海洋工程锚链营运检验指南

海洋工程锚链营运检验指南 目 录 1 适用范围 1 2 检验间隔期 目的和范围 1 3 锚检查 3 4 锚转环检查 3 5 锚链检查衡准 3 6 导链器和锚机的检查 锚链系统 5 7 导缆器和绞盘的检验 钢丝绳系统 6 8 锚链附件的检查 6 9 钢丝绳的检验 8 10 参考文献 10 1 1 1 适用范围 本指南适用于拟按照船级社关于海上移动式平台要求入级的定位锚泊系统 的检查 临时锚泊设备应按船级社钢质海船入级规范进行检验1 2 2 检验间隔期 目的和范围 2 1 年度检查的间隔期为 12 个月 检验进行时 平台应位于作业吃水状态 定位锚泊系统处于使用状态 2 1 1 年度检查目的是确认锚泊系统在下一次年度检验前能 继续实施其预 定的用途 年度检验不应妨碍平台作业 如可行 年度检验应在重新就位迁移过 程中进行 2 1 2 年度检验范围限于绞盘或锚机附近的锚泊部件 根据平台上可见到的 锚泊部件 应对下述情况给予特别注意 锚链 掣链器和锚机链轮凹槽 以下简称 链槽 处锚链肩部的磨耗 链环在锚机链槽中的支撑状况 钢丝绳 变平的钢丝绳 断丝的钢丝绳 磨耗殆尽或腐蚀的钢丝绳 验船师应根据平台作业记录判定在过去的 12 个月内锚泊系统是否出现诸如 断丝 机械损伤 连接卸扣松动以及锚链或钢丝绳跳线等情况 如果年度检验表明可见的锚链或锚索损伤严重或对其管理疏忽 则应扩大检 验范围 凡发现以下典型损伤须进行更为全面的检验 锚链 链径减少超过 4 横档脱落 1 可参照中国船级社 钢质海船入级规范 相关要求执行 2 R4 级以上锚链的横档松动 会引起锚链损伤的已磨损锚链轮 即锚机滚筒 磨耗 钢丝绳 明显的变平或面积减少 会引起钢丝绳损伤的已磨损绞缆桶 严重的磨耗或腐蚀 断丝 2 2 特别检验 特别检验的间隔期为 5 年 其检验范围更为广泛 通常应在遮蔽水域内进行 船级社认为必要时 可缩短两次特别检验的间隔期 2 2 1 假定在间隔期内锚泊系统已得 到合适的保养和维修 特别检验目的是 确保在下一次特别检验前每根锚链能按其预定用途正常作业 2 2 2 特别检验项目应包括 所有锚链连接处的近观检查 100 必要时应予以清洁 扩大的 有代表性的无损探伤检验 5 普通锚链 20 有导缆器作用超过 5 年的锚链 所有连接卸扣 尺寸校核 检验长度须超过 5 个链环 2 2 3 应对下述情况给予特别注意 自上次检验以来在平台作业中与锚机和导链器经常接触的锚链 或钢丝 绳 部位 验船师应确信上述部位的锚链仍适宜在锚机和导链器处使用 连接卸扣的松动程度和销锁紧装置布置 全部锚机和导链器链槽应注意 链槽的异常磨耗或损伤 链槽磨耗速率 包括链环与链槽间相对磨耗率 链环和链槽的不匹配及在链槽中不适当的支撑 在起放锚操作中的锚泊系统的功能试验 并特别注意 链环和 或钢丝绳及连接卸扣在锚机和导链器槽上平滑通过 3 无跳链或其他不规则情况 2 2 4 应对约 1 的链环测量其厚度 直径 选取的链环 应大致均匀分布 在锚链工作段中 若外观检验结果表明恶化程度过分 极少 则上述检验比例可 予以增加 减少 2 2 5 所有已使用 4 年以上的肯特型和螺栓型连接卸扣均应予以拆开 并按 8 2 要求对所有的机加工表面进行磁粉检查 2 3 替代特别检验的循环检验 作为特别检验的替代方法 业主可选择进行循环检验 此方法系指在岸 上额外准备一根同等规格系泊缆 在每年度或其他合适的时间 通过轮流交 替方法 能将到检验周期的系泊缆循环回收陆地检验 3 3 锚检查 应检查锚冠 锚爪和锚杆的损伤 包括裂纹和弯曲 应检查锚卸扣销和锚冠 销 若发现磨损或弯曲过大应予以更换 可动锚爪应能在锚冠停止点之间转动自 如 弯曲的锚爪或锚杆应根据批准的工艺规程加热和适当的校正 其后还应进行 磁粉检查 4 4 锚转环检查 虽然转环已不再普遍采用 但由于啮合转环螺母螺纹的腐蚀已造成锚的失落 此类螺纹应予以仔细检查 若发现有严重的腐蚀 则转环应予以去除或更换 5 5 锚链检查衡准 5 1 所考虑的锚链类型 本节仅适用于横档是按下述方法之一固定的 海洋工程 或 石油平台级 锚链 链环闪光对接焊附近机械压牢和另一端填角焊 例如 IACS R3 级链 1 横档两端均为机构压牢就位 例如 IACS R4 级链 2 其他类型的锚链应予以特别考虑 1 IACS R3 级链相当于 CCS 材料与焊接规范 中 R3 级锚链 下同 2 IACS R4 级链相当于 CCS 材料与焊接规范 中 R4 级锚链 下同 4 海工锚链服役环境要比常规船锚链的服役环境更恶劣 海工锚链遭受作业载 荷的作用时间也较长 海水中循环载荷的长期作用将加大几何和冶金缺陷对疲劳 寿命的不利影响 此外 从统计观点而言 海工锚链链环数量的增多将使锚链更 易于破坏 由于 缺口 效应 例如链环上横档置入凹槽 高强度钢 如 IACS R4 级 锚链所采用的钢材 的疲劳强度与静拉伸强度比值要比典型的低强度钢低 如 IACS R3 级 锚链所采用的钢材 5 2 磨损和腐蚀引起链环直径减少 链径测量应在链环弯曲部位和任何严重磨耗或锈坑区域上进行 应对与锚机 或导链器链槽正常接触的肩部给予特别注意 最小横剖面面积小于原始名义面积 90 的链环应予以废弃 若允许修复 则 应由合格人员按照批准的工艺规程进行修理 注 对 IACS R4 R4S 和 R5 级锚链 不允许进行焊接修理 见 5 3 1 链径减少 5 等价于原始横剖面面积减少 10 应相隔 90 进行两次链径测量 并将平均链径测量值与原始链径 扣除允许的设计余量 进行比较 5 3 锚链横档缺陷的修复或更换 横档在链收放过程中将防止链打结或扭曲 并在承载时支撑两侧以减少拉伸 和弯曲应力 以延长疲劳寿命 横档脱落是不能接受的 脱落横档的链环应予以 去除或按认可的工艺规程重新安装横档 5 3 1 一端由填角焊固定的横档 如果横档松动或焊缝出现裂纹 则横档可能脱落 横档若有任何轴向或侧向移动是不能接受的 该链环必须修复或更换 链环不允许在闪光对接焊端焊接横档 在横档闪光对接焊端处横档和链环间的间隙超过 3mm 1 8 英寸 的链环应 考虑予以报废 如被允许 采用重新进行填角焊来闭合间隙的方法可予以考虑 应尽可能避免有裂纹焊缝的现场修理 如必须进行此操作 应由具备相应资 质的人员按认可的工艺规程施焊 注 对 IACS R4 R4S 和 R5 级锚链 不允许施焊修理 横档两端均靠机械压牢就位的锚链仅能按认可的机械 挤压 横裆复位工艺规程予以修复 不允许在横档两端施焊 在链环闪光对接焊缝邻近的横档端也不允许施焊 现有的两端焊接的横档需要特别考虑 并应进行专门的裂纹探测检查 一般将要 5 求降低闪光对接焊缝处的力学性能 并须经沿岸国主管部门的批准 5 3 2 靠压入配合和 机械锁紧的横档 锚链横档是否松动过大难以定量 应依据验船师对锚链总体情况的判定 确 定拒绝或是接受带有松弛横档的锚链 轴向移动为 1mm 或更小的横档时可以接受的 轴向移动大于 2mm 的链环必 须予以 挤压 修理或去除 轴向移动为 1 2mm 的链环是否允许使用必须根据 平台作业海域的环境条件和下次锚链检查的预期期限而定 不超过 4mm 的横档侧向移动是可接受的 5 4 链环修理 裂缝 凹坑和其他表面缺陷 不包括焊缝裂缝 可经打磨去除 只要链径的 最终减少不超过 5 D D 为链径 以及横剖面面积 由于腐蚀 磨耗和打磨引 起面积减少 不少于原始名义面积的 90 横剖面面积应按相隔 90 测量两个 直径的最小平均值计算 表面缺陷不能靠打磨去除的链环应予以更换 5 5 链环的更换 有缺陷的链环应予以去除 并用连接卸扣 即连接链环 遵照下述良好的海 事实践予以更换 替换连接卸扣应符合 IACS W22 或 API 2F 的技术要求1 连接卸扣应在水平面内通过导链器和锚机 因为连接卸扣的疲劳寿命比普通链环低很多 因此应尽可能地减少使用 平 均而言 两个连接卸扣至少应相隔 122m 400 英尺 如果大量链环应予报废且此类链环分布在整根锚链中 则该根锚链应以新链 替换 6 6 导链器和锚机的检查 锚链系统 6 1 导链器 检查应验证所有导链器在其正常操作必需的全部运动范围内均能绕各自的 1 相当于 CCS 材料与焊接规范 第 1 篇第 10 章第 3 节要求 6 Z 轴转动自如 所有螺栓 螺母及其他用于固定导链器的零部件均应予以检查 必要时应予以更换 导链器与船体的连接应经验证 必要时需进行无损探伤检查 注 存在着由于固定螺栓螺纹腐蚀造成导链器轴上封板的松动 并导致导链器设备严重损伤及使链和导链 器跳动的情况 因此应检查固定螺栓以保证如果导链器处牺牲阳极系统不起作用 螺栓材料仍不会先 腐蚀 6 2 锚机 应特别注意锚机的掣动能力 应检查掣链器及将载荷传递给平台结构的路径 并验证其坚固性 6 3 链槽和锚链支撑 位于链槽内的链环应仅在其四个肩部区域与导链器相接触 以避免链环内出 现危险的弯曲应力 对锚链支撑的可靠性应予以验证 必要时链槽的过大磨损应予以修理 以防 止进一步损伤锚链 锚槽可按由导链器 锚机制造厂提供的标准工艺规程焊补 一般 链槽的硬 度应比链环稍低 其焊补工艺规程必须是针对所用的锚链等级 7 7 导缆器和绞盘的检验 钢丝绳系统 7 1 导缆器 见 6 1 7 2 绞盘 应对绞盘的掣动能力 以及棘爪 棘轮行刹车设备的操作性予以特别关注 将合成载荷至平台结构的路径的坚固性应予以验证 钢丝绳在绞盘卷筒上的合适排列应予验证并使验船师满意 需要时将调整卷 筒和排缆机构 8 8 锚链附件的检查 8 1 一般要求 锚卸扣 大的无挡链环 转环和连接链环应进行外观检验 某些部位应进行 磁粉探伤检查 待检区域应在每个附件上打上清楚的标记 需要时链环和附件应 予以拆开 损伤的附件按现场验船师的要求应予更换 标明有关区域的图例可在 API RP 2I 图 6 中找到 7 需作磁粉检查区域的一般性指南如下所述 大的无档链环 大的无档链环的内接触面 锚卸扣 内接触面和销 转环 转环销 啮合螺纹和啮合面 8 2 连接卸扣 连接链环 8 2 1 实际情况说明 因为连接卸扣的失效 出现了一定数量的未到期锚和 链丢失现象 因此 对于没有等效证明文件 且用在高强度锚链上的连接卸扣 例如 ORQ 采油设备质量等级 及其以上等级1 检验应予特别关注 8 2 2 磁粉检查 所有使用超过 4 年的肯特型或类似型式连接卸扣都应拆卸进行磁粉检查 API RP 2I 图 7 给出了检查区域图示位置 需作磁粉检查区域的一般性指南如下所述 连接卸扣本体 所有链环扣加工面和打磨面以及链环弯曲部分的侧面 连接卸扣横档 仅扣加工面 连接卸扣销 100 8 2 3 疲劳被认为是衡量加工表面的关键衡准 在其它类型表面 上 外形应 打磨光滑 并在打磨完工后即刻进行磁粉检查 通常 打磨完工后所形成册槽的 半径最小为 20mm 沿链环轮廓线的凹槽长度应大于或等于其深度的 6 倍 注 磁粉捡查前喷砂可损伤机加工面 故应予以避免 应采作其他清洁方法 最大许用打磨深度为 5 的公称链径 由于局部打磨和全部腐蚀磨耗的组合效应 打磨修理处最小允许横剖面面积为 90 的名义横剖面面积 由于局部打磨和全面腐蚀磨耗的组合效应 打磨修理处最小允许直径为 95 的公称链径 8 2 4 全面 腐蚀 磨耗 由于均匀腐蚀磨耗所导致的最小允许横剖面面积为 90 名义横剖面面积 等 价于直径均匀减少 5 8 2 5 将连接链环的两个半环锁紧在一起的锥销在其两端应与链 环接触良 好 锥销大头上的钻孔凹孔应塞入铅条并锤紧塞牢以防止锥销松动 1 ORQ 级相当于 CCS 材料与焊接规范 海上设施系泊定位用锚链 R 级 8 8 2 6 重拼装后的松动性 任何重拼装后松动的肯特型或类似型式的连接卸扣须视具体情况作专门考 虑后才可予以接受 注 拼装面之间的松动将大大降低连接卸扣的剩余疲劳寿命 沿横档纵向超 过 0 5mm 的横档移动也可能大大降低连接卸扣的剩余疲劳寿命 9 9 钢丝绳的检验 9 1 接受衡准 接受衡准可从 ISO 标准 4309 得到 进一步的详细说明还可从 API RP 2I 图 18 和 19 给出的报废指南中得到 应注意 ISO 标准 4309 主要适用于起重设备 其安全系数可能比锚泊钢缆 高 验船师在阐明钢丝绳状况中应极其小心 状况明显时接受或拒绝是比较容易 的 但两种状况之内的 灰色 区域是难于评估的 验船师必须根据所有获得的 证据作出正确的评估和技术判断 通常 钢丝绳的服役年限或时间 除了作为验船师在确定检验范围时应考虑 的一个因素外 对接受或拒绝钢丝绳并没有直接的关系 9 2 检验和检查 应进行 100 的外观检验和直径测量 9 2 1 外观检验应对每根钢丝绳锚腿验证和记录下 述项目 断裂钢丝的性质和数量 接头处钢丝断裂情况 外部磨耗和腐蚀 钢丝断裂的集中程度 变形 股断裂 接头面积 钢丝绳直径的减少 包括绳芯破断或挤出 9 2 2 直径测量应以约 100m 的间距进行 并应由现场验船师来决定 如果 发现特别值得注意的部位 检验可集中在这些部位上 并应以更小的间距进行直 9 径测量 9 2 3 如果在下层部位中表明存在严重的内部腐蚀或绳芯的可能断裂或钢 丝破断 应视实际可能性进行内部检查 作为钢丝绳内部检查的指南 见 API RP 2I 3 3 6 3 9 3 钢丝绳损伤指南 钢丝绳失效原因可从所见到的钢缆损坏中推出 钢丝绳失效的大部分类型简 述如下 包括图像实例在内的 较详细的资料可从 ISO 标准 4309 和 API RP 2I 获得 9 3 1 接头处破断的钢丝表示其接头处存在高应力 这可能由接头安装错误 疲劳 过载 或敷设 回收过程中的操作错误等所造成 1 分散型破断钢丝 由 API RP2I 图 9 12 可表明其破坏的原因 绳股顶处冠部断裂或单根钢丝的破断可由过大的张力 疲劳 磨耗或腐蚀所 造成 过大的张力可由钢丝断口的颈缩所表明 疲劳由断裂面垂直于钢丝轴线所表明 腐蚀和磨耗可由钢丝横剖面的减少所表明 两股界面处谷部断裂表示绳股绷紧 通常由破断的绳芯或使绳芯直径减少的 内部腐蚀所造成 谷部断裂可能由高的载荷 紧的滑轮和相对于钢丝绳直径显得太小的滑轮所 造成 2 局部集中在单根股或相邻股中的断裂钢丝可因局部损坏所造成 一旦形成 此种损伤通常将持续恶化 9 3 2 钢丝绳直径的变化可由外部磨耗 钢丝间或 股间磨损 拉伸或腐蚀所 造成 钢丝绳直径的局部减少可表明绳芯断裂 相反 钢丝绳直径的增加可表明 腐蚀导致绳芯胀大 9 3 3 钢丝绳外层股冠部处磨耗可根据腐损部位由与导缆器 平台 结构或海 床间摩擦所造成 钢丝绳内各股间或各根钢丝间的内部磨损是由互相摩擦造成的 并因钢丝绳 弯曲和腐蚀加速磨损 9 3 4 腐蚀减少横剖面面积从而降低钢丝绳强度 腐蚀会招致应 力裂纹的不 10 规则表面从而加快疲劳 腐蚀可由下述情况表征 导缆器处钢丝绳直径将变小 静止不动钢丝绳直径实际上将增大 是因外层股下锈蚀所致 对系泊缆 直径增大是很罕见的 9 3 5 变形 即钢丝绳已出现与其正常结构不同的变化 可引起绳 中不均匀 的应力发布 纽结 弯曲 摩擦 断裂和变平是钢丝绳通常的变形 稍有变形钢 丝绳的强度损失不大 严重的变形可加快钢丝绳的退化 并导致过早的破坏 9 3 6 热损 坏 虽然它在锚泊钢缆正常营运中很少发生 仍可用变色来表明 对由过高或过低温度造成的损坏应给予及时的注意 除了已知非常低的温度对润 滑剂会产生有害的影响外 其对钢丝绳的其他影响尚不清楚 1010 参考文献 10 1 钢丝绳 API RP2I 和 ISO 标准 4309 关于 ISO 标准 见 9 1 10 2 锚链 API RP2I 浮式钻井平台锚泊部件营运检查的推荐标准 No 38 Page 1 of 9 IACS Rec 1995 Rev 1 2010 No 38 cont Guidelines for the Survey of Offshore Mooring Chain Cable in Use 1 Application and Purpose The information herein is intended to provide guidance to Surveyors for inspection of position mooring systems which have been classed by the Society for Mobile Offshore Drilling Units Temporary mooring equipment is to be surveyed under the Rules for Building and Classing Steel Vessels of the Classification Society 2 Survey Interval Purpose and Extent 2 1 Annual Surveys are to be conducted at approximately twelve 12 month intervals with the vessel at operational draft with the position mooring system in use 2 1 1 The purpose of the Annual Survey is to confirm that the mooring system will continue to carry out its intended purpose until the next annual survey No disruption of the unit s operation is intended Ideally the Annual Survey would be done during a relocation move 2 1 2 The scope of the Annual Survey is limited to the mooring components adjacent to the winch or windlass Depending on the mooring component visible from the unit particular attention should be given to Chain Wear on the chain shoulders in way of the chain stopper and windlass pockets Support of chain links in the windlass pockets Wire Rope Flattened ropes Broken wires Worn out or corroded ropes The surveyor should determine if any problems have been experienced in the previous twelve 12 months period with the mooring system e g breaks mechanical damage loose joining shackles chain or wire jumping If the Annual Survey reveal severe damage or neglect to the visible part of chain or cable a more extensive survey should be performed Typical damage warranting a more comprehensive survey could be Chain Reduction in diameter exceeding 4 Missing studs Loose studs in Grade 4 chain Worn out cable lifters i e gypsies causing damage to the chain Wire Rope Obvious flattening or reduction in area Worn cable lifters causing damage to the wire rope Severe wear or corrosion Broken wires No 38 1995 Rev 1 Oct 2010 No 38 Page 2 of 9 IACS Rec 1995 Rev 1 2010 No 38 cont 2 2 Special Periodical Surveys are carried out at intervals of approximately five 5 years and will require extensive inspection usually associated with a sheltered water visit When considered necessary by the Society the interval between Special Periodical Surveys may be reduced 2 2 1 The purpose of the Special Periodical Survey is to ensure that each chain is capable of performing its intended purpose until the next Special Periodical Survey assuming that appropriate care and maintenance is performed on the mooring system during the intervening period 2 2 2 The Special Periodical Survey should include Close visual examination of all links of mooring chains with cleaning as required Enhanced representative NDT sampling 5 on general chains 20 on chain which has been in way of fairleads over last five 5 years All connecting links Dimension checks including length over five 5 links 2 2 3 Particular attention should be given to Those lengths of chain or wire rope which have frequently been in contact with the windlass and fairleads during the unit s operation since the last survey The Surveyor should ensure that these lengths are rated for use in the way of the windlass and fairlead The looseness and pin securing arrangements of the joining shackles All windlass and fairlead chain pockets for Unusual wear or damage to pockets Rate of wear on pockets including relative rate of wear between links and pockets Mis match between links and pockets and improper support of the links in the pockets A functional test of the mooring system during anchor handling operation for Smooth passage of chain links and or wire rope and joining shackles over the windlass and fairleads pockets The absence of chain jumping or other irregularities 2 2 4 The thickness diameter of approximately 1 of all chain links should be measured The selected links should be approximately uniformly distributed through the working length of the chain The above percentage may be increased decreased if the visual examination indicates excessive minimal deterioration 2 2 5 All joining shackles of the Kenter type and bolted type which have been in service for more than four 4 years should be dismantled and an MPI performed on all machined surfaces as per 8 2 No 38 Page 3 of 9 IACS Rec 1995 Rev 1 2010 No 38 cont 2 3 Special Continuous Surveys In lieu of a special periodic survey the Owner may opt for a Continuous Survey by providing an extra mooring line which may be regularly inspected on shore and exchanged with lines installed on the unit on an annual or other appropriate schedule 3 Anchor Inspection The anchor head flukes and shank should be examined for damage including cracks or bending The anchor shackle pin and crown pin should be examined and renewed if excessively worn or bent Moveable flukes should be free to rotate between stops on the anchor head Bent flukes or shanks should be heated and jacked back in place according to an approved procedure followed by Magnetic Particle Inspection 4 Anchor Swivels Although swivels are no longer in common use anchors have been lost due to corrosion of the threads engaging the swivel nut These threads should be carefully examined and if significant corrosion is found the swivel should be removed or replaced 5 Chain Inspection Criteria 5 1 Chain Types Considered This section applies only to Offshore or Rig Quality chains with studs secured by one of the following means Mechanically locked adjacent to the link s IACS R3 chain for example flash butt weld and fillet welded on the other end Studs mechanically locked in place on both ends IACS R4 chain for example Other types of chain will require special consideration The service environment of offshore mooring chain is more severe than the service environment for conventional ship anchoring chain Offshore chain is exposed to service loads for a much longer period of time The long term exposure to cyclical loadings in sea water magnifies the detrimental effect of geometric and metallurgical imperfections on fatigue life Moreover the increased number of links in offshore chains renders the chain more susceptible to failure from a statistical standpoint Due to the effect of notches e g the stud footprint higher strength steels such as that used for IACS R4 chain have a lower ratio of fatigue strength to static tensile strength than typical lower strength steel such as used for IACS R3 chain 5 2 Chain Link Diameter Loss due to Abrasion and Corrosion Diameter measurements should be taken in the curved or bend region of the link and at any area with excessive wear or gouging Particular attention should be given to the shoulder areas which normally contact the windlass or fairlead pockets No 38 Page 4 of 9 IACS Rec 1995 Rev 1 2010 No 38 cont Links with minimum cross sectional area less than 90 of the original nominal area should be rejected If repair is permitted it should be done by qualified personnel using an approved procedure Note WELD REPAIR IS NOT PERMITTED ON IACS R4 R4S and R5 CHAIN See paragraph 5 3 1 A 5 reduction in diameter is equivalent to 10 of the reduction in cross sectional area to original Two diameter measurements should be taken 90 degrees apart and the average compared with original diameter considering with allowable diminution 5 3 Chain Stud Defects and Repair or Replacement Studs prevent knots or twist problems during chain handling and support the sides of the links under load to reduce stretching and bending stresses resulting in longer fatigue life Links with missing studs should be removed or the studs should be refitted using an approved procedure 5 3 1 Chain Studs Secured by Fillet Welds on one End The stud is likely to fall out if it is loose or the weld is cracked Any axial or lateral movement is unacceptable and the link must be repaired or replaced Links with studs fillet welded on the flash butt weld end of the stud are unacceptable Rejection of links with gaps exceeding 3 mm 1 8 inch between the stud and the link at the flash butt weld end of the stud should be considered Closing the gap by renewing the fillet weld may be considered where permitted Field repair of cracked welds should be avoided Welding must be performed by qualified personnel using approved procedures Note WELD REPAIR IS NOT PERMITTED ON IACS R4 R4S and R5 CHAIN Chains with studs mechanically locked in place on both ends may only be repaired by an approved mechanical squeezing procedure to reseat the stud Fillet welding of studs on both ends is not acceptable nor is welding on the stud end adjacent to the link s flash butt weld Existing studs with fillet welds on both ends will require special consideration and will be subject to special crack detection efforts A reduction in mechanical properties in way of the flash butt weld will normally be required and approval of the coastal Administration may also be required 5 3 2 Chain Studs Secured by Press Fitting and Mechanical Locking It is very difficult to quantify excessive looseness of chain studs The decision to reject or accept a link with a loose stud must depend on the surveyor s judgment of the overall condition of the chain complement Axial movement of studs of 1 mm or less is acceptable Links with axial movement greater than 2 mm must be repaired by squeezing or removed Acceptance of chain links with axial movements from 1 to 2 mm must be evaluated based on the environmental conditions of the unit s location and expected period of time before the chain is again available for inspection No 38 Page 5 of 9 IACS Rec 1995 Rev 1 2010 No 38 cont Lateral movement of studs up to 4 mm is acceptable 5 4 Link Repairs Cracks gouges and other surface defects excluding weld cracks may be removed by grinding provided the resulting reduction in link diameter does not exceed 5 and the crosssectional area due to abrasion wear and grinding is at least 90 of the original nominal area Cross sectional area should be calculated for the lowest average of two diameters taken 90 degrees apart Links with surface defects which cannot be removed by grinding should be replaced 5 5 Chain Link Replacement Defective links should be removed and replaced with joining shackles i e connecting links guided by the following good marine practice The replacement joining shackle should comply with IACS W22 or API 2F Joining shackles should pass through fairleads and windlasses in the horizontal plane Since joining shackles have much lower fatigue lives than ordinary chain links as few as possible should be used On average joining shackles should be by 122 m 400 ft or more apart If a large number of links meet the discard criteria and these links are distributed in the whole length the chain should be replaced with new chain 6 Fairlead and Windlass Inspection Chain Systems 6 1 Fairleads Inspection should verify that all fairleads move freely about their respective Z axes to the full range of motion required for their proper operation All bolts nuts and other hardware used to secure the fairlead shafts should be inspected and replaced as required Fairlead attachment to the hull should be verified and NDT conducted as necessary Note There have been cases of closing plates on the fairlead shaft coming loose due to corrosion of the threads of the securing bolts resulting in serious damage to the f