Knowledge of inspection of stainless steel pipe fittings


Stainless steel pipe fitting is a kind of pipe fitting, and its material is made of stainless steel. The types include: stainless steel elbow, stainless steel tee, stainless steel tee, stainless steel reducing pipe, stainless steel pipe cap, etc. The connection mode can be divided into socket stainless steel pipe fittings, threaded stainless steel pipe fittings, flange stainless steel pipe fittings and welded stainless steel pipe fittings.

The main material of stainless steel pipe fittings: 304L, 304L, 316L, 316L.


● Inspection of geometrical dimension and shape of stainless steel tube:

1. Stainless steel pipe wall thickness inspection: micrometer, ultrasonic thickness measuring instrument, both ends of not less than 8 points and record.

2. Stainless steel pipe diameter, ovality inspection: caliper, vernier caliper, ring gauge, measured maximum point, minimum point.

3. Stainless steel tube length inspection: steel tape, manual, automatic length measurement.

4. Stainless steel pipe bending inspection: ruler, level (1m), feeler gauge, fine line bending per meter, full length bending.

5. Stainless steel pipe end groove Angle and blunt edge inspection: square, card plate.

● Stainless steel tube surface quality inspection: 100%

1. Artificial visual inspection: lighting conditions, standards, experience, identification, stainless steel tube rotation.

2. Nondestructive inspection:

a. Ultrasonic inspection UT:

For all kinds of uniform material surface and internal crack defects are sensitive.

Standard: GB/T 5777-1996 Level: C5

b. Eddy current testing ET :(electromagnetic induction)

It is mainly sensitive to spot (hole) defects. Standard: GB/T 7735-2004

Level: B

c. Magnetic particle MT and magnetic leakage inspection

Magnetic flaw detection is applicable to the detection of surface and near surface defects of ferromagnetic materials.

Standard: GB/T 12606-1999 Level: C4

d. Electromagnetic ultrasonic testing:

No need for coupling medium, can be applied to high temperature, high speed, coarse dry stainless steel pipe surface inspection.

e. Penetrant flaw detection:

Fluorescent, coloring, detection of stainless steel tube surface defects.

● Stainless steel management performance inspection

1. Tensile test

Measure stress and deformation, determine the strength (YS, TS) and plastic index (A, Z) of the material

Longitudinal, transverse sample pipe section, arc type, circular sample (¢10, ¢12.5)

Small diameter, thin wall large diameter, thick wall calibration distance.

Note: The elongation after fracture is related to the sample size GB/T 1760

2. Impulse test

CVN, notch C type, V type, work J value J/cm2

Standard sample 10×10×55 (mm) Non-standard sample 5×10×55 (mm)

3. Hardness

Brinell hardness HB, Rockwell hardness HRC, Vickers hardness HV, etc

4. hydraulic

Test pressure, stable pressure time, P =2Sδ/D

● Stainless steel pipe process performance inspection

1. Flattening test:

Circular sample C-shaped sample (S/D > 0.15) H= (1+2) S/ (∝+S/D)

L=40 ~ 100mm unit length deformation coefficient =0.07 ~ 0.08

2. Ring tensile test:

L=15mm without crack is qualified

3. Flaring and crimping test

The apex taper is 30°, 40° and 60°

4. Bending test:

Can substitute for flattening test (for large diameter pipes)