The benefits of SX valves

Valve Types and Material Selection in High-Strength Acid Circulation Systems

– Introducing the NORAM SX™ Triple-Offset Butterfly Valve

Operators in acid and sulfuric acid production are well acquainted with the wide range of valve types employed across a typical acid plant. These include everything from small sampling valves to large gas dampers, and commonly used valve designs such as plug, ball, check, and butterfly valves. This report focuses on valves used in strong acid circulation loops and introduces a new, innovative solution.

Valve Selection and Functional Requirements

Valve selection depends on several factors, including the intended function (control or isolation), the physical state of the media (liquid or gas), presence of solids, and the corrosiveness and chemical properties of the fluid. In a typical acid circulation loop—between the pump’s holding tank and the reactor tower inlet—large-diameter butterfly valves are often used for regulating the temperature of return acid, flow modulation, and balancing acid concentration and levels between storage tanks.

Triple-Offset Butterfly Valve – A Refined Solution

It’s often said, “a butterfly valve is just a butterfly valve.” However, this is a simplification. As George Orwell famously wrote in Animal Farm, “All animals are equal, but some are more equal than others.”

NORAM introduces a valve that is, in many ways, “more equal”—a triple-offset butterfly valve manufactured from NORAM SX™, a high-silicon austenitic stainless steel specifically developed for demanding applications in highly corrosive acid circulation systems in sulfuric acid plants.

A Shift in Plant Materials

Many facilities are moving away from traditional materials such as brick-lined carbon steel vessels and ductile iron piping in strong acid loops, transitioning instead to high-silicon stainless steels for piping and vessels. This raises a key question: Are equivalent valves available in these advanced materials?

The answer is yes—thanks to a collaboration between NORAM and Somas, a leading Swedish valve manufacturer. Together, they have developed and produced triple-offset butterfly valves in NORAM SX™, tailored specifically for the sulfuric acid industry.

The first NORAM SX™ valve was installed in 2014, and since then, NORAM has delivered these valves worldwide, replacing conventional designs in critical applications.

Technical Background – Offset Design

Butterfly valves are categorized by the degree and type of shaft offset relative to the centerlines of the pipe and disc:

Concentric Butterfly Valve: Centered shaft design. Economical, but higher friction and wear due to disc contact with the seat.

Single Offset: Shaft offset from the centerline of the pipe, reducing initial disc-seat friction.

Double Offset: Shaft offset from both the pipe and disc centerlines, improving wear resistance and service life.

Triple Offset: Adds a conical sealing interface between disc and seat, enabling zero-leakage performance and minimizing wear—ideal for hot, corrosive media such as sulfuric acid.

The NORAM SX™ Triple-Offset Valve – Key Features

This advanced design incorporates a unique disc profile optimized for precision control and tight shutoff in sulfuric acid processes, meeting EN 60534-4 Class V shutoff standards.

Material Properties and Construction

Corrosion Resistance: All wetted parts—excluding the seal—are manufactured from high-silicon stainless NORAM SX™. The seal is made of glass-filled PTFE, proven for use with concentrated sulfuric acid at temperatures up to 250°C, and is fully replaceable.

Seal Functionality: Unaffected by high flow velocities or temperature. Easily replaced via the front seal ring during maintenance intervals.

Construction: Body, disc, shaft, and packing box are robustly engineered to Somas’ high manufacturing standards, with thorough testing prior to shipment.

Shaft Packing: Designed to prevent sulfuric acid leakage along the shaft, thereby eliminating sulfate corrosion and shaft seizure.

Actuation Options: Available with manual or actuator operation (all major types supported).

Spare Parts: Complete sealing and packing kits are available for all valve sizes.

Logistics and Inventory

Lead times of 30+ weeks for critical valves are common in the industry. To counter this, NORAM maintains stock of standard valve sizes in Sweden, with custom configurations available for larger diameters. Unmachined valve components are also stocked, enabling complete assembly and delivery in 4–6 weeks.

Field Performance – Case Studies

20” Valve in Hot Acid: A South American sulfuric acid producer experienced repeated failures every 9–12 months due to leakage and shaft seizure. A NORAM SX™ valve installed in October 2020 has now been operating flawlessly for over 50 months.

6” Valve in Vibrating, Hot Acid: A plant that previously faced 1–2 month failure intervals replaced a problematic 6” valve with a NORAM SX™ unit in March 2024. It has now run trouble-free for over 11 months.

Fast Delivery for Critical Maintenance: During a scheduled shutdown in 2024, NORAM and Control Southern delivered a 20” valve with actuator in just six weeks, allowing the facility to stay on track with its operational timeline.

Text & Images: Noram Engineering & Constructors Ltd.