Code for inspection of pressure pipelines in chemical enterprises

Inspection Regulations for Pressure Pipelines of Chemical Enterprises; 1 General Principles

1.1 In order to ensure the safe operation of chemical pipelines and protect the safety of people’s lives and property, these regulations are formulated in accordance with the “Regulations on the Management of Pressure Pipelines in Chemical Enterprises”. ​

1.2 This procedure is the basic requirement for chemical pressure pipeline inspection. Chemical production enterprises must comply with this procedure. ​

1.3 This regulation is applicable to pipelines that meet the following conditions at the same time 1. Inlet pressure Pw≥0.1MPa;

2. Nominal diameter Dg≥50mm;

3. Process pipelines for transporting chemical media and steam pipelines for chemical production. (For chemical pipelines with major hazards, the maximum working pressure is less than 0.1MPa or the nominal diameter is less than 50mm, please refer to the implementation.)

This provision does not apply to the following pipelines: 1. Non-metallic pipelines; 2. Instrument pipelines;

3. The pipeline to which the equipment body belongs;

4. Lined pipes;

5. Pipes with non-flammable media, non-toxic or mildly toxic media. Such as: water, air, inert gas, etc. ​

1.4 The classification of pipelines is as follows: (omitted) 1. Pipelines transporting extremely or highly hazardous toxic media are Class A pipelines. ​

2. Alloy steel and stainless steel pipes whose materials are flammable and combustible media, whose working temperature is greater than 450°C, and carbon steel pipes whose working temperature is greater than 370°C are Class A pipelines.

3. Pipes whose working temperature is higher than or equal to the autoignition point of the medium are Class B pipelines. ​

4. The level of pipelines transporting Class A fire hazardous gases (lower explosion limit <10%) media should be upgraded to Level 2. ​

5. Pipelines transporting moderately hazardous toxic media, Class B fire hazardous gases (lower explosion limit ≥10%), and flammable liquid media with a flash point less than 28°C should be upgraded to one level. ​

6. Pipes with an original design corrosion rate greater than 0.25 mm/year should be upgraded by one level. ​

7. When the same medium is divided into different pipeline levels according to its characteristics (such as flash point and lower explosion limit), the higher level should prevail. ​

8. For mixed media, the medium with the greatest degree of harm shall be used as the basis for classification. ​

​ ​ ​ 2 Inspection The inspection of pressure pipelines in chemical enterprises is divided into: pre-service inspection, online inspection and comprehensive inspection. ​

2.1 Pre-service inspection Pre-service inspection should be carried out by a professional inspection unit (or professional technician) entrusted by the user to conduct a comprehensive acceptance inspection of the manufacturing and installation quality of chemical pipelines (if a professional inspection unit has been entrusted to inspect the quality of the pipeline installation process If supervisory inspection is carried out, pre-service inspection will be exempted.)

2.1.1 Review design technical information including: design specifications, process parameters, construction drawings, construction technical specifications or requirements, etc. ​

2.1.2 Review the manufacturing certificates and quality inspection reports of pipes, pipe fittings and valves, etc., including appearance inspection, chemical composition and mechanical performance reports and re-inspection reports, non-destructive testing reports, test reports and other design and technical requirement reports. Manufacturing quality should comply with GBJ235-82 “Construction and Acceptance Specifications for Industrial Pipeline Engineering” or design requirements quality specifications. Supplementary inspection must be carried out for unqualified items and missing items in the quality inspection report and random inspection.

2.1.3 Review processing and installation records and construction quality inspection reports, which should include machining inspection, welding process evaluation, installation inspection, non-destructive testing report, repair records, heat treatment, pressure test, safety valve debugging, pickling, Construction records, test reports and quality inspection reports such as purging, anti-corrosion and thermal insulation. The installation quality should comply with the inspection and acceptance requirements of GBJ236-82 “Construction and Acceptance Specifications for Field Equipment and Industrial Pipe Welding Projects” or the design regulations. ​

2.1.4 Project quality inspection: The content includes appearance inspection, geometric dimension inspection, installation quality inspection, non-destructive testing, anti-corrosion and insulation and other project quality inspections. The proportion of random inspections for grade A and B pipelines shall not be less than 10%, and the proportion of random inspections for grade C and D pipelines shall not be less than 5%. Non-destructive testing and random inspection: Class A and B pipelines shall not be less than 10% of the welded seams of the entire pipeline, and Class C and D pipelines shall be no less than 5%. 2.2 Online inspection 2.2.1 Online inspection is an inspection carried out by the user under operating conditions. Inspect at least once a year. ​

2.2.2 Online inspection items

a. Leak inspection Check the leakage of pipelines and their interface flanges, joints, welds, valve packings, etc.;

b. Vibration inspection: Check the vibration of the pipeline, the displacement of the movable bracket and the guiding performance. Whether the fixed bracket is firm and reliable, the adjustable bracket is properly adjusted, and there should be no friction between pipes and pipes, and between pipes and adjacent objects;

c. Check the integrity of the insulation layer or anti-corrosion layer d. Check the integrity of the accessories. The valve is flexible in operation and the safety accessories are effective. The grounding resistance between the flanges of pipelines transporting flammable and explosive media should be less than 0.03Ω, and the resistance of the pipeline to ground should not be greater than 100Ω. ​

e. Wall thickness measurement For important monitoring pipelines, ultrasonic thickness gauges can be used to measure wall thickness online if necessary. High-temperature pipeline inspection must use high-temperature probes. ​

2.3 Comprehensive inspection 2.3.1 The comprehensive inspection of chemical pressure pipelines is a relatively comprehensive inspection carried out when the device (system) is shut down for overhaul. The inspection cycle is generally conducted at least once every six years. ​

In case of any of the following circumstances, the inspection cycle should be shortened appropriately:

a. The first inspection after the new pipeline is put into use;

b. Class A and Class B pipelines with corrosion rates greater than 0.25 mm/year;

c. Pipes that may suffer from local corrosion such as stress corrosion, pitting corrosion;

d. Pipes that are likely to develop fatigue (possibly subjected to repeated stress due to vibration, pulsating pressure, temperature cycles, etc.);

e. Pipes that may suffer from material deterioration (see Section 2.3.2.4); f. Pipes in which buried defects in welded joints are found to exceed the quality standards stipulated in construction acceptance specifications or maintenance and inspection regulations during inspection. ​

After pipeline inspection, if the pipeline is evaluated as safe for long-term use, the inspection period may be extended appropriately, but the maximum period shall not exceed nine years. ​

2.3.2 The comprehensive inspection of chemical pressure pipelines is mainly based on macroscopic inspection and thickness measurement, and non-destructive testing and physical and chemical inspection are carried out when necessary. ​

2.3.2.1 Macroscopic inspection items

a. All items for online inspection

b. Pipe surface cracks, folds, heavy skin, local corrosion, bruises and deformation, local overheating, etc.;

c. Cracks, dents, misaligned edges, and undercuts in welded joints;

d. Abnormal deformation of elbows and elbows; 2.3.2.2 Wall thickness measurement

a. Pipe thickness measurement adopts ultrasonic thickness gauge and complies with JB4730-94 standard. ​

b. Measure the thickness of the elbows and tees of the pipelines. The random inspection proportions of pipelines at all levels are: Grade A > 50%, Grade B > 30%, Grade C > 10%, and Grade D > 5%. ​

c. The location of the thickness measurement point should be based on the physical condition of the medium in the pipe (gas phase, liquid phase, presence or absence of suspended solids, etc.) and flow direction, and should be selected in parts that are susceptible to erosion by the medium and parts that may accumulate liquid. Generally, the number of thickness measurement points for elbows and tees should comply with the requirements in Table 2. ​

d. For pipes with a small curvature radius or a large number of pitting corrosion on the inner surface, a small diameter probe should be used for measurement or an ultrasonic flaw detector should be used for auxiliary measurement. ​

e. If an abnormal value is found during thickness measurement, four additional points must be measured 5 mm each in front, back, left, and right of the point. If there are still abnormalities, the thickness measurement range must be further expanded to find the area with abnormal thickness, and at the same time, the pipe must be inspected. All elbows, tees and straight pipe parts must be enlarged and measured according to appropriate proportions. ​

2.3.2.3 Non-destructive testing

a. Conduct surface flaw detection inspection on cracks (or signs of cracks) and suspicious parts found in macroscopic inspection;

b. For stainless steel pipes with damaged insulation layers that may seep into rainwater, penetrant inspection should be carried out on the outer surface of the pipe to check whether there are stress corrosion cracks;

c. For pipelines that are likely to cause fatigue, surface flaw detection should be carried out on the welds and pipe end threads that are prone to stress concentration to check whether there are fatigue cracks;

d. At least 10% of the welds of Class A pipelines and at least 5% of the Class B pipelines shall be randomly inspected by radiographic testing (RT) or ultrasonic testing (UT). For other pipelines, inspectors will determine whether RT or UT spot inspections are required and the proportion of spot inspections based on specific circumstances. If the pipeline is manufactured and installed according to the regulations and standards in good condition, the proportion of RT or UT spot inspections can be halved. During the spot inspection, if defects exceeding the standard (referring to the assessment standards of this regulation, the same below) are found, the inspection proportion should be appropriately expanded; if defects exceeding the standard are continued to be found, they should be dealt with according to the defect status and pipeline usage conditions. ​

e. The non-destructive testing method complies with JB4730-94 standard. ​

2.3.2.4 Physical and chemical inspection The following pipelines shall undergo physical and chemical inspection during comprehensive inspection:

a. Carbon steel and ferritic stainless steel pipes with working wall temperature greater than 370°C;

b. Low alloy steel and austenitic stainless steel pipes with working wall temperature greater than 430°C;

c. Carbon steel and low alloy steel pipes with working wall temperature greater than 220°C in hydrogen medium;

d. Titanium and titanium alloy pipes with working wall temperatures greater than 320°C;

e. The working medium contains carbon steel and low alloy steel pipes containing moisture H2S. ​

The inspection content includes chemical composition analysis, hardness measurement and metallographic structure inspection of the inner surface layer and different depth layers, and mechanical property (tensile, bending and impact toughness) tests. For the above types of pipes, in order to facilitate sampling, it is best to set up detachable monitoring pipes in the pipes before they are put into use to regularly identify the degree of material deterioration.

For pipelines used in stress corrosion-sensitive media, the hardness of welded joints should be measured to find out the effect of weld heat treatment (elimination of welding residual stress), so as to determine the stress corrosion cracking tendency of the pipeline. The location of the hardness measurement point is as follows: As shown in Figure 1. ​

2.3.3 Conduct a comprehensive inspection of high-pressure pipelines connected by flanges;