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Visual Inspection
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ContentsContents
1. General guideline for visual Inspection
2. Visual Defects in Steel Plates & Coils
3. Visual Defects in Welding
2
Definition of Visual Inspection
Visual Inspection is the simplest, fastest, economical and most commonly used test for detecting defect on the surface of the weld and plate/pipe body.
Inspection may be carried out by the use of the eye alone or can be enhanced by using optical systems such as magnifiers and other visual examination aids. A variety of equipments are available for visual examination including mirrors, video scopes etc.
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Conditions for visual inspection
Visual inspection shall take place in a clean, comfortable environment with adequate lighting. There should be reasonable access to the parts to be inspected and attention should be paid to safety, working position, and atmospheric conditions. The test piece should be clean and free from protective coatings, oil grease etc. Any equipment to be used should be calibrated and its operation should be understood by the inspector.
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1.Sufficient Illumination2.Correct eye distance from object
and correct angle between eye & object
3.Magnifying glasses to be use if required
Conditions for visual inspection
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1. Sufficient Illumination :
At least 300 Lux as per API 5L, 45th edition
At least 1000 Lux as per ASME Sec V/ API 5LD.
Conditions for visual inspection
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Near Vision Examination
The applicant shall be capable of reading a minimum of Jaeger No.2 or equivalent type and size of letter at a distance of not less than 12 inches on a standard Jaeger test chart. The ability to interpret an Ortho-Rater 8 or better or a similar test pattern is also acceptable. This test should be administered annually. Candidates must also be capable of differentiating different shades of colors - this color vision must be tested every 5 years. This is specified in ASNT document number SNT-TC-1A. 8
General guideline for Visual Inspection
2. Correct eye distance from object and correct angle between eye & object :
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Access and viewing distance
If unaided visual inspection is to be carried out accurately, observations must be made within 600 mm. (ASME Sec V, Article - 9)
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Viewing angles and distances
The eye's resolving power is dependent on the angle and distance from the test surface. Direct visual examination observations may usually be made within 600 mm of the surface to be examined and and the angle between the eye and test surface not less than 30° (ASME Sec V Article 9).
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Scale Measuring Tapes Vernier Calipers Micrometers Clock gauges Pie Tape Bevel Protector Bead Height Gauge Off Set Gauge
Measuring Equipments / Instruments
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Sliver Scab Rolled-in-Scale Roll Mark Tong mark Dents / Indentation Pitting Pit
Visual Defects in Steels
Seam line Lap Lamination Cracks Arc Burn Hard Spot Excess Reinforcement Under Cut Stretch Mill Indentation
+ + + And So many15
Visual Defects in Steels
Sliver
An extremely thin elongated piece of metal that has been rolled into the surface of the parent metal to which it is attached usually by only one end.
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Visual Defects in Steels
Scab
An imperfection in the form of a shell or veneer, generally attached to the surface by sound metal. It usually has its origin in an ingot defect.
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Visual Defects in Steels
Roll MARK
A term applied to surface imperfections caused by improper roll alignment or roll surface damage.Such imperfections may be periodic or continuous
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Dents
A local change in surface contour caused by mechanical impact, but not accompanied by loss of metal.
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Visual Defects in Steels
Pitting. Pitting, is a form of extremely localized
corrosion that leads to the creation of small holes in the metal.
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Pit
A depression resulting from the removal of foreign material rolled into the surface during manufacture.
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Visual Defects in Steels
Seam Crevice in rolled metal which has
been more or less closed by rolling or other work but has not been fused into sound metal
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Visual Defects in Steels
Cracks
A stress-induced separation of the metal which, without any other influence, is insufficient in extent to cause complete rupture of the material. Quench cracks in steel result from stresses produced during the austenite-to martensite transformation, which is accompanied by an increase in volume
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STRETCH MILL INDENTATION:Localized thinning of the pipe body wall - usually located on the inside surface
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EXCESSIVE REINFORCEMENT (EXCESSIVE OVERFILL):
Outside weld beads which extend above the prolongation of the original surface of the pipe (more than 1/8 in. for pipe having a thickness of 1/2 in. and under, and more than 3/16 in. for a pipe having a thickness of over 1/2 in.
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ARC BURNS: Localized points of surface melting caused by arcing between electrode or ground and pipe surface.
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Improper Grinding Deep Grinding Roller Mark Chip Mark Scratches Mechanical Damage
Visual Defects in Pipe Body
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Visual Defects in Weld
Under Cut:
Under-cutting on submerged-arc welded pipe is the reduction in thickness of the pipe wall adjacent to the weld where it is fused to the surface of the pipe
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Visual Defects in Weld
Porosity:
Voids in a metal, usually resulting from shrinkage or gas entrapment occurring during solidification of a casting or weldment
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Visual Defects in Weld
Crack:
A stress-induced separation of the metal which, without any other influence, is insufficient in extent to cause complete rupture of the material. Quench cracks in steel result from stresses produced during the austenite-to martensite transformation, which is accompanied by an increase in volume
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SURFACE CONDITIONS, IMPERFECTION AND DEFECTS
All pipes shall be free from defects in finished condition
All pipes shall be free from cracks, sweats and leaks
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UNDERCUT Undercuts in SAW pipes shall be investigated, classified, and treated as follows.
a) Undercuts that have a depth ≤ 0,4 mm (0.016 in) are acceptable, regardless of length, and shall be treated in accordance with Clause C.1.
b) Undercuts that have a depth > 0,4 mm (0.016 in) but ≤ 0,8 mm (0.031 in) are acceptable provided they are treated in accordance with Clause C.2 and provided that:
1) their individual lengths are ≤ 0,5 t,
2) their individual depths are ≤ 0,1 t, and
3) there are no more than two such undercuts in any 300 mm (12.0 in) length of weld.
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ARC BURN
Arc burn shall be considered as defects.Arc burns shall be treated in accordance with Clause C.2, C.3 b) or C.3 c), except that they may be removed by grinding, chipping or machining, provided that the resultant cavity is thoroughly cleaned and checked for complete removal of damaged material by etching with a 10% solution of ammonium persulfate or a 5% solution of nital.
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LAMINATIONSLamination having visually determined length the
circumferential direction > 6.4mm shall be considered as
defects
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FLAT SPOTS AND PEAKING
3.2mm maximum in depthMeasured as the gap between the extreme point of thedeviation and the prolongation of the normal contour of the pipe, shall be considered defects and shall betreated in accordance with C.3 b) or C.3 c).
55
HARD SPOT
Maximum 345 HV10 or 327 HBW in 50mm length in any direction shall be classified as a defect . Pipes that contain such defects shall be treated in accordance with C.3 b) or C.3 c).
OTHER DEFECTS
Maximum 0.125 x WT, but not exceed minimum wall thickness. Pipes that contain such defects shall be treated in accordance with C.3
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DENT
For dents, the length in any direction shall be ≤ 0.5 D and the depth, measured as the gap between the extreme point of the dent and the prolongation of the normal contour of the pipe, shall not exceed the following:
a) 3,2 mm (0.125 in) for cold-formed dents with sharp-bottom gouges;b) 6,4 mm (0.250 in) for other dents.Dents that exceed the specified limits shall be considered defects and shall be treated in accordance with C.3 b) or C.3 c).
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STRAIGHTNESS
The total deviation from a straight line over the entire pipe length shall be ≤ 0,15 % of the pipe length. for sour service and/or offshore serviceThe total deviation from a straight line, over the entire pipe length, shall be ≤ 0,2 % of the pipe length For other than sour service or offshore service.
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STRAIGHTNESSThe local deviation from a straight line in the 1,0 m (3.0 ft) portion at each pipe end shall be ≤ 3,0 mm (0.120 in) for sour service and/or offshore service.The local deviation from a straight line in the 1,0 m (3.0 ft) portion at each pipe end shall be ≤ 4,0 mm (0.156 in). For other than sour service or offshore service
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PIPE ENDSRADIAL OFFSET:For SAW and COW pipes, the radial offset of the strip/plate edges shall not exceed the applicable value given in Table
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HEIGHT OF WELD BEADFor ID weld Bead At least 100 mm (4.0 in) from each pipe end.Bead height removed by grinding such that it does not extend above the adjacent pipe surface by more than 0.5 mm.For OD weld BeadIf agreed, At least 150 mm (6.0 in) from each pipe end.Bead height removed by grinding such that it does not extend above the adjacent pipe surface by more than0.5 mm (0.020 in).
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HEIGHT OF WELD BEADFor the remainder of the pipe, the inside weld bead and out side weld bead shall not extend above the adjacentpipe surface by more than the applicable value given in Table
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MISALIGNMENT OF WELD BEAD
Complete fusion and penetration to be achievedMax. 3 mm for WT ≤ 20mmMax. 4 mm for wt > 20mm
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MESUREMENT OF PIPE LENGTH:
For convenience pipe length shall be measured from un-beveled end to beveled face.
Pipe Length
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OUT OF ROUNDNESS:
The greatest distance from a surrounding circle of points on the actual cross-sectional profile of a cylindrical surface
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MASS
If the purchase order specifies a minus tolerance for wall thickness smaller than the applicable value given in Table 11, the plus tolerance for mass shall be increased by a percentage equivalent to the applicable percentage reduction of the minus tolerance for wall thickness. For each order item with a mass of 18 tonnes (20 ton) or more, the mass of the order item shall not deviate from its nominal mass, determined by multiplying the total length of pipe in the order item by its mass per unit length (as per above formula), by more than the following:a) for Grades L175, L175P, A25 and A25P: − 3,5 %;b) for all other grades: − 1,75 %.
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