Radiography Testing RT acceptance criteria ASME-IX 2025 Edition

Radiography Testing RT Acceptance Criteria ASME 9

During welding qualification (either Procedure or Performance), a single film interpretation can mean the difference between a qualified welder and a costly re-test. Whether you are a Welding Coordinator, a Quality Manager, or an NDT Level II technician, understanding the “pass/fail” limits of ASME Section IX is non-negotiable.

Unlike construction codes (like ASME B31.3 or API 650) that look for “service-suitable” quality, ASME Section IX is a “performance” code. Its sole purpose is to determine if a welder has the skill to deposit sound metal. Therefore, the acceptance criteria are strict, binary, and focused entirely on the nature of the discontinuity.

This post covers the Radiography Testing or RT acceptance criteria for the ASME Section IX (9). If you refer the ASME Section 9 code, the RT acceptance criteria is covered by Clause QW 191.1: Radiographic Examination & briefed in QW-191.1.2.2 Sub-clause.

QW191.1 covers the RT method and further sub-clause covers RT requirements as follow:

• QW 191.1.2 RT acceptance criteria.
• QW 191.1.2.1 RT defects terminology
• QW 191.1.2.2 RT acceptance criteria for Welder Performance Qualification.

Note: This RT acceptance criteria is applicable only for Welder Performance Qualification and not for the actual production welding joints.

For production welding, you have to refer the RT acceptance criteria in the construction code, for example- ASME B31.3 or ASME Section VIII Division 1.

ASME Section IX: RT acceptance criteria is more stringent than the construction codes RT acceptance as Section IX is for performance qualification of welder and require to test the welders skills.

The Role of RT in Welder Qualification

Before diving into the numbers, it is critical to understand why we are X-raying the coupon.

• Performance Qualification (WPQ): We are testing the person, not the steel. We want to know if they can fuse the root, control the slag, and avoid porosity.
• Procedure Qualification (PQR): While RT is permitted for WPQ, it is NOT permitted for qualifying a Welding Procedure Specification (WPS) in most cases (Procedure qualification usually requires mechanical testing like bends and tensile pulls).

Code Reference: ASME Section IX, Paragraph QW-142 states that Radiographic Examination may be substituted for mechanical testing for Groove Welds (with some exceptions like GMAW-S short circuiting).

The “Instant Fail” Defects (QW-191.1.2.1)

The code is explicitly clear. Regardless of length or size, the following imperfections result in an immediate failure of the welder’s test coupon:

1. Cracks (C): Any crack, of any size, is a rejection. Cracks indicate a fundamental loss of control over the metallurgy or stress management.
2. Incomplete Fusion (IF): Also known as “Lack of Fusion.” This looks like a straight, dark line on the film where the weld metal failed to fuse with the bevel wall or the previous bead.
3. Incomplete Penetration (IP): A dark, straight line right down the center of the root. This means the welder failed to break down the land or didn’t push the filler metal through.

Interpretation Tip: If you see a straight line with “sharp” edges, it is likely a planar defect (Crack/IF/IP). Reject it.

ASME Section IX Code RT (Radiography Testing) Acceptance Criteria 

This acceptance criteria is applicable for Welder/ operator qualifications who carry out the test using test coupon welding or production test coupon welding (QW304.1 & 305.1).

RT acceptance criteria for Welder performance qualification is covered and explained in ASME Section 9 (IX) clause QW 191.1.2.2 and applies as follow:

• Linear Indications

Welding Defect Type	Acceptance Criteria
Crack	Not acceptable
Incomplete Fusion	Not acceptable
Incomplete penetration	Not acceptable
Slag inclusions	For material thickness (t) up to 3/8 inches (10 mm), maximum slag inclusion of 1/8-inch (3mm) is acceptable. More than 1/8 inch shall be rejected
Slag inclusions	For material thickness (t) > 3/8-inch (10 mm) to 2.25 inches (57 mm), maximum slag inclusion of 1/3t is acceptable.
Slag inclusions	For material thickness (t) >2.25 inches (57 mm), maximum slag inclusion of ¾ inches (19 mm) is acceptable

• Rounded Indications

Welding Defect Type	Acceptance Criteria
Rounded indications (e.g., porosity or pores	1/8-inch (3 mm) maximum or 20% of material thickness (t), whichever is smaller.
Rounded indications: For material less than 1/8-inch (3 mm) thickness (t)	Maximum nos. of rounded indications shall not be more than

For an illustrative explanation of Rounded indications acceptance in ASME Section IX, it covered by figure QW-191.1.2.2 (b) (4).

This figure explains the rounded indications (usually welding porosity) distribution based on their quantity and maximum permitted size as estimation guide for different material thicknesses.

Linear Indications (Slag & Elongated Defects)

Reference: QW-191.1.2.2 (a)

For imperfections that have length (like Slag Inclusions or “Wagon Tracks”), the acceptance criteria depend on the thickness of the weld coupon (t).

The “Zone of Rejection”

A linear indication is unacceptable if its length (L) exceeds:

1. L > 3mm (1/8inch) for coupon thicknesses (t) up to 10mm (3/8inch).
2. L > 1/3 x t for coupon thicknesses (t) between 10mm and 57mm (3/8inch to 2.25 inch).
3. L > 19mm (3/4inch) for coupon thicknesses (t) greater than 57mm (2.25 inch).

Example Calculation:

• Scenario: A welder takes a test on a standard 6-inch Schedule 80 pipe.
• Wall Thickness (t): 11mm (0.432inch).
• The Limit: Since t is between 10mm and 57mm, the limit is 1/3 x 11mm = 3.66mm.
• Result: A slag line measuring 4mm is a FAIL. A slag line measuring 3mm is a PASS.

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🌕 Rounded Indications (Porosity)

Reference: QW-191.1.2.2 (b)

Rounded indications are defects where the length is no more than three times the width (L \le 3W). These are typically gas pockets (Porosity) or tungsten inclusions.

1. Maximum Size of a Single Pore

The Code limits the sheer size of any single “bubble” in the weld:

• For t < 3mm (1/8inch): Max size is ¼ t.
• For t ≥3mm (1/8inch) to 6mm (1/4inch): Max size is 1/3 x t.
• For t > 6mm (1/4inch): Max size is 1.5mm (1/16inch).
• Absolute Max: For very thick coupons (t > 50mm), porosity can be up to 3mm (1/8inch) or ¼ t (whichever is smaller).

Reality Check: On a standard 10mm plate test, any pore larger than a pinhead (1.5mm) fails the welder.

2. “Cluster” Porosity vs. Random Porosity

ASME IX is relatively generous with “Assorted” or “Random” porosity compared to construction codes like API 1104. However, Cluster Porosity (a group of non-aligned pores) is rejected if the concentration exceeds the density shown in Appendix I of Section IX.

The “Total Accumulation” Rule (QW-191.1.2.3)

This is where most NDT interpretations go wrong. Even if individual defects are small enough to pass, their combined length might fail the coupon.

The Rule: The sum of the lengths of all inclusions (Linear + Rounded) shall not exceed $t$ (the coupon thickness) in any $6t$ length of weld.

Exception for Long Welds:

If the weld is longer than 12t, the accumulation is simply proportional. But for standard pipe coupons, the “6t” window is the critical measurement zone.

Example:

• Coupon: 10mm Plate.
• Window: We look at a 60 mm 6 times 10) section of the film.
• Defects Found: Three slag lines, each 3 mm long.
• Individual Check: Each is 3 mm. The limit for 10 mm plate is 3.3 mm (1/3 x t). So individually, they PASS.
• Accumulation Check: Total length = 3 + 3 + 3 = 9 mm.
• Limit: The limit is t 10mm).
• Result: 9 mm < 10 mm. The welder PASSES.

Summary of RT Acceptance as per ASME Section IX

A summary of welding defects acceptance based on RT acceptance as per ASME Section IX is given below:

• Welding cracks of any type are not permitted.
• Incomplete Welding Fusion is not permitted.
• Incomplete weld penetration is not permitted.
• Slag inclusion permitted within the tolerances given in Table 1.
• Welding porosity (any type) is permitted within the tolerance given in Table-2.

Production Welds vs. Test Coupons (A Critical Distinction)

A common mistake is applying “Production” criteria (like ASME B31.3 Normal Fluid Service) to a “Qualification” coupon.

• Production Codes often allow for some Lack of Fusion or longer slag lines depending on the service pressure.
• Qualification (ASME IX) does NOT. It is zero tolerance for planar defects.
• Why? If a welder leaves a crack in a controlled test booth with perfect fit-up and no time limit, they will almost certainly leave cracks in the field.

❓ Frequently Asked Questions

Q: Can I use Ultrasonic Testing (UT) instead of RT for Welder Qualification?

A: Yes! Under QW-191.2, Ultrasonic Examination is permitted substituting RT, provided it meets the acceptance criteria of QW-191.2.1 (which essentially mirrors the strictness of RT). However, UT is generally reserved for thicker coupons (>10 mm}) where it is more accurate.

Q: Does the root reinforcement (penetration) height matter in RT?

A: No. RT measures internal soundness. Excessive root penetration (e.g., 5 mm drop-through) is a Visual Inspection (VT) failure, not an RT failure. The RT film will just show a lighter density area. The NDT interpreter is only looking for discontinuities within the metal, not the geometry (unless the undercut is severe enough to show as a density line).

Q: What happens if a welder fails RT?

A: Under QW-321, the welder has two options:

1. Immediate Retest: Make two consecutive test coupons for each position failed. Both must pass.
2. Further Training: Undergo training and then make one new test coupon.

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