Chapter 17 — Welding, heat treatment and examination

Welding changes the local material condition. Weld metal, adjoining heat-affected zone (HAZ) and unaffected parent material can have different composition and properties. The fusion boundary separates fused metal from adjoining material. Consumable selection, thermal treatment, hardness locations, examination and repair must address the actual region and process-exposed root. A satisfactory cap observation does not establish the HAZ or root condition.

Figure 17.1. Authored schematic of a completed butt joint. Zone widths, reinforcement and measurement locations are illustrative. The figure identifies distinct regions. It is not a qualified weld preparation or a prescribed hardness survey.

The butt/cap and fillet/T-joint sections and location inset distinguish material regions, near-surface depth and HAZ fusion-line offsets. Hardness-location interpretation supplies their method context.

Establishing what is qualified

The Welding Procedure Specification (WPS) defines production instructions and permitted variables. The Procedure Qualification Record (PQR) records the qualification weld and its required tests; personnel performance qualification establishes capability within its own range. Procedure suitability and personnel capability are separate requirements.

The applicable construction code and adopted fabrication requirements determine the qualification route. ASME Section IX is a common qualification basis for pressure piping and related equipment, while the construction code and service specification add requirements for the finished item. Pipeline, tank and structural work can have different applicable routes. Historical references do not establish the edition or jurisdiction governing a new job. Establish that basis before applying qualification ranges.

Material, thickness, joint form, welding process, filler and shielding arrangements affect applicability. A qualification for one combination cannot be extended by resemblance alone. The WPS identifies essential variables, nonessential variables and supplementary essential variables where required by the qualification basis. A change that requires requalification is different from a change that requires revision of instructions within an existing qualification. Both changes need to reach production before work proceeds.

Supplementary tests can establish properties that a basic qualification does not address. Hardenable steels or a stress-corrosion-cracking service may require cross-sectional hardness traverses through weld metal, HAZ and parent metal. A notch-toughness requirement connects qualification and filler selection to the required test temperature. Duplex procedures may add corrosion, impact, ferrite and metallographic examinations. A qualified butt weld may still require a representative fillet, attachment or tube-to-tubesheet arrangement when the geometry or service creates another question.

A tube-to-tubesheet mock-up illustrates the purpose of this additional representation. Its production materials, thicknesses, joint preparation, access restrictions, bead placement, preheat, heat input and expansion method are reproduced as specified. Sectioning and targeted examination then assess the local joint that will actually be made. A conveniently accessible flat specimen would not establish the effect of a restricted production arrangement. The mock-up supplements the required procedure evidence rather than replacing the qualification route.

Postweld heat treatment also belongs in qualification. Test specimens required to represent the treated production condition receive the specified treatment. Repeated heat treatment can change material properties, so the qualification may need sufficient aggregate holding time for a further treatment after repair. For a procedure qualified to two treatments, this provision supports that stated accumulated cycle. It does not grant unlimited reheating. The production record preserves which cycles each joint actually received.

Choosing and controlling the joining process

Process selection distinguishes covered-electrode SMAW, gas-protected GTAW/GMAW, externally gas-protected or self-shielded FCAW, and mechanized wire/flux SAW. GMAW transfer mode and the qualified equipment/program can constrain applicability.

Access and joint stage affect selection. A root made from one side has a different support and examination situation from a root that can be gouged to sound metal and welded from the other side. A process accepted for fill passes may be excluded from a single-sided root, socket joint or branch connection. A process restricted to a shop may be unsuitable at an exposed field location even if the material and thickness appear identical. The permitted position, equipment, consumable diameter and transfer mode must remain within the adopted procedure.

Transfer mode deserves particular attention in GMAW. Short-circuiting, spray, globular and pulsed modes must not be grouped under a single unrestricted permission. The procedure defines the electrical characteristics and the applications permitted for each mode. Modified-waveform or pulsed processes can also depend on the qualified equipment model and program. A replacement power source with a similar nameplate rating may not reproduce that qualified process. The production controls need the actual equipment and settings relevant to the qualification.

Consumables contribute composition and properties to the joint. The specified electrode or wire classification, flux combination, shielding gas and handling condition belong together. Some adopted procedures bind manufacturer and product identity as additional qualification variables. A neutral SAW flux with alloy wire is not interchangeable with deliberate alloy addition through another flux. An electrode suitable for a non-pressure attachment is not thereby suitable for a pressure-retaining joint. A general carbon-steel filler designation may not establish the required low-temperature toughness.

Hydrogen control also reaches the consumable and its storage. Low-hydrogen consumables, their drying and exposure controls, and the permitted root-pass exceptions follow the selected procedure. An exception for a cellulosic root or hot pass does not authorize its use throughout the joint or on another material group. FCAW diffusible-hydrogen classifications and material/service restrictions may differ between specifications. Selecting a wire because it can deposit metal rapidly does not resolve these qualifications.

Root protection is a separate interface with the process side of the joint. Back purge or other specified shielding must protect the region for the required passes or deposited thickness. Gas composition and the means of verifying its condition are part of the method, particularly for alloy and stainless joints. A substitute technique or flux-coated wire alone cannot satisfy an adopted procedure that requires purge. An alternative that permits welding without backing gas has its own qualified process, wire and shielding conditions. The alternatives cannot be assembled selectively into an unqualified hybrid.

From prepared joint to completed weld

The prepared joint gives the process access to the intended fusion surfaces. Profile, root face, gap and alignment are checked before welding. Cutting oxides, cutting fluids, moisture, detrimental contamination and damaged bevels are removed by the applicable preparation method. A poorly fitted joint needs a controlled correction. Inserting extra metal or building up a bevel to hide an excessive gap is not equivalent to the specified preparation. Any permitted buttering, backing or consumable insert carries its own chemistry, fusion and examination conditions.

Incorporated tacks retain the finished joint's procedure, material, preheat and soundness requirements. Back-gouging, root, branch and attachment examinations need access before later passes or assembly conceal the required surface. Fabrication and construction establishes dimensional realization and work access.

Temporary attachments and accidental arc strikes also change pressure-boundary material. Removing a dog by hammering can leave a damaged area. Permitted removal and dressing must preserve the required wall and include the specified surface examination. Grinding an arc strike until its appearance disappears does not necessarily establish that the affected material or a crack has been removed. In a sour or cracking-sensitive application, the repair route can require etching, thickness measurement and surface examination, or removal of the affected pipe section. The criterion is the remaining material condition, not a neat surface alone.

Pipeline handling and alignment-clamp release must suit the incomplete joint and its prescribed welding sequence. Mainline release, incomplete-weld protection and reheating conditions belong to the selected pipeline method; see pipeline construction.

Join the online deposit to the surveyed run material

For an online attachment, the selected temper-bead placement connects each deposit to a particular live run region. Its order, first-layer contact and final-pass location are part of the represented thermal method, together with actual wall, pressure, contents and cooling. A qualified scalar heat input cannot stand in for a changed contact geometry or an unexamined run-pipe toe. Through fit-up and production, preserve the selected attachment shape and bead-order instructions. A sleeve sequence does not establish a branch sequence by resemblance.

The preweld coverage footprint likewise distinguishes thickness-location sampling from the full required defect/lamination examination region. Root and cap access, material-appropriate surface methods, hardness regions and delayed-cracking examinations then address the actual resulting weld at their specified stages. Relocating the branch after the survey, concealing a root before examination or changing the run's operating condition can invalidate the corresponding evidence. Retaining the original joint number on the final report does not prevent that loss.

Carrying the drawing instruction through production

The spool's weld symbol must be decoded into a physical member, joint side, preparation and deposit extent before fit-up is released. Those drawing fields and the procedure address connected questions. A specified root opening must be achievable in the prepared joint. A member-specific bevel must be cut on the intended member.

A required opposite-side operation must remain accessible in the assembly sequence. A leg dimension, contour mark or all-around instruction describes the selected joint. It does not by itself demonstrate procedure qualification or establish the examination acceptance criteria.

Thread sealing and selected short-root bridging add another concealment boundary. Proper engagement and dry makeup are established before covering exposed threads. Coverage of thread runout, fitting face and the specified bridge region is checked afterward. Keep the run-to-fitting attachment, the root sealing/bridge deposit and the valve's thermal exposure distinguishable in the work record. A continuous exterior deposit or a successful pressure test cannot recover evidence of a fit-up condition that was never checked. Additional bridge metal does not automatically establish full-strength or fatigue suitability.

Thermal control has several purposes

Preheat establishes the required temperature of the joint region before and during welding. Interpass temperature describes its condition before a subsequent pass. The procedure can set a minimum, a maximum or both. Uniform heating and measurement at the specified locations matter. A hot spot near a torch does not show that the required material volume is at temperature. A satisfactory initial reading does not establish the condition several passes later.

The thermal cycle affects the weld and HAZ. In a hardenable ferritic material, the combination of local structure, hydrogen and welding stress can create a cracking condition. Preheat and controlled cooling are parts of its prevention, together with consumable and procedure controls. For stainless materials, excessive temperature exposure can create different metallurgical concerns. More preheat is therefore not an automatically conservative choice. The range is selected for the actual material, joint and required properties.

The procedure identifies the heating method, heated extent, means of measurement and necessary calibration. Gas rings, suitable torches, resistance or induction heating can have different applications. A method acceptable for preheat is not automatically an acceptable PWHT method. The record must be capable of showing the actual operation. This includes component identity, temperatures, timing, heating/cooling and any interruption that changes the intended cycle.

Arc energy as a controlled production quantity

Amperage, voltage and travel speed are among the production variables recorded in welding procedures. Their relationship can be taught by separating electrical arc energy from the material's resulting thermal condition. For a steady illustrative pass, V is measured arc voltage in volts and I is current in amperes. Travel speed v is in millimeters per minute. The electrical energy per unit travel E is

The factor 60 converts the time basis from minutes to seconds. The factor 1000 converts joules to kilojoules. This expression assumes steady representative V and I. A waveform process may require the qualified method's measured energy rather than multiplication of simple averages.

Electrical energy per length is also not automatically net heat absorbed by the work. A thermal-efficiency factor requires a defined method and a supported factor. A procedure's term heat input must retain its actual measurement definition before the result is compared with its limit.

Current alone does not define energy per length. Material, thickness, waveform/transfer mode, pass arrangement, preheat and interpass conditions remain required alongside the procedure's measurement definition.

Hydrogen bakeout and the prior-service condition

A new-material welding procedure cannot automatically be applied to metal that has acquired hydrogen in service. Wet H₂S, certain acid services and high-temperature hydrogen exposure can require a preweld bakeout under their defined conditions. The service history, material and exposure are therefore inputs to the weld route. A line name alone may omit the water, pH, concentration, temperature or hydrogen-partial-pressure condition that makes the requirement applicable.

The important mechanism is the combination of hydrogen, a susceptible local material condition, stress and temperature. In prior-service Cr-Mo equipment, welding directly on the base metal can create a hard HAZ and high welding residual stresses. If sufficient hydrogen remains and the joint subsequently reaches a susceptible temperature, hydrogen embrittlement cracking can occur. Bakeout aims to remove a contributing ingredient before the new weld is made. Hydrogen outgassing can also cause porosity in the weld pool. These mechanisms explain why a specified bakeout precedes cutting or welding rather than being treated as a later cosmetic repair.

Bakeout temperature and duration depend on the adopted material/service method and thickness. They cannot be transferred from a carbon-steel schedule to every alloy, or from an equipment procedure to an undefined line. The actual heated region and thermal record matter as well as a heater setting. The procedure may require cooling control between welding and PWHT. An unplanned loss of preheat needs its own disposition and any specified examination before work resumes.

Cladding and overlay complicate this route. If the welding thermal cycle reaches the ferritic base metal through a thin stainless layer, the base-metal HAZ remains part of the hydrogen-cracking question. If a sufficiently thick protected layer and a qualified method prevent formation of that HAZ, a specified exception may apply. Conversely, the stainless layer can prevent an effective bakeout of the relevant base-metal area unless it is removed by the adopted procedure. Under the discussed conditions, hydrogen removal from stainless cladding is much less effective than from ferritic steel. Thus, “heat the clad item longer” is not an established substitute for the required preparation.

The possibility of stress-related cracking beneath thick overlay is a separate, more uncertain question from formation of a hard base-metal HAZ. It should not be presented as an equally established reason to prescribe bakeout for every clad repair. The useful decision is to determine the actual substrate, prior service, overlay/cladding condition, anticipated heat penetration and applicable method. Repair and modification carries this distinction into the intervention plan and return to service.

Postweld heat treatment and its sequence

PWHT is selected for the material, construction code and service. A service can require it where a basic thickness rule would not. Its procedure states the holding range and time, heating and cooling controls, heating arrangement, thermocouple locations and component support. The treatment has to reach the relevant metal. One favorable temperature trace at an unrepresentative location is insufficient evidence of a required through-thickness condition.

Furnace treatment can treat a complete assembly, while local resistance or induction treatment acts on a selected region. Each arrangement needs a suitable procedure. Local heating creates temperature differences along and around the pipe, and the heated extent, insulation and measurement locations become consequential. Direct flame impingement or an unqualified heating substitute can fail to provide the specified cycle. Lined or clad assemblies also have venting, differential material and protection considerations.

The interval between welding and PWHT is not governed by one universal sequence. A procedure for specified low-alloy materials may require maintaining preheat through PWHT. It can provide a separate hydrogen-removal and slow-cooling route when treatment must be delayed. Another adopted fabrication procedure permits slow cooling under an insulation blanket when immediate PWHT is unavailable. Those instructions belong to their full material and service basis. “Wrap the weld and treat it later” must not silently replace the first route.

Material transformation can require an intentional intermediate cooling step. For example, a particular 9Cr-1Mo route specifies cooling to 200°F (93°C approximately) before PWHT to complete its metallurgical transformation. This is a local material instruction, not loss of control or permission for other alloys to cool indiscriminately. The specified treatment record must show the actual sequence, not merely the final holding temperature.

Attachment welding, forming and dimensional correction also reach the treatment history. For a fabrication basis that prohibits further welding or forming after final PWHT, those operations precede it. An unplanned later operation requires a new accepted disposition. A repair that repeats PWHT must remain within the qualified aggregate thermal exposure and preserve the required strength, toughness and other material properties. Increasing holding time to obtain a lower hardness reading can create another unacceptable property change.

Final NDE and hardness testing are performed in the required treatment condition. Ferrite measurements can have a specified pre-PWHT timing even when final defect examinations are performed afterward. Thus “all examination after PWHT” is too broad. The joint record identifies the sequence and the result established at each stage. Construction uses this route to place attachments and permit access. The system testing and readiness account uses the released joint condition when defining the assembled boundary.

Distinguish interruption from a planned delay

Loss of minimum preheat before a weld is complete changes the production state. The unfinished seam has experienced a cooling history different from the qualified sequence, and a later heater reading cannot establish whether cracking has already developed. One specified route for P-4, P-5A and P-5B low-alloy work requires magnetic-particle examination of the entire incomplete seam before welding resumes after such a failure. Resume only after the actual interruption, examination and permitted reheat disposition have been addressed. A convenient examination of the last visible bead is not the stated seam coverage.

That interruption is different from deliberately delaying PWHT after welding is complete. Under the same low-alloy route, intentional ambient cooling for more than a few hours requires a hydrogen-removal/slow-cooling stage.

Under this low-alloy route, if intentional ambient cooling will exceed a few hours, complete the following before removing preheat:

• Heat to at least 600°F.
• Then apply the specified 1-in insulation blanket over the greater of one pipe diameter or 6 in on both sides.

The method specifies no additional 600°F hold beyond the wrapping operation. Another adopted fabrication route supplies its own blanket-cooling and pre-resumption examination instructions. Neither is a general permission to substitute a blanket for the first route's hydrogen-removal stage or to improvise an unspecified alternative examination method. The distinct 9Cr-1Mo transformation cooling step above also retains its own purpose.

The work record therefore identifies when cooling began, whether the joint was complete, the affected material/seam, attained temperatures, duration and the examination/heat-treatment response. These inputs distinguish an interrupted weld, a deliberately delayed treatment and the designed metallurgical cooling step. They make a later decision inspectable without claiming that preheat alone proves freedom from cracking.

Material and service variants

Carbon and low-alloy steels

Carbon and low-alloy steels require their material grouping, actual condition and service to remain connected to the procedure. Low-hydrogen consumable control, preheat, delayed-treatment precautions, hardness and any required PWHT work together. Cr-Mo grades are not interchangeable merely because all are called low-alloy steel. The particular composition and original treatment affect the required production and examination route.

Sour and stress-corrosion-cracking services can add hardness or stress-control conditions. Caustic, amine, ammonia, acid and hydrogen applications have their own concentration, water and temperature definitions. Prior alkaline exposure can also require neutralization and cleaning before welding. A method appropriate to a specified alkaline residue must not be applied to every chemical residue without its material and contamination assessment. The service definition in hazardous and sensitive services supplies the local environment in which the joint will operate.

A test result outside a specified hardness limit requires a controlled correction and recheck. Removing and rewelding, or an accepted further heat treatment, may be alternatives. Their effect on properties and qualification differs. Repeatedly testing another spot until a favorable number appears does not establish the intended correction, and a hardness result cannot independently establish low-temperature toughness.

Austenitic and stabilized stainless steels

Stainless procedures preserve cleanliness, filler composition, root protection and thermal exposure. Tools and abrasives used on other materials can leave detrimental deposits. Dedicated suitable equipment is required where specified. Low-carbon or specified dual-grade material reduces the carbide-precipitation concern in appropriate applications, but its name does not eliminate all temperature/service conditions. Generic ferritic-steel preheat and stress-relief rules must not be exported to austenitic stainless work.

Weld-deposit ferrite is another controlled property. The selected filler and procedure may target a Ferrite Number (FN) range, verified by a calibrated magnetic method at specified locations and stages. FN is an instrument-related scale used in the prescribed method, not a general volume percentage that can be substituted for microscopic ferrite measurements. Service temperature and stabilized filler grade can change the selected range. An average of six readings is meaningful only where that procedure defines the averaging method and sampling locations. An arbitrary handful of accessible points does not reproduce it.

Stabilized grades and heater tubes can require a further heat-treatment route tied to grade, consumable combination, wall and temperature. One stabilization basis addresses grades 321 and 347 base material welded with grade 347 root and fill consumables. Its prose requires treatment for wall below 1 inch (25 mm) when piping/equipment operating temperature, or the flame-side tube-metal temperature of a fired heater, exceeds 800°F (427°C). It separately excludes non-process-wetted welds.

Its schedule gives a 750°F (399°C) threshold for the corresponding thin-wall 347/347 combinations. These are piping/control-system roots made by GTAW or modified-wave short circuit, and fired-heater roots made by GTAW with back purge. The fill process is listed as unrestricted within that row. The schedule uses operating temperature for piping and tube-metal temperature for the heater.

For a process-wetted joint matching those material, thickness, consumable and process conditions, a relevant temperature above 750°F but not above 800°F lies in the interval where the two instructions diverge. That specific stabilization decision requires a disposition before release. Selecting 750°F as the apparently conservative value would silently change the prose condition. Selecting 800°F would silently exclude work covered by the schedule. This discrepancy does not erase the useful qualification, production and treatment method or stop unaffected work. It also does not turn fluid temperature into tube-metal temperature at a fired-heater surface.

Choose austenitic treatment against both cracking and sensitization

Stress relief of 300-series austenitic stainless piping addresses a service question as well as a fabrication question. Reducing welding stresses can reduce a contributing factor in stress corrosion cracking (SCC), but the added thermal exposure can promote sensitization and susceptibility to intergranular attack. A treatment that helps one mechanism can worsen another. Neither a low-carbon designation, a stabilized grade nor a completed stress-relief cycle establishes immunity to SCC.

Actual grade/carbon specification, prior/proposed thermal history and both internal and external environments determine treatment selection.

One adopted method distinguishes unstabilized 304, 316 and 317 material whose carbon specification permits up to 0.08% from low-carbon grades limited to 0.03%. It discourages stress relief of those non-L grades because of sensitization. Where intergranular corrosion is the greater concern, including applicable acid services, that method instead favors low-carbon material without stress relief. Stabilized grades can serve different elevated-temperature duties, but their composition and treatment history still matter. The stabilization route described above and a casting's grade-specific solution treatment answer different questions from this stress-relief choice.

Internal SCC assessment includes actual aqueous chlorides, caustic concentration, operating temperature and a history of cracking. Low points and locations downstream of water injection can create a local environment different from the nominal main stream. Under the adopted method, known SCC environments above 140°F include aqueous streams with more than 50 ppm chlorides and streams with a cracking history. Its caustic provisions address all caustic services above 140°F and caustic concentrations above 30 wt% at temperatures above 110°F. These are conditions of that selection method, not universal onset temperatures or permission to ignore cracking below them.

The adopted instructions are not fully consistent at their operating-temperature boundaries. Their general large-pipe low-carbon/stabilized selection excludes services below 150°F, while the detailed internal-service selection uses 140°F. A matching service between these temperatures needs a disposition of the applicable selection basis. Choosing the lower number does not resolve the difference. The carbon and intergranular-attack exclusions must also remain attached to the service choice rather than being lost in a temperature shortcut.

External exposure is a separate input. Chlorides in air, wash water or insulation can reach the outside of a line whose process stream does not promote internal SCC. The detailed method considers service above 200°F with saltwater firewater or washdown, or a coastal location combined with personnel/plant-reliability consequences or difficult and expensive replacement. Its condensed selection route includes the coastal and consequence/replacement conditions but does not separately reproduce the saltwater branch.

Preserve that difference when selecting the applicable route. Qualified stress reduction can reduce susceptibility under the actual conditions. It does not eliminate every external cracking possibility. Service and exposure assessment retains the environment, shutdown and contamination conditions affecting the material.

High-pressure hydrogen adds a leak-consequence input under this method. Its prose identifies hydrogen partial pressure greater than 100 psia. The condensed route labels the threshold in psi and reaches the hydrogen question after earlier material, intergranular-attack and temperature questions. Retain the absolute partial-pressure reference and that branch qualification.

Do not replace it with total gauge pressure. Do not turn it into a universal hydrogen material envelope. Material qualification and the hydrogen service envelope remain with the service assessment.

Table 17.1. Different reasons for considering or opposing austenitic stress relief. The structured treatment comparison retains the inputs, contrary cases and local method limits.

Once treatment is selected, specify its own fabrication cycle and covered joints. One adopted stainless stress-relief procedure uses 1550–1650°F. Its hold is 1 h per inch of nominal wall, with a minimum of 1 h. Cooling is in still air with the heat source removed. The cycle requires through-wall temperature and heating/cooling compliance within its grade/service basis. Under that method, selected treatment covers butt welds at NPS 2 and larger and all welds through the first block valve for piping below NPS 2. The separate small-pipe selection provisions retain their known chloride-cracking scope. Neither size nor a completed cycle removes the prior material/service decision.

Carry the resulting treatment or waiver basis into production, examination and later repair. A changed washdown practice, insulation condition, fluid chemistry or replacement grade can invalidate the assumptions used to select it. Preserve the actual grade, joints covered and accumulated thermal record so that later welding does not simply repeat a treatment whose original purpose no longer governs.

Duplex stainless steels

Duplex joints require a material-specific route rather than a generic stainless permission. The thermal cycle and composition affect the phase condition and properties to be examined. Heat input, interpass temperature, filler and purge composition are therefore connected controls. Qualification can add toughness, corrosion and ferrite examinations and can restrict production thickness relative to its specimen. Dissimilar joints involving duplex retain the applicable duplex tests and the distinct requirements of the other material.

The following envelope illustrates a particular adopted duplex welding procedure for its specified product grades, including UNS S31803/S32205 wrought products in the required solution-treated condition. Its numbers and exclusions apply only with that complete material and qualification basis. They are not a general envelope for all duplex alloys.

Table 17.2. Scoped duplex welding procedure conditions.

The metric and inch energy bands are rounded statements of the same nominal envelope. They are not two independently exact thresholds to combine at a boundary. The applicable controlling units and measurement definition must be retained. The 35–65 vol% criterion is likewise distinct from the FN scale discussed for an austenitic weld. Corrosion or impact qualification tests are not replaced by a rapid screening test where the procedure expressly excludes that use. The production release depends on the qualified combination and required observations, not on heat input alone.

Dissimilar joints, overlay and clad restoration

A dissimilar-metal weld has to join its materials while providing a deposit and transition suitable for their service. Filler selection can depend on temperature and chemical compatibility. The procedure may restrict the sequence of depositing a nickel alloy and stainless material. A consumable that can join the pieces mechanically is not necessarily compatible with the process exposure at the fusion boundary.

In a defined wet-H₂S service, an adopted restriction can exclude a full-penetration dissimilar weld whose fusion boundary is directly exposed to the process. The concern is hydrogen charging and cracking at that transition. A protected clad joint, socket joint or other specifically excepted configuration has a different exposure or leak-path situation. These exceptions must retain their geometric and service conditions. They do not create a general waiver for all dissimilar-metal welds in sour service.

Overlay and clad restoration combine a structural substrate with an alloy surface. Preparation strips the required clad material without reducing the base below its required thickness. It exposes and joins the base seam. Examination of that seam precedes concealment by alloy restoration.

The restored layer then needs its specified chemistry, undiluted depth, surface continuity, ferrite and bond condition. A thick-looking deposit can have excessive dilution or incomplete bond. A composition spot analysis does not establish both. If a repair penetrates into the substrate, restoring the structural section precedes the alloy repair under the selected method.

What the examination establishes

An indication is an observation produced by an examination. Its evaluation determines whether it represents a relevant discontinuity and whether that discontinuity is acceptable under the selected criteria. Method, technique, coverage, stage and acceptance criterion are separate decisions. “NDE complete” is not a sufficient description of which part of a joint was observed or what the observation establishes.

Table 17.3. Examination questions and evidential limits. The structured examination tables retain these method roles.

The table describes method roles. It does not assign an acceptance level or authorize substitution. Qualified examination personnel use the required written technique, calibration and evaluation basis. An inaccessible branch or small joint may prevent conclusive radiography, requiring the expressly permitted alternative rather than a nominal report of incomplete coverage. An overlay bond examination asks about the interface. Its UT response and sampling route differ from simply measuring pipe-wall thickness.

Hardness testing particularly illustrates the importance of location. A qualification traverse can target weld metal, both HAZs and parent materials on a polished section. One production scheme requires a weld-center reading and a reading on each adjacent HAZ at the pipe location. Another specified production method measures the cap only, using circumferentially distributed locations according to diameter.

These are different observations. A cap-only result cannot be represented as a completed HAZ survey, and a production surface result is not a substitute for the qualification cross section. Vickers HV10 and Brinell HB/HBW values have different measurement definitions. Their numerical limits must not be compared as though they used one scale.

Examination extent also needs a denominator and selection rule. A specified fraction can apply per welder, per WPS, per line class or across a defined production set. Progressive examination during fabrication gives feedback before many later joints are made. Random selection, initial-weld checks and follow-up examination after a rejectable indication can be separate obligations. They are not necessarily counted toward one nominal percentage. The record identifies the population and actual selected joints so that “ten percent examined” has an inspectable meaning.

Locate hardness indentations in the material region they are meant to test

The joint-region schematic already distinguishes an illustrative butt-joint traverse from a cap observation. Its extension below adds a fillet/T-joint section and a second question: where is an indentation located relative to a surface and a fusion line? A cross-sectional survey must reach the intended weld metal, HAZ and parent regions in the actual geometry. A row that crosses a butt weld horizontally cannot simply be copied onto a fillet where the fusion boundaries turn around two intersecting members.

The schematic includes butt/cap and fillet geometries and a location inset. The inset uses two separate distance references. In the selected historical butt-weld survey illustration, the near-surface location is marked 1.6 mm (0.063 in) below the surface. In the corresponding selected SCC-service qualification requirement, microhardness indentations in the HAZ are at most 0.5 mm from the fusion line.

The first is a depth referenced to the surface. The second is a maximum offset referenced to the fusion boundary, within the HAZ. They are not alternative limits for the same dimension, and 1.6 mm does not mean that a HAZ indentation may be 1.6 mm away from the fusion line. Structured location references and geometry.

The selected fillet example samples both sides of the projecting member's attachment, with points in the deposited metal, adjacent thermally affected parent material and parent metal farther away. Its fusion boundaries and HAZ routes follow the fillet geometry rather than the cap's accessible exterior alone. Points and zone widths in the authored extension illustrate these relationships. They do not prescribe an indentation count, spacing or load. Establish the prepared cross section, actual fusion-line location and intended test region before applying the selected survey method. A point that appears “near the weld” may still lie in weld metal or unaffected parent material instead of the HAZ being assessed.

The selected qualification requirement applies to PQRs submitted for stress-corrosion-cracking services. It assigns carbon-steel hardness limits through NACE RP0472 and other-material limits through NACE MR0103. The illustrated survey cites RP0472-2005. This is the retained historical method context, not a statement of current standard compliance. Establish the applicable edition, material/service basis, scale and method before choosing an acceptance value. No hardness number or conversion between HV and HB/HBW can be recovered from a location diagram alone.

Keep the measurement tied to the weld's represented thermal history. The companion qualification provision requires enough aggregate PWHT holding time to permit one additional treatment, for two treatments in total. That scoped requirement links a possible repair cycle with qualification evidence. It does not grant unlimited reheating or establish that a small valve's protected internals can tolerate another cycle.

Valve thermal observation addresses that assembly interface. A record that retains both indentation location and treatment history supports a meaningful comparison with the qualified condition. A hardness value without either can answer the wrong question.

Specify both the selected welds and the observations on each

A percentage selects a population. It does not describe the measurements within each selected weld. A particular service/material-qualified production-hardness method uses at least 10% of butt welds and at least 10% of fillet welds per WPS per line class. It tests 100% of locally postweld-heat-treated welds. Its comparison hardness method measures the prepared weld cap, not the HAZ.

For piping up to NPS 6 it calls for two circumferential positions approximately 180° apart. At NPS 8 and above it calls for four approximately 90° apart. The applicable final-treated condition, service/material eligibility, hardness scale/limit and local surface preparation remain part of that method. These figures do not establish a sampling rule for every line.

The butt and fillet minima apply separately; the locally treated population still requires 100% testing. Circumferential cap positions are not HAZ observations.

Table 17.4. Different sampling and local-observation questions, with structured scope and teaching arithmetic.

A second adopted method's centre/HAZ readings and personnel/process/spool selection cannot be converted into the first by renaming a column. Likewise, a material-identity spot analysis has its own location, denominator and expansion after an unacceptable result. Keep the weld map, required population, selected joints and observations connected so that a rejected result leads to the correct affected set rather than to another convenient spot.

Repair, reexamination and closure welds

Repair starts by locating and characterizing the affected discontinuity. The removal method and examination of the excavation establish whether the defective material has been removed. The repair procedure then defines the preparation, consumable, preheat, welding, treatment and final examination for the remaining section. Repairing an indication at an unconfirmed location can remove sound material and leave the defect intact.

The new weld and thermal cycle reopen the relevant evidence. If PWHT is required, final acceptance examinations are performed in their required treated condition. Hardness corrected by rewelding or another permitted heat treatment is retested. A repaired overlay may require renewed bond, surface, composition or other checks for its actual affected region. A previous passing report does not automatically cover the new repair operation.

Repeated repairs can indicate a process or personnel problem rather than an isolated defect. Repair-count limits, escalation points and production repair-rate triggers are specified by the selected basis. Some general fabrication procedures permit a further repair after an accepted detailed method and root-cause explanation. A particular closure-weld route can prohibit repair of a repair and require weld removal. The two rules must not be merged into a universal allowance of “two repairs.” The consequence of repetition is to investigate the actual joint, process, material and work conditions and use the applicable disposition.

Restore a casting under its material-specific repair route

A casting weld repair can reopen the supplied component's material condition as well as its local defect evidence. One supplementary route applies to its specified pressure-casting materials. It classifies a repair as major if any of these conditions applies:

• The casting leaked during hydrostatic testing.
• The prepared cavity depth exceeds the smaller of 20% of wall thickness or 1 in.
• The cavity area exceeds approximately 10 in².
• The casting will see the defined hydrogen service.
• The repair is on an internal surface exposed to stress-corrosion-cracking service.

Any one condition can establish that classification. A shallow cavity is not automatically minor when its service or leak history triggers another condition.

The structured casting-repair conditions and examples preserve the alternatives and material/treatment limits.

The material specification, grade, service, defect location and actual excavation dimensions determine the qualified repair and engineering disposition.

Surface examination of the prepared cavity verifies removal before the repair conceals it. Subsequent examination must be no less in type and extent than that used to identify the original defect, as well as meeting the method's minimum surface examination.

Heat treatment belongs to the repaired casting grade. For example, this route calls for postweld solution treatment of weld-repaired SA-351 austenitic castings under its stated supplementary requirement, except grades HK, HT and CT15C. That exception is not a general no-treatment permission for all austenitic castings. Final examination follows the final heat treatment. The useful release evidence joins the remaining casting, repaired region, qualified thermal history and renewed examination. A passing test from before excavation does not cover the new repair.

Under the ASME B31.3 closure route discussed here, a closure weld is the final weld connecting piping systems, subassemblies or components that have already been successfully leak tested under the applicable requirements. Impracticality of testing the completed system does not establish this prerequisite or exempt an arbitrary final weld from testing. Eligibility also depends on the governing code, service, line designation and responsible engineering or regulatory disposition.

The particular in-process-examination and traveler route illustrated here is limited to eligible new construction and excludes tie-ins to previously commissioned piping systems. That restriction belongs to this procedure. It does not establish a universal prohibition on other duly permitted intervention or test alternatives. Within this eligible route, the prepared joint, materials, WPS, qualified personnel, thermal conditions and each accessible stage are monitored and recorded. Required volumetric and other final examinations remain part of that route.

The closure-weld traveler and weld map identify the actual joint, its monitoring stages, examiner, welder, treatment, examinations, repairs and disposition. A record assembled retrospectively from memory cannot recreate observations of a root that is now concealed. System examination and testing establishes whether this alternative is permitted for the boundary and what remaining leak or service tests apply. This chapter establishes the joint-production and examination evidence on which that permitted route relies.

Qualification and examination of nonmetallic joints

Metallic weld qualification cannot be extended to a polymer or reinforced-resin joint by replacing the consumable name. HDPE fusion, solvent-cemented thermoplastic joints and adhesive or wrapped reinforced-resin joints have different materials, preparation, process variables and failure observations. Their qualified procedures and personnel must represent the production method. Construction carries these conditions into actual handling, access, alignment and installation.

For HDPE butt fusion, the procedure identifies the pipe/resin combination, equipment, end preparation and alignment, heater condition, heating and fusion sequence, pressure and cooling. Procedure qualification and bonder performance qualification are distinct. A visually regular bead provides useful production evidence, but the required qualification testing of samples examines questions that appearance alone cannot settle. Dissimilar pipe or resin fusion has its specified compatibility and qualification route, not a permission inferred from equal outside diameters.

The machine pressure setting illustrates the difference between an indication and the physical joining action. For a hydraulic machine using the specified force-area method, Aₚ is the cross-sectional area of the pipe wall to be joined. The total effective machine-piston area is Aₘ. The procedure's required interface pressure is pᵢ. The measured drag pressure needed to move the clamped pipe is p_d. The required machine setting is

All areas use the same squared-length units. All pressures use one consistent unit. The area ratio transforms the required interface force into hydraulic pressure, and the measured drag term is added under this procedure's setup. The pipe-wall area is not the area inside the bore. Heating and fusion can use different procedure pressure factors. Equal gauge readings on machines with different piston areas do not establish equal interface force.

The machine/pipe areas, measured drag and qualified heating/fusion factors, timing, heater temperature and cooling conditions determine production applicability. An example parameter chart is not a qualified bonding procedure.

Reinforced-resin joints require compatible components and adhesives, prepared joining surfaces, trained personnel and prescribed curing. Visual examination can reveal damaged fibers, delamination, poor surface preparation, excessive adhesive or incomplete external work, while the selected procedure adds its required qualification and acceptance checks. A cured-looking outside surface does not establish every internal bond condition. Load or pressure testing occurs only after the required cure and under the material-specific test route. Solvent-cemented thermoplastic joints likewise retain material-compatible cement, shelf-life and curing conditions.

Connect bead observations to the selected trial test

Figure 17.2. The selected bead-height reference, example adverse appearances and bend fixture support the method below. The bead view is qualitative and the fixture uses its separate pipe-wall reference t. Structured observations, specimen rules and test sequence.

For the specifically adopted HDPE examination route:

• Measure bead height H from the pipe surface to the bead crest.

The complete double-bead width W is 2–2.5H. The depth d of the V between the beads is no greater than 0.5H. Keep the reference surface with those ratios. The valley's height above the pipe is not the V-depth, and H is not the pipe-wall thickness.

The beads must be uniform in size and shape around the joint. Observe rollback to the pipe surface as well as overall dimensions. Excessive rollback, incomplete rollback and a deep V are distinct adverse appearances. Their schematic shapes help locate the observation but do not measure an actual joint.

This route applies the visual requirements to both external and internal beads and requires examination of the inside bead where accessible. Plan that opportunity at flange adapters and the early fusions of elbows and tees before further assembly conceals it. The route also prohibits bead removal. For a pipe-to-molded-fitting fusion, a slightly irregular fitting-side bead alone need not cause rejection when the pipe-side bead has the correct shape and the V is correct. That narrowly conditioned exception does not apply to fittings fabricated from pipe shapes or excuse an incorrect pipe-side bead.

The selected route requires each operator's first fusion of the day to pass its cooled four-strip bend trial before production; a failed trial is repeated before work proceeds. The trial exposes the cross-section and puts the interior fusion root in tension; voids, discontinuities and fusion-area failure are not permitted. Specimen preparation and fixture dimensions remain in the structured trial method, separate from the installed-joint geometry.

This daily trial supplements procedure/bonder qualification and production-joint examination; it does not replace the installed pressure test in System testing. Internal bead examination must occur where accessible before further assembly conceals it.

Carrying the joint evidence into service and change

The joint record connects component/deposit identity, procedure, thermal history, examination and repairs. These records establish the actual material and treatment condition for later repair or modification; see engineering records.

Operating history can change the conditions for the next weld even though the original joint was acceptable. Hydrogen charging, residues, deterioration, damaged cladding or an altered service can require a different preparation and repair route. A replacement fitting can also change material, wall, procedure applicability or required examination. The affected basis is reconsidered rather than relying on the old WPS number alone.

A sound local joint remains part of an interacting installation. Dimensional realization must preserve the alignment and mechanical arrangement, while testing, cleanliness and readiness establishes the assembled boundary and internal/service configuration. The welding account supplies the joint's actual material and examination condition. Keeping these warrants connected makes later inspection and repair or modification possible without treating any single report as proof of the whole system.