Flange Welding Cracks Require Verified Material and Preheat

The 3-1/8-in flange welded to A106 pipe cracked while E6010/E7010 electrodes were in use, and the welding team does not have the flange material test certificate (MTC). Treat the flange grade as unverified until its heat number is traced to the manufacturer’s records; a pipe-only P1 welding procedure specification (WPS) does not establish that this flange is P1.

Document the flange, joint, and crack before repair

Record the complete flange marking, the pipe identification and grade, the joint configuration, and the crack’s location and direction. Photograph the marking and crack before grinding or repair. Record whether the crack appeared during welding, immediately after a pass, or after cooling, and whether it starts at the weld metal, fusion boundary, or heat-affected zone (HAZ). The HAZ is the base metal next to the weld whose properties changed during welding.

The marking supplied for this flange is:

H/N G5247 ADO S/L 09147-2 3"-1/8 API 5K R-35X2-27 MIN BORE XXS P/N 142349-01-03-01 REV03 PAK 6A PS TUDD-NL EE-NL PSL1 6A-0553 04/09

Preserve punctuation and spacing when asking the manufacturer or supplier to trace the item. The marking includes product and traceability tokens, but the welding team cannot establish the steel grade or chemical composition from the transcription alone. Do not treat “A106” as the flange grade: it identifies the pipe material stated for the joint, not the attached flange.

Cracks that appear during or shortly after welding can result from more than one condition. Hydrogen from a consumable, rapid cooling, restraint, thermal gradients, unsuitable filler metal, or a mismatch between the actual flange material and the qualified WPS can contribute. The crack location and timing guide investigation; neither alone proves a cause.

1. Record the weld process, electrode classification, pass sequence, and any preheat or interpass temperature actually used.
2. Map the crack relative to the weld and note when it became visible.
3. Keep the flange heat/lot number and marking legible for traceability.

Check 1: The inspection record identifies the crack location and timing, and the complete flange marking is captured before material is removed.

Trace the flange heat to an MTC

Request the MTC and heat/lot traceability from the flange supplier or manufacturer using the marking and purchase records. The certificate must identify the supplied item or heat and provide the material specification, grade, and chemical and mechanical results required for the governing material specification. If records cannot connect this particular flange to a heat, a generic certificate or catalog description does not resolve the material identity.

Do not assign P1 based on the flange’s appearance, product description, country of manufacture, or a guess that a 3-1/8-in API flange is a particular alloy. The evidence includes suggestions that this type of flange may be made from alloy steel and that 4130 or 8630 could be possible; those suggestions are reasons to verify the material, not proof of this flange’s grade. The discussion also refers to flexible chemistry under API 6A, but it does not supply this flange’s actual chemistry or a material-specification basis for classifying it.

For the same reason, do not use reported minimum-yield or chemistry figures from a historical specification discussion to classify the item. Obtain the applicable material specification and certificate for the marked heat. If the heat cannot be traced, stop welding pending disposition by the responsible engineering and quality authorities.

1. Ask the supplier/manufacturer to match the heat/lot marking and part number to the MTC.
2. Compare the MTC’s grade and chemistry with the flange purchase specification and governing design documents.
3. Escalate a missing, mismatched, or illegible traceability chain for formal disposition; do not presume the flange is weldable under the existing WPS.

Check 2: The MTC identifies a material specification and grade that can be tied to the flange heat/lot. If it cannot, the material remains unverified and welding stays on hold.

Determine whether the P1 WPS covers both materials

A WPS qualifies a defined welding process and range of materials and conditions; the label “P1” on the available WPS is not a universal authorization to weld any steel described as carbon steel. Compare the verified flange material and A106 pipe material against the WPS and its supporting qualification records. Check the applicable material group, thickness range, joint design, process, filler metal, preheat/interpass controls, and any other essential variables required by the governing construction or repair rules.

Both sides of a dissimilar-material joint matter. A procedure that covers the pipe but not the flange does not qualify the joint as a whole. If the MTC identifies an alloy flange, or the actual material cannot be classified against the WPS, have the responsible welding engineer determine whether a separately qualified procedure is required. Do not resolve uncertainty by increasing preheat alone.

Before authorizing work, confirm that the approved WPS names an electrode classification suitable for the verified materials and sets the applicable preheat and interpass requirements. The evidence mentions E6010/E7010 as the electrodes in use and recommends E7018 or another low-hydrogen approach; it does not establish a qualified procedure for this flange-and-pipe combination.

1. Read the material and thickness ranges on the approved WPS and its qualification documentation.
2. Match both the flange and pipe materials, joint, process, and consumable to those limits.
3. Obtain an approved, qualified WPS covering the actual joint before restarting if any variable falls outside the existing procedure.

Check 3: The approved WPS and its qualification records explicitly cover both verified base materials and the joint conditions to be welded.

Control hydrogen from the welding consumable

Cellulosic electrodes such as E6010/E7010 introduce more diffusible hydrogen than low-hydrogen consumables. Hydrogen can diffuse into susceptible steel and contribute to delayed cracking, particularly when high hardenability, rapid cooling, and weld restraint coincide. A crack appearing during welding still requires investigation of thermal stress, restraint, and material condition; hydrogen should not be named as the sole cause without confirming evidence.

Use only the consumable classification and handling method specified by the applicable WPS. If that procedure requires low-hydrogen electrodes, follow its storage, exposure, and rebaking controls. The field report recommends E7018 from a rod oven or a fresh unopened can, but that advice is not a substitute for the project’s WPS or consumable manufacturer’s handling instructions. Do not switch electrode type mid-repair without approval: filler-metal classification and process are procedure variables.

Record the electrode classification, package condition, issue/storage controls, and any exposure or conditioning required by the approved procedure. If cellulosic electrodes were used contrary to the WPS, include that deviation in the weld nonconformance investigation rather than assuming a later low-hydrogen pass will remove the risk.

Check 4: The electrode classification and handling record match the WPS, and the welding log records the consumable actually used for each affected pass.

Set preheat from the approved procedure and actual thickness

A thick flange can extract heat from the weld faster than the pipe, increasing cooling rate and the risk of a hard, crack-sensitive HAZ. The relevant heat sink is not necessarily just the nominal wall thickness: the flange hub and raised face can add substantial mass around the joint. Measure and document the flange geometry used for the WPS thickness determination, including the hub and raised face where applicable, and use the governing procedure’s definition of thickness.

Preheat reduces the temperature gradient and slows cooling, but the correct minimum is material- and procedure-dependent. The source contains three different suggestions—150°F at 1.5-in thickness in any direction, 200°F to 250°F minimum, and approximately 400°F or more. They conflict and are not a single code requirement. None should be adopted as the setpoint for this joint without confirmation against the applicable WPS, material chemistry, thickness, and governing rules.

Measure preheat with a suitable temperature-measuring method at the locations and distances required by the WPS. Record the readings before welding and interpass readings during the weld. Avoid localized, uneven heating: temperature differences across a heavy flange can create thermal stress and contribute to cracking. Follow the specified heating method and sequence rather than applying heat by eye.

1. Measure the flange and pipe thicknesses using the procedure’s thickness rules; include the flange hub/raised-face mass where the rules require it.
2. Read the required minimum preheat and maximum interpass temperature from the qualified WPS for the verified material combination.
3. Heat uniformly and record actual readings at the specified locations before and during welding.

Check 5: Recorded temperatures meet the WPS minimum preheat and stay within its interpass limits; readings cover the flange mass as well as the pipe side.

Repair only after crack disposition and thermal controls

Do not weld over a crack or assume grinding the visible line is sufficient. Have the responsible inspection authority determine the crack extent and disposition under the applicable repair requirements. Remove the defect by an approved method, then inspect the excavation to confirm the crack is gone before depositing weld metal. The required examination method and acceptance criteria come from the governing project documents; they are not supplied by the flange marking.

For an approved repair, use the qualified WPS, controlled consumables, uniform preheat, and a balanced sequence that limits abrupt local heating and restraint. Record the repair location, excavation results, material identification, electrode, temperature readings, and welder/process details. If cracks recur after the procedure and material controls are met, stop and reassess the heat traceability, material chemistry, restraint, and WPS qualification rather than repeating the same repair.

Check 6: Inspection records show the crack was fully removed before repair welding and the repaired weld meets the specified examination and acceptance criteria.

Complete end-to-end release checks on the flange joint

Release the joint only after material identity, procedure coverage, consumable controls, temperature records, repair inspection, and final documentation agree. A successful bead alone does not prove that the flange material met its specification or that the weld was made under a qualified procedure.

1. Material: Verify the flange heat/lot against its MTC and confirm the pipe material from its records. Expected result: both sides have documented identities and the flange chemistry/grade matches the purchase and design requirements.
2. Procedure: Verify the WPS qualification covers the actual flange-to-pipe joint. Expected result: both base materials, thicknesses, process, and consumables fall within the approved range.
3. Execution: Review the weld and temperature log. Expected result: electrode handling follows the WPS, and measured preheat/interpass temperatures meet its limits.
4. Integrity: Review crack-removal and final inspection records. Expected result: no crack remains and the completed joint meets the project’s acceptance criteria.

Check 7: The quality record closes all four checks with traceable documents and acceptable inspection results before the flange returns to service.

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