7/30/2019 3.03.OperatingProcedures.visual Inspection of Welds http://slidepdf.com/reader/full/303operatingproceduresvisual-inspection-of-welds 1/12 3.03 WELDING PROCEDURES MANUAL Page1of 12 OPERATING PROCEDURES VISUAL INSPECTION OF WELDS12/31/06 HIS SECTIONPROVIDES STANDARD PROCEDURES for visual inspection of steel welds. T GENERAL Visual inspection of welds will be performed by individual(s) qualified by education, training and/or experience. The welding inspector (inspector) must: Be able to verify that welding is being performed in accordance with the construction specifications and the welding procedures (see Section 2.20: “Qualified Welding Procedure Specifications (QWPS)”) Understand the specifications before arriving on the job site in order to be able to respond quickly and appropriately if the work or procedures are not being followed Be equipped with the proper inspection equipment to check and monitor the welding parameters listed in the welding procedure All field welds are subject to visual inspection and/or non-destructive testing to: Verify weld integrity Provide for the correction of improper welding techniques when indicated by recurring defects Verify welder qualification in the production weld process Qualified welders are responsible for the quality of their work. The Company will assign inspection personnel as necessary to verify contractor and Company weld quality and conformance to applicable procedures. If upon visual inspection it is determined the weld may be defective, it must be inspected by non-destructive means or removed from the pipeline and destructively tested. The inspection may be made before, during, or after the weld has been completed. The Company has the right to accept or reject any weld for any reason.
Transcript
7/30/2019 3.03.OperatingProcedures.visual Inspection of Welds
HIS SECTION PROVIDES STANDARD PROCEDURES for visual inspection of steel
welds.
TGENERAL
Visual inspection of welds will be performed by individual(s) qualified by education,
training and/or experience. The welding inspector (inspector) must:
Be able to verify that welding is being performed in accordance with the construction
specifications and the welding procedures (see Section 2.20: “Qualified Welding
Procedure Specifications (QWPS)”)
Understand the specifications before arriving on the job site in order to be able torespond quickly and appropriately if the work or procedures are not being followed
Be equipped with the proper inspection equipment to check and monitor the welding
parameters listed in the welding procedure
All field welds are subject to visual inspection and/or non-destructive testing to:
Verify weld integrity
Provide for the correction of improper welding techniques when indicated by
recurring defects
Verify welder qualification in the production weld process
Qualified welders are responsible for the quality of their work. The Company will assign
inspection personnel as necessary to verify contractor and Company weld quality and
conformance to applicable procedures.
If upon visual inspection it is determined the weld may be defective, it must be inspected by
non-destructive means or removed from the pipeline and destructively tested. The
inspection may be made before, during, or after the weld has been completed. The
Company has the right to accept or reject any weld for any reason.
Every weld made on Company piping should be visually inspected; however, visualinspection may not substitute for other non-destructive test requirements.
The inspector must be familiar with the applicable codes and standards, the inspectionequipment necessary to perform these tasks and have experience in these areas. Further,the inspector must acknowledge any personal lack of understanding with appropriatepersonnel so that appropriate training can be completed before undertaking any specificassignment.
The visual inspection should include, but not be limited to:
General workmanship
Compliance with the requirements of the applicable Qualified Welding ProcedureSpecification (QWPS)
Presence of surface defects that could affect the integrity of the weld, including:
Arc burns
External undercut
Low crown
Lack of fusion on the cap
Porosity
The inspector may reject any weld that:
Shows evidence of poor workmanship
Did not follow the specifications set forth in the QWPS or specific instructions of theinspector
Has an arc burn present (only for propane piping and pipelines operating at or above40% SMYS)
Has a dent in excess of 0.250 inch in depth
Contains visible surface defects that could affect weld integrity
Other conditions which, in the judgment of the Inspector, indicate an unacceptable weld
INSPECTION RESPONSIBILITIES PRIOR TO WELDING The inspector must review QWPS and bring any questions about the welding proceduresfor a particular application to the immediate attention of the individual overseeing weldingactivities.
The inspector must also check certification records for each welder working on constructionprojects to ensure that proper and current qualification data is on file for the processesbeing welded.
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Before welding, the inspector should also check pipe and fittings to be welded for:
Scabs
Split seams or laminations
Rust
Scale
Other harmful surface conditions
The inspector should also check:
Pipe ends for proper joint design and dents caused by improper handling
Welding equipment and filler metal to be used for correctness and condition
NOTE: Whenever questionable or unacceptable equipment or conditions arefound, they must be corrected prior to welding.
The surface of all pipe and components for defects that could affect theirserviceability
NOTE: Any gouge, groove, dent or other defect which exceeds the allowable depthin accordance with the applicable material standard must be either removedby grinding or the entire section replaced as a cylinder. Grinding to eliminategouges or grooves must be followed by wall thickness measurements toensure the remaining wall thickness of the pipe or component is withinspecification limits. Unless otherwise directed, the wall thickness tables in
API 5L govern the thickness for pipe.
TABLE 3.03.1: WALL THICKNESS TOLERANCES
OUTSIDE DIAMETER IN INCHES(ALL PIPE TYPES
EXCEPT AS NOTED)
TOLERANCE, PERCENT(GRADE B OR LOWER)
TOLERANCE, PERCENT(GRADE X42 OR HIGHER)
2.875 +20.0-12.5
+15.0-12.5
2 7/8 but 20 +15.0-12.5
+15.0-12.5
20 (Welded pipe only) +17.5
-12.5
+19.5
-8.0
20 (Seamless pipe only) +15.0-12.5
+17.5-10.0
When assembling pipe and components together prior to welding, the inspector shouldensure the alignment and root space are in accordance with the approved weldingprocedure and that the resulting weld will not produce abnormal residual stress.
The inspector must ensure the weld joint is clean and free of all foreign material (e.g., dirt,oil, coating material, etc.). The end bevels should be inspected for defects such aslaminations, improper bevel angle, and an improperly machined root face. The inspector is
also responsible for remediating defects such as dents and root face damage.
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Each process (Shielded Metal Arc [SMAW] or Gas Metal Arc [GMAW]) has certain
characteristics which must be considered for each application. Also, each process has
ses. While each process has a different defect potential, with proper
certain features that require constant observation to ensure that the process is beingproperly applied.
Table 3.03.2 presents items the inspector should consider when inspecting welds madewith these procesapplication both can yield excellent weld quality.
TABLE 3.03.2: EXAMPLE WELDING INSPECTION COMPONENTS ANDCHARACTERISTICS BY PROCESS
PROCESS COMPONENT COMPONENT CHARACTERISTIC
Elec of the coating
A
e wire
e coating
trodes Moisture content
ge of the electrodes
Eccentricity of the coating to cor
General condition of th
SMAW
Welding Machines
les (condition and size)
Machine settings
Machine condition
Welding leads or cab
Ground connections
Wire Protection from weather, dirt, etc.
CleanlinessShielding Gas % Argon / Proper type of gas; 100 % CO2; 75
25% CO2
Free from moisture
Proper fittings and hoses (tightness andleaks)
Gas separation considerations
Bottle safety
Wire Feeders
s and condition
te start porosity
Cleanliness of unit
Proper drive roll
Pre-purge to elimina
GMAW
Welding Machines
n and size)
d condition of gun
Proper machine capability
Machine settings
Ground connections
Weld cables (conditio
Contact tip on welding gun an
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The use of steel grounds that have been sharpened or “torch cut” to a point and placedinto the weld joint may not have the proper cross-section for the amperage involved. This leads to overheating of the ground and welding cable. The small “point” contactresults in a “choke” or “resistor” effect in the electrical circuit, which creates overheatingand reduces the welding machine’s capability to provide proper amperage and voltageat a given setting.
To avoid ground and cable overheating by providing the proper cross-sectional area of ground contact in the weld groove or, when possible, by using commercially availableground clamps (see Table 3.03.3 below).
TABLE 3.03.3: WELD CABLE WIRE DIAMETER/CROSS-SECTIONWELD CABLE COPPER WIRE DIAMETER (INCHES) AREA OF WIRE (SQ. INCHES)
#4 1/4 .05
#2 3/8 .11
1/0 7/16 .15
2/0 1/2 .20
3/0 9/16 .25
4/0 5/8 .30
NOTE: Steel has an electrical conductivity factor of approximately one-seventh that of copper. Therefore, steel ground contact surfaces should be seven times that of the cross-section of the welding cable. While this is impractical, provide asmuch steel ground contact area as possible to eliminate a choking effect oncurrent flow.
PIPE CONDITION
In general, most pipe purchased by the Company conforms to API 5L (“Specification for Line Pipe”), which provides standards for chemical composition, dimensionaltolerances, and mechanical properties for the pipe. The inspector must understand thisspecification and how to inspect pipe at the pipe mill, in the stack or on the right-of-way
(ROW). This includes measuring the pipe’s diameter, wall thickness, and ovality(specifically, checking for “out-of-roundness”), as well as checking for residualmagnetism which can affect the welding arc.
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The inspector should be familiar with the following pipe inspection tools for checking
pipe tolerances and magnetic fields: Diameter or “Pi” tape (measure to three decimal places)
Digital or dial caliper (6-inch)
Inside diameter micrometer (various diameters)
Outside calipers (various diameters)
Gaussmeter (Hall-effect type, such as F.W. Bell)
Pipe bevel and land gauge
JOINT DESIGN
The success of any welding operation including pipeline welding begins with theselection of the proper bevel and root face. Although several joint designs have beenevaluated for pipe welding, the accepted bevel and root face (land) when using manual
welding processes is 30-35 and 1/16 inch 1/32 inch respectively (see Figure 3.03.1):
1 16”-1 8”
30-35DegreesOn Bevel
1/16”1/32”
Figure 3.03.1: Typical Joint Design for Pipe Welding
This joint design is used because:
The joint is sufficiently wide at the top to permit access for making the root pass The angle of the bevel permits good tie-in (fusion) to the bevels by weld metal
The completed joint provides desirable geometric characteristics for radiography
The opening between adjacent pipe ends to be welded is called the root space(sometimes referred to as the “root opening” or “gap”). This dimension isextremely important in terms of achieving a quality root-pass weld. The nominaldimension for the space will vary depending on the welding process or electrodesize to be used for the root pass.
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EXAMPLE: The GMAW process may require a slightly wider space (3/32
inch) to ensure full penetration and good tie-in to both root facesor lands of the weld joint. On the other hand, for the SMAWprocess, a 1/16-inch space is sufficient due to the highpenetration characteristics of the process.
Regardless of the electrode size or process used, an improper space around thecircumference will cause one of two types of defects:
Excessive space will cause burn-through
Tight space may cause inadequate penetration
The inspector should ensure that the joint space conforms to the welding procedurerequirements. This will eliminate any guesswork if problems are discovered duringradiographic film interpretation.
VISUAL INSPECTION DURING WELDING
Inspection during welding provides an opportunity to discover pipe laminations or splitseams since they tend to open up during welding because of the weld heat.
When GMAW is used, filler wire protruding into the pipe must be kept to a minimum.
Welds must present a neat workmanlike appearance free of surface defects, including:
Cracks
Inadequate penetration
Burn-through
Porosity
Other defects
WELDING PARAMETERS
The inspector should always be aware of (and have equipment to measure) the keywelding procedure parameters:
Amperage
Voltage
Travel speed
The impact or effect of each parameter is discussed below:
Amperage
Amperage is the welding current which dictates the burn-off or melting rate of theelectrode. A range of amperage is usually presented for each electrode diameter.For example, a 5/32” diameter E7010-G might have a typical amperage range of 130-170. It is important to note that the specific amperage range presented in theprocedure is only established during actual welding procedure development.
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Arc voltage is a function of the length of the arc (i.e., the longer the arc, the higherthe voltage). During the deposition of the root pass, the arc should be buried andthe resulting arc voltage will be low (20-23) with a 5/32” diameter E6010 electrode.
When depositing the hot pass, the arc voltage will be somewhat higher and will varyas the arc length changes as the welder manipulates the arc to wash out any slag inthe edges of the root pass.
The fill and cap pass voltage will be fairly consistent, and in the 25-30 volt range.
Due to electrical resistance in the welding leads, ground, etc., arc voltage may be 2-3 volts higher at the terminals of the welding machine than at the electrode holder. If
the difference exceeds 4 volts, check lead sizing and ground quality.
Open Circui t Voltage (OCV)
Although not a part of the procedure’s welding parameters, OCV controls the arccharacteristics.
Some welding machines include OCV as part of the fine current selector. Whenthis type of machine is used for procedure and field welding, the OCV increasesas the fine selector is increased for current. High OCV results in a deeplypenetrating, highly forceful (almost cutting) type of arc. This is not desirablewhen depositing a root pass or making a cap pass. High OCV may result in
excessive force, thereby creating potential for internal or external undercutting inthe root or cap pass, respectively. To eliminate undercutting, low OCV ispreferred for the root and cap pass.
Understanding how OCV can affect arc characteristics enables the inspector toassist the welder and the contractor.
Travel Speed
Travel speed is the indicator for speed of welding. The inspector should use astopwatch and tape to measure travel speed and compare it to the weldingprocedure.
Excessive travel speed usually indicates that excessive amperage is being used andvice versa. This may lead to a thinner than desirable root bead and perhaps rootbead cracking.
PREHEAT
Preheating (and elevated inter-pass temperature) is conducted to lower the cooling ratein the weld and the heat-affected zone for a more ductile metallurgical structure, therebyminimizing the risk of extraordinary hardness and cracking. Preheating also aids indriving out hydrogen from the weld deposit, which can contribute to weld cracking.
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Preheat temperatures are generally measured by touching the pipe adjacent to the weld
bevels with a temperature indicating crayon (e.g., Tempilstik®
), or a contact or infraredpyrometer.
Cooling rates will be faster for a weld made without preheat than with preheat. Thehigher the preheat temperature, the slower the cooling rates will be after the welds havebeen completed.
A further effect of rapid cooling, even if cracking does not occur, is low ductility andtoughness in the welded joint. The composition of the pipe material and the weldingprocedure will determine the extent to which ductility and toughness are lowered.
WELD PASSES
The number of weld passes required to complete a pipe weld is usually not a significantvariable where mechanical properties are concerned. However, the number of weldpasses can be a significant factor in determining the toughness of the weld deposit,especially for welds subjected to low temperatures.
ELECTRODES
To ensure a good pipe weld when selecting the correct electrode, consider:
Electrode type (as to coating and deposit analysis)
Electrode diameter
Base the selection, type and size on:
The pipe’s chemical composition
The pipe’s wall thickness
Mechanical property requirements (e.g., tensile, yield, certain alloys, etc.)
Construction specification requirements for the weld deposit
Age and storage conditions play an important role in the electrode’s moisture content,which if not cared for can affect the weld. In general, electrodes over a year old may besuspect in terms of proper moisture. Cellulose-coated electrodes (6010, 7010, etc.)
should be stored above freezing and below 100 F due to moisture inherent to theseelectrodes. Iron powdered coated electrodes (7018, 8018, etc.) should be stored in rod-
ovens to maintain moisture levels within acceptable tolerance by maintaining atemperature of 350 - 400 F or in accordance with manufacturer’s storagerecommendations.
PIPE GROOVE WELDS
Root Pass
When preheating is required by the welding procedure, measure the preheattemperatures with temperature indicating crayons (e.g., Tempilstik® brand) or apyrometer. Maintain preheating temperatures while completing the root pass.
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The inspector will check the general condition of the root pass electrodes and
determine that the proper AWS classification and diameter are being used. Theinspector should examine the welding cable connections at the machine todetermine that the correct polarity is being used. Most pipeline welding proceduresutilize direct current – reverse polarity (DCRP) settings. This is also recognized asdirect current – electrode positive (DCEP). The electrode lead should be connectedto the positive output of the welder and the ground lead connected to the negativelead.
During root pass welding, periodically measure the amperage, voltage and travelspeed to determine compliance with the approved welding procedure.
Root pass travel speed and amperage are closely related. Excessive root pass
travel speed usually indicates that excessive amperage is being used, and viceversa. With either of these outside the limits of the welding procedure parameters,the potential increases for a thinner than desired root bead possibly leading to rootbead cracking.
Hot Pass
The inspector should:
review the condition of the hot pass electrodes and determine that the properAWS classification and diameter are being used
ensure that the time specified in the approved welding procedure between the
root pass and the hot pass is not exceeded periodically measure amperage, voltage and travel speed during the deposition
of the hot pass to ensure compliance with the approved welding procedure
require that the completed hot pass be cleaned of all slag by power brushing
Fill Passes
The inspector should:
inspect fill pass electrodes to determine their condition, AWS classification anddiameter
confirm that the welding procedure is being followed in terms of the number of fillpasses for the respective wall thickness
periodically measure amperage, voltage and travel speed to determinecompliance with the approved welding procedure
when checking voltage at the terminals of the welding machine, allow for a 2-3volt drop at the arc depending on the length of the welding cable
during welding, periodically ensure that interpass cleaning is sufficient toeliminate slag entrapment between passes
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inspect all welds to ensure compliance with the approved welding procedure.
For welds consider the weld shrinkage which occurs and require that thecomponents to be joined are properly spaced prior to welding.
ensure all welds have at least two weld passes. This requirement is intended toeliminate any potential leak path.
unless otherwise specified, inspect welds using the following acceptance criteria:
the weld leg size will conform to the approved welding procedure and be no
smaller than the thinnest pipe wall thickness and shall be slightly concave orflat in the center of the bead.
the weld will exhibit good workmanship, blend smoothly into the run pipe andfitting, and be uniform in appearance around its entire circumference
VISUAL INSPECTION AFTER WELDING
Completed welds will be visually inspected to determine weld acceptability. To inspect fordefects, the weld surface must be thoroughly and carefully cleaned of oxide and slag, sothat cracks, arc burns and/or other surface defects are not hidden (see Section 3.11: “WeldDiscontinuities”).
Also, visually inspect the welds to ensure: Undercut at the toe of the fillet weld is less than 1/64 inch deep regardless of length
There are no:
Pinholes or porosity
Cracks of any length
Arc burns on LP lines or on natural gas pipelines operating above 40% SMYS
INSPECTION EQUIPMENT
Visual inspection of pipe welding involves certain instruments and inspection tools to
measure pipe and components for conformance to purchasing specifications, weldingparameters and material defects.
The following equipment is recommended for the inspector to ensure welding activity is incompliance with applicable codes and standards:
Amperage meter (Tongmeter, 0-300 amps, e.g., Fluke model 336)
Voltmeter for voltage measurement (same Fluke instrument)
6-inch Vernier caliper (for accurate measurement of root face, pipe wall thicknessat the ends, tensile specimens, etc.)
Pit measurement gauge or dial-indicator depth gauge
