Hardbanding Inspection and Acceptance Criteria

Hardbanding inspection comes down to seven items: deposit height, width, placement, crack condition, spalling, undercut, and hardness verification. Each one exists because a specific downhole failure mode has been traced back to it, yet most checklists never explain that connection. This article walks through each acceptance criterion, the numbers inspectors typically work to, and the root causes behind the most common rejections.

For background on alloy behavior and why these criteria differ between alloy families, see How Hardband Alloys Resist Abrasion Downhole and the Oilfield Hardbanding: The Complete Field Guide.

What is the correct hardband deposit height?#

Deposit height is the single most measured dimension in hardbanding inspection, and it is the one most often out of spec in the field. The target for most rotary-shouldered connections is a net deposit height of roughly 2 to 3 mm (0.080 to 0.125 in) above the tool joint OD surface, measured from the machined or as-welded base surface to the crown of the bead. Always confirm the governing specification, because operator and alloy supplier datasheets vary.

Why it matters downhole: hardband exists to be consumed. The joint is designed so the deposit wears down over a run cycle while protecting the tool joint steel beneath. If the deposit is too thin, it wears through early and the tool joint itself starts losing OD, which accelerates into undersized joints, gauge problems, and eventual scrap. If the deposit is too thick, you gain almost nothing, because wear life scales with usable height, not total height, and thick deposits carry a real cost: higher residual stress, more severe dilution gradients, and a much higher probability of cracking and spalling.

Inspection practice:

• Measure height at multiple points around the circumference, not just one spot. Bead profile varies with torch or electrode position.
• Use a depth gauge, bridge gauge, or a profile gauge against a known flat reference.
• Flag any single reading more than about 0.25 mm (0.010 in) outside the specified band.
• Check height relative to the tool joint OD, not the previous deposit layer, especially on re-coated joints.

How are hardband width and placement inspected?#

Deposit width and placement are inspected together because they define where the hardband actually rides against the casing and the formation. Typical practice places a single band 50 to 90 mm (2 to 3.5 in) wide on the pin end tool joint, offset from the shoulder per the applicable drill pipe specification, with the band centered so it contacts the casing wall evenly across its width.

Placement matters for three downhole reasons:

1. Casing wear. A hardband band that sits proud of the tool joint at the wrong axial position concentrates casing contact on a narrow ring. That ring acts like a lapidary wheel on the casing ID. Correct placement spreads the contact load.
2. Contact stress. If the band is too narrow, all the lateral load carried by the tool joint concentrates on a small area, raising local contact stress on both the hardband and the casing. If it is too wide relative to the joint, the crown profile tends to be uneven and the edges lift.
3. Shoulder clearance. Deposits that creep too close to the rotary shoulder interfere with makeup and can mask shoulder damage during visual inspection. Keep hardband well clear of the shoulder and the thread runout.

Inspectors should verify band width with a tape or caliper at several circumferential positions, confirm axial placement against the drawing, and check that the band does not wrap over the tool joint edge or blend into the hardface on the opposite side of the connection.

Which hardband cracks are acceptable and which are defects?#

Crack acceptance in hardbanding depends entirely on the alloy family. Inspectors who apply one rule to all hardbands either reject perfectly good joints or pass joints that should never go downhole. Chromium carbide and most tungsten carbide deposits are designed to check-crack, while other alloy families are engineered to deposit without cracking at all.

Crack-intentional alloys#

Chromium carbide and most tungsten carbide deposits are designed to check-crack. As the weld cools, the brittle carbide-rich deposit relieves contraction stress by forming fine, evenly distributed transverse cracks, typically spaced a few millimeters to a couple of centimeters apart depending on the alloy and procedure. These are not defects. They are the alloy doing what it was designed to do. For more on the metallurgy behind this, see Crack-Free Hardband Alloys: What Actually Works, which also covers the alloys engineered to deposit without cracking at all.

What inspectors actually reject#

Regardless of alloy, the following crack conditions are cause for rejection or engineering review:

• Cracks that run the full height of the deposit and terminate in the base material or heat affected zone (HAZ), indicating the crack is acting as a stress riser into the tool joint.
• Wide, open cracks with chipped or missing edges, which indicate the deposit is already disbonding.
• Longitudinal cracks along the bead axis, which are rarely part of a controlled check pattern and usually signal excessive restraint, bad procedure, or excessive thickness.
• Cracks crossing the toe of the weld where the deposit meets the tool joint.
• Any crack accompanied by rust staining or oxidation products flowing out of it, which suggests the crack existed through a thermal cycle.

A useful field rule: fine, closed, evenly spaced transverse checks are normal for crack-intentional alloys; anything coarse, open, directional, or interacting with the toe is a defect. When in doubt, compare against a known-good reference coupon from the same alloy and procedure.

Why is hardband spalling the highest-consequence defect?#

Spalling, the loss of discrete chunks of hardband in service, is the most consequential hardbanding defect because it does not just end the deposit’s life. It converts the deposit into abrasive debris. A detached carbide fragment circulating in the mud stream erodes casing, damages other tool joints, and can plug flow paths in downhole tools.

Root causes of spalling#

• Excessive deposit height. Thick deposits build residual stress that the bond line cannot hold. This is the most common cause on re-coated joints where layers are stacked.
• Re-application over unsound deposit. Welding over cracked, oxidized, or partially detached old hardband creates a weak composite. The new layer inherits the old layer’s defects and adds new stress. See Re-Applying Hardband Over Existing Deposits for the correct removal and preparation sequence.
• Undercut and poor tie-in. A deposit with undercut at the toe has a stress concentration exactly where bending loads are highest.
• Hydrogen and procedure errors. Inadequate preheat, damp consumables, or wrong heat input can produce hydrogen-assisted cracking that later opens into spalls. The full procedure sequence is covered in Hardbanding Welding Procedure: Preheat to Cool-Down.
• Dilution problems. Excessive heat input dilutes the deposit with tool joint steel, producing a weak, mixed-composition zone that fails at the interface.

How spalling is inspected and handled#

Inspection for spalling is primarily visual and tactile: look for fresh metallic crater edges, missing chunks at crack intersections, and sharp edges that catch a fingernail or pick. On used joints being inspected for re-coating, any spalled area means complete removal of the remaining deposit in that area before re-welding, never cosmetic build-up.

Why is undercut at the hardband toe a rejection risk?#

Undercut is a groove melted into the base material at the weld toe, leaving the deposit edge sitting in a notch. It is easy to miss on a coarse hardband surface and it is disproportionately damaging. Undercut is a fatigue risk to the tool joint itself, not just a cosmetic weld defect.

Why it matters downhole: the tool joint flexes under cyclic bending in doglegs and during trips. An undercut groove is a geometric notch at the highest stress location on the joint. Cyclic loading plus a notch is the textbook recipe for fatigue crack initiation in the base material, which is far worse than any hardband defect because it can lead to joint washout or separation.

Acceptance practice:

• Undercut on the tool joint surface at the deposit toe should be measured with a gauge and compared against the governing weld acceptance criteria; in practice, any undercut you can feel with a pick is worth measuring.
• Deep or continuous undercut around the band is an automatic rejection.
• Local undercut can sometimes be repaired by re-welding the toe, but only within the qualified procedure and with the joint re-inspected afterward.

How is hardband hardness verified?#

Hardness verification confirms that a hardband deposit will actually resist abrasion, and it is the fastest way to catch procedure errors, because heat input, dilution, and cooling rate all show up in the hardness number. Visual and dimensional inspection only tells an inspector that the deposit is present and sound. Hardness is the primary predictor of wear performance for a given alloy.

How hardness is checked#

• Grind a small flat spot on the deposit crown to give the indenter a clean bearing surface. Do not grind deep enough to remove the working layer.
• Use a portable hardness tester appropriate for the deposit. Hardband deposits are hard and often heterogeneous, so take multiple readings and expect scatter from carbide particles.
• Compare readings against the alloy supplier’s specified range, not a generic number. Chromium carbide and tungsten carbide alloys have very different target hardnesses, and casing-friendly alloys are deliberately softer than maximum-wear alloys. See Casing-Friendly vs Abrasive Hardband Alloys for why the “hardest possible” deposit is often the wrong choice.
• Recheck outliers. One low reading may be a dilution zone or a spot where the indenter landed on a ferrite pocket; a cluster of low readings means the deposit is under-hard and will wear out early.

What hardness deviations tell you#

What are the common hardband failure modes and their root causes?#

Tying inspection findings to root causes is what separates a useful inspection from a checkbox exercise. The table below maps the defects inspectors find to the mechanisms that produce them and the downhole consequences if the joint is run anyway.

Most of these root causes trace back to procedure control rather than operator skill. Shops that maintain qualified procedures, verify parameters per joint, and keep reference coupons per alloy reject far fewer joints after the fact. The Hardbanding QA Checklist: Before the Pipe Leaves is designed to catch these items before the pipe ships rather than at the wellsite.

What should hardband inspection records document?#

Every hardbanded joint inspected should be traceable to the alloy used, the procedure qualified, the operator, and the inspection results, including hardness readings and any accepted anomalies. An inspection is only as good as its records. Documentation matters for three practical reasons: re-coating decisions years later depend on knowing what is on the joint now; failure investigations need the history to identify the root cause; and operators increasingly require documented acceptance as a condition of running the pipe.

At minimum, record:

• Joint number and position in the string
• Alloy and consumable lot
• Deposit height and width measurements (with locations)
• Crack condition and any accepted deviation, with reference to the alloy’s crack behavior
• Hardness readings, method, and number of readings
• Inspector identity and date

Key Takeaways#

• Deposit height, width, and placement define wear life and casing contact. Measure them at multiple points, not once.
• Fine transverse check cracks are normal for carbide alloys. Reject cracks that are open, longitudinal, crossing the toe, or interacting with the HAZ.
• Spalling is the highest-consequence defect because detached hardband becomes cutting debris in the mud system.
• Undercut is a fatigue risk to the tool joint itself, not just a cosmetic weld defect. Measure it, do not just note it.
• Hardness verification catches procedure errors that visual inspection cannot, but always compare against the alloy’s specified range rather than a generic number.
• Most rejections trace back to procedure control: heat input, thickness, substrate preparation, and stacking over old deposit.