Depth is probably the most immediate problem 
facing offshore pipelaying. Distance is also an 
important but less urgent problem. Crude oil 
pipelines have been laid in 340-foot waters. How- 
ever, methods for laying the large diameter, 
high-pressure gas pipelines have not been tested for 
water depths greater than 300 feet. Pipelines have 
been laid up to 100 miles in shallow water in the 
Gulf of Mexico. An 88-mile, 22-inch line was laid 
recently in the Persian Gulf in 300 feet of water. A 
French firm demonstrated in 1966 that under- 
water pipelines can be laid in greater depths when 
they laid an experimental, small-gauge line in the 
Cassidaigne Deep near Marseille in waters as deep 
as 1,080 feet. 
The low cost of tanker transportation may limit 
the laying of long-distance underwater lines. Be- 
fore the Suez Canal was closed, oil could be 
shipped around the Arabian Peninsula from the 
Persian Gulf to the Mediterranean at the same cost 
as it was moved less than a third that distance 
across the peninsula by pipeline. 
With costs declining as tanker sizes increase and 
with offshore lines costing two to five times as 
much as onshore lines, the probability of many 
long-distance underwater pipelines being con- 
structed seems to be diminishing. On the other 
hand, the new supertankers have such deep drafts 
that they are unable to enter many major ports 
and must be loaded and unloaded offshore. In 
addition, mooring a large tanker is very difficult in 
open, unprotected waters. Finally, long-distance 
underwater lines require the same support facilities 
as onshore lines (e.g., stations, valves, operators, 
manifolds, etc.) plus much more expensive corro- 
sion protection. 
The problems of gas pipeline support appear 
similar to those of oil pipelines in the ocean 
environment and in some cases are intensified 
because of special characteristics of gas pipelines. 
For example, their greater diameters cause han- 
dling and fabrication to be more difficult and 
make the pipelines more vulnerable to disturbance 
and damage by subsurface ocean currents and deep 
turbulence created by storms. 
3. Cost Factors 
Laying an offshore line is at least twice and 
more often five times as expensive as laying an 
onshore line, making costs a major consideration. 
Wall thickness and welding improvements offer 
promise of reduced costs. 
a. Wall Thickness Wall thickness of onshore 
pipelines is governed by operating pressure. Off- 
shore it is governed by stresses encountered in 
laying and heavy-wall pipe is used to lower such 
stresses. It is estimated that $2.7 million could be 
saved in the construction of a proposed 30 inch 
Red Snapper line offshore Louisiana if the wall 
thickness were reduced from 0.562 to 0.500 inch. 
Subsequent studies found that with adequate 
handling equipment, the 30-inch, 0.500 inch wall 
thickness pipe could be used safely in 150 feet of 
water and that the factor of safety during the 
laying operation could be increased by continuous 
applications of tension to the pipe. These findings 
emphasize the need for further improvement in 
pipelaying procedures. 
b. Other Factors Increased acceptance of micro- 
wire and fully automatic welding will contribute 
to lower costs. The pace of welding is a predomi- 
nant factor determining the rate of offshore 
pipelaying; the other is keeping the pipelaying 
barge supplied with pipe in rough seas. Any 
development that saves time and reduces delays 
will cut costs. 
4. Forecasts 
Since natural gas pipelines require large diam- 
eters, they are more expensive and present more 
difficult technological problems. Hence _ their 
depth and distance to shore are more restricted 
than oil pipelines. Tankers could be used when 
these depth-distance limits are exceeded; however, 
to do this the gas must be liquefied. Cryogenic 
liquefaction of natural gas is economical only for 
long-distance transportation and requires major 
installations for liquefaction, handling, and stor- 
age. Such a program is already planned or under 
way between Algeria and France, between Libya, 
Italy, and Spain, and between Alaska and Japan. 
It is difficult to predict what, if any, future 
advances may allow production of natural gas 
from greater water depths or longer distances from 
shore. It appears that offshore pipelines will 
continue in use primarily to transport offshore 
production to onshore facilities over relatively 
short distances, less than 200 miles. 
VI-171 
