Inspectioneering Journal

The Effect of Operating Conditions on Corrosion in HF Alkylation Units - Part 2

By Jonathan D. Dobis at JDD Consulting Inc., Dana G. Williams at Marathon Ashland Petroleum LLC, and David L. Bryan, Jr. at Marathon Ashland Petroleum LLC. This article appears in the July/August 2004 issue of Inspectioneering Journal.
This article is part 2 of a 2-part series.
Part 1Part 2


The following is the final part of a 2 part series. Part 1 covered the following considerations that are critical in establishing effective reliability and inspection programs for these complex units:

  • HF Alkylation Process Description
  • An extensive explanation of how HF alky unit process conditions affect corrosion for the various sections of these types of units

The abstract, introduction, explanation of terms, references, figures and a typical unit PFD are re- iterated in part 2 as reference materials.


Corrosion and fouling in HF Alkylation Units are closely linked to feed quality and operating conditions. This paper outlines the relationship between key operating parameters and corrosion that has been used to develop a set of guidelines to define an operating envelope. These guidelines have been used to benchmark operating units and to help maintenance and inspection groups understand how corrosion is directly affected by operating parameters. An example where this methodology has been used to troubleshoot operating problems is included. A web-based data collection system has been used as a tool to build a database of actual operating conditions found in the unit, and the corresponding problems or damage observed.


The methodology described in this paper was developed to help maintenance and inspection groups gain a better understanding of the manner in which corrosion is directly affected by operating parameters. Although much of this information is available to process licensees, it is generally not disseminated among the various disciplines in the refinery in a manner which can be clearly understood and applied.

Significant damage can occur when operating parameters drift outside recommended limits, or when licensor-recommended operating procedures are not followed. Except where noted, these issues apply to both UOP and Phillips licensed processes (1).

There has been considerable interest over the past several years in reducing the risk of operating HF Alkylation (HFA) Units1, but little information has been published on the effects of operating conditions. Most of the recent efforts have focused on ancillary issues including galvanic couples and the effect of residual elements in steel 2-7, and materials of construction guidelines 8-11, usually based on laboratory test data and/or exposures in anhydrous acid.

A noteworthy reference is the detailed work published by H. Helle12. This book contains significant information on corrosion and the effects of operating parameters, some of which is reflected in the discussions in this paper. Other relevant articles describing experience with HFA units identify the types of corrosion problems13-16; areas of vulnerability; and the use of hydrogen probes to monitor hydrogen activity 17.

Explanation of Terms

Several terms that are unique to HF alkylation units and that are used throughout this paper are defined below.

Acid Concentration is the concentration of hydrofluoric acid based on its water content. For example, a solution of 98 wt% HF concentration indicates that there is 2 wt% water in the acid.

This content is available to registered users and subscribers

Register today to unlock this article for free.

Create your free account and get access to:

  • Unlock one premium article of your choosing per month
  • Exclusive online content, videos, and downloads
  • Insightful and actionable webinars
Interested in unlimited access? VIEW OUR SUBSCRIPTION OPTIONS

Current subscribers and registered users can log in now.

Comments and Discussion

Posted by Senthurvadivelan Arunachalam on March 15, 2024
This article is useful for the HF handling... Log in or register to read the rest of this comment.

Add a Comment

Please log in or register to participate in comments and discussions.

Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Training Solutions

Improve your skills in key mechanical integrity subjects.

Case Studies

Learn from the experience of others in the industry.


Inspectioneering's index of mechanical integrity topics – built by you.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.


Read short articles and insights authored by industry experts.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.


Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

Videos & Webinars

Watch educational and informative videos directly related to your profession.


Commonly used asset integrity management and inspection acronyms.