Replacement of 42 Anchor Bolts in a Mitsubishi–MAN Diesel Engine

At the Lower Base site in Saipan, Northern Mariana Islands, Alphatec Engineering was tasked by Commonwealth Utilities Corp. to repair the foundation of a Mitsubishi–MAN diesel engine (type 18V52/55B).

Installed in 1989 to drive a 13 MW brushless alternator, the unit had developed significant vibration problems, forcing a reduction in engine speed and compromising its efficiency.

Features

Client

Commonwealth Utilities Corp.

Final user

Saipan Main Power Plant

Project

Foundation Repair, Anchor Bolts Replacement, Regrout, Re-alignment and Re-choking

Equipment

Mitsubishi-Man Diesel Engine 18V52/55B

Work period

August – September 2016

Location

Lower Base, Saipan Northern Marianas Island

01 The Challenge and Strategy

The engine was affected by damage to its foundation: oil had infiltrated the gaps between the poorly grouted anchor bolts and the surrounding concrete, leading to weakened compressive resistance and ultimately causing a sheared crankcase bolt.

To stabilise the engine, a complete repair was essential. Alphatec Engineering developed a six-step process that included diamond core drilling, diamond wire cutting, removal of concrete blocks, installation of new anchor bolts alongside rebar and concrete replacement, and regrouting with high-performance ALPHATEC® 800 green epoxy grout.

02 Highlights

A specialised team was mobilised and, due to the site’s remote location, all necessary equipment was shipped to Saipan. The initial step involved cutting out concrete blocks with diamond wire to remove the existing, damaged 2.31 m anchor bolts.

With hydraulic jack units (Alphapads®) supporting the engine’s weight, the engine frame was carefully aligned. A fresh pour of replacement concrete lifted the level to 280 mm below floor level, and ALPHATEC® 800 epoxy grout was subsequently poured to achieve a secure finish.

Following the curing process, final alignment was carried out using a digital web deflection tool and the anchor bolt nuts were replaced with Supernuts to eliminate any residual movement in the crankcase.

03 Outcome

The comprehensive repair – encompassing removal of deteriorated concrete, installation of new 25CrMo4 steel anchor bolts (M39 x 1300 mm), and precise regrouting – restored the foundation of the engine.

The remedial work eliminated the excessive vibrations and enabled the unit to operate at full capacity, thereby ensuring continued productivity and enhancing safety in the power generation process.

The specialised epoxy grout used in the repair is rated to withstand compressive forces exceeding 12,000 psi, providing long-term durability for the foundation.