HRSG - Heat Recovery Steam Generation

TFL Responsive Engineering manufactured two HRSG plugs which were urgently needed at an oil rig in Thailand. Under the full-time observation of an independent inspector, TFL teams worked to build the two plugs in tandem to meet the strict deadline, while resolving issues related to the requirement of extremely tight tolerances on the diameters. The two plugs were completed on time and achieved the quality assurance requirements specified within the contract documents.

Two heat recovery steam generator plugs were required at short notice for a rig based in Thailand, to replace two that had failed during operation – leaving the rig unable to runs its steam turbines to generate electricity.

Assessing and problem-solving

The delivery deadline was critical: a specialist cargo plane had been booked to fly the plugs over to Thailand. On this project time was money. It was agreed that, to enable the deadline to be achieved, the two plugs would be built in parallel to each other, men working days and nights to reduce the manufacturing window. A detailed plan of manufacture was developed using Microsoft Project and agreed with the client prior to order acceptance. The client installed a full time third party inspector at our premises to witness ongoing production against a detailed inspection and test plan (ITP).

Accuracy was crucial: the plugs had to be manufactured to extremely tight tolerances on the diameters to ensure the plug would slide within its housing and seal it when closed. Tolerances specified required the tubular legs to be positioned in place to 1mm from the centre line on completion of welding.

This was achieved by designing and building two full-sized assembly jigs, with components laser cut to ensure accuracy. The jig components were assembled and welded in place using a series of lasers to position parts and control dimensions. The jig build was a success and the tolerances were achieved to the client's satisfaction.

Completing the project

Each plug measured approximately 11.8 metres in length and the seal plug was 3.3 metres in diameter; the acoustic baffle was approximately 8 metres long and had a diameter of 1.1 metres.

We manufactured the plugs from grade 316 stainless steel. All the materials used were subjected to a 100% Positive Material Identification (PMI) inspection by an independent company prior to inclusion in the fabrication. The plug components were welded using GMAW and GTAW welding techniques, all of which received a dye penetrant examination on completion.

TFL produced welding procedures and welding qualifications to ASME IX standards for all the aspects of the process, which included full penetration pipe butt welds, full penetration plate butt welds and fillet welds. After welding the plugs were acid cleaned and passivated at our works.

HRSG - Heat Recovery Steam Generation Banner Image

The acoustic section of the plug was produced from a 3mm perforated cylinder wrapped around a rolled flat bar cage. Insulation sprags were welded in place then 150mm of ceramic fibre insulation and a retaining blanket were installed within the cylinder, all held in place with washers, nuts and a ceramic cloth blanket. Three tubular legs were then mounted along the acoustic cylinder at 120 degree spacings, held in position by a series of square bar ladders.

On completion the plugs were shrink-wrapped, made water tight and packed into two very large crates at our premises; the crates had to be hand built around the fabrications.

“We're all extremely proud of the skills, expertise and commitment shown by our workforce during the manufacture of the plugs. Time was tight, tolerances were challenging and the odds were against us succeeding. However we did succeed, and credit must be given to all involved”

Paul Rodgers, managing director, TFL Responsive Engineering