Curing for Paint and Coating
After application, the unvulcanized linings require to be vulcanized or cured. Depending upon the composition of the lining and the size of the vessel, vulcanization can be achieved through:
Vulcanization in autoclave (with steam and pressure).
Internal steam pressure vulcanization (treating the vessel as an autoclave).
Exhaust steam vulcanization (with steam only).
Chemical vulcanization (without steam).
Final curing shall be accomplished by following the supplier‟s recommendation for curing the particular sheet rubber lining as follows:
Smaller shop projects can be autoclave cured with steam under pressure that results in a shorter cure cycle. Atmospheric steam, internal pressure, hot boiling water, or chemical additive cures are typically used for field installations.
Atmospheric steam cure is the most common method for field installations and is performed by introducing steam into the vessel until the proper temperature is achieved. The temperature should be maintained for the time duration that is specified in the supplier‟s product data sheet or supplier‟s recommendations. Attention should be given to the placement of temperature monitoring devices to make certain that cold spots are not present during the cure cycle. In an internal pressure cure, the vessel acts as its own autoclave.
The vessel should be checked to see if it has been fabricated to withstand the pressure developed during this type of cure. Gauges and preset pressure relief valves must be in place to monitor both temperature and pressure. Hot water cure typically requires special recommendations
from the supplier.
Chemical cure is normally small and used after cure for post-curing defects found in the lining. Chemical cure rubber and curing agents are used for small areas or parts and for post cure repairs on vulcanized linings when it is in the specification to allow for such repairs.
3.9 Inspection
Upon completion of cure, the lining is to be spark tested and a check of the Hardness against the manufacturer’s specification. Post cure inspection is typically performed using Shore A or D durometer instruments, which measure the hardness of the lining. Acceptable hardness ranges should be provided by the rubber lining supplier. Other ASTM tests for adhesion and peel testing are also typically performed and can be used to verify the overall suitability of the application.
These tests are destructive and can be performed on test panels prepared with the same process as the vessel or tank, including all steps in pre-cure inspection: visual check for entrapped air (blisters), loose seams, and spark tests for pinholes. The supplier must provide verified data on the
correct values for all linings in their product data information.
Guidelines and instructions that must be followed on conducting the lining work are covered Section 10, 11 and 12 of this manual. They are general same as described for coating jobs.
3.10 Handling And Storage Of Materials
All materials shall be shipped, handled and stored in accordance with manufacturer’s instructions.