Manual inspection of mild steel pipes

Manual inspection is a crucial step in ensuring the consistency of mild steel pipe quality and is a mandatory quality control procedure before pipe delivery. This guide is optimized and streamlined based on commonly used international steel pipe standards (such as ASTM A53, ASTM A106, EN 10210, EN 10216, API 5L) and factory inspection systems, and can serve as a reference for enterprise quality control, third-party inspection, and overseas customer technical audits.

Preparation Before Inspection

1. Preparation of Inspection Tools and Marking Materials

The on-duty inspector should prepare the paint and high-temperature resistant chalk required for inspection and grade marking for application.

Check that the external surface lighting and internal surface inspection lights are functioning properly. Inspection must not be carried out at night if the external surface inspection lighting is not turned on.

2. Inspection of Measuring Tools

Check measuring tools such as vernier calipers and micrometers, confirming that the measuring tools are within their specified calibration validity period and that the zero points of the micrometer and vernier calipers are aligned.

3. Document Preparation

Subsequent inspectors should carefully review work records to understand major quality issues and outstanding problems; carefully review production plans, process notices, or relevant standards to understand the steel pipe types, specifications, and quality requirements for this level of inspection.

Seamless Steel Pipe Inspection Conditions

1. Process Card Verification

Before inspecting each batch of steel pipes, a production process card returned from the finished product processing area is required.

2. Comparison with Contract & Plan

Inspectors must verify that the production process card is consistent with the production plan, physical contract number, batch number, standard, specification, and steel type. If there is any discrepancy, the foreman of the finished product processing area in the special seamless steel pipe plant should be contacted to clarify the cause. If there is no discrepancy, no verification is required.

Mild Steel Pipe Inspection Items and Methods

1. Visual Inspection of External Surface

According to the requirements of relevant standards, visually inspect the quality of the external surface of each steel pipe; using an internal surface inspection lamp, visually inspect the quality of the internal surface of each steel pipe according to the requirements of relevant standards.

2. Measurement of Steel Pipe Outer Diameter and Wall Thickness

Use vernier calipers to measure the outer diameter of the steel pipe at the pipe end. The two outer diameter values, D1 and D2, should be perpendicular to each other.

Use a micrometer to measure the wall thickness of the steel pipe at the pipe end, measuring the wall thickness at four evenly spaced points. (D1 and D2 are the two outer diameter values; S1, S2, S3, and S4 are the wall thickness values at the four points.)

3. Visual Inspection of Bending Degree

When steel pipes need to be bent, the degree of bending must be visually inspected.

If a row of steel pipes is pressed together, and the pipe body shows obvious bending and gaps, production personnel should be notified, and the bent steel pipes should be removed for correction or scrapped.

If the degree of bending is not severe but there are objections, the steel pipes should be removed, and the degree of bending should be measured using a wire drawing method or a ruler method.

Mild Steel Pipe Quality Inspection Marking

1. Marking of End-Cutting Areas

For steel pipes requiring end-cutting and repair, when the removal portion is within 0.6 meters of the end, a line should be drawn on the section to be cut using high-temperature resistant chalk, and the defect name should be marked. The cut should be drawn as a dashed line, covering the entire cylindrical surface of the pipe section as much as possible.

2. Marking of End Defects >0.6m

When the end defect to be removed is greater than 0.6 meters from the end, a zigzag line should be drawn on the pipe end using high-temperature resistant chalk, and the cutting location and defect name should be marked with an arrow. The zigzag line should cover the entire cylindrical surface of the pipe section as much as possible.

3. Scrap Marking

For scrap products, mark “Ä” and the defect name within 0.5 meters of the pipe end.

5. Repaired Product Marking

For inspected repaired products, a “™” mark can be drawn on the repaired defect. After the repaired and grounded product passes inspection, a “V” mark can be added by the team. If the repaired and grounded product fails to meet standards, mark it with "™" at 0.5 meters from the pipe end and then mark it with "Ä" before disposing of it as waste.

6. Re-inspection

Steel pipes that have been re-cut, ground, and straightened should be re-inspected.

Random Sampling Frequency of Mild Steel Pipe Geometric Dimensions

When receiving and replacing the first 10 steel pipes according to specifications, their geometric dimensions must be measured at the specified measurement points. After approximately half of the steel pipes in each batch have been inspected, the geometric dimensions of 10 steel pipes should be randomly selected for measurement. The recorded geometric dimension values for each batch of steel pipes should not be less than 60 values from 10 branch pipes.

Completion of Quality Records

For each batch of steel pipes that has been inspected or is awaiting delivery but has not yet been inspected, a "Finished Product (Semi-finished Product) Inspection Record" must be completed.

The handwriting should be clear and legible when filling out the record, and no alterations are allowed. The recorded data should be accurate, and geometric dimensions should be measured randomly.

The data should be recorded together with the inspection results, and no remarks should be added. The person who modifies the record should sign it.

Inspection records are collected periodically by the site statistician or assessor and are then compiled and archived by the statistician.

Transmission of Abnormal Quality Information

When inspectors discover that the same defect persists, they should promptly notify the shift supervisor, requesting them to investigate the cause and eliminate the fault.

FAQ

1. Why do mild steel pipes require manual inspection?

Manual inspection can detect minute surface defects (such as microcracks, indentations, pits, scratches, and oxide scale) that are difficult to identify with automatic detection.

Furthermore, manually measuring dimensions such as outer diameter, wall thickness, and curvature ensures that the steel pipes meet international standards such as ASTM, EN, and API.

2. What items are mainly checked during manual inspection?

Manual inspection typically includes the following items:

External Visual Inspection,

Internal Visual Inspection,

Outer Diameter Measurement,

Wall Thickness Measurement,

Straightness, Ovality, and Pipe End Condition Inspection.

Conclusion

Manual inspection is a crucial step in ensuring that mild steel pipes meet international standards. Through standardized inspection procedures, clear labeling methods, and a systematic sampling inspection system, the stability of finished product quality can be effectively improved, increasing the trust and acceptance rate of export customers.

Read more: Difference between mild steel pipe and carbon steel pipe