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Main Quality Requirements for Steel Pipe Anticorrosion Lining
Time：2014-03-28
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Detailed introduction
Steel pipe lining materials include cement mortar or epoxy resin, etc.
A. Quality Requirements for Cement Mortar Lining
a. Pre-lining Inspection: The ellipticity of the pipe should not exceed 2% of the pipe diameter. The inner wall of the pipe should be free of rust, debris, grease, etc. The height of the weld inside the pipe should not be greater than 1/3 of the lining thickness.
b. Material Selection: Use 525 silicate cement, and clean medium sand (particle size 0.15-1.2mm). The weight ratio of cement mortar should be selected within 1:1 to 2. The slump should be 60-80mm, and the compressive strength should be ≥30MPa.
c. Lining Thickness and Tolerance: Refer to Table 2 for details.
d. Inner Wall Roughness: The roughness coefficient of the inner wall after cement mortar lining should be n≤0.012.
e. Cracks due to Shrinkage: Cracks caused by shrinkage of the lining, if the width is ≤0.8mm, and the axial length is not greater than the circumference and not greater than 2m, can be left unrepaired; otherwise, they should be repaired.
f. Surface Defects: If the area of surface defects (such as pits, sand holes, and voids) is greater than 5cm2, the depth is greater than the allowed tolerance of the lining thickness, or the hollow area is greater than 400cm2, repairs should be made.
B. Quality Requirements for Epoxy Resin Internal Spray Lining
Due to the lack of national standards for the material and operational requirements of epoxy resin used for internal spray lining, the following requirements are proposed with reference to the petroleum and natural gas industry standard "SY/T4057-93":
a. The inner wall of the steel pipe should be derusted by sandblasting or other methods to meet the Sa2.5 level standard of GB/T8923, exposing the metal's natural color.
b. The liquid epoxy resin used for internal spray lining should have a hygiene license from the Ministry of Health, and the construction process should be harmless to humans.
c. The total thickness of the lining should be ≥400μm (usually applied in five coats, with the first primer coat applied within one hour after sandblasting and rust removal, and subsequent coats applied after the surface has dried).
d. The coating adhesion should reach levels 1-2 (tested according to GB1720).
e. There should be no scratches when tested with a 2H pencil (tested according to GB6739).
f. The flexibility should be 1.0mm (tested according to GB1731).
g. The impact resistance should be ≥4.9 (tested according to GB1732).
h. The viscosity should be ≥0.2Pa.s (tested according to GB1723).
i. The fineness should be ≤80μm (tested according to GB1724).
j. The surface drying time should be ≤4h, and the thorough drying time should be ≤24h (tested according to GB1728).
k. The solid content of component A should be ≥70%, and the solid content of component B should be ≥80% (tested according to GB1725).
l·.The coating should pass the 180-day chemical reagent resistance test in 10% NaOH, 30% H2SO4, and 10% NaCl respectively (tested according to GB1763).
m.The coating should achieve level 1 in the 500-hour salt spray resistance test (tested according to GB1771).
n.The coating should pass the 90-day sewage resistance test at 100°C (tested according to GB1733 Method B).
o. After spray lining, random inspections should be conducted on coating thickness, pores, bubbles, and mechanical damage. Any defects found should be repaired promptly.
(1.4) Quality Requirements for External Corrosion Protection of Steel Pipes
With reference to the Petroleum Ministry Standard "SYT28-87," the following requirements are proposed:
a. The surface rust removal of steel pipes should meet the Sa2.5 level standard of GB8923-88. The pipes should exhibit their natural metal color and be free of visible attachments such as grease, dirt, rust, etc.
b. The anticorrosion material should be resistant to acids, alkalis, and microbial erosion. Steel plates coated with anticorrosion materials should be soaked in 10% hydrochloric acid and 10% caustic soda solutions for 90 days each, and in a 30% sulfuric acid solution for 7 days, without any changes to the appearance of the anticorrosion layer.
c. The shear bond strength should be ≥ 4Mpa, the impact strength should be 1.2J, the power frequency breakdown strength should be ≥ 20kv/mm, the volume resistivity should be ≥ 1×1012Ω.cm, the cathodic disbondment should be ≥ grade 3, the water absorption rate should be ≤ 0.4%, and the resistance to aerobic microbial erosion should be ≥ grade 2.
d. The anticorrosion layer should solidify within 24 hours and have a uniform thickness, be dense, free of warping, wrinkles, hollow drums, color leakage, and not sticky to the touch, with an intact appearance.
e. After the anticorrosion layer has cured, a knife cannot be used to delaminate the coating, indicating good adhesion between the primer and the metal surface.
f. The surface of the anticorrosion layer should have good hardness and wear resistance, and a steel wire rope suspension should not leave a trace of 0.1mm.
g. Both immediately after curing and three months later, the insulation performance of the anticorrosion coating should be good. The breakdown voltage detected by an electric spark tester should reach 10,000v, with a minimum of not less than 6000v. Additionally, only two pinhole breakdowns above 6000v are allowed per square meter.
h. The application process should be convenient and harmless to humans and the environment.
i. When using epoxy coal tar anticorrosion paint, the primer should be applied within one hour after sandblasting and rust removal. A total thickness of ≥600μm with five coats of oil and two layers of cloth can meet the above requirements.
A. Quality Requirements for Cement Mortar Lining
a. Pre-lining Inspection: The ellipticity of the pipe should not exceed 2% of the pipe diameter. The inner wall of the pipe should be free of rust, debris, grease, etc. The height of the weld inside the pipe should not be greater than 1/3 of the lining thickness.
b. Material Selection: Use 525 silicate cement, and clean medium sand (particle size 0.15-1.2mm). The weight ratio of cement mortar should be selected within 1:1 to 2. The slump should be 60-80mm, and the compressive strength should be ≥30MPa.
c. Lining Thickness and Tolerance: Refer to Table 2 for details.
d. Inner Wall Roughness: The roughness coefficient of the inner wall after cement mortar lining should be n≤0.012.
e. Cracks due to Shrinkage: Cracks caused by shrinkage of the lining, if the width is ≤0.8mm, and the axial length is not greater than the circumference and not greater than 2m, can be left unrepaired; otherwise, they should be repaired.
f. Surface Defects: If the area of surface defects (such as pits, sand holes, and voids) is greater than 5cm2, the depth is greater than the allowed tolerance of the lining thickness, or the hollow area is greater than 400cm2, repairs should be made.
B. Quality Requirements for Epoxy Resin Internal Spray Lining
Due to the lack of national standards for the material and operational requirements of epoxy resin used for internal spray lining, the following requirements are proposed with reference to the petroleum and natural gas industry standard "SY/T4057-93":
a. The inner wall of the steel pipe should be derusted by sandblasting or other methods to meet the Sa2.5 level standard of GB/T8923, exposing the metal's natural color.
b. The liquid epoxy resin used for internal spray lining should have a hygiene license from the Ministry of Health, and the construction process should be harmless to humans.
c. The total thickness of the lining should be ≥400μm (usually applied in five coats, with the first primer coat applied within one hour after sandblasting and rust removal, and subsequent coats applied after the surface has dried).
d. The coating adhesion should reach levels 1-2 (tested according to GB1720).
e. There should be no scratches when tested with a 2H pencil (tested according to GB6739).
f. The flexibility should be 1.0mm (tested according to GB1731).
g. The impact resistance should be ≥4.9 (tested according to GB1732).
h. The viscosity should be ≥0.2Pa.s (tested according to GB1723).
i. The fineness should be ≤80μm (tested according to GB1724).
j. The surface drying time should be ≤4h, and the thorough drying time should be ≤24h (tested according to GB1728).
k. The solid content of component A should be ≥70%, and the solid content of component B should be ≥80% (tested according to GB1725).
l·.The coating should pass the 180-day chemical reagent resistance test in 10% NaOH, 30% H2SO4, and 10% NaCl respectively (tested according to GB1763).
m.The coating should achieve level 1 in the 500-hour salt spray resistance test (tested according to GB1771).
n.The coating should pass the 90-day sewage resistance test at 100°C (tested according to GB1733 Method B).
o. After spray lining, random inspections should be conducted on coating thickness, pores, bubbles, and mechanical damage. Any defects found should be repaired promptly.
(1.4) Quality Requirements for External Corrosion Protection of Steel Pipes
With reference to the Petroleum Ministry Standard "SYT28-87," the following requirements are proposed:
a. The surface rust removal of steel pipes should meet the Sa2.5 level standard of GB8923-88. The pipes should exhibit their natural metal color and be free of visible attachments such as grease, dirt, rust, etc.
b. The anticorrosion material should be resistant to acids, alkalis, and microbial erosion. Steel plates coated with anticorrosion materials should be soaked in 10% hydrochloric acid and 10% caustic soda solutions for 90 days each, and in a 30% sulfuric acid solution for 7 days, without any changes to the appearance of the anticorrosion layer.
c. The shear bond strength should be ≥ 4Mpa, the impact strength should be 1.2J, the power frequency breakdown strength should be ≥ 20kv/mm, the volume resistivity should be ≥ 1×1012Ω.cm, the cathodic disbondment should be ≥ grade 3, the water absorption rate should be ≤ 0.4%, and the resistance to aerobic microbial erosion should be ≥ grade 2.
d. The anticorrosion layer should solidify within 24 hours and have a uniform thickness, be dense, free of warping, wrinkles, hollow drums, color leakage, and not sticky to the touch, with an intact appearance.
e. After the anticorrosion layer has cured, a knife cannot be used to delaminate the coating, indicating good adhesion between the primer and the metal surface.
f. The surface of the anticorrosion layer should have good hardness and wear resistance, and a steel wire rope suspension should not leave a trace of 0.1mm.
g. Both immediately after curing and three months later, the insulation performance of the anticorrosion coating should be good. The breakdown voltage detected by an electric spark tester should reach 10,000v, with a minimum of not less than 6000v. Additionally, only two pinhole breakdowns above 6000v are allowed per square meter.
h. The application process should be convenient and harmless to humans and the environment.
i. When using epoxy coal tar anticorrosion paint, the primer should be applied within one hour after sandblasting and rust removal. A total thickness of ≥600μm with five coats of oil and two layers of cloth can meet the above requirements.
