Are you saying that these problems were unique to Esso Northumbria? If so, why did Esso keep her in service longer than other members of the class? I suggest that most of the early VLCCs were too lightly built and the problems you refer to are due to design deficiencies. This would be well known to Esso, which is why the stress gauges where installed in the ship.
When an owner orders a class of ships from a number of builders, the owner supplies the design and specification for the class. The builder creates production drawings, which are submitted to the owner’s designer for approval. All these documents are also approved by the various regulatory authorities before construction starts. The problem with the leap to VLCCs was that neither the owners’ designers, nor the regulatory authorities, fully understood the structural problems involved.
Each steel plate used in shipbuilding has a quality test certificate issued by an independent authority and each individual plate is tracked to its exact position in a ship. This information is passed to the owner. Esso would know the exact characteristics of the individual cracked plates and it would be clear that the design of the ship was imposing stresses that were beyond the strength of the plates.
Like most VLCC builders, Swan Hunter had a Panel Line. Plates were automatically butt welded along their long edge to form a flat panel then the frames and stiffeners added. The “I” beams referred to were positioned by a machine that supported and rolled in each beam from the side of the line, clamped it into place, then automatically welded it to the panel. Sample X-Rays were taken from every panel to ensure the process was sound. In my view the beams could only have been dislodged by excessive flexing of the structure fracturing the welds.
Neither the Esso pair, nor Texaco Great Britain were the subject of unusual guarantee claims. I left Swan Hunter in 1972, but as far as I am aware there were no subsequent claims from the ships’ owners. I think that if there were a build problem, the American oil companies involved would have raised it!