Heat exchangers are complex, highly sophisticated pressure vessels, and never more so than when designed with the precision and thoroughness of computer-aided programs. In these circumstances, with the final design approaching nearer and nearer to the theoretical ideal, it is essential that they be fabricated to the required tolerances and to a high standard of workmanship. Thus inspection can no longer be regarded as a desirable appendage but must be an essential, built-in feature of the fabrication process. There are two inspection functions, the manufacturer’s own in-house quality control, and third- party inspection by approved authorities who are empowered to issue certificates acceptable to most international inspection authorities. The functions of the two inspection organizations are separate and independent, but complementary in requiring the same end result-a soundly constructed and safe heat exchanger.

Third-party inspection must, by virtue of its responsibilities to government legislation, be more comprehensive than in-house inspection, and commences with design assessment of the pressure-containing parts. Practice varies from country to country; in the United Kingdom normally triplicate copies of the construction drawings should be forwarded to the relevant inspection organization who, when satisfied with the design, will confirm their approval in writing or, if necessary, by stamping the drawings-retuming one copy to the manufacturer, forwarding a second to their inspector, and retaining the third copy. Manufacturers should not proceed with construction before drawings have been approved, and a similar arrangement should be followed with drawing revisions. It is generally necessary in the case of orders for export contracts that the drawings for approval and any revisions be forwarded in ample time to the appropriate inspection or certification authority of the country where the plant will eventually operate. The drawings should be translated into the language of the importing countiy, dimensions should be in the correct units, and the design should be strictly in accordance with the requirements and regulations applicable within the importing country. The recipient authorities will often delegate inspection to a recognized inspection authority in the manufacturing country or confirm the particular inspection arrangements. Once the drawings have been approved, the third-party inspection organization will carry out the required stage inspections to ensure that the completed vessel is constructed in accordance with the specification and the approved drawings. An important aspect of inspection is the scrutiny of radiograph films and ultrasonic reports and witnessing dye penetrant, magnetic particle, hydraulic, pneumatic test, etc., as required. Upon satisfactory completion of manufacture and testing, the vessel nameplate is branded with the inspection authority’s mark, and a certificate is issued.

It is normally necessary and indeed good practice for the manufacturer to produce a dossier containing copies of the approved drawings, material certificates, nondestructive testing results, welding certificates, and the inspection authority’s certificate. For certain countries details may have to be recorded in prescribed forms and, of course, there are usually additional requirements to be met; for example, some countries require by law that the copper rivet heads attaching the vessel nameplate be marked with the inspection authority’s stamp.

Close liaison between the manufacturer and the inspection authority is essential to ensure that the construction documentation is in order and acceptable to the overseas authority.