Main Data

Mat'l BS3100 Grade BT2 BHN248-302
Weight Fin Weight 4.75 Tons
Date 09-11-2017
Drawn By P. Wilson

Sea Lion: Dredge Pump Spares Impeller Assembly

Designers: Seadrec Limited


Nigerian Ports Authorities


Built in The Netherlands


1. Description

ITEM ‘A’ – Fully machined 4 bladed impeller assembly as per Drawing No. P3, Item 1-4

2. Materials

The material for the components is as follows:-

DRG No. S5244 – Impeller assembly

Item No.DescriptionMaterialGradeHardness1ImpellerCast Steel260 Cr 25BHN400* * Material hardness to be increased above the BS3100 standard range within practical manufacturing limits but must be not less than HB350 for the finished component.

3.1  Cast Components                                                                        

Due to the arduous nature of the operating conditions and the extremely abrasive materials being handled, it is essential that the casting be of sound material, homogeneous in quality, free from warp, distortion and defects which would affect the safety and/or service life of the components.

They must also be true to the drawing shape and profile, with specified metal thickness maintained as minimum.

Repairs will only be permissible for very local defects and then only with our written approval. Full details of the location and extent of effected areas, including ultrasonic and/or radiographic examination require to accompany any written requests for rectification working.

Where repair of a casting is approved it must be carried out in accordance with the relevant sections of BS4570 Part 1 – Fusion Welding of Steel Castings.

The casting must be of good commercial quality supplied in a clean fettled shotblasted condition with mould part lines, feeder head bosses, etc., dressed flush with adjacent surfaces.

3.2  Test Samples & Material Certificates

Tensile, bend and impact test pieces cast integral with or separately at the time of pouring the mould from the same ladle plus associated test certificates to be provided.

3.2  Test Samples & Material Certificates (Cont)

Witness sample tests by Seadrec’s appointed representative to be at our discretion.

Duplicate sets of all test certificates, clearly identifying the associated component by means of the appropriate detail drawing and item reference numbers, to be submitted for our attention prior to the items being machined.

3.3  Screw Thread

Screw thread to be machined wholly in accordance with requirements and limits specified  on the drawing and to the correct engagement fit with Seadrec ‘free issue’ screw gauge, made available for checking purposes.

4.4 Pattern Equipment

New pattern equipment required which will become the property of Seadrec Limited

All patterns and coreboxes to be clearly marked with the Seadrec name plus associated detail drawing and item reference numbers.

5. Machining of Components 


a)  Machining of the shrouds to be axially true to the impeller centreline and set up to achieve the specified drawing thickness while maintaining the dimension to the end of the screw boss.

b)  Clean-up of the shroud and vane outside diameter to achieve a reasonable concentric and balanced component and hence minimise work during the static balance operation.

f)  To meet this requirement all components must be machined strictly to drawing sizes within the specified tolerances.

g)  Under no circumstances must mating components be machined to sizes other that those given on the relevant detail drawings or to limits out with the grade of fit stipulated.

h)  Machining operations must be wholly in accordance with drawing details, with no deviations and/or amendments without due reference to and written approval of Seadrec.

6. Static Balance 

Slow speed static balance to be carried out on the impeller and where necessary, the balance ribs cast integral with each impeller vane to have material removed or weld deposit added to achieve balance in accordance with the relevant sections of BS 5265  Part 1 1979, with a certificate provided to confirm the grade of balance achieved and the amount of weight added or deducted to achieve same.

7. Painting/Protection 

External unmachined surfaces to be treated as follows:-

Surfaces must be free from scale, rust or weld spatter. . 

All machined surfaces including screw threads treated with one coat of anti-corrosion compound, to provide durable protection during transportation and storage prior to use.