Installation Process of A335 P11 Alloy Steel Pipe
Installation Process of A335 P11 Alloy Steel Pipe
P11 alloy steel pipe installation process is different from ordinary carbon steel installation methods, including welding, heat treatment and non-destructive testing, etc.
1 Introduction
A335P11 is ASTM (American Society for Testing and Materials) an alloy steel material code, nominal composition of 1.25Cr-0.5Mo, and the national standard 15CrMo composition of the most similar. P11 alloy steel pipe in the manufacturing process to ensure that the mechanical properties for the protection of chemical plants in the safe operation, especially petrochemical enterprises high temperature and high pressure pipeline stability is of great significance.
2. Material acceptance
P11 and other chrome-molybdenum alloy steel pipe should have a quality certificate, quality certification documents include the following:
1) Material standard code
2) material specifications, grades and characteristics data
3) material production batch number and supply status
4) Production unit name
5) Check the printed label
3. Appearance quality inspection before use
Before the use of P11 alloy steel pipe should also check its material, specifications and grades, the appearance of quality inspection, and meet the following requirements:
1) the surface shall not have cracks, folding, hair lines, sandwich, scarring and other defects.
2) The depth of the surface rust, dent and other mechanical damage should not exceed the thickness of the corresponding product standards allow negative deviation.
3) There is a logo that complies with the product specification.
4. Welding
(1) welding methods and welding material selection
According to my company P11 welding process assessment 09-28 content, welding methods using TIG welding and welding arc welding. More than two inches pipe welding joint form in the form of docking, generally using argon arc welding, arc welding cover surface of the welding method; two inches below the thin-walled pipe welding joint form for the socket welding angle access, the use of all argon Welding method.
The selection of welding materials should be based on the chemical composition of welded steel, mechanical properties and the use and conditions of welding comprehensively considered, selected 09-28 in the selection of ER80S-B2 welding wire and E8018-B2 electrode. However, for P11 and carbon steel or other chromium molybdenum alloy steel composition between the dissimilar steel welded joints, according to the lower alloy content of the steel side of the selection of welding materials.
(2) welder requirements
Participate in P11 and other chromium molybdenum alloy steel welding welder must be "boiler pressure vessel pressure pipe welder examination and management rules" requirement for examination. Qualified welders are responsible for the welding of the corresponding items.
(3) Preparation before welding
Pre-welding preparation, including groove preparation, group and positioning, etc., and ordinary carbon steel welding is no different, not described here in detail.
(4) welding operations
Welding operations should be carried out within the scope of the welding process requirements. But also for wall thickness greater than 10mm of P11 before welding pipe should be preheated, preheating temperature of 150 ~ 200 ℃. Weldments to achieve preheat temperature should be promptly after welding, in maintaining the preheating temperature conditions, each weld should be a continuous welding finished. Weldment to achieve preheating temperature should be promptly after welding. Welding should be immediately after the end of the clean-up weld to remove welding slag, splash, etc., for visual inspection.
5. Post-weld heat treatment
(1) heat treatment requirements
For P11 and other chrome-molybdenum alloy steel design documents generally require the immediate elimination of stress after welding heat treatment. P11 alloy steel heat treatment temperature of 700 ~ 750 ℃, the shortest temperature time is not 2h. Heat treatment of the heating rate and cooling rate should meet the following requirements:
1) heating to 300 ℃, the heating rate should be 5125 / T. ℃ / h, and not more than 220 ℃ / h;
2) During the constant temperature of the measuring point temperature should be within the provisions of the heat treatment temperature range, the difference shall not exceed 50 ℃;
3) after cooling the cooling rate should be 6500 / T. ℃ / h, and not more than 260 ℃ / h. Cooling 300 ℃ after the natural cooling. (Note: T is the actual thickness of the pipe mm)
After heat treatment, the weld shall not be immediately subjected to heat treatment. After welding, the heat treatment shall be carried out at a temperature of 300 ~ 350 ℃ for 10 ~ 15min immediately after the welding, and then slowly cooled to room temperature. And then weld should be welded to check to confirm that no cracks and other defects before the welding process can continue to be the original welding, the conditions are available after the post-weld heat treatment.
(2) heat treatment quality inspection
According to the specification, after welding heat treatment of welded joints, weld and heat affected zone should be tested for hardness values. The Brinell hardness value after heat treatment of P11 weld and heat affected zone shall not exceed 225 (refer to SH / T 3501, Table 10), and the weld shall be re-heat-treated for unqualified hardness test. Heat treatment after the hardness test is also a work can not be ignored, it will directly affect the P11 steel pipe installation progress.
According to SH / T 3501-2011, weld and heat affected zone should be 100% hardness value detection. However, according to GB 50517-2010 "Petrochemical Pipeline Engineering Construction Quality Acceptance" requirements, in the heat treatment furnace heat treatment furnace can be checked every 10% of the welding joint hardness testing [3], which will reduce the part of the workload . But for the small diameter pipe and the horn joint, because the detection instrument diameter and the detection space limit hardness testing work is difficult to carry on, but at present only in Zhenhai area SH / T 3554-2013 "petrochemical steel pipe welding heat treatment specification "Provides that: for specifications or structural reasons can not be hardness testing of fillet welds and branch connections welded joints, when the construction unit can provide a hardness test with qualified welding process assessment report, can avoid the corresponding hardness of the welded joint testing. I think, SH / T 3554-2013 publicity will be used on the use and development of P11 play a role in promoting.
6. Non-destructive testing
P11 and other chrome-molybdenum alloy steel is prone to delay cracking and reheat cracking tendency of the material, non-destructive testing should be completed in the welding 24h and heat treatment after the completion of both. The ratio of non-destructive testing can be found in Table 12 of SH / T 3501-2011 and Table 9.3.1 of GB 50517-2010. It is to be noted that for butt welds of pipe grades SHA1, SHA2, SHB1, and SHB2, both internal defect detection (detection method RT or UT) and surface defect detection (inspection) are to be performed simultaneously according to SH / T 3501-2011 Method PT or MT), which is different from carbon steel and stainless steel.
7. Matters needing attention during construction
P11 alloy steel pipe in the construction process should be noted that the occurrence of the most mixed with carbon steel, in the event of high temperature and pressure conditions there are significant security risks. So in the construction process should be set up a special material management personnel, and other special steel P11 according to the relevant provisions of brushing color standard and full management of P11 and other alloy steel with the use, payment. Should also strengthen supervision and inspection of the construction site to prevent the occurrence of mixed materials. Another noteworthy is the use of welding materials, in order to prevent the welding material with the wrong, norms SH / T 3501-2011 and GB 50517-2010 are required for each pipeline to extract at least two welds for chemical composition testing, At present, the main detection method is fast spectroscopy.
