API TR 655-2021

$21.45

Vapor Corrosion Inhibitors for Storage Tanks

Published By	Publication Date	Number of Pages
API	2021	28

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Category: API

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Description

1 Scope

1.1 General

1.1.1 The purpose of this technical report (TR) is to provide information to owner/operators regarding the use of vapor corrosion inhibitors (VCI) and to provide guidance for their use in corrosion protection of aboveground storage tank (AST) bottoms, specifically from soil-side corrosion of carbon steel. The VCI chemistries discussed in this document are from the amine-carboxylate group.

1.1.2 Certain practices recommended herein may also be applicable to metallic tanks in services other than hydrocarbon under special circumstances.

1.1.3 VCI manufacturers should be able to assist in determining the suitability of VCI use for each situation, along with proper concentration and application method for their products. VCI professionals working for the manufacturers or working in conjunction with the owner/operators will need information about the tank to make valid recommendations. Annex A provides a list of relevant information that may be required to make an informed decision.

1.1.4 The potential for corrosion can occur in void spaces where cathodic protection (CP) will not be effective because of oxygen concentration cells, from contaminants in the foundation pad, or contaminants that may ingress, such as water and oxygen. VCIs may be beneficial in these situations.

1.1.5 VCI molecules disperse through the foundation materials from their source based on their vapor pressure. Because these molecules are lighter than air, they will adsorb to the surface of materials in the foundation. Also, they have a higher attraction to steel than to the sand, gravel, concrete, or asphalt and other surfaces. Uniform distribution of the VCI source material is not required since the vapor pressure of the VCI molecules will eventually complete the distribution under the tank bottom.

1.2 Limitations

1.2.1 For VCIs to protect the tank bottom from soil-side corrosion, the tank foundation design shall provide a means to contain the VCI beneath the bottom.

1.2.2 While most manufacturers' VCI chemistries for use in tank bottom applications have similarities, each has unique characteristics and chemistries. Owner/operators should review the characteristics of the chemistries to determine which product best suits their needs.

1.2.3 In cases where API 651 identifies several foundation designs or details where CP may not be effective or may offer limited protection, VCIs may be an effective alternative or may work in conjunction with CP to improve protection.

1.2.4 VCIs volatize into vapors that may be inhaled. VCIs, in powder form, may create dust when handled. If engineering or administrative controls are not effective in reducing exposures, proper PPE should be worn when handling the VCI during installation. At very large concentrations, the dust may be combustible. Concentrations in air from mixing or applying VCI powder are considerably below the concentrations susceptible to combustion. Consult the Safety Data Sheet for additional information.

1.2.5 Since VCIs may be discharged to the ground at any time during installation and service, it is imperative that all federal, state, and local discharge permit requirements be followed. This may preclude the use of VCIs, depending on the jurisdiction’s discharge permit requirements.

1.2.6 When using VCI powder near welding operations, VCI powder shall not be in the weld zone. The powder is not combustible, but may affect the quality of the weld, as would other contaminants.

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