1.1 本规程涵盖了测量聚乙烯储罐外壁中超声波速度的程序。横向纵向斜梁（L CR公司 )波浪由楔形物沿罐壁的周弦激发。数字超声波探伤仪用于通过传输模式发送接收搜索单元。对观察到的速度进行温度校正，并将其与与待评估材料相同的新未暴露材料样品的预期速度进行比较。观察到的速度和温度校正速度之间的差异决定了储罐的紫外线暴露程度。 1.2 本规程适用于聚乙烯罐壁的外表面。退化通常发生在约3.2 mm（0.125 in.）的外层厚的 由于该技术不会检测储罐内壁，因此除了了解储罐内壁可能的导波（兰姆）效应或反射外，壁厚不是一个考虑因素。除用干净抹布擦拭该区域外，无需特殊表面处理。内壁特性并不重要，因为纵波不会撞击该表面。必须通过选择激发频率来避免兰姆波的激发，使波长与壁厚之比小于等于五分之一。 1.3 外表面的紫外线降解导致材料硬化，杨氏模量和纵波速度增加。 1.4 以国际单位制表示的数值应视为标准值。括号中给出的值是英寸-磅单位的数学转换，仅供参考，不被视为标准值。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 测量材料中的超声波速度是一种独特的非破坏性确定物理特性的方法，物理特性可能因制造过程和环境攻击而变化。 速度与弹性模量直接相关，弹性模量可以根据环境暴露和制造过程而变化 CR公司 本文描述的方法能够测量表面上两个相邻点之间的速度，因此与对面墙上的条件无关。毫无疑问，该方法将应用于聚合物储罐以外的领域，并可能在生产线以及在役模式中进行检查。

1.1 This practice covers a procedure for measuring the ultrasonic velocities in the outer wall of polyethylene storage tanks. An angle beam lateral longitudinal (L CR ) wave is excited with wedges along a circumferential chord of the tank wall. A digital ultrasonic flaw detector is used with sending-receiving search units in through transmission mode. The observed velocity is temperature corrected and compared to the expected velocity for a new, unexposed sample of material which is the same as the material being evaluated. The difference between the observed and temperature corrected velocities determines the degree of UV exposure of the tank. 1.2 The practice is intended for application to the outer surfaces of the wall of polyethylene tanks. Degradation typically occurs in an outer layer approximately 3.2 mm (0.125 in.) thick. Since the technique does not interrogate the inside wall of the tank, wall thickness is not a consideration other than to be aware of possible guided (Lamb) wave effects or reflections off of the inner tank wall. No special surface preparation is necessary beyond wiping the area with a clean rag. Inside wall properties are not important since the longitudinal wave does not strike this surface. The excitation of Lamb waves must be avoided by choosing an excitation frequency such that the ratio of wavelength to wall thickness is one fifth or less. 1.3 UV degradation on the outer surface causes a stiffening of the material and an increase in Young's modulus and the longitudinal wave velocity. 1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Measuring the velocity of ultrasound in materials is a unique method for determining nondestructively the physical properties, which can vary due to both manufacturing processes and environmental attack. Velocity is directly related to the elastic moduli, which can vary based on environmental exposure and manufacturing process, The L CR method described herein is able to measure the velocity between two adjacent points on a surface and therefore is independent of the conditions on the opposite wall. Applications of the method beyond polymer tanks will undoubtedly be developed and examination may occur in the production line as well as in the in-service mode.