AWS D10.10/D10.10M:1999 (R2009) An American National Standard
Recommended Practices for Local Heating of Welds in Piping and Tubing
AWS D10.10/D10.10M:1999 (R2009) An American National Standard
Approved by the American National Standards Institute October 20, 1999 Reaffirmed: May 5, 2009
Recommended Practices for Local Heating of Welds in Piping and Tubing
3rd Edition
Supersedes AWS D10.10/D10.10M:1999
Prepared by the American Welding Society (AWS) D10 Committee on Piping and Tubing
Under the Direction of the AWS Technical Activities Committee
Approved by the AWS Board of Directors
Abstract This standard provides information on recommended practices, equipment, temperature control, insulation, and advantages and disadvantages for the methods presently available for local heating of welded joints in pipe and tubing.
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Foreword
This foreword is not part of AWS D10.10/D1010M:1999 (R2009), Recommended Practices for Local Heat-ing of Welds in Piping and Tubing, but is included for informational purposes only. This recommended practice is intended to supply useful information to those with a need to apply heat to welds in piping and tubing under circumstances that do not permit placing the entire component in a furnace or oven. The first edition of the recommended practice prepared by the AWS Committee on Pip-ing and Tubing was approved and published as AWS D10.10-75, Local Heat Treatment of Welds in Piping and Tubing. The second edition, ANSI/AWS D10.10-90, was revised to bring the document abreast of the present “state-of-theart,” and to reemphasize certain important topics; particularly, thermocouple selection and placement, proper provision for insulation, and use of the radiant heating methods. The present edition of D10.10 has been extensively revised to: identify/consider related domestic and international codes, standards and practices; more fully recognize the range of purposes for local heating; introduce terminology for local heating; consider the issues affect-ing important parameters and provide recommendations for specifying these parameters; con-sider both local 360-degree band and spot heating; expand the information regarding thermo-couple location, attachment and accuracy; expand/update the information relating to insula-tion; expand the information regarding the thermal cycle; identify common process deviations and responses; introduce considerations regarding service environment; introduce quality as-surance system considerations; and update and emphasize the heating methods most com-monly used. During preparation of the present edition, it was attempted to include recommendations based upon the best available, most current data regarding local heating. In most cases, the recommendations given are based upon published research, with extensive references pro-vided. It is acknowledged that in some cases, the resulting recommendations may exceed the prevailing practice within industry, especially domestically. However, it is felt that the objec-tive of The documentcode is to present recommended practices based on an ordered assess-ment of available research and information, rather than a summary of current practice. Comments and suggestions for the improvement of this standard are welcome. They should be sent to the Secretary, AWS D10 Committee on Piping and Tubing, American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126. A formal reply will be issued after it has been reviewed by the appropriate personnel fol-lowing established procedures.
Recommended Practices for Local Heating of Welds in Piping and Tubing 管道焊缝局部加热的推荐实践 1. Scope 适用范围 These recommended practices describe several methods of applying controlled heat to weld joints and a limited volume of base metal adjacent to the joints, as opposed to heating the complete weldment in a furnace or oven. This standard makes use of both U.S. Custom-ary Units and the International System of Units (SI). The measurements are not exact equiva-lents; therefore, each system must be used independently of the other without combining val-ues in any way. U.S. Customary Units are listed first and SI Units are listed second in paren-theses ( ) when used in the text. 这些推荐的实践所描述了有关焊接接头和相邻接头于之有限体积母材在局部热处理应用控制上的一些方法，这有别于整体焊件件在热处理加热炉或热处理热处理箱。在本标准所使用的单位制包括了美国习惯的单位和国际单位制(SI)这两种，而这两种单位之测量值并非绝对相等的。因此，在任何情况下每个系统都必须独立使用而不能与另一单位制并用。在文本使用中所使用之美国习惯单位是列在国际制单位之前且国际制单位表示在括号中。
2. Reference Documents
参考文献
Extensive reference to local heating requirements found in common piping codes, stand-ards and practices is made to aid the user of the documentcode. These referenced codes, standards and practices are listed below. Except for bake-out and postheating, specific hold temperature and time requirements are not discussed. 对于一些常见之管道规范、标准和实践中已对局部加热要求给出了广博的基准，以帮助本规范使用户取得所需的讯息。
这些参考规范、标准和实践如下所列。
除热处理加热炉、热处理热处理箱和后热处理外，于本规范中不具体讨论持温之温度和持温时间要求。
2.1 Piping Fabrication Codes
管道制造规范
(1) Power Piping (ANSI/ASME B31.1), 1995 Edition, with addenda through 1997. ANSI/ASME B31.1 动力管道 – 1995 版含至 1997 之补遗
(2) Process Piping (ANSI/ASME B31.3), 1996 Edition, with addenda through 1997. ANSI/ASME B31.1 工艺管道 – 1996 版含至 1996 之补遗
(3) ASME Boiler and Pressure Vessel Code, Section III, Division 1—Subsection NB, Class 1 Components, Rules for Construction of Nuclear Power Plant Components, 1998 Edi-tion. (Note: Although direct reference is made to Subsection NB and its related paragraphs, Subsections NC and ND for Class 2 and 3 components have essentially the same require-ments.) ASME 锅炉与压力容器规范–1998第Ⅲ部 NB分卷《核设施 1级组件建造规范》。
(注：虽然直接引用 NB卷和其中之相关段落，但 NB卷 2 级组件和 NC卷 3 级组件在基本上具有相同的要求)。
(4) British Standard Specification for Class I Arc Welding of Ferritic Steel Pipework for Carrying Fluids (BS 2633), 1987 Edition, with Amendments to No. 2, July 1992.
英国标准规范 BS 2633-1987 with Amendment 1 & 2《Specification for Class I Arc Welding of Ferritic Steel Pipework for Carrying Fluids》。
2.2 Repair Codes
返修规范
(1) NBIC National Board Inspection Code (ANSI/NB-23), 1995 Edition, with Addenda through 1996. ANSI/NB-23-1995含 1996补遗。
(2) API Piping Inspection Code [Inspection, Repair, Alteration, and Rerating of In-Ser-vice Piping Systems] (ANSI/API 570), June 1993 Edition, with Supplements through #1, Jan-uary 1995. ANSI/API 570-1993管道检验规范《在役管道系统之检查、返修、更换和重新分等级》含至 1995 年 1 月增补之。
2.3 Recommended Practices Regarding Service Environment 有关工况环境之推荐作法
(1) Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments (NACE RP0472-95), 1995.
NACE RP0472–1995《在炼油腐蚀性环境中防止在役碳钢焊件产生裂纹之方法与控制》。
(2) Avoiding Environmental Cracking in Amine Units (ANSI/API 945), 1990.
ANSI/API 945 - 90《避免在胺装置环境介质中产生裂纹》。
3. Introduction
简介
These recommended practices consider the various issues associated with local heating of welds in piping and tubing. They specifically address application of controlled heat to the weld metal, heat-affected zone (HAZ), and a limited volume of base metal adjacent to the weld, as opposed to heating the entire component (piping or tubing system) in a furnace or oven. The recommended practices generally address issues associated with circumferential butt welds. As such, primary emphasis is given to considering local 360-degree band heating. However, limited consideration of local spot heating is also provided. Although aimed at lo-cal heating, various issues common to both local and furnace heating are also discussed.
在这些推荐做法中已考虑了与公称管道和管子管道中局部加热焊缝有关的各种问题；而这些推荐做法具体涉及到焊缝金属、热影响区(HAZ)和相邻于焊缝之有限体积母材的受控加热应用，这有别于将将公称管道或管子管道系统之整个节将放在炉或箱中加热。
推荐做法通常是为了解决与还向对接焊缝有关之问题， 因此，首要强调的是局部 360 度加热带上的问题考虑。
然而，还提供局部点加热的特定考虑。
尽管本规范是针对局部加热，但其中亦论及局部加热和炉中加热所共通的各项问题。
In the manufacture, field fabrication and/or repair of piping and tubing, it may be neces-sary to heat components before welding (bake-out or preheating) between passes (interpass heating) or after welding (postheating or postweld heat treatment [PWHT]). The docu-mentcode addresses all of these purposes for heating, with the main emphasis on PWHT. 公称管道和管子管道之制造、现场制造和／或返修中，可能需要在焊接之前前加热管节(烘烤或预热加热)以及在每道间加热(道间加热)或在管节焊接完成后再加热(后热或和焊后热处理)。在本规范中阐述了将具有在 PWH 主要重点应用到所有这些局部加热的目的。
Although heating of piping and tubing may be performed in a furnace, component size, convenience, or use of a process such as preheat/interpass heating may preclude the use of a furnace. In such cases, the weld and adjacent material may be locally heated by one of the methods discussed in these recommended practices. Local heating is also very common dur-ing field fabrication and/or repair of components. The method used will often be determined by the availability of equipment, the accessibility of the area to be heated, constraints im-posed by adjacent materials or components, and the type of heating operation to be per-formed.
尽管可以在炉中进行公称管道和管子管道的加热，但管节尺寸便于局部加热或诸如预热/道间所采用加热方法可不采用加热炉。
在此情况下，焊缝和相邻于材料之焊缝可藉由在那些推荐实践中所讨论共通知各种方法之其一进行局部加热。
在现场制造和/或管节返修期间应用局部加热乃常见之事。
所使用的方法通常是由设备的可用性、待加热带域的可接近性、相邻材料或管节施加的拘束性以及所要执行之加热操作类型来确定。
The need for PWHT is driven by code requirements and/or concerns regarding the service environment. So-called “code required” PWHT is generally aimed at improving resistance to brittle fracture. To accomplish this, PWHT attempts to improve notch toughness and relax re-sidual stress. When service requirements dictate the need for PWHT, additional objectives such as hardness reduction and/or stress relaxation aimed to be below a specific threshold level become important, depending upon the environment. The PWHT considerations and recommendations discussed in Section 6 are aimed at “code required” PWHT. Section 13 considers some of the issues and objectives associated with service environments and makes additional recommendations. The strategy followed in providing recommendations for local, “code required” PWHT was to attempt to duplicate the outcome of furnace heating (e.g., heating the entire component) within a localized region (soak band) surrounding the weld. While a similar strategy is applied to meet the additional objectives associated with service environments, the ability of furnace and/or local PWHT to meet these objectives must be carefully assessed based upon the specific environment. 对 PWHT 的需求源至于规范要求和/或涉及所关注工况环境。所谓的“规范要求的” PWHT通常旨在提高抗脆性断裂的性能。为了实现此目标，PWHT尝试提高切口韧性和消除残余应力。当工况要求指示对 PWHT的需求时，其旨在获得低于特定阈值水平的额外目标(例如硬度降低和/或应力消除) 就变得极为重要。第 6款中讨论到 PWHT所关注的项目和针对“规范要求之” PWHT提出建议；而 在第13 款则考虑了与工况环境有关的一些问题和目标，并提出了其他建议。为“规范所需之”局部 PWHT所提供之建议策略是试图让局部区域(均温带)内之周围焊缝能复制到如同在加热在炉中加热(例如，加热整个部件)的结果。
当应用类似策略以满足与工况环境相关的附加目标时，但加热炉和/或局部 PWHT是否能满足这些目标的能力仍必须基于具体环境进行仔细评估。
4. Purposes for Local Heating
局部加热之目的
Brief discussions of the purposes for bake-out, preheat/interpass heating, postheating, and PWHT are provided in this section. 在本款中对烘烤、预热/道间加热、后热和 PWHT之目的提出了简要地探讨。
4.1 Bake-Out.
Although a standard term for this process is not recognized by AWS, such heating is performed to remove hydrogen from material prior to manufacture, fabrication or repair activity. At the temperatures commonly used for such heating, removal of atomic hy-drogen (H), as opposed to molecular hydrogen (H 2 ), is generally the objective. Molecular hy-drogen which is trapped at voids such as inclusions, weld defects, blisters, etc. will not be re-moved unless the temperature is raised sufficiently to dissociate it to atomic hydrogen. The temperature required to accomplish such dissociation is typically near that used for PWHT. When molecular hydrogen is present, care must be exercised such that temperature and hy-drogen partial pressure do not result in conditions under which high temperature hydrogen at-tack can occur. As a result, temperature limitations may be imposed. 烘烤
尽管此加热方法之标准术语没有得到 AWS 的承认，但是在生产、建造或返修作业前进行这种加热以从材料中除去氢是其所公认的目的。在这个温度通常用来加热的目的是去除氢原子(H)，而绝对不是氢分子(H 2 ) 。在用于这种加热的温度下之主要目的是去除氢原子(H)，而绝非是氢分子(H 2 )。
除非温度升高到足以将氢分子解离为氢原子，否则将不会除去被困在空隙(例如夹杂物、焊缝缺陷、气泡等)处的氢分子。
实现解离所需的温度通常接近用于 PWHT的温度。
当存在氢分子时，必须注意温度和氢分压不会导致发生高温高温氢蚀，其结果是温度限度可能被限制。
One common source of hydrogen is the service environment, such as found in wet H 2 S ser-vice. Therefore, this heating is frequently applied to service exposed material prior to repair activity. The purpose for removing the molecular hydrogen is to prevent hydrogen-induced (delayed) cracking in the weld metal and/or HAZ. Since the objective is to facilitate diffusion to free surfaces, time-temperature parameters are selected such that sufficient molecular hy-drogen mobility is provided to accomplish the desired degree of removal during the allotted hold time. 氢常见来源是工况环境，例如在工况中所发现之湿硫化氢。
因此，这种加热经常应用于暴露材料之返修作业前。
除去氢分子之目的是防止焊缝金属和/或 HAZ 中可能因分子而诱发(延迟)龟裂。
由于加热目的是促进氢分子向自由表面扩散，所以在选择时间 - 温度参数时，被选参数应提供足够的氢分子迁移率以在所指定的持温期限内达到所期望的去除程度。
Considerations in selecting parameters include the following: 选择参数时的注意事项包括如下：
(1) Initial atomic hydrogen content (dependent upon welding process and/or service environment), 初期氢原子含量(取决于焊接方法和/或工况环境)，
(2) Desired final molecular hydrogen content (based upon knowledge of the critical level for the material), 所需的最终氢分子含量(基于对材料的临界水平的了解)。
(3) Hydrogen diffusion coefficient
as a function of temperature for the material,
氢扩散系数作为材料的温度系数，
(4) Diffusion path or distance to free surface (typically one-half of the material thick-ness),
扩散途径或距自由面的距离(通常为材料厚度的一半)。
(5) Model to describe the diffusion process, 描述扩散过程之类型
(6) Selection of temperature based upon knowledge of molecular hydrogen trapping, and 基于对被困氢分子的知识选择温度，和 (7) Temperature restrictions to avoid adverse effects upon the material. 温度限制，以避免对材料产生不利影响。
A detailed methodology for selecting hydrogen removal parameters is available (Reference 1). In most cases, a quantitative approach (e.g., one accounting for all of the above considera-tions) for the selection of parameters is not applied. Instead, experience-based parameters are used. The cited fabrication codes contain no guidance with regard to bake-out parameters. However, API 945 (see 4.5.3) does provide recommendations: 450°–600°F (230°–315°C) for 2 to 4 hours. When specifying experience-based parameters, it is recommended that time be specified as a function of thickness to account for the variable diffusion path, with a mini-mum time requirement. For example, 500°–600°F (260°–316°C) for 2 hours per inch (25 mm) of thickness, with 2 hours minimum, is reported (Reference 1) to be a reasonable ap-proach for carbon and low alloy steels. However, based upon concerns with regard to molec-ular hydrogen trapping, it appears prudent to use temperatures of 600°F (316°C) and higher. Temperature restrictions may need to be imposed to avoid high temperature hydrogen attack▲
and/or adverse metallurgical reactions such as temper embrittlement.
选择氢去除参数之可用方法论见参考文献 1。在大多数情况下，不应用于选择参数的定量方法(例如，考虑所有上述所考虑的方法)，反而是使用基于经验的参数。所引用的制造规范不包含有烘烤参数的指导。然而，在 API 945(见 4.5.3) 提供了烘烤参数的建议：在 450°至 600°F (230°至 315°C) 间持温 2至 4 小时。当指定基于经验参数时，所建议之持温时间是以厚度为参数，以考虑可变扩散路径，并且具有最小持温时间要求。例如，参考文献 1 报告了在 500°至 600°F (260°至 316℃) 间每英吋(25 mm)厚度为 2 小时(不满 1 英吋仍为 2 小时)，以最为钢碳和低合金的合理方法。然而，基于被困氢分子考虑时，使用≧600°F (316℃) 的温度似乎是谨慎的。应遵守持温度限度以避免高温氢蚀▲ (可参照 API RP 941)和/或不利的冶金反应，例如回火脆化。
▲ High Temperature Hydrogen Attack (HTHA) is an insidious condition that can occur in process equipment exposed to hydrogen at elevated temperatures (at least 400F or 204C), under dry conditions, when hydrogen disassociates into nascent (atomic) hydrogen, which is then driven into the steel by the tem-perature and pressure of the environment. The atomic hydrogen then reacts with unstable carbides in steel to form methane gas, which accumulates in the microstructural grain boundaries, eventually leading to crack-ing. This is often hazardous as the equipment usually contains hydrocarbons at high pressures and tempera-tures. HTHA is a time-temperature-pressure dependent phenomenon. This means the longer that a piece of equipment is exposed to temperatures and hydrogen partial pressures above its resistance limit, the more damage to the steel will accumulate; and the higher the temperature rises above the limit of the steel, the more rapidly the damage will occur. 4.2 Preheating and Interpass Heating.
These processes generally have the same pur-poses and are aimed at achieving the minimum preheat and interpass temperatures. The for-mer is applicable to the base metal immediately prior to the start of welding and the latter to the weld area (weld metal, HAZ, and adjacent base metal) prior to start of each pass in a multi-pass weld.
预热和道间加热。这些方法通常具有相同的目的并且旨在实现最低预热和道间温度。前者适用于刚要开始焊接之前的母材，并且在多道后续焊接中的每道次开始之前可以应用于焊接区域(焊缝金属，HAZ和相邻的母材)。
One reason for preheat/interpass heating is to prevent hydrogen cracking in the weld metal and/or HAZ. This objective is accomplished by the interaction of several effects includ-ing: driving off moisture prior to the start of welding, reducing the cooling rate, and increas-ing the rate of hydrogen diffusion. A second reason for preheating and interpass heating is the redistribution of solidification stresses that results from the greater time for this to occur af-forded by the slower cooling rate. A third reason for preheating and interpass heating is to re-duce the cooling rate in materials that form hard or brittle microstructural constituents when cooled too rapidly from welding temperatures. 预热/道间加热的原因是防止焊缝金属和/或HAZ中产生氢龟裂。该目的通过多种作用的相互作用来实现，其中包括：在焊接开始之前驱除水分，降低冷却速率和增加氢扩散速率。预热和道间加热的第二个原因是凝固应力的再分布，这是由于加热降低了冷却速率因而可得产生再分布的更长时间。预热和道间加热的第三个原因是降低当从焊接温度冷却得太快时，冷却速率快到足以在材料中形成硬或脆性微细晶粒结构。
The previously referenced fabrication and repair codes provide guidance or requirements regarding specific temperatures. The temperature requirements are typically based upon com-position (carbon equivalent) and thickness. These fabrication codes may also utilize pre-heat/interpass temperature requirements to provide exemptions from PWHT.
先前所提及之制造和返修规范提供了有关特定温度的指导或要求。温度要求通常基于组成(碳当量)和厚度。这些制造规范还可以利用预热/层间温度要求来提供对 PWHT的豁免。
More restrictive preheat/interpass heating requirements should be imposed for repairs in-volving highly restrained weldments and for specialized welding such as controlled deposi-tiontemper bead. In addition, for materials with higher hardenability and for welding pro-cesses or consumables with increased hydrogen potential, maintenance of preheat/interpass heating may be required until the application of postheating or PWHT.
对于涉及高拘束性焊件和专门焊接(例如受控沉积焊接)▲ 的返修，应有更严格的预热/道间加热要求。此外，对于具有较高可淬性之材料和具有增加氢势的焊接方法或焊接耗材，可能需要维持预热/道间加热，直到应用后热或 PWHT。
▲ Definition of Controlled-deposition welding: Any welding technique used to obtain controlled grain refinement and tempering of the underlying heat affected zone (HAZ) in the base metal. Various controlled-deposition techniques, such as temper-bead (tempering of the layer below the current bead being deposited) and half-bead (requiring removal of one-half of the first layer), are included. For reasons explained above, most welding procedures specify a minimum preheat/in-terpass temperature that must be maintained whenever welding takes place. Many welding procedures also specify maximum interpass temperatures, which should not be exceeded prior to depositing the next pass in the same area. A maximum interpass temperature may be specified for metallurgical reasons such as maintaining the notch toughness of ferritic steels or the corrosion resistance of austentitic stainless steels and some non-ferrous alloys. A maxi-mum interpass temperature may also be specified to protect the health and effectiveness of the welder. 由于上述原因，大多数焊接程序规定了在采用焊接时必须保持的最小预热/道间温度。许多焊接程序还规定了最大道间温度，在相同区域中沉积下一道次之前不应超过该最大道间温度。可以出于冶金原因规定最大层间温度，例如保持铁素体钢的缺口韧性或奥氏体不锈钢和一些非铁合金的耐腐蚀性。也可以规定最大层间温度以保护焊工的健康和效率。
4.3 Postheating . By definition, this process encompasses all heating performed after welding has been stopped (both after completion and at an intermediate point), including PWHT. However, it is generally recognized that postheating is performed at a lower tempera-ture, generally 300°–600°F (149°–316°C) versus 1000°–1400°F (538°–760°C) for PWHT, and with a different primary objective than PWHT. 后热。基于定义，该过程包括在焊接已经停止(在完成之后和在中间点处)时执行的所有加热(包括 PWHT)。然而，通常认为后热是在较低的温度[300°-600°F (149°-316℃) ]下进行加热，相对于 1000°-1400°F (538°-760℃) 之 PWHT来说是具有与 PWHT的不同主要目标。
The primary objective for postheating is the removal of hydrogen and the prevention of hydrogen-induced cracking. The latter is also known as delayed cracking since it can occur up to 48 hours after the weldment has been cooled to ambient temperature. This is of special concern when joining high strength and alloyed steels (other than austenitic stainless steels), when the potential for introducing hydrogen from the welding consumables or base metal is not adequately controlled, or when preheat/interpass heating is not sufficient. As such, much of the bake-out discussion in 4.1 is also applicable to this section. Depending upon the actual temperatures used, some degree of tempering may also occur. Also, the higher the martensite forming temperature in the HAZ and weld metal, the greater the self-tempering on cooling. 后热之主要目的是除去氢和防止氢诱导所产生的龟裂，而后者也被称为延迟龟裂，因它可在焊件冷却至环境温度后达 48 hr时后才发生。当从焊接耗材或母材引入氢的可能性没有被充分控制时，或者当预热/道间加热不充分时，这在接合高强度和合金钢(除奥氏体不锈钢以外)时是最有影响的。因此，4.1 中的大部分讨论也适用于本节。基于所使用的实际温度，也可能发生一定程度的回火。此外，HAZ和焊缝金属中的马氏体形成温度越高，冷却时的自回火就越大。
If postheating is deemed necessary due to concerns regarding hydrogen cracking, the minimum preheat/interpass temperature should be maintained until the application of such postheating. 如果考虑到氢裂化的问题而认为需要后热时，则应该保持最低预热/道间温度，直到应用后热。
Frequently, postheating is applied in situations where some delay is expected between the completion of welding and the application of PWHT. In those cases where it is not practical or cost effective to maintain the preheat/interpass temperature until PWHT, postheating may be used. Similarly, a delay may be necessary before completion of welding. Again, when and not practical to maintain the preheat/interpass temperature until welding is resumed, so-called “intermediate” postheating may be used. Another example is the use of postheating with con-trolled deposition welding as described below. 通常，后热是在焊接完成和 PWHT应用之间预期会延迟一段时间的情况下才会被应用。当维持预热/层间温度直到 PWHT是不实际时或基于成本效益考虑下，可以使用后热。类似地，在完成焊接之前可能需要延迟一段时间，且维持预热/层间温度直到重新开始焊接不实际时，可以使用所谓的“中间”后加热。另一个实例是使用具有如下所述的受控沉积焊接的后热方式。
Fabrication or repair code requirements for postheating are generally associated with tem-per bead or controlled deposition welding when used as an alternative to PWHT. For exam-ple, ASME Section III and NBIC provide such requirements. The Section III (paragraph NB-4622.9) requirement (for P-No. 1 materials) is 450°– 550°F (232°–288°C) for a minimum of 2 hours, while the NBIC (Part RD-1000) requirement is 500°–550°F (260°– 288°C) for a minimum of 2 hours. It is again recommended to specify time as a function of thickness to account for the variable diffusion path, with a minimum time requirement. Temperatures in the range of 500°– 600°F (260°–316°C) for 2 hours per inch (25 mm) of thickness, with 2 hours minimum, is consistent with requirements for carbon and low alloy steels found in vari-ous codes. However, based upon concerns with regard to molecular hydrogen trapping, it ap-pears prudent to use temperatures of 600°F (316°C) and higher. Temperature restrictions may also be necessary, as discussed in 4.1, due to adverse metallurgical reactions.
制造或修理的后热规范之要求通常是与替代 PWHT的回火焊道或受控沉积焊接相关联。例如，ASME 第 III部分和 NBIC提供了此类要求。NB-4622.9对于 P-No.1材料要求为在 450°至 550°F (232°至 288℃) 至少持温 2 小时，而 NBIC RD-1000的要求为在 500°至 550°F (260°至 288°C) 至少持温 2 小时。再次建议以指定持温时间作为厚度的参数，以考虑可变扩散路径，具有最小时间要求。在 500°至 600°F (260°至 316℃) 范围内的温度，每英寸 (25mm) 厚持温 2 小时，不足 1 英吋仍须持温 2 小时，这与在各种规范中所发现的碳和低合金钢的要求是一致。然而，基于被困氢分子考虑时，使用≧ 600°F (316℃) 的温度似乎是谨慎的。由于不利的冶金反应，温度限制也可能是必要的，如 4.1 中所述。
4.4 Postweld Heat Treatment (PWHT) . As discussed in the previous section, PWHT is performed after welding, generally at a higher temperature and with different objectives than postheating. As with postheating, PWHT may need to be applied without allowing the temperature to drop below the minimum for preheat/interpass.
4.4 焊后热处理 (PWHT) 。如前段中所讨论的，PWHT 是在焊接后进行，通常在与后加热不同的目的之更高的温度下进行。与后加热一样，可能需要限制 PWHT 温度和持温时间。
Local PWHT of carbon and low alloy steels is typically performed below the lower criti-cal trans...
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