The use of reinforced thermoset plastic (RTP) vessels operating at pressures not exceeding 15 psig external and/or 15 psig internal above any hydrostatic head, which contain corrosive and otherwise hazardous materials, dictates the need for rules and/or stress analysis concerning materials of construction, design , fabrication, quality control, and inspection of such equipment. In developing rules for RTP, the Committee has adapted to RTP the principles of rules included in Section VII, Division 1, of the ASME Boiler and Pressure Vessel Code, wherever they are applicable
Adaptation of standard rules to RTP requires recognition of differences which exist between metallic materials and RTP. These differences are addressed in the remainder of this Introduction.
Materials and Assembly
In the absence of ASTM Standards, RTP laminate specifications (Appendix M-1) have been developed for use with this ASME Standard. These specifications include laminate composition and properties. Laminates (composites) manufactured by contact molding and by filament winding are covered.
These materials of construction are not available in commerce as mill shapes such as sheet and plate for forming and joining by the Fabricator. They are produced in situ on a mandrel or mold by the Fabricator during fabrication of RTP equipment components. Each Fabricator, as part of his shop qualification to this Standard, must demonstrate capability to produce laminates meeting the requirements of the laminate specifications.
Assembly of components such as shells, heads, and nozzles requires joining by secondary bonding. This operation involves fit-up, surface preparation, and over wrapping with a laminate of composition equivalent to the laminates being joined. Secondary Bonders must be qualified individually by the procedures detailed in Appendix M-7.
Design by formulas and by stress analysis are both included in this Standard. Consideration is given both to ultimate strength and to limiting strain. Time and temperature dependence of RTP laminate properties is recognized.
The ultimate stress consideration is required to assure safety against catastrophic failure over a reasonably long term. The design factors of Subparts 3A and 3B include consideration of variability of quality in the labor intensive fabricating operation. The strain considerations are required to assure long-term operation under cyclic stress (fatigue) without cracking the resin matrix of the composite laminate, thus maintaining maximum corrosion resistance. More than 20 years of successful experience, together with test data have shown these considerations to be valid.
Reliance is placed on careful auditing of the Fabricator's Quality Control Program and close visual inspection of equipment during fabrication and of finished equipment.
User's Basic Requirements Specification
It is the responsibility of the user, or an agent acting in his behalf , who intends that a vessel be designed, constructed, inspected, tested, and certified to be in compliance with this Standard, to provide or cause to be provided for such vessel a User's Basic Requirements Specification (UBRS). The UBRS shall set forth the intended operating conditions of the vessel to provide the basis for design and shall identify the external environment to which the vessel will be exposed, the intended function of the vessel, mechanical loads imposed on the vessel, specific installation requirements, and specific codes and laws applicable at the location where the vessel will be installed. The user also must specify within the UBRS the type of resin required or define the contents to which the vessel shall be exposed.