekstrade off between HI & PHT / INTpredicted ∆T800-500 ,hardness, tensile

• Weld Tests ⇒⇒⇒⇒ PQR in 4 weeks two consumables, two torch conditions

• At least 50% reduction cost & schedule . . .. . . eliminated one testing cycle, maybe two

Case Study B

• Specific to GMAW narrow groove welds

• Tool development with welding contractors– Improve user interface for cooling time predictions– Customize for various methods of measuring HI

• Other possibilities– Project specific trials where consistency properties are essential

• Solicit stakeholders for baseline materials data

Current Status

• Opportunity to unify all parameters that affect cooling rates– Heat input– Wall thickness– Preheat temp.– Interpass temp.– Bevel geometry– Travel speed

02/02/2016 20

Significance

Keep cooling rate within rangeAllow contractor to manage tradeoffs

• Methodology answers engineering need for more reliable decisions• without cost & schedule burden of traditional approaches

• Change mechanisms– Codes & standards are largely reactionary

. . . ASME & AWS made small positive steps

– Goal is an alternative approach as an option• Improve reliability of procedure development & PQR

• Focus only on the welding variables that are really important(primary drivers & maybe secondary drivers . . . )

Summary

Final Thought

What is better for the industry?

• Regulatory reaction to a problem

• Informed industry consensus

• Prediction accuracy

Case Study B

850

900

950

1000

1050

850 900 950 1000 1050

Pre

dic

ted

UT

S (

MP

a)

Measure UTS (MPa)

ER110S-G ER120S-G 1:1 Reference Line

Current Capabilities & Limitations

STEP 1 – COOLING TIME, ∆T800-500

Controlled by welding process variable interactions and computed with confidence

STEP 1 – COOLING TIME, ∆T800-500

Controlled by welding process variable interactions, slag – metal interactions and

base metal dilution.

STEP 2 – MICROSTRUCTUREGleeble simulations used to document

interaction between chemistry & welding thermal cycles. Establishes

lower bound properties.

STEP 3 – PERFORMANCEEstimate properties from

microstructure & mechanical test history

Weld Properties (Fusion Zone or HAZ)

Thermal Cycle (Fusion Zone or HAZ)

Chemistry (Fusion Zone or HAZ)

Microstructure (Fusion Zone or HAZ)

• FCAW-G, SMAW, SAW add complexity with slag, chemical reactions and dilution.

Axial Spray Transfer – Traditional Method Works

Note the minimal difference in

values

Pulse – Traditional Method Does Not Work

Note the large difference

between row 1 and 2&3

RapidArc ® – Traditional Method Does Not Work

Note the large difference

between row 1 and 2&3