1. Scope
This procedure covers wet fluorescent magnetic-particle (WFMT) examination of cross-country pipeline girth welds in carbon-steel and low-alloy-steel transmission pipelines per API 1104, current edition. It is intended as a supplementary surface-examination method where RT is not feasible (e.g., field-weld zones with restricted radiation access, repair welds, or thin-wall welds where small surface cracks govern weld quality). Wall thickness range: 6 mm to 25 mm.
2. References
- API 1104 — Welding of Pipelines and Related Facilities, current edition (Section 9 acceptance and Section 11 NDT)
- ASTM E709 — Standard Guide for Magnetic Particle Examination
- ASTM E1444 / E1444M — Standard Practice for MT
- 49 CFR §192 / §195
- ASNT SNT-TC-1A or CP-189
3. Personnel Qualification
MT examination shall be performed by ASNT NDT Level II in MT, qualified per a Written Practice that meets SNT-TC-1A or CP-189. Level III review per the customer Written Practice and 49 CFR.
4. Equipment
- AC yoke prod certified for 4.5 kg lift at 200 mm pole spacing (e.g., Magnaflux Y-7, Parker B310S). Lift test at start of each shift; documented.
- Fluorescent wet MT bath compliant with AMS 3041 — concentration measured by centrifuge tube (settling test) per ASTM E1444 §6 — typical fluorescent bath concentration 0.1 – 0.4 mL/100 mL.
- UV-A lamp (LED or mercury vapour) with measured intensity ≥ 1000 µW/cm² at 38 cm (15 in) at the examination surface.
- White-light meter for booth ambient (≤ 20 lux) and UV-A radiometer (within 12-month calibration).
- Field-direction indicator (pie gauge) and magnetic-flux strip indicators.
- Background-paint: non-fluorescing white background where coating contrast aids interpretation.
5. Surface Preparation
Examination surface (the weld plus 25 mm of adjacent base metal on each side) shall be free of:
- Weld spatter, paint scale, slag, and loose mill scale
- Oil, grease, and moisture
- Coating thicker than 0.05 mm (0.002 in) over the examination area
Where the pipeline coating is fusion-bonded epoxy (FBE) or three-layer-polyethylene (3LPE), local removal in the inspection zone is required — coatings of these thicknesses block MT.
6. Magnetization
6.1 Yoke Placement
AC yoke prods placed across the weld with pole spacing 75 mm – 200 mm. Magnetization applied in two perpendicular directions at each examination area.
6.2 Particle Application
Wet fluorescent bath applied as a low-velocity flood while current is on (continuous method) — applied by squeeze-bulb sprayer or low-pressure hose; not by high-velocity spray that washes away indications.
6.3 Field-Strength Verification
Field strength verified using a pie gauge or magnetic field indicator on the examination surface at the most distant point from the prods — indicator shall produce a clearly defined pattern of magnetic flux.
7. Examination Conditions
- White-light ambient at the inspection booth: ≤ 20 lux (2 fc)
- UV-A intensity at the examination surface: ≥ 1000 µW/cm²
- Examiner dark-adaption: ≥ 1 minute
- UV-protective eyewear required (visible-light-transmitting yellow lens)
Examination performed immediately after the magnetization is removed — wet fluorescent particles continue to indicate until they dry; do not allow drying before observation.
8. Indication Classification
Indications classified per API 1104 §9.6:
- Crack: any linear indication is treated as a crack until proven otherwise by removal and re-examination. Rejectable.
- Linear indication: length ≥ 3× width. Length > 3 mm in any 25 mm of weld is rejectable per §9.6.2.
- Rounded indication: length < 3× width. Rounded indication > 3 mm major dimension is rejectable per §9.6.3.
- Cluster: four or more rounded indications in any 25 mm of weld where their cluster falls within a 12 mm circle — rejectable per §9.6.4.
Non-relevant indications (geometric, magnetic-writing, dirt) shall be identified by mechanical cleaning and re-examination; if the indication re-appears, treat as relevant.
9. Repair and Re-Examination
Defects removed by grinding to a depth where the indication is no longer visible by re-MT examination. Cavity dimension verified per the pipeline repair procedure (typically not to exceed the limits of API 1104 §10). Re-welded repairs re-examined by both RT and MT per Section 11.
10. Reporting
Per API 1104 §11.4 — minimum: pipeline / spread / station number; weld number; date; technician number and ASNT certification; equipment serial numbers; bath concentration and certification batch; UV-A intensity verified at the examination location; field-direction verification result; sketch / weld map with location, length, orientation, and classification of every recordable indication; disposition and re-examination record where applicable.
Records retained per 49 CFR §192.243 / §195.234.
11. Safety
PPE per project — minimum eye protection (UV-blocking), gloves, and skin coverage. Bath solvent management per local environmental authority — typical kerosene-based fluorescent baths are flammable; storage and disposal per project HAZMAT plan. Yoke-cable inspection daily for nicks or cuts that compromise insulation. Confined-space considerations for tie-in welds in stations.
This procedure is a published reference. Production use requires customer / AI approval against the current API 1104 edition. Generate a custom WFMT procedure including bath chemistry, UV intensity zone, and acceptance limits at the free AI Procedure Generator.