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  • 储罐焊接的操作流程
  • 本站编辑:杭州萧山升达防腐设备厂发布日期:2019.11.17
 
 
储罐焊接工程比较常见,特别是大型储罐焊接要求比较严格,这里以大型立式储罐为例简单介绍一下储罐焊接工程的操作过程及焊接技巧。
 
立式圆筒形储罐是由中心轴垂直于地面的圆形罐壁、平的圆盘形罐底和不同形式罐顶组成立式罐体,由立式罐体、附件(如梯子、平台等)及配件(如液面测量、消防设施等)构成的储罐。一般公称容积大于100m³的储罐称为大型储罐,标准采用:GB50128-2005。
 
一,储罐基础
 
储罐基础是储罐安放的地方,要求结实、牢固;它不仅影响美观,而且会导致储罐受力不均。储罐基础属土建范畴,必须按基础施工图及技术标准要求。储罐安装前必须对储罐的基础进行检查,合格后方可安装。
 
二,预制组装
 
对于大型立式储罐制造,一般进行分部、分段预制及组合,然后再总装,对于提高生产效率很有帮助,首先应对建造储罐选用的材料和配件进行复验,标准采用:GB74003-88应达到Ⅲ级标准为合格。预制组装内容包括:底板、壁板、浮顶和内浮顶、固定顶顶板、抗风圈、加强圈、包边角钢等构件、部件。
 
三,储罐的焊接
 
1,焊接工艺评定
 
对于首次使用的钢种,应根据钢号、板厚、焊接方法及焊接材料等,按国家现行的标准规定进行工艺评定,以确定合适的焊接工艺。焊接工艺评定采用对接焊缝试件及T形角焊缝试件,其中对接焊缝试件做拉伸试验和横向弯曲试验。
 
2,焊工要求
 
对于从事焊条电弧焊、埋弧焊以及气电立焊的普通焊工,通常应按GB50236-1998进行考核;对于按“特种设备焊接操作人员考核细则”考试合格并取得质量技术监督部门颁发的钢材类别、组别和试件分类代号合格证的焊工,可以从事储罐部位的焊接,不需要再考试。
 
3,焊前准备
 
为了保证焊接质量,焊接设备应满足储罐焊接施工的要求,对于抗拉强度σb≥430MPa、板厚≥13mm的罐壁对接焊缝应采用低氢型焊条施焊。焊材焊前应按产品说明书或 图1 的规定进行烘干和使用,烘干后的低氢型焊条应保存在100℃~150℃的保温筒内,随用随取。值得一提的是密封的药芯焊丝和密封盒装的药芯焊丝原则上不再烘干,药芯焊丝烘干后应冷却至室温才能使用。
 
4,接施工
将合格的钢板清理干净,按图要求制作好坡口,进行定位焊接需夹具的一定要固定牢靠。每段定位焊缝的长度,普通碳素钢和低合金钢不宜小于50mm;屈服强度大于390MPa的低合金钢不宜小于80mm。在焊接前应检查组装质量,清除坡口面及坡口两侧20mm范围内的泥沙、锈蚀、水份、和油污、垢等,并应从分干燥。
 
焊接中因保证焊道始端和终端的质量,始端应在坡口内采用后退起弧法,必要时可采用引护板;终端熄弧时应将弧坑填满;多层焊的层间接头应错开。注意:引弧与熄弧都应在坡口内或焊道上。双面焊的对接接头在背面在焊接前应清根,当采用碳弧气刨时,清根后应用砂轮修磨;当σs≥390MPa时,清根后应进行渗透探伤。板厚大于6mm的搭接角焊缝至少焊两遍。
 
特殊天气不得进行焊接,如:雨天、雪天;手工焊时风速≥8m/s;气电立焊或气体保护焊时风速≥2m/s;普通碳素钢<-20℃;低合金钢<-10℃;σs≥390MPa的低合金钢<0℃;大气相对湿度≥90%。预热温度应根据钢板的材质、厚度、接头拘束度、焊接材料及气候条件等因素,经焊接性试验及焊接工艺评定确定,预热时应均匀加热,预热的范围不得小于焊缝中心线两侧各3倍板厚,且不小于100mm。预热温度应用测温笔、表面温度计、红外测温仪等测量。对于焊前预热的焊缝,焊接层间温度不得低于预热温度。
 
需要后热进行消氢处理的焊缝,应在焊接完毕立即进行销氢处理,加热温度一般为200~350℃,保温时间不少于0.5h(参考标准:JB/T4709-2000)。对于焊接强度不同的钢材时,宜选用与强度较低的钢材相匹配的焊接材料,选用与强度较高的钢材相应的焊接工艺。焊接不锈钢储罐时,焊前应将坡口两侧20mm范围内的水、油、污垢清除干净,在100mm范围内涂白垩粉或防飞溅涂料;奥氏体不锈钢在保证焊透及熔合良好的条件下,应选用小线能量、短电弧和多层多道焊工艺,层间温度不宜高;耐蚀性要求高的双面焊缝或表面与介质接触焊缝应最后施焊;不锈钢储罐在进行酸洗、钝化处理时,要注意保护环境。
 
焊接不锈复合钢板储罐时,应严防基层和过渡层焊条熔敷在覆层上;焊接过渡层时为减少合金元素的稀释,宜选用小电流、窄焊道、短电弧焊接;焊接覆层时应将落在覆层坡口表面的飞溅仔细清理干净,最后覆层施焊。
 
5,储罐的焊接顺
 
在储罐制造过程中,为了减少焊接变形,保证储罐尺寸以及减少焊接应力,除了必要的夹具,焊接顺序非常重要。
 
中幅板,焊接时应先焊短焊缝后焊长焊缝;焊长焊缝时,焊工应均匀对称布置,由中心向外施焊,第一层焊缝采用分段退焊或跳焊。
 
边缘板,首先焊接边缘板外侧位于罐壁下方的300mm对接焊缝;然后焊接罐壁与罐底连接的角焊缝,角焊缝焊完后,焊接边缘板剩余的对接焊缝,焊工应对称布置,由外向里施焊;再后焊接底板、边缘板与中幅板之间的搭接焊缝,这条环焊缝有较多的搭接量以补偿收缩变形,常被称作收缩缝。焊接收缩缝时,焊工应对称布置,沿同方向施焊,首层用分段退焊或跳焊。
 
罐底与罐壁环形角焊缝时应由数对焊工分别对称布置在罐内和罐外,罐内焊工约在罐外焊工前方500mm处,然后沿同一方向分段施焊,首层焊道采用分段退焊或跳焊。
 
罐壁,应先焊纵向焊缝,再焊环向焊缝底圈纵向焊缝焊完后再焊底圈罐壁与罐底的角焊缝;其它相邻两圈壁板的纵缝焊完后,再焊其间的环向焊缝,焊接时焊工对称布置,沿同一方向施焊;
 
固定顶顶板,先焊顶板内侧的断续焊缝,再焊外侧长焊缝,连续焊缝应先焊环向短焊缝,再焊径向长焊缝,由中心向外分段退焊。
 
包边角钢,它与壁板对接时应先焊角钢连接的对接焊缝后焊角钢与罐壁的对接焊缝;包边角钢与壁板搭接时,在焊完角钢的对接焊缝后,再焊角钢与壁板的搭接焊缝。
 
浮顶,对于船舱内、外侧边缘板,应先焊纵焊缝,后焊角焊缝;单盘板、船舱底板、船舱顶板的焊接顺序与中幅板的焊接顺序相同;对于船舱与单盘板的连接应待船舱和单盘板全部焊缝焊完后再进行焊接,焊接时焊工均匀对称分布,分段退焊;浮顶如直接在罐底铺设组装时,其下表面所有焊缝应待浮顶升起并落到支柱上后再进行焊接。
 
对于不锈钢储罐的罐底与罐壁连接的角焊缝,为了防止过热,不应罐内、罐外同时施焊,应先焊罐内侧角焊缝,再焊罐外侧角焊缝。
 
6,储罐的返修
 
在制造、运输和施工过程中免不了产生各种表面缺陷(如划伤、电弧擦伤、焊疤等),只须打磨修整即可,但修整后的钢板厚度应大于或等于钢板公称厚度减去允许负偏差值。当打磨深度超过1mm时,应进行焊补。
 
焊缝内部超标缺陷返修前,应探测缺陷的位置及深度,确定确陷的清除范围,清除的深度不宜超过板厚的2/3,大于板厚2/3的缺陷应从两面清除。返修后的焊缝应按规定的方法进行探伤,并要达到合格标准。返修焊接时焊道长度不应小于50mm。同一部位的返修次数不宜超过2次,否则须施工单位技术总负责人同意。
 
对于σs≥390MPa的低合金钢,缺陷清除后应进行渗透探伤确认缺陷清除后方可返修焊接,焊接时宜采用回火焊道,焊后应打磨及修磨,使其表面平滑并进行渗透探伤或磁粉探伤;当焊接缺陷深度超过3mm时,应对返修部位进行射线探伤。
 
五,储罐的工程验收
 
储罐竣工后,建设单位应按设计文件和标准对工程质量进行全面检查和验收,施工单位应提交的完工资料有:储罐交工验收证明书;竣工图或施工图(附设计修改文件及排料图);材料和附件出厂质量合格证书或检验报告;储罐基础检查记录;储罐管体几何尺寸检查记录;隐蔽工程检查记录;焊缝射线探伤报告;焊缝超声波探伤报告;焊缝磁粉探伤报告;焊缝渗透探伤报告;焊缝返修报告;强度及严密试验报告;基础沉降观测记录。
 
 
 
When welding stainless steel composite tank, prevent the base layer and transition layer welding electrode on the cladding layer. In order to reduce the dilution of alloy elements, it is advisable to select small current, narrow pass and short arc welding. When welding cladding should fall on the surface of the cladding groove splash carefully cleaned, finally cladding welding.
 
 
5. Weld the tank smoothly
 
 
In the process of tank manufacturing, in order to reduce welding deformation, ensure tank size and reduce welding stress, in addition to the necessary fixture, welding sequence is very important.
 
 
For plate with medium amplitude, short weld should be welded before long weld. When welding long welds, welders should be evenly symmetrical layout, from the center to the outside of the welding, the first layer of welding using segment-back welding or jump welding.
 
For the edge plate, firstly weld the 300mm butt weld on the outside of the edge plate under the tank wall; Then weld the fillet weld of the connection between the tank wall and the tank bottom. After the fillet weld is finished, weld the remaining butt weld of the edge plate. Then weld the lap weld between the bottom plate, the edge plate and the mid-width plate. This girth weld has more lap weld to compensate for the shrinkage deformation, which is often called the contraction joint. When welding shrinkage seam, the welder should be symmetrical layout, welding along the same direction, the first layer with section back welding or jump welding.
 
The circular fillet weld between the bottom and the wall of the tank should be arranged in the tank and outside the tank by several pairs of welders, the welder inside the tank is about 500mm in front of the welder outside the tank, and then the welding should be carried out in sections in the same direction. The first layer of welding bead should adopt section back welding or skip welding.
 
For the tank wall, the longitudinal weld should be welded first, and then the fillet weld between the tank wall and the tank bottom of the bottom ring should be welded after the longitudinal weld is finished. After the longitudinal seam of other adjacent two rings of wall boards is welded, the circumferential weld between them is welded. During the welding, the welder is arranged symmetrically and welded in the same direction.
To fix the top roof, discontinuous weld on the inside of the roof shall be welded first, and then long weld on the outside. Continuous weld shall be welded with ring to short weld first, then radial long weld, and backweld from center to outer section.
 
When the Angle steel is welded with the wall panel, the butt weld of the Angle steel should be welded first and then the butt weld of the Angle steel and the tank wall. After welding the butt weld of the Angle steel, the lap weld of the Angle steel and the wall plate shall be welded.
 
Floating roof, for the cabin, the outside of the edge plate, should first weld longitudinal weld, then weld fillet weld; The welding sequence of single-plate plate, cabin bottom plate and cabin roof is the same as that of mid-amplitude plate. As for the connection between the cabin and the single plate, the cabin and the single plate shall be welded after all the welding seams are finished. During the welding, the welder shall distribute evenly and symmetrically. When the floating roof is directly laid and assembled on the bottom of the tank, all the welds on the bottom surface should be welded after the floating roof is raised and falls on the pillar.
For the fillet weld of the connection between the bottom of the stainless steel tank and the tank wall, in order to prevent overheating, welding shall not be carried out in the tank and outside the tank at the same time. The inner fillet weld shall be welded first, and then the outer fillet weld shall be welded.
6. Tank repair
In manufacturing, transportation and construction process inevitable produce all sorts of surface blemish (if scratch, arc is scraped, weld scar to wait), just burnish is trimmed can, but the steel plate thickness after dressing should be greater than or equal to steel plate nominal thickness minus allowable negative deviation value. When the grinding depth exceeds 1mm, weld repair shall be carried out.
Before repair, the position and depth of the defects should be detected and the clearance range of the defects should be determined. The clearance depth should not exceed 2/3 of the plate thickness, and the defects larger than 2/3 of the plate thickness should be cleared from both sides. The repaired weld shall be inspected according to the specified method and shall meet the qualified standard. The length of weld bead shall not be less than 50mm during repair welding. The number of repair of the same part should not exceed 2 times, otherwise the construction unit must agree with the chief technical person in charge.
For the low alloy steel with ≥390MPa, the defect should be confirmed by penetrant inspection after the defect is removed, and the repair and welding can be done after the defect is removed. The backfiring pass should be adopted for welding, and the surface should be polished and polished to make it smooth and conduct penetrant inspection or magnetic particle inspection. When the depth of welding defect exceeds 3mm, radiographic inspection shall be performed on the repaired part.
Acceptance of tank engineering。
 
 
 
 
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