20 April 2026

Project Overview

This project involved the design and manufacture of a large-capacity horizontal double-skin stainless steel sump tank engineered specifically for offshore application. The tank was developed to support waste oil management requirements on a North Sea offshore platform, where operational efficiency, safety, and environmental compliance are critical.

The solution delivered a robust and reliable means of collecting and storing waste oils over extended periods, significantly reducing the frequency of manual draining operations on the platform.

Operational Challenge

Offshore platforms generate waste oils as a by-product of routine operations. Traditionally, these wastes require frequent draining, increasing operational downtime, maintenance workload, and exposure risks for personnel.

The key challenge was to design a sump tank capable of:

• Safely storing large volumes of waste oil offshore
• Withstanding the harsh marine environment and platform installation constraints
• Reducing the need for frequent waste handling and transfer operations
• Complying with applicable offshore design codes and testing standards

In addition, the tank’s size, weight, and installation location introduced abnormal design considerations that required enhanced engineering validation.

Engineered Solution

The final solution was a 196 m³ horizontal, double-skin sump tank manufactured entirely from 316L stainless steel, selected for its high resistance to corrosion in offshore environments.

The tank was designed to operate across a wide temperature range and featured a segregated internal configuration to manage oil and water effectively. Its double-skin construction provides secondary containment, enhancing environmental protection and leak detection capability.

Key functional benefits included:

• Extended waste oil storage capacity
• Reduced operational intervention offshore
• Improved environmental safeguards
• Long-term durability in aggressive offshore conditions

Design and Engineering

The project followed a structured design lifecycle spanning approximately seven months, beginning with early conceptual design, and evolving into a fully detailed final design prior to fabrication.

Suretank’s engineering team is focused on providing engineering solutions for our customers. It’s what we do every day, because every product that we build is engineered exactly to our customer’s requirements.

Due to the tank’s large dimensions and offshore installation location, the engineering team carried out abnormal structural and pressure calculations beyond standard configurations. These assessments ensured the tank could safely withstand operational loads, transportation stresses, and installation constraints on the platform.

Materials, wall thicknesses, pressure ratings, and support structures were all optimised to meet offshore performance requirements while maintaining compliance with relevant industry standards.

Manufacturing and Quality Assurance

The tank progressed through a comprehensive production and inspection programme, including:

• Precision cutting and forming of stainless-steel plates
• Welding and fabrication of the internal vessel
• Fabrication of the external containment vessel
• Assembly and joining of both vessels into the final double-skin structure
• Handling and manoeuvring of an oversized fabricated unit

To ensure quality and integrity, an extensive testing regime was applied:

• Non-Destructive Testing (NDT) of welds
• 100% dye penetrant testing on critical pressure-retaining welds
• Hydrostatic testing of the inner and outer vessels (conducted separately)
• Factory Acceptance Testing (FAT) of installed equipment and interfaces

This rigorous approach ensured full confidence in structural integrity, leak tightness, and operational reliability before deployment.

Deployment Environment

The completed sump tank was manufactured for installation on the EA2 offshore platform in the North Sea, an environment characterised by:

• Corrosive saline conditions
• Limited space and strict handling constraints
• High safety and environmental compliance requirements

The tank’s design and finish were tailored accordingly, including passivated stainless-steel surfaces and offshore-grade protective coatings on structural elements.

Project Outcome

The delivered solution successfully met all operational and engineering objectives. Once installed, the tank enabled:

• Efficient collection and extended storage of waste oils
• Reduced frequency of waste drainage operations
• Improved safety for offshore personnel
• Enhanced environmental protection through secondary containment

The project demonstrates the ability to deliver large-scale, bespoke offshore storage solutions that combine advanced engineering, robust manufacturing, and stringent quality control — even where abnormal size and installation conditions apply.