Weld rework during the manufacturing pr​εocess cannot be complet$±↕ely avoided. In order to ensure the quπ¶←ality of welding rework, there are several requ♠​♠★irements as follows.

　　Rework conditions

　　There are oversized defects in th<£e welded joint, and the defects are often ±¥repaired by welding after removal. For su  rface defects located in the weld ±ed joint, it is appropriate to use grindinγ∏®¥g wheel grinding and other methods to r↑✔£‍emove defects, such as grin§♠ding depth does not exceed the standardσ​γ allowable value, it can be exempt from we‍&€✘lding rework.

　　This is particularly important for¶ε↔≤ pressure vessels in use, because t¶•'¶he use of site welding conditiγ✔ons (such as welding position, welding e®∑nvironment and preheating and slow cooling, et∏♥c.) and the level of operatioα&‍÷n of the welder, and often there is a÷ ₽β gap between the manufacturing enterprise→γ↓, welding rework process ÷₩↔★may cause other hidden problems.

　　Rework requirement←Ω $s

　　Carefully analyze the ca•×βuses of over-standard defects, research prev↕↕∏ention and control measures, §↔<¶is to improve the pre£☆↕mise of welding rework. Generally sp∑↓eaking, welding rewor&÷k consists of the following processes.

　　(1) First of all, the defect removal

　　Defects can be removed using cold ↑•(such as grinding wheel grindin¶✘☆g), hot (such as carbon '✘©arc gas planing) two processing methods. The choi♦♦↓≥ce of removal method is relat₹✘↕ ed to the material strength level and ↕ε≠ alloy content.

　　The standard tensile strength of the lower ≥≤≈↓limit of Rm ≥ 540MPa steel and Cr-M↑×ε•o low-alloy steel, the use of hot≠↔ processing methods to remov<πe defects should be noted to ↔εγavoid the presence of surface hard☆£ening layer induced by the↔‌ expansion of the original €×defects or the emergence of€>↑ new defects.

　　Can also use a combination of α ♦cold and hot processing₽β method, that is, after the carbo≤₽©n arc air planing and then use the grindin&≠↕≥g wheel to repair the hardened l©✘ayer of the surface off.

　　(2)Inspection of defect < removal

　　Defect removal is generally used after↔δ​§ the magnetic partic¶πle, penetration and other n± ✔γon-destructive testing methods to conf↕≠irm that the defect removal is cle£® ®an and thorough, which is the key t>π♦✘o the quality of welding reworkε↓.

　　(3) welding rework before the process →γδ€evaluation

　　As the process of rework a✘✘&nd product welding process may be★≥≥ different, such as we₩∑≈¶lding is automatic welding and manual  ¥electrode arc welding rework, so it is neces₩​×sary to rework before the ♠₽'γwelding process assessment. If the origin÷φ↑al process has been assessπ∑ ed according to the reΩ©☆levant provisions of NB/T 4•↓7014 can cover the rework process, it is deemed t≥♥'o have been assessed before the rework process.→×

　　(4) welding rework after the inspection

　　In order to ensure the quality of ≠÷πrework, the same non-destructi☆βve testing methods should be used with the app♦₽↑®lication of welding (internal RT or UT, su∞¶rface MT or PT) with the passing le↑εδ©vel, the reworked weld ins≥₩pection to confirm that there is no over-standa← &rd defects.

　　Rework timing

　　The purpose of post-weld heat treat>δ←€ment is to eliminate excessive weld α♥stress, therefore, requΩ¥☆↔ire post-weld heat treatment of tφ☆φβhe vessel should generally be p§λ≥ost-weld heat treatment before the welding r¥π₩ework.

　　After the pressure test requires ®≈welding rework, when the rework →©÷"depth is greater than 1‌↔/2 wall thickness, acβ§​¶cording to China'sΩ≤×← relevant regulations, standards (such as GBβφ£¶ / T150), should be re-pressure test.

　　Number of rework

　　Previously, there was concerπ•n that the same part  σof the weld reworked several ti​≤Ω®mes, will be repeatedly heated to γ ∞ cause grain growth affect the safet‌←>πy of the operation of £↑α♠the vessel, after several tests$✔ to prove that the tenden® ♠cy of grain growth due to re• ♠peated rework is not obvious, will not pos¥✘©§e a threat to the safe operation of thδ↑✘e vessel.

　　Therefore, when the sa♠₽me part of the weld is reworked m♥€§φore than 2 times when the weld is sentenced ↓ ®to scrap is not based on.

　　Based on the above reasons€®, our standards on the same pa"₹rt of the weld rework limit is non≥∞€-mandatory, so the use of "should not exc↕♥eed 2 times" this expression, the phenomeno✔‌≥n of more than 2 times the following warning ☆λ measures, that is, "rework should be apprγ ★>oved by the technical direct≈‌or of the manufacturing unit before, the nu<¶∑♠mber of rework , parts and reworking should be re±♦corded in the quality certi™↑αficate of the container ", the purpose>ε is to serious welding process di★₽€§scipline.

　　Stainless steel vessel welding rework

　　Along the metal grain bo≈>αundary corrosion called intergranular corro '₹sion. Intergranular corrosion is one of t∏π×εhe main forms of corrosion of stainless steel, ¥λ®its welded joints and heat-affected σ zone often produce intergranular→✔ corrosion phenomenon, the reason&© ε is that stainless steel in 500 ℃ ~ 7♣∞λγ00 ℃ after a period of time, due ₩≈‌to the precipitation of c §≈hromium carbide caused by intergranular poo↕→↔≤r chromium, which leads to intergranular‌γε$ corrosion.

　　Intergranular corrosion is a dangerous↑£>✘ form of damage in stainless steel container♥∞>↔s, which is characterized by the shape and size$♠ ₩ and metal luster almost unchan♣★ ₩ged, but the mechanical properties of"​ the material decreased s"♥ignificantly. To prevenγπ↔σt intergranular corrosion, the need t$≥σo choose the appropriate me♣δπthod from the stainless steel '€₹∏intergranular corrosion susceptibility t≈ ε♠est method in the relevant standards, the maλβ≠terial (including wel♠♥≤ding material) to be strictlπ>₽y screened to ensure that the re♠δquirements of intergranular corrosion r ★€esistance.

　　Welding rework due to improper selection∞$♣ or operation, may destroy th>↓≤e original ability to resist intergranular®ε∏₽ corrosion, therefore, GB 150 and other requφ∑↔≤irements "have special c​↕orrosion requirements of the contain™←∑er or pressurized components, rework pa≥δ÷rts still need to ensure no less than the origina< φl corrosion resistance".

　　Therefore, the reworki↓↔♥ng of the lowest possibl ≥e welding heat input, multi-layeε≤r welding should be strict₹>ly controlled interlayer tem♥☆>♠perature, to be cooled ∏<to about 60 ℃ before th•π→e next weld, in order to reduce the resid£λence time of the welded joint in thα₩‌e range of sensitization temperature;

　　In addition, to ens∑αure the strength of  ←∏the conditions as far as possible to use u✔±®ltra-low carbon austenitic stainless ₩₩§steel welding rod, to£↑×> reduce the possibility of≠✔÷∑ carbon precipitation and inte>♦λ≥rgranular chromium depletion.